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Clusterization process of water molecules called “water pockets” in the imidazolium-based room temperature ionic liquid (RTIL) 1‑butyl‑3‑methylimidazolium nitrate ([C4mim][NO3]) was investigated using Raman spectroscopy. Changes of Raman spectra were observed in four different spectral regions when the content of heavy water (D2O) in the RTIL-D2O system was continuously increased. It was found that different parameters of the Raman bands were sensitive to the added content of D2O. Discontinuous distribution in the concentration dependencies of those parameters was registered. The extent of “water pockets” formation process was determined from discontinuities in the concentration dependencies of monitored shifts and integral intensities of the Raman bands. The blue shift of symmetric NO3− stretching mode at 1041 cm−1 and the stretching mode at 2nd carbon position C(2)–H at 3100 cm−1 of imidazolium ring was noticed in the spectra even after adding of infinitesimal content of water to the mixture. The identical behavior analyzing the Raman band at 706 cm−1 assigned to NO3− bending mode was discovered. Moreover, the ratio of integral intensities of two Raman bands at 600 and 625 cm−1 assigned to GT and TT forms of butyl chain was also found to be dependent on the content of D2O in the mixture. The distribution among relative integral intensities of Raman bands assigned to vibrations of different water clusters was sensitive to the content of D2O in the mixture too. Overall, the lower boarder of “water pockets” formation process (X = 0.6 molar D2O ratio) in [C4mim][NO3] came up with the discontinuous spectral changes observed for NO3− stretching mode, and vibrational modes of different water clusters. The upper boarder of “water pockets” formation process (X = 0.86 M D2O ratio) was found out from discontinuities in concentration dependencies of imidazolium ring stretching mode, and vibrational modes of different water clusters. The conformational changes of [C4mim]+ cation at the same D2O concentration corresponding to the upper boarder of “water pockets” formation were observed.

1‑chloro-1-chloromethylsilacyclohexane (1-Cl-1-ClMSiCH) is a newly synthesized molecular compound whose conformational analysis was performed by means of vibrational spectroscopy and theoretical calculations. Conventional ATR-FTIR and Raman spectroscopic methods were used to obtain vibrational spectra of the liquid sample. Additionally, FTIR spectra of the compound isolated in low-temperature neon and nitrogen matrices were registered to make a complete assignment of the experimental vibrational spectral bands. All theoretically possible 38 canonical ring conformations considering axial/equatorial and cis/trans/gauche-/gauche + positions of the Cl and CH2Cl group were analyzed by utilizing MP2 and B3LYP at aug-cc-pVTZ theory level. The most stable local energy minima were investigated in detail, with the global energy minimum structure being in the chair axial trans conformation. Detailed analysis of the potential energy surface revealed the transition states (TS) and the energy barriers. The conformational path was found to be the chair→ envelope/half-chair (TS)→ skew-boat C1→ boat (TS)→ skew-boat C2. The energy barrier for 1C4 to 1S3 conversion was found to be 4.94 kcal/mol while for the reverse process–it was calculated to be 0.26 kcal/mol. The vibrational analysis and the experimental spectra suggest that the four lowest energy (chair ring) conformers coexist at room temperature. The energy barrier for gauche to trans conversion is 1.15 kcal/mol for axial and 1.04 kcal/mol for equatorial conformers, and it is possible to observe these processes in low-temperature matrices.

The cation-anion interactions present in the 1-butyl-3-methylimidazolium nitrate ionic liquid [BMIm][NO3] were studied by using density functional theory (DFT) calculations and the experimental FT-Raman spectrum in liquid phase and its available FT-IR spectrum. For the three most stable conformers found in the potential energy surface and their 1-butyl-3-methylimidazolium [BMIm] cation, the atomic charges, molecular electrostatic potentials, stabilization energies, bond orders and topological properties were computed by using NBO and AIM calculations and the hybrid B3LYP level of theory with the 6-31G* and 6-311++G** basis sets. The force fields, force constants and complete vibrational assignments were also reported for those species by using their internal coordinates and the scaled quantum mechanical force field (SQMFF) approach. The dimeric species of [BMIm][NO3] were also considered because their presence could probably explain the most intense bands observed at 1344 and 1042 cm−1 in both experimental FT-IR and FT-Raman spectra, respectively. The geometrical parameters suggest monodentate cation-anion coordination while the studies by charges, NBO and AIM calculations support bidentate coordinations between those two species. Additionally several quantum chemical descriptors were also calculated in order to interpret various molecular properties such as electronic structure, reactivity of those species and predict their gas phase behaviours. Fil: Kausteklis, Jonas. Vilnius University; Lituania Fil: Aleksa, Valdemaras. Vilnius University; Lituania Fil: Iramain, Maximiliano Alberto. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Brandan, Silvia Antonia. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Inorgánica; Argentina

Structural and vibrational characterizations for the 1-butyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid ([BMIM][OTF]) were performed combining the experimental Raman spectrum with density functional theory (DFT) calculations based in the hybrid B3LYP/6-311++G** level of theory. Structurally, the trifluoromethanesulfonate anion, [OTF] is linked to 1-butyl-3-methylimidazolium cation, [BMIM] by a bidentate coordination by means of two different S?O??H hydrogen bonds. The [OTF] anion plays a very important role in the structure and stability of [BMIM][OTF], as observed by the strong increase in the dipole moment value when the anion is added to cation. Intramolecular H and halogen bonds evidence the high stability of ionic liquid, as supported by NBO and AIM calculations. Very good correlations were observed between the predicted infrared and Raman spectra with the corresponding experimental ones. The different Mulliken charges observed on the O atoms of O??H bonds support the asymmetric bidentate coordination of [OTF] anion with the [BMIM] cation. The [OTF] anion increase the reactivity of [BMIM][OTF], as compared with [BMIM][NO3]. In addition, the [OTF] anion reduces drastically the electrophilicity and nucleophilicity indexes of cation evidencing the strong influence of anion on the properties of cation. The vibrational analyses have revealed a very important shifting of one of the two antisymmetric modes of [BMIM][OTF] towards lower wavenumbers due probably to an asymmetric of S[dbnd]O⋯H bond interaction which is no observed in the anion. The complete vibrational assignments were performed for ionic liquid, cation and anion and the harmonic scaled force constants were reported at the same level of theory. Fil: Kausteklis, Jonas. Vilniaus Universitetas; Fil: Aleksa, Valdemaras. Vilniaus Universitetas; Fil: Iramain, Maximiliano Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia; Argentina Fil: Brandan, Silvia Antonia. Universidad Nacional de Tucumán; Argentina

Since 1-chloromethyl-1-fluorosilacyclohexane is a newly synthesized molecular compound its structural parameters and conformational stability is unknown. Raman and infrared vibrational spectroscopy methods were employed for analysis of this molecule. IR spectra were recorded for both gas phase and liquid sample, whereas the Raman experiments were performed in the liquid state. Additionally, low temperature matrix isolation infrared spectra were recorded after isolating the molecule in argon and nitrogen matrices. For the assignment of the experimental spectral bands, theoretical DFT/B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ calculations were performed. From the calculations it was found that 1-chloromethyl-1-fluorosilacyclohexane may exist in twelve different conformational forms out of which the chair axial trans conformer is the most stable form. However, there are three more chair type conformers – equatorial trans, equatorial gauche and axial gauche that are stable enough to be observed in the experimental spectra.

The phase behavior of the imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide and chloride ([C10mim][Br], [C10mim][Cl]) were studied by 2D Raman correlation spectroscopy and principal component analysis. The hydrogen-bonded network changes and the liquid crystalline ionogel phase formation were observed when water content was continuously increased in the system, and the Raman shift of C–H stretching modes in spectra was monitored. The extent of liquid crystalline ionogel phase was determined from the discontinuities in the concentration dependencies. The focus to the Raman bands originated from the imidazolium ring C–H stretching mode region (3000–3200 cm−1) when water content in the IL was increased allowing to determine the lower border of ionogel phase formation in RTIL/water systems. The upper border of the ionogel phase was determined when main attention was carried out to the Raman bands originated from the O–H stretching vibration region (3200–3800 cm−1). The hypothesis of weaker hydrogen bonds involving the C(4)-H and C(5)-H groups and stronger hydrogen bonds of the C(2)-H groups was supported by Raman results. Copyright © 2016 John Wiley & Sons, Ltd.

Raman spectra of liquid, and infrared spectra of gaseous as well as matrix isolated 1,1,2,2-tetrachloro-1,3-disilacyclopentane were recorded and analyzed with the aid of DFT calculations. Complete assignment of the experimental vibrational spectral bands is made. Experimental results and DFT calculations confirm that 1,1,2,2-tetrachloro-1,3-disilacyclopentane exists as single twist conformer in gaseous and liquid states as well as isolated in Ar and N2 matrices. Fast dissociation of 1,1,2,2-tetrachloro-1,3-disilacyclopentane takes place in gas phase, while the molecule remains stabile in condensed phase. The spectral data and results of DFT calculations in anharmonic approximation confirm that dissociation of 1,1,2,2-tetrachloro-1,3-disilacyclopentane starts with the cleavage of CC bond of the five membered ring. Dichlorodimethylsilane and HCl were found to be the main products of the dissociation. The geometry and stability of the title molecule is discussed in the light of recent publications on the studies of similar substituted disilacyclapentanes.

Raman spectra of 1,1-difluoro-1-silacyclohexane as a liquid, and as a solid at 78 K were recorded and depolarization data obtained. The infrared spectra of the vapour, liquid and amorphous and crystalline solids have been studied. In the low temperature IR and Raman spectra eight and three bands, respectively, were shifted a few cm −1 when the sample crystallized. No bands vanished after crystallization in agreement with the assumption that only one conformer (chair) was present in all the states of aggregation. The compound exists in the stable chair conformation, whereas in the parent silacyclohexane a possible twist form should have more than 15 kJ mol −1 higher energies than the chair, as derived from various calculations. The wavenumbers of the vibrational modes were calculated in the harmonic and anharmonic approximation employing B3LYP/cc-pVTZ calculations. The 27 A′ and 21 A″ fundamentals were assigned on the basis of the calculations, infrared vapour contours, Raman depolarization measurements and infrared and Raman band intensities. An average, relative deviation of 1.5% was found between the observed and the anharmonic wavenumbers for the 48 modes.

A 1,1-disubstituted silacyclohexane, 1-chloro-1-methyl-1-silacyclohexane, C5H10SiClCH3, was synthesized and studied by infrared and Raman spectroscopy. The infrared spectra of the vapor and liquid were recorded at ambient temperature and the solid sample investigated at 78 K. Negligible spectral changes ocurred at 78 K compared with the fluid state, but after annealing to ca. 165 K an apparent crystal was formed. Raman spectra of the liquid were recorded at 293 K and depolarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143 K. A supercooled liquid appeared after slow cooling, but an amorphous solid phase was observed after shock freezing to 78 K. After annealing, a plastic phase was observed and an anisotropic crystal appeared after further annealing. In the crystalline phase spectral shifts and some vanishing bands were observed and only the a (Cl) conformer remained. The compound exists in two conformers, equatorial (Cl) (e) and axial (Cl)(a) in the liquid, amorphous and plastic phases, but only the a-conformer was present in the crystal. The experimental results suggest that the a-conformer has 1.5 ± 0.5 kJ mol−1 lower enthalpy than e in the liquid. B3LYP calculations with various basis sets and the G3 model chemistry gave conformational energy difference ΔE (a–e) in the range 3.2–2.4 kJ mol−1. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the two conformers were calculated. The 32 A′ and 25 A″ modes for the e(Cl) and a(Cl) conformations were assigned, supported by anharmonic B3LYP/cc-pVTZ calculations.

Raman spectra of of 1-methyl-1-silacyclohexane as a liquid were recorded at 293 K and depolarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143 K, and intensity changes with temperature of certain Raman bands were detected. A supercooled liquid appeared after slow cooling, but an amorphous phase was observed after shock freezing to 78 K. After annealing, first a plastic phase and subsequently a crystal were observed. In the crystalline phase spectral shifts and some vanishing bands were observed. The infrared spectra of the vapor and liquid were studied at ambient temperature and the solid sample investigated at 78 K. Negligible spectral changes ocurred at 78 K compared with the fluid state, but after annealing to ca. 170 K an apparent crystal was formed and a few bands vanished and others were shifted. The compound exists in two conformers, equatorial ( e ) and axial ( a ) in the liquid, amorphous and plastic phases, but only the e -conformer was present in the crystal. The experimental results suggest that the e- conformer has 0.6 kJ mol −1 lower energy than a in the liquid. B3LYP calculations with various basis sets gave a conformational enthalpy difference Δ H ( a – e ) around 2.4 kJ mol −1 while G3 model chemistry gave 0.6 kJ mol −1 . Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The fundamental wavenumbers were also derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations. A relative deviation of 0.94% and 1.31% between the observed and calculated wave numbers for the 57 modes of the e- and a -conformers, respectively, was obtained.

Raman spectra of silacyclohexane as a liquid was recorded and depolarization data obtained. The infrared spectra of the vapour and liquid have been studied. The compound exists in the stable chair conformation, whereas a possible twist form should have more than 15 kJ mol −1 higher energies for silacyclohexane derived from numerous calculations. The wavenumbers of the vibrational modes were derived in the harmonic and anharmonic approximation in B3LYP/cc-pVTZ calculations. The 27 A′ and 21 A″ fundamentals were assigned on the basis of the calculations, on infrared vapour contours, Raman depolarization measurements and infrared and Raman band intensities. An average, relative deviation of ca 0.77% was found between the observed and the anharmonic wavenumbers for the 48 modes.

The infrared spectra of 1-chloro-1-silacyclohexane have been studied as a vapour and liquid at ambient temperature and as amorphous and annealed crystalline solids at 78 K. Various infrared bands present in the vapour and liquid states vanished in the crystalline state upon cooling. Raman spectra of the liquid were recorded at 293 K and polarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 163 K, and intensity changes with temperature of certain Raman bands were detected. A crystalline phase was observed around 140 K, leading to spectral shifts and a number of vanishing bands. The compound exists in two conformers, equatorial (e) and axial (a) in the fluid phases, but only the a-conformer was present in the crystal. The experimental results suggest that the a-conformer has 2.8 kJ mol−1 lower enthalpy than e in the liquid, leading to 69% of the a conformer at 293 K. B3LYP calculations with various basis sets and the G3 model chemistry gave conformational energy difference ΔE (e − a) in the range 0.4–1.4 kJ mol−1. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The fundamental wavenumbers were also derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations, a relative deviation of less than 2% between the observed and calculated wave numbers for the 48 modes of the e- and a-conformers was obtained.

Raman spectra of 1-fluoro-1-silacyclohexane as a liquid were recorded at 293 K and polarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143 K, and intensity changes of certain bands with temperature were investigated. An apparently plastic phase was observed around 170 K, but no definite crystallization was ever obtained on cooling. The infrared spectra have been studied of the vapor, of an amorphous solid at 78 K and of the liquid in the range 600–100 cm −1 . No infrared bands present in the vapor or liquid vanished upon cooling. The compound exists a priori in two conformers, equatorial ( e ) and axial ( a ), and the experimental results suggest an equilibrium in which the a- conformer has 1.2 kJ mol −1 lower enthalpy than the e- conformer in the liquid, leading to 60% a- conformer at ambient temperature. B3LYP calculations with various basis sets and the G3 model chemistry gave conformational enthalpy difference Δ H ( e − a ) in the range 0.6 and 1.8 kJ mol −1 . Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The wavenumbers of the vibrational modes were derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations. An average relative deviation of ca. 1% between the observed and calculated wavenumbers for the 48 modes of the e and a conformers was found.

Calcium hydroxyapatite containing amorphous phosphate phase (ACP-CaHA) and nano-structured hydroxyapatite (CaHA) have been prepared by two sol-gel synthesis routes. The structural organization of hydroxyl groups in both materials has been determined by means of 1H MAS NMR and FTIR spectroscopy. It has been shown that the amount of structural –OH groups in nano-structured CaHA is significantly higher than that from adsorbed water and vice versa in ACP-CaHA. A precise signal shape analysis has been carried out for both studied samples. The 31P NMR signals have been found being Voigt-shaped in the wide-line as well as in MAS spectra. The 1H and 31P spin-lattice and spin-spin relaxation time measurements have revealed that the fast spin motion takes place in ACP-CaHA. The corresponding correlation time τ ~ 7 · 10–7 s at ~300 K has been determined. The effect of MAS rate on the 31P signal shape also confirms that this motion runs in the time scale of microseconds or even nanoseconds. The magnitude of the anisotropic broadening 1220 ± 20 Hz determined for nano-structured CaHA is very close to the maximum of the dipolar 1H–31P coupling distribution profile estimated using CP MAS kinetics. The dynamics of 1H–31P spin interactions in nano-structured CaHA (τ ~ 3.3 · 10–5 s) is much slower than in ACP-CaHA.

Infrared spectra of gaseous, liquid, and matrix-isolated samples of newly synthesized 1,1-dimethyl-2-oxy-1-silacyclohexane were recorded. Raman spectra of 1,1-dimethyl-2-oxy-1-silacyclohexane in liquid and solid states were obtained in the temperature range from 170 to 340 K. Ab initio HF and DFT B3LYP calculations were performed in order to determine the possible conformations of 1,1-dimethyl-2-oxy-1-silacyclohexane and to make accurate assignment of the vibrational spectral bands. The study confirms the existence of only one chair-type conformer of 1,1-dimethyl-2-oxy-1-silacyclohexane.

Ozonization reaction of ethene in neat film at 77 K was performed. Separation of ethene secondary ozonide from the other products of the reaction was performed by continuous pumping of the reactor. Only the products, which evaporated from the walls of the reactor at 185 K, were transferred to the gas cell. The high-resolution infrared absorption spectrum of gaseous ethene secondary ozonide (C(2)H(4)O(3)) in a static gas long-path absorption cell has been recorded in the 900-1100 cm(-1) spectral region at 185 K. The spectral resolution was 0.003 cm(-1). Analyses of the nu(7)(A) band at 1037.0 cm(-1), the nu(8)(A) band at 956.1 cm(-1), and the nu(18)(B) band at 1082.1 cm(-1) have been performed using the Watson Hamiltonian model (A, reduction; III(r), representation). A set of ground-state rotational and quartic centrifugal distortion constants have been obtained, and upper state spectroscopic constants have been determined for the bands investigated. A local resonance observed in nu(18) is explained as c-Coriolis interaction with nu(10) + nu(11).

The infrared spectra of 1,2-diphenylethane were recorded as a melt and crystalline solid in capillary films and as a pellet in KBr and polyethylene in the 4000‐ 50 cm 21 range. Moreover, the sample was isolated in an argon matrix at ca. 5 K, and the spectra recorded in the range 3100‐ 450 cm 21 , before and after annealing. Raman spectra of the melt were recorded between 295 (supercooled) and 357 K, and spectra of the crystalline solid were obtained at ambient temperature. A number of infrared and Raman bands in the melt vanish in spectra of the crystal, and the compound undoubtedly exists as a mixture of two conformers in the melt, probably anti and gauche. Various non-coincidences between the infrared and Raman bands of the crystals agree with C2h symmetry of the anti conformer. The intensity variations with temperature of two band pairs in the liquid phase Raman spectra were used for van’t Hoff plots, giving a value of 2.4 ^ 0.5 kJ mol 21 for DH (gauche‐ anti). The anti conformer had the lower energy and was also present in the crystal. Very small intensity changes were detected when the matrix spectra were annealed to 36 K (argon) revealing that the conformational barrier was too high to allow significant conversion from gauche to the anti conformer even at the highest annealing temperature of 36 K. Ab initio calculations were carried out with the GAUSSIAN 98 program at the RHF/6-311G* level and the vibrational frequencies for the anti and gauche conformers including infrared and Raman intensities were calculated. After appropriate scaling, a reasonably good agreement was obtained between the experimental and calculated wavenumbers for both conformers. Nearly all of the 78 fundamentals of the anti and 24 of the gauche conformers were tentatively assigned. However, strong overlap between the anti and gauche conformer bands was observed in most of the spectral region, and additional accidental degeneracy in the spectra prevented reliable assignments for all the vibrational bands. q 2003 Elsevier B.V. All rights reserved.

at 5 K were recorded before and after annealing to 20–36 K. Raman spectra of the compound as a liquid were recorded at various temperatures between 300 and 153 K and spectra of the amorphous and crystalline solids were obtained. The spectra revealed the existence of two conformers (anti and gauche) in the fluid phases and in the matrices. When the vapour was shock-frozen on a cold-finger at 78 K and subsequently annealed to 120–130 K, 10 Raman bands and eight IR bands of the liquid were reduced in intensity in the amorphous phase and vanished in the crystal. Frequent intensity variations were observed in the infrared spectra of argon and nitrogen matrices before and after annealing. These spectra revealed the existence of one conformer (anti) in the crystal. From intensity variations of four independent pairs of anti and gauche bands in the Raman spectra between 300 and 150 K, an average value 1H ◦ (gauche–anti) =4 .6 ± 0. 3k J mol −1 was obtained in the liquid. Annealing experiments on n-propyltrichlorosilane in the matrices demonstrate that the gauche bands vanish after annealing, revealing that the anti conformer has the lower energy. The spectra of both conformers were interpreted in detail.Ab initio and DFT calculations gave optimized geometries, infrared and Raman intensities and scaled vibrational wavenumbers for the anti and gauche conformers. The conformational energy difference derived was 7.6 and 6.4 kJ mol −1 for the HF/6–311G ∗ and B3LYP/6–311G ∗ basis sets, respectively, with anti being the low-energy conformer. Copyright  2004 John Wiley & Sons, Ltd.

The infrared spectra of dimethylvinylsilane and dimethylvinylsilane- d 1 (CH 2 CH(CH 3 ) 2 SiH(D)) were recorded in the vapour phase and as amorphous and crystalline solids in the 4000–50 cm −1 range. Moreover, they were isolated in argon and nitrogen matrices at ca. 5 K, and the parent molecule was dissolved in liquefied krypton between 218 and 173 K and the spectra recorded in the range 3100–450 cm −1 . Raman spectra were recorded at room temperature and at various temperatures between 295 and 153 K. Spectra of the amorphous and crystalline solids were obtained at 50 K (in the infrared) and at 80 K (in the Raman spectra). The compound exists as two conformers, probably syn and gauche , and probably eight infrared and Raman bands present in the vapour, liquid and amorphous states in the parent molecule and in the isotopomer clearly vanished after crystallization. The intensity variations with temperature of one band pair in the liquid phase Raman spectra of the parent molecule and the d 1 isotopomer were used for van't Hoff plots. These gave a value of 0.9±0.3 kJ mol −1 for Δ H (syn–gauche). Variable temperature studies of the infrared spectra in liquid krypton resulted in the value Δ H (syn–gauche)=0.7±0.04 kJ mol −1 . The gauche conformer had the lower energy and was also present in the crystal. Intensity changes were detected when the matrix spectra were annealed to 37 K (argon) or 34 K (nitrogen) revealing that the gauche conformer was the more stable in the matrices. Ab initio calculations were carried out with the gaussian 98 program at the HF/6-311G*, RHF/6-311G* and MP2/6-311+G(2d,2p) levels and the vibrational frequencies for the syn and gauche conformers including infrared and Raman intensities were calculated. After appropriate scaling, a reasonably good agreement was obtained between the experimental and calculated wavenumbers for both conformers.

Infrared spectra of 1,1,1-trifluoropropyltrifluorosilane (CF3CH2CH2SiF3) were obtained in the vapour, amorphous and crystalline solid phases in the range 4000–50 cm−1. Additional spectra in argon and nitrogen matrices at 4.8 K were recorded before and after annealing to temperatures of 20–36 K. Raman spectra of the compound as a liquid were recorded at various temperatures between 298 and 163 K and spectra of the amorphous and crystalline solids were obtained. The spectra revealed the existence of two conformers (anti and gauche) in the fluid phases and in the matrices. When the vapour was shock-frozen on a cold-finger at 78 K and subsequently annealed to 120–150 K, 12 mostly weak Raman bands vanished in the crystal. Much smaller variations were observed in the corresponding infrared spectra after annealing. However, the spectra indicated the existence of two different crystals, formed after annealing the amorphous solid to 120 and to 150 K; both crystals contained the same conformer (anti). Raman and IR spectra of 1,1,1-trifluoropropyltrifluorosilane in cyclohexane, carbon tetrachloride and acetonitrile revealed conformational displacements with solvent polarity. From intensity variations between 298 and 223 K of the Raman pair 639/665 cm−1, ΔH° (gauche–anti) = 3.4 ± 0.3 kJ mol−1 was obtained in the liquid. Annealing experiments indicate that the anti conformer also has a lower energy in argon and nitrogen matrices; moreover, the low-energy conformer is present in the crystal. The spectra of both conformers have been interpreted in detail. Ab initio calculations at the HF/6–311(d), HF/6–311 G (3df,3pd) and MP2/G–31(d) levels gave optimized geometries, infrared and Raman intensities and scaled vibrational wavenumbers for the anti and gauche conformers. The conformational energy difference derived was 5.3 kJ mol−1 with anti being the low-energy conformer. Copyright © 2003 John Wiley & Sons, Ltd.

The Raman spectrum of liquid ethyldibromosilane, CH3CH2SiHBr2, was recorded at various temperatures between 298 and 218 K, and the spectrum of the crystal was obtained at 210 K from a sample sealed in a capillary. Additional spectra of the amorphous and annealed crystals, which were deposited on a copper finger cooled with boiling liquid nitrogen, were recorded. The infrared spectra were recorded of the vapor and amorphous and crystalline solid in the range 4000–50 cm−1 and mid-infrared spectra isolated at 4.8 K in argon and nitrogen matrices were also observed. These vibrational spectra show that two conformers, anti and gauche, are present in the vapor and in the liquid, but only the anti conformer remains in the crystalline solid. Three conformer pairs in the Raman spectrum of the liquid phase were used to obtain the enthalpy difference, which gave an average value of 128 ± 17 cm−1 (1.53 ± 0.2 kJ mol−1) with the anti form lower in energy. At ambient temperature it is estimated that there is 52 ± 2% of the gauche conformer present in the liquid. The optimized geometries, infrared and Raman intensities, and scaled vibrational wavenumbers for the anti and gauche conformers were obtained from ab initio MP2/6–31G(d) calculations with full electron correlation. The conformational energy difference was also obtained from ab initio MP2/6–311 + G(d,p) calculations which gave a predicted energy difference of 97 cm−1 with the anti form the conformer of lower energy. These spectroscopic and theoretical results are discussed and compared with the corresponding quantities for some similar molecules. Copyright © 2003 John Wiley & Sons, Ltd.

Ethyl iodosilane (CH 3 CH 2 –SiH 2 I) was synthesized for the first time. Infrared spectra were recorded in the vapour, amorphous and crystalline solid phases in MIR and FIR regions. Additional MIR spectra of the compound isolated in argon and nitrogen matrices were obtained at 5 K. Raman spectra of the liquid, excited by argon and by Nd 3+ YAG lasers, were recorded at room temperature including polarization measurements. The spectra were studied in an extended temperature range 173–353 K and a Δ H value of 1.2±0.3 kJ mol −1 was obtained with gauche being the low energy conformer. Spectra of the amorphous and crystalline solids were obtained at liquid nitrogen temperature. Ethyl iodosilane exists in an equilibrium between anti and gauche conformers, in the vapour, liquid and amorphous states. After careful annealing the amorphous solid on a cold Cu finger (Raman) or on a CsI or Si window (infrared) to 160 K a partly crystalline solid was formed. A number of IR and Raman bands were reduced in intensity after annealing, although they did not vanish completely. From comparison between the observed and calculated vibrational modes it was apparent that the gauche conformer was present in the crystal. The sample was mixed with argon and nitrogen in a ratio 1:1000, deposited on a window at 5 or 10 K and annealed to temperatures between 5 and 36 K (argon) and 5–30 K (nitrogen). IR bands attributed to the anti and gauche conformers were reduced and increased in intensities, respectively. Thus, the gauche conformer was the low energy conformer in the matrices and probably also in the vapour phase. Ab initio calculations were performed at the RHF/3-21 G* and 6-311G* B3LYPs and gave optimized geometries, IR and Raman intensities and vibrational frequencies for the anti and gauche conformers. An enthalpy difference of 0.9 kJ mol −1 was obtained from the calculations with gauche being the low energy conformer. After scaling, a reasonably good agreement between the experimental and calculated wavenumbers for the anti and gauche conformer was obtained. The spectra of ethyl iodosilane were closely related to those of the corresponding ethyl fluoro, ethyl chloro and ethyl bromosilane.

The infrared spectra of ethyl bromosilane, CH 3 CH 2 SiH 2 Br and the Si-d 2 isotopomer, were recorded in the vapor, amorphous and the crystalline solid phases in the range 4000–400 cm −1 . The mid-infrared spectra of the ‘light’ compound, isolated at 4.8 K in the argon and the nitrogen matrices were also observed. Raman spectra of the liquids were recorded at various temperatures between 298 and 218 K, and the spectrum of the crystal was obtained from a sample sealed in a capillary at 210 K. Additional spectra of the amorphous and annealed crystals, which were deposited on a copper finger cooled with liquid nitrogen, were recorded. These vibrational spectra show that two conformers— anti and gauche —are present in the vapor and in the liquid, but only the gauche conformer remains in the crystalline solid. Six conformer pairs in the liquid phase were used to obtain the enthalpy difference which gave an average of 140±25 cm −1 (1.67±0.3 kJ/mol) with gauche form lower in energy. Additionally variable temperature (−120 to −155 °C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out and the enthalpy difference has been determined to be 130±13 cm −1 (1.56±0.16 kJ/mol), again with the gauche conformer the more stable form. At ambient temperature it is estimated that there is 22±2% of the anti conformer present. The optimized geometries, infrared and Raman intensities, and scaled vibrational frequencies for the anti and gauche conformers were obtained from ab initio MP2/6-31G(d) calculations. The conformational energy difference was also obtained from ab initio MP2/6-311+G(d, p) calculations which gave a predicted energy difference of 129 cm −1 with the gauche form the lowest energy. From the isolated Si–H stretch frequencies from the Si-d 1 isotopomer the Si–H distances were determined to be 1.481 and 1.480 A for the gauche and anti conformers, respectively. The spectroscopic and theoretical results are discussed and compared to the corresponding quantities for some similar molecules.

Chloromethyl methyl dichlorosilane (ClCH2CH3SiCl2) was synthesized and the infrared spectra of its vapour, and of the amorphous and crystalline states, cooled to the temperature of liquid nitrogen were recorded. Additional mid IR spectra of the compound, isolated in both argon and nitrogen matrices, were taken at 5 K. Raman spectra of the liquid were recorded in a capillary at various temperatures between 298 and 223 K. The crystal was also studied in a capillary at 210 K and deposited onto a copper finger cooled with liquid nitrogen. The compound occurs as anti and gauche conformers in its vapour and liquid states. Approximately five Raman bands, some of them weak, present in the fluid phases vanished upon crystallization. An additional eight IR bands disappeared or were reduced in intensity after crystallization. Two band pairs in the Raman spectra were used to calculate the enthalpy difference between the conformers in the liquid phase giving a value: ΔH(liq)(anti–gauche) of 0.0(±0.4 kJ mol−1. In the argon and nitrogen matrices, various small intensity variations in the IR bands were observed after annealing to ca. 36 K (argon) or 32 K (nitrogen). The gauche bands generally increased and the anti bands decreased in intensity, suggesting that gauche has a lower energy in the matrices. The conformational barrier was estimated to be 8–10 kJ mol−1. The optimized geometries, infrared and Raman intensities, and scaled vibrational frequencies for the anti and gauche conformers were derived from ab initio calculations at the RHF/6-311G∗level. The derived conformational energy difference was 7.2 kJ mol−1, gauche being the conformer of lowest energy. The calculated dipole moments of the anti and gauche conformers were 4.2 and 2.0 D, respectively. Correlation between the observed and calculated wave numbers of both conformers revealed that gauche was present in the crystal, and assignments of the spectra have been carried out.

Infrared spectra of 2-chloroethyl trifluorosilane (CETFS) (ClCH2CH2SiF3) were obtained in the vapour, amorphous and crystalline solid phases in the range 4000–50 cm−1. Additional variable temperature spectra in liquefied xenon and spectra in argon and nitrogen matrices at 5 K were recorded. Raman spectra of the compound as a liquid were recorded at various temperatures between 298 and 180 K and amorphous and crystalline solids were obtained. The spectra of CETFS revealed the existence of two conformers (anti and gauche) in the vapour and in the liquid. Large variations in the infrared and Raman spectra were observed when the vapour was shock-frozen on a window at 80 K and subsequently annealed. An intermediate phase appeared at ca. 125 K containing both conformers. A crystal was formed at 160 K, and ca. 18 infrared and/or Raman bands present both in the fluid phases and in the 125 K solid vanished in this crystal. From the intensity variations between 293 and 183 K of four Raman band pairs, Δ H 0 (anti−gauche)=0.8±0.3 kJ mol −1 was obtained in the liquid. In liquid xenon under pressure a ΔH value of −0.7±0.1 kJ mol−1 was calculated from the intensity variations between 218 and 173 K of two band pairs in the infrared spectra. Annealing experiments indicate that the anti conformer has slightly lower energy in argon and nitrogen matrices. Also, the anti conformer has the lower energy in liquid xenon, whereas the more polar gauche rotamer is the low energy conformer in the liquid and is also present in the crystal. The spectra of both conformers have been interpreted in detail. Ab initio calculations were performed using the gaussian 94 program with the HF/6-311G∗ basis set and gave optimized geometries, infrared and Raman intensities and scaled vibrational frequencies for the anti and gauche conformers. The conformational energy difference derived was 3.8 kJ mol−1 with anti being the low energy conformer.

The conformational stability of newly synthesised bicyclo[3.3.1]nonane-2,6-dione C 9 H 12 O 2 (D26) and bicyclo[3.3.1]nonane-2,9-dione C 9 H 12 O 2 (D29) was studied. Ab initio calculations (HF level using 6-31G ∗∗ basis set) reveal that due to six-membered ring inversion four conformers exist in the case of D26, whereas five of them exist for D29. The double-chair (CC) conformer is the most stable for D26 and the chair–boat (CB) conformer is 3.4 kJ mol −1 higher in energy. On the contrary, the chair–boat (CBo) conformer of D29 is the most stable and the chair–chair conformer (CC) is 2.5 kJ mol −1 higher in energy. Raman and IR spectra of the title compounds were recorded in solid, liquid and gas phases for the first time. Assignment of vibrational spectral bands for both molecules was made by comparing theoretical and experimental spectra.

The infrared (IR) spectra of dichloromethylmethyl dichlorosilane (Cl2CHCH3SiCl2) were recorded in the vapor, amorphous and partly crystalline phases between 4000 and 50 cm−1. IR spectra (4000–450 cm−1) of the compound were also obtained when isolated in argon, nitrogen and krypton matrices at 4.8 K before and after annealing to temperatures in the range 15–50 K. Raman spectra of the liquid were recorded at various temperatures between 295 and 147 K. Spectra of the amorphous and annealed crystal deposited on a copper finger at 78 K were obtained. The spectra showed the existence of two conformers — anti and gauche — in the vapor and in the liquid. Approximately 12 IR bands were reduced in intensity and 6 Raman bands present in the fluid phases vanished upon crystallization. From the intensity variations of two band pairs with temperature, a ΔH0 value of 0.4±0.3 kJ mol−1 between the conformers was obtained in the liquid, anti being the low-energy conformer. Small increases and decreases in the IR band intensities were observed in the matrix spectra after annealing to 32 (nitrogen), 36 (argon) and 50 K (krypton). The enthalpy difference between the conformers is low in the matrices, but the anti conformer had lower energy than the gauche. Ab initio calculations were performed using the Gaussian -94 program with the RHF/6-311G∗ basis function and gave optimized geometries, IR and Raman intensities and scaled vibrational frequencies for the anti and gauche conformers. The conformational energy derived was 4.4 kJ mol−1 with anti being the low-energy conformer. The dipole moments were calculated to be 1.2 and 3.1 debye for the anti and gauche conformers, respectively. Correlation between the observed and calculated wavenumbers of both conformers revealed that anti was present in the crystal, and complete assignments of the spectra have been carried out.

The infrared spectra of dichloromethylmethyldichlorosilane (Cl2CHCH3SiCl2) were recorded in the vapour, amorphous and partly crystalline phases and when isolated in argon, nitrogen and krypton matrices at 5 K. Raman spectra of the liquid were recorded at various temperatures between 295 and 147 K. Spectra of the amorphous and annealed crystal deposited on a copper finger at 80 K were obtained. The spectra showed the existence of two conformers, anti and gauche, in the vapour and in the liquid. Approximately 12 infrared bands were reduced in intensity, and six of the same bands present in the fluid phases in the Raman spectra vanished upon crystallization. From the intensity variations of two band pairs with temperature, a 1H ◦ value of 0.4 ± 0. 3k J mol −1 between the conformers was obtained in the liquid, anti being the low-energy conformer. Small increases and decreases in the IR band intensities were observed in the matrix spectra after annealing to 32 K (nitrogen), 36 K (argon) and 50 K (krypton). The enthalpy difference between the conformers is low in the matrices, but the anti conformer had lower energy than the gauche conformer. Ab initio calculations were performed at the HF/6‐311G ∗ level and gave optimized geometries, vibrational wavenumbers and infrared and Raman intensities for the anti and gauche conformers. The conformational energy derived was 4.4 kJ mol −1 with anti being the low-energy conformer. The dipole moments were calculated to be 1.2 and 3.1 D for the anti and gauche conformers, respectively. Correlation between the observed and calculated wavenumbers of both conformers revealed that anti was present in the crystal, and complete assignments of the spectra were carried out. Copyright  2001 John Wiley & Sons, Ltd.

The Raman spectra (3500–20 cm−1) of liquid with depolarization values and solid, as well as the infrared spectra of the gas, the sample isolated in argon and nitrogen matrices at ca. 5 K and solid dimethyl vinyl fluorosilane, CH2 CHSi(CH3)2F, have been recorded. Both gauche and syn rotamers have been identified in the fluid phases but only the syn conformer remains in the solid. Variable temperature (−55 to −150°C) studies of the infrared spectra (4000 and 400 cm−1) of dimethyl vinyl fluorosilane dissolved in liquid xenon and krypton have been recorded. From the xenon and krypton data, the enthalpy differences have been determined to be 53±9 cm−1 (0.64±0.10 kJ/mol) and 44±7 cm−1 (0.53±0.09 kJ/mol), respectively, with the gauche conformer being the more stable form. The intensity variations with temperature of the Raman spectrum of the liquid gave an enthalpy difference of 25±15 cm−1 (0.30±0.18 kJ/mol) also with the gauche conformer being the more stable form. Vibrational assignments are provided for both conformers. Complete equilibrium geometries have been determined for both rotamers using ab initio calculations employing the 6-31G(d), 6-311+G(d,p) and 6-311+G(2d,2p) basis sets at the levels of restricted Hartree–Fock (RHF) and/or with full electron correlation by the perturbation method, Moller–Plesset (MP), to second order. The syn conformer is predicted to be the more stable conformer from all ab initio calculations except those of MP2/6-31(d) which predict the gauche form being the more stable conformer by 54 cm−1 (0.65 kJ/mol) although the values favoring the syn form are all very small. These results are compared to the corresponding quantities of some similar molecules.

Chloromethylmethyldifluorosilane (CH2ClCH3SiF2) was synthesized for the first time. Raman spectra of the liquid were recorded at various temperatures between 298 and 175 K and spectra of the amorphous and crystalline solids were obtained. Infrared spectra were recorded in the vapour, amorphous and crystalline solid phases in the MIR and FIR regions. Additional MIR spectra of the compound isolated in argon and nitrogen matrices were obtained at 10 K. The spectra of chloromethylmethyldifluorosilane showed the existence of two conformers, anti and gauche, present in the vapour and in the liquid. By careful annealing the amorphous solid formed by depositing the vapour on a cold Cu finger (Raman) or on CsI or silicon windows (infrared) at 80 K, two different crystals were formed. One of these, obtained after annealing to 125 K (crystal I), contained the anti conformer; the other, achieved after annealing to ca 170 K (crystal II), contained molecules in the gauche conformation. If the liquid was cooled, crystal II was formed, suggesting this crystal to be stable, whereas crystal I appeared to be metastable. The anti and gauche conformers had approximately the same enthalpy in the liquid, giving a negligible ΔH (gauche–anti) equal to 0.2 ± 0.4 kJ mol−1, but gauche was the conformer of the stable crystal II. Intensity variations in the matrix spectra after annealing indicated that gauche was the low-enthalpy conformer in both matrices and probably also in the vapour. These experimental data make a very reliable assignment of the conformer bands possible. Ab initio calculations were performed at the HF/6–311G* level, from which optimized geometries, infrared and Raman intensities and scaled vibrational wavenumbers for the anti and gauche conformers were obtained. The conformational energy derived was 5.9 kJ mol−1, with gauche being the low-energy conformer. Copyright © 2000 John Wiley & Sons, Ltd.

The infrared spectra of 1,1,1-trifluoropropyl trifluorosilane were recorded in the vapour, amorphous and crystalline solid phases in the range 4000–50 cm −1 . Additional MIR spectra of the compound isolated in argon and nitrogen matrices at 5 K before and after annealing to temperatures in the range 15–35 K were obtained. Raman spectra of the liquid were recorded at various temperatures between 298 and 163 K. Spectra of the amorphous solid on a copper finger were recorded and spectra of crystalline solids cooled by different techniques were obtained. The spectra showed the existence of two conformers – anti and gauche – present in the vapour and in the liquid. Approximately five Raman bands present in the fluid phases vanished upon crystallization, but only small changes occurred in the corresponding infrared spectra. From intensity variations with temperature in the Raman spectra of the liquid, the enthalpy difference was determined to be ΔH(gauche-anti)=3.2 kJ mol −1 . Ab initio calculations were performed using the Gaussian 94 program with the HF/6-311G* basis set and gave optimized geometries, infrared and Raman intensities and scaled vibrational frequencies for the anti and gauche conformers. The conformational energy was calculated to be 5.3 kJ mol −1 with anti being the low energy conformer.

Ethyl bromosilane (CH 3 CH 2 SiH 2 Br) and ethyl dibromosilane (CH 3 CH 2 SiHBr 2 ) were synthesized and their infrared and Raman spectra determined in vapour (IR), liquid (Raman), amorphous solid, and crystalline states. Additional infrared spectra of the compounds isolated in argon and nitrogen matrices at 5 K were recorded before and after annealing to temperatures in the range of 15–35 K. Raman spectra of the liquid were recorded at various temperatures between 295 and 153 K. Both the spectra showed the existence of two conformers – anti and gauche – present in the fluid and amorphous phases. The crystals contained the gauche conformer for bromide and anti conformer for the dibromide in accordance with the results for the chloro and iodo homologues. The enthalpy differences in the liquids measured in Raman gave: Δ H (anti-gauche) = 1.8 ± 0.3 and Δ H (gauche-anti) = 2.1 ± 0.3 kJ mol −1 , respectively. Ab initio calculations were performed using the Gaussian 94 program with the HF/6-311G* basis set and gave optimized geometries, infrared and Raman intensities and scaled vibrational frequencies for the anti and gauche conformers. The conformational energies were calculated to be 0.02 kJ mol −1 for ethyl bromosilane and 0.3 kJ mol −1 for ethyl dibromosilane with the anti and gauche conformers having the lower energy, respectively.

The Raman spectra (3500 to 30 cm−1) of allyltrifluorosilane, CH2CHCH2SiF3, in the liquid with quantitative depolarization ratios and solid states, and the infrared spectra (3500 to 30 cm−1) of the gas and solid have been recorded. Additionally, the mid-infrared spectra of the sample dissolved in liquified xenon as a function of temperature (−100° to −55°C) have been recorded. All of these data indicate there are two conformers, the more stable gauche rotamer and a very small amount of the cis conformer in the fluid states, but only the gauche form remains in the polycrystalline solid. The variable temperature studies of the infrared spectrum of the xenon solution indicate a relatively large enthalpy difference of 354±30 cm−1 (4.23±0.36 kJ/mol) between the conformers. The fundamental frequencies for the asymmetric (54 cm−1) and SiF3 (48 cm−1) torsions for the gauche conformer were observed in the far infrared spectrum, and from the SiF3 torsional frequency the barrier to internal rotation is calculated to have a value of 525 cm−1 (6.28 kJ/mol). A complete vibrational assignment is presented for the gauche conformer that is consistent with the predicted wavenumbers utilizing the force constants from ab initio MP2/6-31G* calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational wavenumbers have been obtained from RHF/6-31G* and/or MP2/6-31G* ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with corresponding results for some similar molecules.

Bromomethyl dimethyl silane, CH 2 Br(CH 3 ) 2 SiH (BDS), and its deuterated analogue, CH 2 Br(CH 3 ) 2 SiD (BDSD), were synthesised for the first time. Raman spectra of both liquids were recorded at various temperatures between 295 and 160 K and spectra of the amorphous and crystalline solids were obtained. Infrared spectra were recorded in the vapour phase and in the amorphous and crystalline states in the range 4000–60 cm −1 . Additional infrared spectra of the compounds isolated in argon and nitrogen matrices were recorded at 5 K before and after annealing to temperatures in the range 15–35 K. The compounds exist in anti and gauche conformers due to restricted rotation of the CH 2 Br group. Raman temperature studies gave an average Δ H conf 0 ( gauche–anti ) of 0.6±0.3 kJ mol −1 , anti being the low energy conformer in the liquid and in the matrices. Two different crystals were observed for these molecules after careful annealing of the amorphous solid in the range 110–150 K: one crystal (I) containing molecules in the gauche conformation and one crystal (II) with molecules in the anti conformation. For the parent molecule, both of these crystals were repeatedly investigated in the infrared and in the Raman spectra, while crystallisation was much more difficult to achieve for the deuterated compound. However, two different crystals (I, III) both containing the gauche conformer, was observed in the Raman spectra and one with anti (II) in the infrared spectrum of the deuterated compound. Ab initio calculations at the HF/6-311G* level gave vibrational frequencies and Raman and infrared intensities for both conformers. Complete assignments were made for the anti and gauche conformer spectra of both molecules.

A vibrational spectroscopic study of bromomethyl dimethyl chlorosilane (CH 2 Br(CH 3 ) 2 SiCl) was carried out. Infrared spectra of the vapour, the amorphous and crystalline solids at liquid nitrogen temperature, and spectra of argon and nitrogen matrices (1:1000) at about 5 K were recorded. Raman spectra of the liquid were obtained at five temperatures between 295 and 190 K, and spectra of the crystalline solid were recorded. Owing to restricted rotation around the CSi bond, the compound apparently exists as anti and gauche conformers. Approximately five IR and Raman bands present in the fluid phases vanished upon crystallization. From intensity variations with temperature in the Raman spectra of the liquid, a ΔH o value of 1.0 ± 0.4 kJ mol −1 was obtained. The high energy conformer bands did not vanish in the matrix spectra after annealing to approximately 39 K in the argon matrix, suggesting a barrier higher than 10 kJ mol −1 . Ab initio calculations were carried out with the gaussian 94 program using the basis sets HF/3-21G∗ and HF/6-311G∗; optimized geometries, IR and Raman intensities, and the vibrational frequencies for the anti and gauche conformers were calculated. After appropriate scaling, reasonably good agreement was obtained between the experimental and calculated wavenumbers for the anti and gauche conformers, suggesting the anti conformer to be the more stable and present in the crystal.

The IR spectra of chloromethyl dimethyl chlorosilane (CH 2 Cl(CH 3 ) 2 SiCl) were recorded as a vapour and as amorphous and crystalline solids in the 4000-50 cm −1 range and isolated in argon and nitrogen matrices at ca. 5 K. Raman spectra were recorded at room temperature and at various temperatures, partly as a super cooled liquid between 295 and 188 K and spectra of the amorphous and crystalline solids were obtained at 80 K and at 185 K. The compound exists in anti and gauche conformers, and six IR bands and Raman bands present in the vapour, liquid and amorphous states vanished upon crystallization. The intensity variations with temperature of four band pairs in the Raman spectra of the liquid were employed in van't Hoff plots and gave a value of 0.7 ± 0.2 kJ mol −1 for ΔH o ( gauche-anti ). The anti conformer had the lower energy and was also present in the crystal. Only small changes were detected when the matrix spectra were annealed to 39 K (argon) or 34 K (nitrogen) suggesting a conformational barrier larger than 10 kJ mol −1 . Ab initio calculations were carried out with the gaussian 94 program using the basis sets HF/3-21G∗, HF/6-31 G∗, HF/6-311G∗ and MP2/6-311G∗; optimized geometries, IR and Raman intensities and the vibrational frequencies for the anti and gauche conformers were calculated. After appropriate scaling a reasonably good agreement was obtained between the experimental and calculated wavenumbers for both conformers.

The H/D exchange process in the imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide- and chloride ([C10mim][Br] and [C10mim][Cl]) in D2O solutions of various concentrations was studied applying (1)H, (13)C NMR, and Raman spectroscopy. The time dependencies of integral intensities in NMR spectra indicate that the H/D exchange in [C10mim][Br] at very high dilution (10(-4) mole fraction of RTIL) runs only slightly faster than in [C10mim][Cl]. The kinetics of this process drastically changes above critical aggregation concentration (CAC). The time required to reach the apparent reaction saturation regime in the solutions of 0.01 mole fraction of RTIL was less 10 h for [C10mim][Br], whereas no such features were seen for [C10mim][Cl] even tens of days after the sample was prepared. The H/D exchange was not observed in the liquid crystalline gel mesophase. The role of anions, self-aggregation (micellization), and mesophase formation has been discussed. Crucial influence of Br(-) and Cl(-) anions on the H/D exchange rates above CAC could be related to the short-range ordering and molecular microdynamics, in particular that of water molecules. The concept of the conformational changes coupled with the H/D exchange in imidazolium-based ionic liquids with longer hydrocarbon chains can be rejected in the light of (13)C NMR experiment. The revealed changes in (13)C NMR spectra are caused by the secondary ((13)C) isotope effects not being the signal shifts due to the conformational trans-gauche transition.

The infrared (3100–40 cm −1 ) spectra of gaseous and solid and Raman (3200–20 cm −1 ) spectra of liquid with qualitative depolarization values and solid n -propyltrifluorosilane, CH 3 CH 2 CH 2 SiF 3 , have been recorded. Additionally the infrared spectra of the sample in nitrogen and argon matrices have been recorded. Both the anti and gauche conformers have been identified in the fluid phases but only the anti conformer remains in the solid. Variable temperature (−105 to −150 °C) studies of the infrared spectra of the sample dissolved in liquid krypton have been recorded and the enthalpy difference has been determined to be 135±14 cm −1 (1.62±0.17 kJ mol −1 ) with the anti conformer the more stable form. At ambient temperature it is estimated that there is 51±2% of the gauche conformer present. Also the enthalpy difference in the liquid was obtained from variable temperature studies of the Raman spectra and from three conformer pairs an average value of 179±18 cm −1 (2.14±0.22 kJ mol −1 ) was obtained again with the anti form the more stable conformer. Relatively complete vibrational assignments are proposed for both conformers based on the relative infrared and Raman spectral intensities, infrared band contours, depolarization ratios which are supported by normal coordinate calculations. The geometrical parameters, harmonic force constants, vibrational frequencies, infrared intensities, Raman activities, depolarization ratios, and energy differences have been obtained for the anti and gauche conformers from ab initio MP2/6-31G(d) calculations. Structural parameters and energy differences have also been obtained utilizing the larger 6-311+G(d, p) and 6-311+G(2d, 2p) basis sets. By utilizing the previously reported microwave rotational constants for five isotopomers of CH 3 SiF 3 along with ab initio predicted structural values, r 0 parameters have been obtained for methyltrifluorosilane. Similarly, from the ab initio predicted parameters ‘adjusted r 0 ’ parameters have been estimated for both conformers of n -propyltrifluorosilane. The results are discussed and compared with those obtained for some similar molecules.