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The microwave spectrum of isopropylisocyanate, (CH 3 ) 2 CHNCO, has been investigated from 11,000 to 21,000 MHz and 18 transitions for the more stable trans conformer were assigned and A = 6693.23(15), B = 2263.10(3), C = 1960.05(2) MHz were obtained. By utilizing these rotational constants along with ab initio MP2(full)/6-311 + G(d,p) predicted structural values, adjusted r 0 parameters have been obtained for the trans conformer along with estimated values for the gauche conformer. Variable temperature Raman and infrared spectra of xenon solutions have been recorded and a ΔH value of 115 ± 11 cm −1 (1.38 ± 0.13 kJ/mol) has been determined. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to cc-PVQZ for MP2(full) and 6-311 + G(3df,3pd) for density functional theory calculations by the B3LYP method. From the MP2(full)/cc-PVQZ calculations an energy difference of 87 cm −1 (1.04 kJ/mol) is predicted between the trans and the gauche forms and 168 cm −1 (2.01 kJ/mol) for the cis form which is a transition state.

Fourier transform microwave spectrum of cyclopentylamine, c–C5H9NH2 has been recorded, and seven transitions have been assigned for the most abundant conformer, and the rotational constants have been determined: A = 4909.46(5), B = 3599.01(4), and C = 2932.94(4). From the determined microwave rotational constants and ab initio MP2(full)/6-311 + G(d,p) predicted structural values, adjusted r0 parameters are reported with distances (A): rCα–Cβ = 1.529(3), rCβ–Cγ = 1.544(3), rCγ–Cγ = 1.550(3), rCα–N = 1.470(3), and angles (°) ∠CCN = 108.7(5), ∠CβCαCβ = 101.4(5), and τCβCαCβ′Cγ′ = 42.0(5). The infrared spectra (4000–220 cm−1) of the gas have been recorded. Additionally, the variable temperature (−60 to −100 °C) Raman spectra of the sample dissolved in liquefied xenon was recorded from (3800–50 cm−1). The four possible conformers have been identified, and their relative stabilities obtained with enthalpy difference relative to t-Ax of 211 ± 21 cm−1 for t-Eq ≥ 227 ± 22 cm−1 for g-Eq ≥ 255 ± 25 cm−1 for g-Ax. The percentage of the four conformers is estimated to be 53% for the t-Ax, 11 ± 1% for t-Eq, 20 ± 2% for g-Ax and 16 ± 2% for g-Eq at ambient temperature. The conformational stabilities have been predicted from ab initio calculations by utilizing several different basis sets up to aug-cc-pVTZ from both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been provided for the observed bands for all four conformers, which are predicted by MP2(full)/6-31G(d) ab initio calculations to predict harmonic force constants, wavenumbers, infrared intensities, Raman activities, and depolarization ratios for all of the conformers. The results are discussed and compared to the corresponding properties of some related molecules. Copyright © 2014 John Wiley & Sons, Ltd.

Variable temperature (-50 to -100 degrees C) Raman spectra (3500-136 cm(-1)) were recorded of ethynylcyclopentane, c-C5H9CCH in liquid xenon. The envelope-equatorial (Eq) conformer was determined more stable than envelope-axial (Ax) form with enthalpy difference of 94 +/- 9 cm(-1) (1.12 +/- 0.11 kJ/mol) and 39 +/- 2% Ax conformer present at ambient temperature. The conformational stabilities have been predicted from ab initio calculations with basis sets up to aug-cc-pVTZ. From previously reported microwave rotational constants and ab initio Mp2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters are reported Eq [Ax] distances (angstrom) rC=C = 1.211(3) [1.211(3)], rC(alpha)-C C = 1.461(3) [1.467(3)], rC(alpha)-C-beta = 1.542(3) [1.542(3)], rC(beta)-C-gamma = 1.541(3)[1.542(3)], rC(gamma)-C-y' = 1.556(3)[1.555(3)] and angles (degrees) angle C alpha-C C = 179.4(5) [179.9(5)], angle C beta C alpha-C C = 113.7(5) [111.5(5)], angle C beta C alpha C beta' = 102.6(5) [102.1(5)], angle C alpha C beta C gamma = 103.7(5) [103.7(5)], angle C beta C gamma C gamma' = 106.0(5) [105.9(5)] and tau C beta C alpha C beta'C gamma' = 40.8(5) [41.6(5)]. Vibrational assignments are reported, supported by ab initio predictions and results are discussed. (C) 2013 Elsevier B.V. All rights reserved.

The Raman and infrared spectra (4000 to 50 cm–1) of the gas, liquid or solution, and solid have been recorded of n-propylamine, CH3CH2CH2NH2. Variable temperature (−60 to −100 °C) studies of the Raman (1175 to 625 cm–1) and far infrared (600 to 10 cm–1) spectra dissolved in liquid xenon were carried out. From these data, the five possible conformers were identified and their relative stabilities obtained with enthalpy difference relative to trans–trans (Tt) for trans–gauche (Tg) of 79 ± 9 cm–1 (0.9 ± 0.1 kJ/mol); for Gg of 91 ± 26 cm–1 (1.08 ± 0.3 kJ/mol); for Gg′ of 135 ± 21 cm–1 (1.61 ± 0.2 kJ/mol); for Gt of 143 ± 11 cm–1 (1.71 ± 0.1 kJ/mol). The percentage of the five conformers is estimated to be 18% for the Tt, 24 ± 1% for Tg, 23 ± 3% for Gg, 18 ± 1% for Gg′ and 18 ± 1% for Gt at ambient temperature. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug-cc-pVTZ from both second-order Moller–Plesset (MP2, full) and density functional theory calculations by the Becke, three-parameter, Lee–Yang–Parr method. Vibrational assignments were provided for the observed bands for all five conformers, which are supported by MP2(full)/6-31G(d) ab initio calculations to predict harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. Estimated r0 structural parameters were obtained from adjusted MP2(full)/6-311+G(d,p) calculations. The results are discussed and compared with the corresponding properties of some related molecules. Copyright © 2012 John Wiley & Sons, Ltd.

The Raman and infrared spectra (4000-50 cm(-1)) of the gas, liquid or solution, and solid have been recorded of isopropylamine, (CH3)(2)CHNH2. Variable temperature (-50 to -100 degrees C) studies of the Raman spectra (3500-100 cm(-1)) dissolved in liquid xenon have been carried out. From these data, both the trans and gauche conformers have been identified and their relative stability obtained. The enthalpy difference has been determined to be 113 +/- 11 cm(-1)(1.35 +/- 0.13 kJ mol(-1)) with the trans conformer the more stable form. The percentage of the gauche conformer is estimated to be 54 +/- 1% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug-cc-pVTZ from both MP2(full) and density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants along with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters have been obtained for the trans conformer. The determined heavy atom and NH2 distances are (angstrom) C-C = 1.530(3), C-N = 1.465(3), N-H = 1.019(3) and angles in degrees (degrees) angle NCC = 108.9(5), angle CCC = 111.0(5), angle HNC = 110.3(5). The structural parameters for the gauche conformer were estimated by using the same adjustment differences to the gauche form as those obtained for the corresponding trans parameters. Vibrational assignments have been provided for the observed bands for both conformers which are supported by MP2(full)/6-31 G(d)ab initio calculations to predict harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are discussed and compared to the corresponding properties of some related molecules. (C) 2011 Elsevier B.V. All rights reserved.

In this second part, the authors study the convergence of the iterative procedures based on the stepwise coupling methods in the second order case: especially the Eigenvector Method of H. J. BECHER and R. MATTES and the Matrix Polynomial Expansion Method of A. ALIX. It is shown that under some simple conditions on the number m0 of iterative cycles and on the function which defines the stepwise introduction of the kinematic coupling, that the limit obtained is unique. The expression of that limit and its properties are discussed in detail.

Full infrared and Raman vibrational assignments of pyrazine N-oxide and its fully deuterated analogue have been made. Three changes are recommended to an earlier assignment of the -d0 compound. Coupling within the molecule is examined employing the νD/νH ratio and by comparisons with similar molecules.

The formation of halogen bonded complexes between trimethylamine (TMA) and the trifluoro halomethanes CF 3 I, CF 3 Br and CF 3 Cl dissolved in liquid xenon, krypton and argon, respectively, has been investigated using FTIR spectroscopy. For all Lewis acids, evidence was found for the formation of C–X⋯N halogen bonded 1:1 complexes. This study provides the first experimental characterization of a complex formed under thermodynamic equilibrium conditions in solution via a C–Cl⋯N halogen bond. Using spectra recorded at different temperatures, the complexation enthalpies for the complexes were determined to be −28.7(1) kJ mol −1 (CF 3 I · TMA), −18.3(1) kJ mol −1 (CF 3 Br · TMA) and −8.9(2) kJ mol −1 (CF 3 Cl · TMA). The results from the cryospectroscopic study are compared with ab initio calculations at the MP2/6-311++G(d,p) + LanL2DZ∗ level.

The site-selectivity of Pd-catalyzed reactions of 2,3-dihalopyridines [2,3-dichloropyridine (1), 2,3-dibromopyridine (3) and 2-chloro-3-iodopyridine (2)] has been studied by computing the oxidative addition process using DFT calculations. The activating effect of the azine nitrogen atom on C(2) and C(3) has been obtained by comparison with the corresponding dihalobenzene [1,2-dichlorobenzene (4), 1,2-dibromobenzene (5) and 1-chloro-2-iodobenzene (6)]. The performed calculations involve the use of Pd(PPh3)2, Pd(BINAP) and Pd(XANTPHOS) as catalysts. The formation of pre-reactive complexes proved to be a very important factor in the determination of the activation energy values. A comparison with the simplified systems Pd(PPH3)2, Pd(H-BINAP) and Pd(HXANTPHOS) revealed that care has to be taken when simplified catalyst systems are used for the simulation of the oxidative addition process.

Infrared and Raman spectra of solutions in liquid argon and krypton containing dimethyl ether or its fully deuterated isotopomer and (12)CO(2) or (13)CO(2) are investigated. The spectra lead to new data on the nu(1) (CO(2) )/2 nu(2) (CO(2) ) resonances appearing in the complex of CO(2) with the ether. The experimental data, and their interpretation, is supported by MP2/6-311++G(2d,2p) calculations of the cubic and quartic force constants and of the first and higher order dipole moment derivatives required for the modelling of the Fermi and Darling-Dennison resonances observed.

Vibrational modes in an achiral molecule may acquire rotational strength by complexation to a chiral molecule, as happens for achiral solvent molecules complexed to a chiral solute. We investigate this transfer of chirality in vibrational circular dichroism for the pulegone molecule in CDCl3 solvent from the point of view of the robustness concept introduced recently. It turns out that the transfer of chirality yields nonrobust modes, which means that, although they are observed in vibrational circular dichroism (VCD) experiments, the sign of these modes cannot be predicted reliably with standard (Density Functional Theory) VCD calculations. This limits the usefulness of the induced chirality phenomenon for obtaining information on the intermolecular interactions that give rise to it. Chirality 21:E287–E297, 2009. © 2010 Wiley-Liss, Inc.

The mid (4000–500 cm−1) and near (10,000–4000 cm−1) infrared spectra of solutions in liquid krypton containing mixtures of F2ClCH and FCD3 or of Cl2FCH and FCD3 show the formation of 1:1 complexes. MP2/6-311++G(2d, 2p) ab initio calculations suggest that the main interaction responsible for the formation of the complexes is the hydrogen bond between the haloform C–H bond and the fluorine atom of the base molecule. The observation of blue shifts upon complexation of 24.8, 51.5 and 87 cm−1 for the fundamental, the first and the second overtone of the haloform ν1 in F2ClCH, and of 25.0, 50.2 and 87 cm−1 in Cl2FCH show that in either case the hydrogen bond is of the blue-shifting type. Upon complexation the intensity of the fundamental ν1 in F2ClCH decreases by a factor of approximately 5, while that in Cl2FCH increases, by a factor of approximately 4. At the same time, the intensities of the first and second overtones reveal only modest decreases. The MP2/6-311++G(2d, 2p) calculations predict the existence of more than one conformer for either complex. No spectral evidence for conformational equilibria in the complexes has been detected. One-dimensional anharmonic model calculations have been made to simulate the blue shift and intensity behaviour of the haloform ν1 vibrations. For both complexes these calculations reproduce the experimental data with reasonable success.

It is shown how the presence of a chiral compound in solution induces chirality in the surrounding solvent molecules. Using Vibrational Circular Dichroism on camphor dissolved in deuterated chloroform, it is found that the C–D stretch in the latter indeed becomes VCD active. The experimental results agree with ab initio computed spectra for 1:1 associations between the solvent and solute.

The intramolecular amination of N -(3-bromopyridin-2-yl)azaheteroarylamines and N -(2-chloropyridin-3-yl)azaheteroarylamines was investigated. In this way we unraveled the mechanism of the ring closure reaction in the auto-tandem amination (inter- and intramolecular Pd-catalyzed amination) of 2,3-dibromopyridine with amino(benzo)(di)azines and 2-chloro-3-iodopyridine with amino(benzo)(di)azines, respectively. Depending on the substrate a Pd-catalyzed amination, a base-assisted nucleophilic aromatic substitution or a combination of both is occurring. An explanation based on the aromaticity of the amidine, supported by theoretical calculations, is provided. In addition we gained evidence that the intramolecular metal-catalyzed amination of N -(3-bromopyridin-2-yl)azaheteroarylamines and N -(2-chloropyridin-3-yl)azaheteroarylamines indeed involves a nitrogen atom that is not substituted with a hydrogen atom.

Reports on the successful oxidative alkylamination of azines by the SNH-reaction, with the use of alkylamines other than methylamine, are very scarce. Hitherto, the experimental limitation to extend oxidative amination of azines with NH3/KMnO4 to oxidative alkylamination is solely ascribed to the low solubility of KMnO4 in alkylamines and the increased sensitivity of alkylamines towards oxidation in comparison with ammonia. Our experimental data for the first time prove that there is also a substrate dependence in this type of reaction. 2-Alkylamino-5-nitropyridines and 4-alkylaminoquinazolines were smoothly obtained by the treatment of 3-nitropyridine and quinazoline, respectively, with alkylamine/AgPy2MnO4. Although KMnO4 still gives moderate to good results with 3-nitropyridine, it is completely useless for reactions with quinazoline with the same alkylamines. The use of AgPy2MnO4 was found to give equal or superior results to those of KMnO4 depending on the alkylamine and the substrate used and therefore seems to be a promising general oxidant for successful oxidative alkylaminations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The absolute configurations of four bicylco[3.3.0]octane derivatives: endo -bicyclo[3.3.0]octane-2,6-diol, endo -2,6-diacetoxybicyclo[3.3.0]octane, endo -bicyclo[3.3.0]octane-2,6-dione and bicyclo[3.3.0]octa-2,6-dien-2,6-bistriflate were studied by vibrational circular dichroism (VCD). These chiral derivates are of interest as intermediates in the asymmetric synthesis of enantiomerically pure natural products and chiral ligands for asymmetric catalysis. VCD has been used to determine the absolute configuration of each compound, proving the capability of VCD for molecules with several stereogenic centres. IR and VCD spectra have been simulated at the B3LYP/6-31G ∗ level for all possible diastereomers. Based on the agreement between the experimental and the calculated spectrum, the stereochemistry of each compound could be assigned. The predicted absolute configurations are found to agree with literature data.

Variable temperature (-55 to -150 degrees C) studies of the infrared spectra (3200-100 cm(-1)) of cyclopropylmethyl isothiocyanate, c-C(3)H(5)CH(2)NCS, dissolved in liquefied rare gases (Xe and Kr), have been carried out. The infrared spectra of the gas and solid, as well as the Raman spectrum of the liquid, have also been recorded from 3200 to 100 cm(-1). By analyzing six conformer pairs in xenon solutions, a standard enthalpy difference of 228 +/- 23 cm(-1) (2.73 +/- 0.27 kJ.mol(-1)) was obtained with the gauche-cis (the first designation indicates the orientation of the CNCS group with respect to the three-membered ring, the second designation indicates the relative orientation of the NCS group with respect to the bridging C-C bond) rotamer the more stable form, and it is also the only form present in polycrystalline solid. Given statistical weights of 2:1 for the gauche-cis and cis-trans forms (the only stable conformers predicted); the abundance of cis-trans conformer present at ambient temperature is 14 +/- 2%. The potential surface describing the conformational interchange has been analyzed, and the corresponding two-dimensional Fourier coefficients were obtained. From MP2 ab initio calculations utilizing various basis sets with diffuse functions, the gauche-cis conformer is predicted to be more stable by 159-302 cm(-1), which is consistent with the experimental results. However, without diffuse functions, the conformational energy differences are nearly zero even with large basis sets. For calculations with density functional theory by the B3LYP method, basis sets without diffuse functions also predict smaller energy differences between the conformers, although not nearly as small as the MP2 results. A complete vibrational assignment for the gauche-cis conformer is proposed, and several fundamentals for the cis-trans conformer have been identified. The structural parameters, dipole moments, conformational stability, vibrational frequencies, and infrared and Raman intensities have been predicted from ab initio calculations and compared to the experimental values when applicable; the r(0) structural parameters are also estimated. The energies for the linear CNCS moiety were calculated. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.

The absolute configurations of two precursors, that is, 1-(3′,4′-dichlorophenyl)-propanol and 1-(3′,4′-dichlorophenyl)-propanamine, of a potent 2-mercapto-imidazoleCCR-2 receptor antagonist, JNJ-27553292, were determined using vibrational circular dichroism. As a consequence, the absolute configuration of the antagonist itself was also determined. The two precursor compounds were subjected to a thorough conformational analysis and rotational strengths were calculated at the B3LYP/cc-pVTZ level of theory. Based on these data, vibrational circular dichroism spectra were simulated, which in turn were compared with experimental spectra. Agreement between the spectra allowed the assignment of the absolute configuration, which is in agreement with the proposed configuration based on stereospecific reactions on similar compounds. Chirality 18:609–620, 2006. © 2006 Wiley-Liss, Inc.

Complexation enthalpies of the complexes of the haloforms HCCl(n)F(3-)(n) (n = 0-3) with dimethyl ether, oxirane, and acetone have been determined in liquid krypton and/or liquid argon using infrared spectroscopy. The same quantities were derived starting from ab initio complexation energies, calculated at the MP2=FULL/aug-cc-VTZ level, and by correcting these energies for thermodynamic and solvent contributions. The two sets of data are compared and discussed.

Mid-infrared spectra of cyclopropene (c-C3H4) mixtures with HCl or BF3, dissolved in liquefied argon and in liquefied nitrogen have been examined. Evidence was found for the formation of two different isomers of the 1:1 complexes: a pi-type complex in which the interaction occurs with the pi-bond of cyclopropene, and a sigma-type complex in which the electron acceptors interact with one of the CC single bonds. At lower temperatures, indications for the formation of a 1:2 chain-type complex were found. Using spectra recorded between 90 and 124 K in liquid argon, the complexation enthalpies for the pi- and sigma-complexes with HCl were determined to be -8.8(3) and -7.9(3) kJ mol-1, respectively. For the pi-complex with BF3 a value of -7.4(3)kJ mol-1 was found. Structural and spectral information on the 1:1 complexes was obtained from B3LYP/6-311++G(d,p) and MP2(FC)/6-31+G(d) calculations. Using Free Energy Perturbation Monte Carlo simulations to calculate the solvent influences, and statistical thermodynamics to account for zero-point vibrational and thermal contributions, the solution enthalpies were transformed into complexation energies with values of -15.5(6) and -13.8(8) kJ mol-1 for the pi- and sigma-isomers of c-C3H4.HCl, respectively, and of -12.7(8) kJ mol-1 for the pi-type BF3 complex.

Mid-infrared spectra of mixed solutions in liquid xenon containing fluoroform and either ammonia or pyridine have been investigated at temperatures between 173 and 213 K. For both Lewis bases, a new band is found in the CH stretching region at a frequency approximately 5 cm(-1) higher than that of monomer fluoroform, which is assigned to a complex between fluoroform and the Lewis base. A detailed analysis of the nu1/2nu(4) Fermi resonance in the proton donor shows that the blue shifts observed for the complexes are not caused by a strengthening of the CH bond during the complexation, but are due to the changes in the Fermi resonance interactions. Information on the nu1/2nu(4) Fermi resonance was also obtained for the complexes of fluoroform with dimethyl ether and trimethyl amine.

Frequency shifts of the C−H stretching mode, ν1, of the haloforms CHF3, CHClF2, CHCl2F, and CHCl3 because of complexation with dimethyl ether have been calculated from an ab initio interaction pote...

Density functional theoretical (DFT) calculations using the 6-311+G* basis set were carried out to study the vibrational spectrum of E-1,2-bis(3-methoxy-2-thienyl)ethene in the solid state. Based on the calculated frequencies, infrared intensities and potential energy distributions (PED), the experimental IR and Raman spectra of the solid phase were assigned.

Infrared (3500-50 cm - 1 ) spectra of gaseous and Raman (3500-50 cm - 1 ) spectra of liquid aminomethyl cyclopropane (cyclopropyl methylamine), c-C 3 H 5 CH 2 NH 2 have been recorded. Additional variable temperature (-55 to -100 °C) studies of the mid-infrared (3500-400 cm - 1 ) spectra of the sample dissolved in liquid xenon as well as variable temperature (-79 to -112 °C) studies of the far-infrared spectra (600-50 cm - 1 ) of krypton solutions have been obtained. From these data the enthalpy difference has been determined to be 109 ′ 11 cm - 1 (1.30 ′ 0.13 kJ/mol) between the most stable gauche-gauche-1 (Gg-1) conformer (the first gauche designation, capital G, for the heavy atom conformation along the C-C bond, and the second gauche designation, lower case g, for the amino torsion along C-N bond) and the second most stable conformation, gauche-trans (Gt). The third most stable conformer is the cis-gauche (Cg) form with an enthalpy difference of 267 ′ 28 cm - 1 (3.19 ′ 0.33 kJ/mol) to the most stable conformer. Larger enthalpy values of 400 ′ 40 cm - 1 and 480 ′ 48 cm - 1 were obtained for the Gg-2 and Ct conformers, respectively. From these data, the following conformer percentages are estimated at ambient temperature: 49% Gg-1, 29% Gt, 13% Cg, 7% Gg-2, and 2%, Ct. Ab initio calculations have been carried out with several different basis sets up to MP2/ 6-311G(2df,2pd) as well as with diffuse functions to determine the conformational stability. Without diffuse functions, the Gt conformer is predicted as the most stable conformer, whereas with diffuse functions, the Gg- 1 form is predicted to be the most stable rotamer, and the density functional calculations by the B3LYP method with the same corresponding basis sets all predict the Gt form as the most stable conformer. Additionally, force constants, infrared intensities, Raman activities, depolarization ratios, and scaled vibrational frequencies have been determined from MP2/6-31G(d) calculations. Vibrational assignments are provided for most of the fundamentals for the Gg- 1 and Gt conformers. Adjusted r 0 structural parameters have been obtained by combining ab initio MP2/6-311+G(d,p) predicted values and previously reported microwave data for the Gg-1 and Gt forms. Many of the determined results are compared to the corresponding parameters for some other similar organoamines.

The infrared spectra of the solid phases of fluorocyclohexane (FCH) and bromocyclohexane (BCH) have been investigated at temperatures between 77 and 286 K and between 77 and 216 K, respectively. The solid films were formed by cooling liquid films and by condensing vapors of FCH or BCH onto a cold window. During annealing of the deposited film of the FCH a metastable phase, which was interpreted to be the undercooled plastic phase, was observed in the temperature interval between 100 and 143 K; in this phase both axial (a) and equatorial (e) conformers are present with similar concentrations. Near 143 K, an irreversible transition from the undercooled plastic phase to an anisotropic phase was observed. In this phase a non-negligible and reproducible amount of the a-conformer remains. Using dissolution experiments in liquid krypton, the concentration ratio of the conformer (ce/ca)solid in the anisotropic phase was determined to be 17(1). At 188 K the reversible phase transition from the anisotropic to the plastic phase was observed. The infrared spectra of the plastic phase of FCH in the temperature interval between 188 and 283 K indicate the existence of a conformational equilibrium e ⇆ a. The similarity of the spectra suggests this phase is identical to the phase observed between 77 and 143 K. The standard enthalpy difference ΔH° between the conformers in this phase is found to be 1.16(5) kJ mol−1, with the e-conformer being more stable. During the annealing of the deposited BCH film a new metastable, anisotropic phase, crystal I, was observed in the temperature interval between 77 and 160 K. At ca. 160 K an irreversible phase transition from crystal I to another anisotropic crystalline phase, crystal II, takes place. In both crystalline phases only the e-conformer is present. From the experiments it was concluded that the conformational mobility dominates the formation of the anisotropic phase of FCH and of the lower temperature anisotropic phase I of BCH.

Complexes of haloforms of the type HCCl(n)F(3-)(n) (n = 1-3) with dimethyl ether have been studied in liquid argon and liquid krypton, using infrared spectroscopy. For the haloform C[bond]H stretching mode, the complexation causes blue shifts of 10.6 and 4.8 cm(-1) for HCClF(2) and HCCl(2)F, respectively, while for HCCl(3) a red shift of 8.3 cm(-1) is observed. The ratio of the band areas of the haloform C[bond]H stretching in complex and monomer was determined to be 0.86(4) for HCClF(2), 33(3) for HCCl(2)F, and 56(3) for HCCl(3). These observations, combined with those for the HCF(3) complex with the same ether (J. Am. Chem. Soc. 2001, 123, 12290), have been analyzed using ab initio calculations at the MP2[double bond]FC/6-31G(d) level, and using some recent models for improper hydrogen bonding. Ab initio calculations on the haloforms embedded in a homogeneous electric field to model the influence of the ether suggest that the complexation shift of the haloform C[bond]H stretching is largely explained by the electric field effect induced by the electron donor in the proton donor. The model calculations also show that the electric field effect accounts for the observed intensity changes of the haloform C[bond]H stretches.

Midinfrared spectra of solutions of fluorocyclohexane, C6H11F, in liquid Kr (LKr) have been investigated at temperatures between 120 and 188 K. Three temperature intervals are distinguished for the equatorial (e) ⇌ axial (a) conformational relaxation. At temperatures below 141 K the rate of conformational equilibration is negligible and the population ratio of the conformers is “frozen”, while at temperatures above 151 K the equilibrium is established nearly instantaneously. In the intermediate temperature interval, the relaxation times are such that the equilibration can be followed using FTIR spectroscopy. From spectra recorded between 151 and 188 K the standard enthalpy difference ΔH° in LKr was determined to be 1.3 (4) kJ mol-1. Between 141 and 151 K, and starting from solutions with nonequilibrium conformer populations, the conformational relaxation was studied as a function of time. From these data, the enthalpy ΔH⧧ and entropy ΔS⧧ of activation for the a- to e-conformer interconversion were found t...

FT-microwave spectroscopy was carried out where the trans conformer was identified to be the most stable conformer. Variable temperature (-60 to -100 degrees C) studies of the Raman spectra (4000-50 cm(-1)) of ethylamine, CH3CH2NH2 dissolved in liquefied xenon have been carried out. From these data both conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 62 +/- 6 cm(-1) (0.746 +/- 0.072 kJ mol(-1)) with the trans conformer the more stable form. The percentage of the gauche conformer is estimated to be 60% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations with the Moller-Plesset perturbation method to the second order (MP2(full)) and the fourth order (MP4(SDTQ)) as well as with density functional theory by the B3LYP method by utilizing a variety of basis sets. Vibrational assignments have been made for the observed bands which have been predicted by MP2(full)/6-31G(d) ab initio calculations which includes harmonic force fields, frequencies, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are discussed and compared to the corresponding properties of some similar molecule. (C) 2014 Published by Elsevier B.V.

The mid infrared spectra of methylcyclopropane−HCl and methylcyclopropane−BF3 mixtures, dissolved in liquid argon (LAr) or liquid nitrogen (LN2), have been examined. In LAr solutions, evidence was found for the formation of two different isomers of the 1:1 van der Waals complexesan asymmetric complex, in which the electron acceptor interacts with the C−C bond adjacent to the methyl group, and a symmetric complex in which the interaction occurs with the opposite C−C bond. At higher concentrations, indications were found for the formation of a chain-type 1:2 complex. In LN2 solutions, only the two 1:1 isomers of the HCl complex have been observed. Using spectra recorded at different temperatures, the complexation enthalpy ΔH° in LAr was determined to be −9.5(4) and −8.3(3) kJ mol-1 for the symmetric and asymmetric MCP·HCl complexes, and −9.1(2) and −6.7(5) kJ mol-1 for the symmetric and asymmetric MCP·BF3 complexes, respectively. In addition, for all investigated species, full MP2/6-31+G(d,p) geometry optim...

Mid-infrared spectra of solutions in liquid argon, krypton, and xenon of methyl nitrite, which occurs as a mixture of cis and trans conformers, have been investigated. In liquid argon and in liquid...

The gas phase structure and vibrational spectrum of tetrabromothiophene are calculated by ab initio methods. Unscaled DFT/B3LYP/TZVP frequencies fit conveniently well to the solid phase Raman spect...

The formation of weak molecular complexes between methylenecyclopropane (MeCP) and HCl or DCl dissolved in liquid argon and liquid nitrogen has been investigated using infrared spectroscopy. Evidence was found for the formation of a 1:1 complex in which the HCl molecule binds to the CC double bond. Weaker bands due to the two different 1: 2 complexes derived from the 1:1 complex were observed. From spectra recorded at different temperatures between 90 and 130 K, the complexation enthalpy for the 1:1 complex formed was determined to be −9.9(3) kJ mol−1, while the corresponding value for the most stable 1:2 complex, MeCP·HCl·HCl, was determined to be −14.6(4) kJ mol−1. Structural and spectral information for the 1:1 and the 1:2 complexes was obtained from DFT calculations at the B3LYP/6-311++G(d,p) level. Using free energy perturbation Monte Carlo simulations to calculate the solvent influences, and statistical thermodynamics to account for zero-point vibrational and thermal contributions, the complexation energies for the 1:1 complex and the 1:2 complex were estimated from the experimental complexation enthalpies to be −16.9(12) and −28.7(14) kJ mol−1. These numbers are compared with single-point energies calculated at the MP2/aug-cc-PVTZ level.

Variable temperature (-60 to -100 degrees C) studies of the Raman spectra (4000-300 cm(-1)) of 2,2,2 trifluoroethylamine, F3CCH2NH2 dissolved in liquid xenon have been carried out. From these data both conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 267 +/- 27 cm(-1) (3.19 +/- 0.32 kJ mol(-1)) with the trans conformer the more stable form. The percentage of the gauche conformer is estimated to be 35 +/- 3% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug-cc-pVTZ for both MP2(full) and density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants along with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters have been obtained for the trans conformer. The determined heavy atom structural parameters are for the distances (angstrom): C-1-C-2 = 1.513(3), C-2-N-3 = 1.447(3), C-1-F-4= 1.344(3), C-1-F-5,F-6 = 1.347(3) and angles in degrees (degrees) angle N3C2C1 = 115.2(5), angle F4C1C2 = 111.4(5), angle C2C1F5, F-6 = 111.6(5), angle F4C1F5 = 107.6(5), and angle F51F6 = 106.9(5). Vibrational assignments have been provided for the observed bands which have been supported by MP2(full)/6-31G(d) ab initio calculations to predict harmonic force fields, frequencies, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are discussed and compared to the corresponding properties of some similar molecules. (C) 2012 Elsevier B.V. All rights reserved.

The conformational behaviour of trimethyl phosphate was studied by infrared spectroscopy in the liquid phase and as 1% solutions in a wide range of solvents. Variable temperature studies carried out in carbon disulphide and liquid xenon solutions, and in the pure liquid phase, showed a reversal in the relative stability of the two conformers between liquid xenon and carbon disulphide solutions. In liquid xenon solution the less polar conformer II is ≈ 1.8 kJ mol−1 lower in energy, whereas in CS2 solution the more polar conformer I is ≈ 1.4 kJ mol−1 more stable. In the pure liquid, the energy difference between the two conformers is similar to that in carbon disulphide solution. Ab initio calculations predict that conformer II has C3 symmetry with all the methoxy groups in the gauche configuration, whereas conformer I has C1 symmetry with one trans and two gauche methoxy groups.

Using FTIR and Raman spectroscopy, the formation of halogen bonded complexes of the trifluorohalomethanes CF(3)Cl, CF(3)Br and CF(3)I with ethene and propene dissolved in liquid argon has been investigated. For CF(3)Br and CF(3)I, evidence was found for the formation of C-X···π halogen bonded 1:1 complexes. At a higher ratio of CF(3)I/propene, weak absorptions due to a 2:1 complex were also observed. Using spectra recorded at different temperatures, the complexation enthalpies for the complexes were determined to be -5.3(2) kJ mol(-1) for CF(3)Br·ethene, -7.5(2) kJ mol(-1) for CF(3)I·ethene, -5.6(1) kJ mol(-1) for CF(3)Br·propene, -8.8(1) kJ mol(-1) for CF(3)I·propene and -16.5(6) kJ mol(-1) for (CF(3)I·)(2)propene. The complexation enthalpies of the hydrogen bonded counterparts, with CF(3)H as the Lewis acid, were determined to be -4.6(4) kJ mol(-1) for CF(3)H·ethene and -5.1(2) kJ mol(-1) for CF(3)H·propene. For both hydrogen bonded complexes, a blue shift, by +4.8 and +4.0 cm(-1), respectively, was observed for the C-H stretching mode. The results from the cryospectroscopic study are compared with ab initio calculations at the MP2/aug-cc-pVDZ(-PP) level.

Using FTIR and Raman spectroscopy, the formation of halogen bonded complexes of the trifluorohalomethanes CF(3)Cl, CF(3)Br and CF(3)I with dimethyl sulfide (DMS) dissolved in liquid krypton has been investigated. For CF(3)Br and CF(3)I, evidence was found for the formation of C-XS halogen bonded 1:1 complexes. At higher concentrations of CF(3)I weak absorptions due to a 2:1 complex were also observed. Using spectra recorded at temperatures between 118 and 163 K, the complexation enthalpies for the complexes were determined to be -9.5(5) kJ mol(-1) for CF(3)Br·DMS, -17.4(1) kJ mol(-1) for CF(3)I·DMS and -30.8(16) kJ mol(-1) for (CF(3)I·)(2)DMS. The results from the cryospectroscopic study are compared with ab initio calculations at the MP2/aug-cc-pVDZ(-PP) level. Apart from vibrational modes localized in the trifluorohalomethanes and the DMS moieties, for both CF(3)Br and CF(3)I, an additional band, which we assign as the intermolecular stretching mode in the complex, was identified in the infrared and Raman spectra.

Pyrido[1,2-a]benzimidazoles1, 2a are interesting compounds both from the viewpoint of medicinal chemistry2–7 (solubility,7 DNA intercalation3) and materials chemistry8 (fluorescence). Of note among the former is the antibiotic drug Rifaximin,5 which contains this heteroaromatic core. The classical synthetic approach for the assembly of pyrido[1,2-a]benzimidazoles is by [3+3] cyclocondensation of benzimidazoles containing a methylene group at C2 with appropriate bielectrophiles.2a However, these procedures are often low-yielding, involve indirect/lengthy sequences, and/or provide access to a limited range of products, primarily providing derivatives with substituents located on the pyridine ring (A ring, Scheme 1).2–4 Theoretically, a good alternative synthetic method for the synthesis of pyrido[1,2-a]benzimidazoles with substituents in the benzene ring (C ring) should be accessible by intramolecular transition-metal-catalyzed CN bond formation in N-(2-chloroaryl)pyridin-2-amines, based on chemistry recently developed in our research group.9 These substrates themselves are easily available through SNAr or selective Pd-catalyzed amination10 of 2-chloropyridine with 2-chloroanilines.11 If a synthetic procedure that eliminated the need for preactivation of the 2-position of the 2-chloroarylamino entity could be developed, this would be even more powerful, as anilines are more readily commercially available than 2-chloroanilines. Therefore the synthesis of pyrido[1,2-a]benzimidazoles (4) by a transition-metal-catalyzed intramolecular CH amination approach from N-arylpyridin-2-amines (3) was explored (Scheme 1).

All you need is an open vial! The direct α arylation of cyclic alkylamines (see scheme) requires an open vial, as the hydrogen atom involved in the C(sp3)H-activation process is ultimately released as hydrogen gas. Reports on the formation of hydrogen gas in direct transition-metal-catalyzed functionalizations are still rare. Open-vial reactions proved crucial to this direct arylation procedure as, upon sealing, catalyst deactivation occurs.

Infrared spectra obtained in gas and liquid argon phases are reported for (12)CF(2) horizontal line(12)CH(2) and (12)CF(2) horizontal line(13)CH(2). These spectra firmly establish the positions of nu(3)(A(1)) and nu(6)(A(2)) for both isotopomers. Using anharmonicity constants from MP2 calculations, Fermi resonances affecting nu(1)(A(1)), nu(2)(A(1)), nu(3), and nu(8)(B(1)) are analyzed. Deperturbed fundamental frequencies from these analyses are used in conjunction with unaffected fundamentals and ab initio anharmonicity data to predict all 12 "observed" harmonic frequencies. A Darling-Dennison type resonance between 2nu(6) and nu(11) + nu(12) is diagnosed, the calculation of which from ab initio data requires modification of the existing second-order treatment of such constants, where Fermi resonance type terms are also present. Predictions are made of many overtone and combination band frequencies, aiding assignment of observed spectra. From the isolated CH stretching frequency obtained here of 3125.4 cm(-1), the C-H equilibrium bond length is predicted to be 1.0762(11) A.

Oxidative alkylamination of electron-deficient (hetero)aromatic compounds, via the nucleophilic substitution of hydrogen, is a methodology that has made significant progress since the introduction of AgPy(2)MnO(4) as oxidant. This oxidant generally gives good conversions and yields, whereas the use of KMnO(4) only sometimes works equally well. In order to rationalize this, the reaction mechanism of oxidative alkylamination has been studied. 3-Nitropyridine (1), 1,3-dinitrobenzene (2), and quinazoline (3) were chosen as model substrates and n-butylamine and pyrrolidine as model alkylamines. The rate-limiting step of the mechanism for these substrate/alkylamine combinations was determined. With the use of (1)H NMR spectroscopy thermodynamic properties of sigma(Eta)-adduct formation were deduced and the effect of additives on the adduct formation was investigated. The fundamental insights resulting from these studies led to the identification of a cheap additive (tetrabutylammonium chloride), which in combination with the standard and cheap oxidant KMnO(4) generally gave excellent yields, similar to the ones previously obtained with more expensive AgPy(2)MnO(4).

The formation of weakly bound molecular complexes between dimethyl ether (DME) and the trifluoromethyl halides CF(3)Cl, CF(3)Br and CF(3)I dissolved in liquid argon and in liquid krypton is investigated, using Raman and FTIR spectroscopy. For all halides evidence is found for the formation of C-X...O halogen-bonded 1:1 complexes. At higher concentrations of CF(3)Br, a weak absorption due to a 1:2 complex is also observed. Using spectra recorded at temperatures between 87 and 125 K, the complexation enthalpies for the complexes are determined to be -6.8(3) kJ mol(-1) (DME x CF(3)Cl), -10.2(1) kJ mol(-1) (DME x CF(3)Br), -15.5(1) kJ mol(-1) (DME x CF(3)I), and -17.8(5) kJ mol(-1) [DME(x CF(3)Br)(2)]. Structural and spectral information on the complexes is obtained from ab initio calculations at the MP2/6-311++G(d,p) and MP2/6-311++G(d,p)+LanL2DZ* levels. By applying Monte Carlo free energy perturbation calculations to account for the solvent influences, and statistical thermodynamics to estimate the zero-point vibrational and thermal influences, the ab initio complexation energies are converted into complexation enthalpies for the solutions in liquid argon. The resulting values are compared with the experimental data deduced from the cryosolutions.

The formation of a C–H⋯π bonded complex between halothane, CF3CHBrCl, and ethene has been studied in liquid krypton in the temperature range between 119 and 143 K, using infrared and Raman spectroscopy. The standard complexation enthalpy of the 1:1 complex was measured to be −5.0(2) kJ mol−1. The stretching mode of the C–H bond involved in the formation of the complex was observed to red shift by 7.2(1) cm−1, while its intensity increased by a factor of 2.1(2). The results are compared with ab initio calculations at the MP2/6-311++G(d,p) and MP2/aug-cc-PVXZ (X = D, T and Q) levels.

The complex of halothane (CF(3)CBrClH) with ([D(3)])methyl fluoride is investigated theoretically by means of ab initio calculations at the MP2/6-311++G(d,p) level and experimentally by infrared spectroscopy of solutions in liquid krypton. The complexation energy is calculated to be -12.5 kJ mol(-1). The dipole moment of halothane monomer as a function of the C-H stretching coordinate is calculated with different methodologies and the value of (partial differential(mu)/partial differential(Q(1)))0 is found to be positive. In the spectra, formation of a 1:1 complex is observed. The standard complexation enthalpy is measured to be -8.4(2) kJ mol(-1). The C-H stretching vibration of halothane shows a blueshift of +15.4 cm(-1) on complexation, and its infrared intensity ratio epsilon(complex)/epsilon(monomer) is found to be 1.39(7). The frequency shift is analyzed by a Morokuma analysis, and the infrared intensities are rationalized by using a model which includes the mechanical and electrical anharmonicity of the C-H stretching vibration.

The VCD spectra of pulegone, dissolved in CDCl3, CD2Cl2 and CS2 have been recorded in the frequency range from 1000 to 3000 cm(-1). The assignment of the absolute configuration was performed by comparing the experimental data with theoretical spectra computed at the B3LYP/6-311+G(d,p) level. Analysis of the agreement in several spectral regions revealed significant shortcomings when comparing with vacuum calculations. It is shown that the agreement improves when the solvent effects are taken into account by a continuum model. For the measurements in CDCl3 and CD2Cl2 further improvement was found when considering explicitly 1 : 1 complexes between a pulegone and a CDCl3 or CD2Cl2 solvent molecule in vacuo, while the best agreement was obtained when embedding these in a continuum model. The presence of the chiral solute was found to induce a VCD active C-D stretch band which could be modeled also at ab initio level.

Complete infrared and Raman vibrational assignments of pyrazine N , N ′-dioxide and its fully deuterated analogue have been made employing the Product Rule. A few changes are recommended to an earlier assignment of the - d 0 compound. Coupling within the molecule is examined employing the ν D /ν H ratio and by comparisons with similar molecules.

The complex of halothane (CHClBrCF(3)) and dimethyl ether has been investigated experimentally in solutions of liquid krypton using infrared spectroscopy and theoretically using ab initio calculations at the MP2/6-311++G(d,p) level. The formation of a 1:1 complex was experimentally detected. The most stable ab initio geometry found is the one in which the C--H bond of halothane interacts with the oxygen atom of dimethyl ether. The complexes in which the chlorine or the bromine atom of halothane interacts with the oxygen atom of the ether were found to be local energy minima and were less stable by 14.5 and 9.3 kJ mol(-1), respectively, than the global minimum. The formation of a single complex species was observed in the infrared spectra; the standard complexation enthalpy of this complex was determined to be -12.3(8) kJ mol(-1). Analysis of the observed complexation shifts supports the identification of the complex as the hydrogen-bonded species. The C--H stretching vibration of halothane was found to show a redshift upon complexation of 19(2) cm(-1). The infrared intensity ratios epsilon(complex)/epsilon(monomer) for the fundamental and its first overtone were measured to be 6.5(1) and 0.31(1). The frequency shift was analyzed using Morokuma-type analysis, and the infrared intensity ratios were rationalized using a model including the mechanical and electric anharmonicity of the C--H stretching fundamental.