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1H-Benzotriazole crystallizes as two different polymorphs, namely 4aα and 4aβ. One polymorph is chiral and it resolves spontaneously as conglomerates. The other polymorph crystallizes in a centrosymmetric space group and it is therefore achiral. In both polymorphs supramolecular structures are formed starting from achiral monomers. An analysis of these two polymorphs of 1H-benzotriazole has been carried out by a complete strategy involving different solid-state experimental techniques and quantum chemical calculations (DFT, Density Functional Theory). In particular, X-ray crystallography, NMR spectroscopy and vibrational spectroscopy techniques (FarIR, IR and Raman) that are not sensitive to chirality have been used to characterize the two polymorphs structurally. Vibrational spectroscopy (VCD, Vibrational Circular Dichroism) that is sensitive to chirality was employed to determine the absolute configuration (M or P helices) of the chiral supramolecular structure of 4aα., The authors thank Professor Maria Gdaniec (Adam Mickiewicz University, Poznan´, Poland) for providing the so-called ‘commercial sample’ (the b form). This work was carried out with financial support from the Spanish Ministerio de Ciencia, Innovación y Universidades (Project No. CTQ2015-63997-C2-2-P and RTI2018- 097416-B-C21), CICE/Junta de Andalucía (P08-FQM-04096) and CICE/JA-FEDER-UJA: Plan de Fortalecimiento de las Capacidades de I+D+i/2014-15 (UJA2013/08/03) and Comunidad Autónoma de Madrid (Project FOTOCARBON, ref. S2013/MIT-2841). Computer, storage and other resources from the CTI (CSIC) are gratefully acknowledged. The authors thank the University of Jae´n for continuing financial support, for bridge projects (UJA2015/08/07 and UJA2016/08/15), for Accio´n 2: Financiacio´n de Incentivos a la Excelencia de I+D+i de la UJA 2014-15 in 2014 and 2015 calls and to its CICT for instrumental facilities. M.M.Q.M. thanks the University of Jaén for both pre- and post-doctoral fellowships.

1H-Indazole derivatives exhibit a remarkable property since some of them form chiral supramolecular structures starting from achiral monomers. The present work deals with the study of three perfluorinated 1H-indazoles that resolve spontaneously as conglomerates. These conglomerates can contain either a pure enantiomer (one helix) or a mixture of both enantiomers (both helices) with an enantiomeric excess (e.e.) of one of them. The difficulty of the structural analysis of these types of compounds is thus clear. We outline a complete strategy to determine the structures and configurations (M or P helices) of the enantiomers (helices) forming the conglomerates of these perfluorinated 1H-indazoles based on X-ray crystallography, solid state NMR spectroscopy and different solid state vibrational spectroscopies that are either sensitive (VCD) or not (FarIR, IR and Raman) to chirality, together with quantum chemical calculations (DFT)., This work was carried out with financial support from the Ministerio de Economía y Competitividad (Project No. CTQ2014- 56833R and CTQ2015-63997-C2-2-P), CICE/Junta de Andalucía (P08-FQM-04096) and CICE/JA-FEDER-UJA: Plan de Fortalecimiento de las Capacidades de I+D+i/2014-15 (UJA2013/08/03) and Comunidad Autónoma de Madrid (Project FOTOCARBON, ref. S2013/MIT-2841). Computer, storage and other resources from the CTI (CSIC) are gratefully acknowledged. Authors thank the University of Jaén for continuing financial support, for bridge projects (UJA2015/08/07) and (UJA2016/08/15) and for Accion 2: Financiacion de Incentivos a la Excelencia de I+D+i de la UJA 2014-15 in 2014 and 2015 calls and to its CICT for instrumental facilities. Authors also thank the FQM-323 research group, especially Rafael Lopez Blanco, David Moreno Gonzalez and Jose Robles Molina, for their help in the laboratory. M. M. Q. M. thanks the University of Jaen for a pre-doctoral fellowship. The CNRS is acknowledged for support

The biochemically important interconversion process between aldoses and ketoses is assumed to take place via 1,2-enediol or 1,2-enediolate intermediates, but such intermediates have never been isolated. The current work was undertaken in an attempt to detect the presence of the 1,2-enediol structure of glycolaldehyde in alkaline medium, actually a 1,2-enediolate, and to try to clarify the scarce data existing about both the formation of deprotonated enediol and the aldo-enediolate equilibrium. The Raman spectra of neutral and basic solutions were recorded as a function of time for eleven days. Several bands associated with the presence of the enediolate were observed in alkaline medium. Glycolaldehyde exists as three different structures in aqueous solution at neutral pH, that is, hydrated aldehydes, aldehydes and dimers, with a respective ratio of approximately 4:0.25:1. Additionally, the formation of Z-enediolate forms takes place at basic pH, together with an increase in the concentration of aldehyde species, such as 2-oxoethan-1-olate, and a decrease in the concentrations of the hydrated aldehyde and dimeric forms. The theoretical ratio of ≈1.5:1 for aldehyde:Z-enediolate reproduces the experimental Raman spectrum in basic medium, with an additional contribution of the previously mentioned ratio between the hydrated aldehyde and dimeric forms. Finally, Raman spectroscopy allowed us to monitor the enolization of this carbohydrate model and conclude that aldo-enediol tautomerism - formally aldo-enediolate - happens when a suitable amount of basic species is added., LMA thanks the MICINN for a PhD grant (No. BES-2010-031225). MMQM thanks the Universidad de Jaén for a predoctoral fellowship. This work has been supported by the CTQ2012-35513-C02- 02 (MINECO), P08-FQM-04096 (CICE, Junta de Andalucía) and S2013/MIT-2841 (Fotocarbon, Comunidad Autûnoma de Madrid) Projects. Computer, storage and other resources from CTI (CSIC) are gratefully acknowledged. Gratitude is also due to the University of Jaén for continuing financial support and to its CICT for instrumental facilities. The authors also thank D. Francisco Hermoso Torres for his help in the laboratory

A study of the molecular structure of (1R,2S,5R)-(−)-menthol and the hydrogen bond networks formed by this species in solution is carried out. Molecular structures of monomers and H-bonded dimers and trimers of the title compound are optimized using quantum chemical calculations in the isolated molecule approach. In addition, IR, Raman and VCD techniques are used to study CCl4 solutions and thin films of the target compound. Their corresponding vibrational spectra are then analysed, both theoretically (HF and DFT) and experimentally, to characterize the different monomers (rotamers) and H-bonded oligomer species in menthol solutions as a function of the concentration.

From the analysis of the vibrational Mid-IR, Raman and Far-IR spectra of the α-amino acids l -phenylalanine and l -tyrosine, we are able to explain the conformational preference of their zwitterionic forms, which are of biological interest. The recorded spectra of l -Phe and l -Tyr in the solid state have been analyzed and compared with a large set of quantum chemical calculations in order to better understand the zwitterionic structures experimentally detected. In this way, analysis of the low frequency region between 500 and 30 cm −1 reveals much information in order to assign the most stable structures. The present work reveals that IR, Raman, and Far-IR, combined with quantum chemical calculations, are helpful and complementary techniques to characterize biological systems, such as amino acids.

( S )-(−)-Perillyc acid (4-isopropenylcyclohexene-1-carboxylic acid) is an intermediate in the limonene and pinene pathway degradation and its measurement in urine is used to monitor cancer patients receiving oral limonene. For the first time, a theoretical study of the conformational preference in the monomer and H-bonded dimers complemented with a theoretical and experimental analysis of the infrared, raman, and vibrational vircular dichroism spectra of ( S )-(−)-perillyc acid in solution and solid phases is presented. With regard to the monomer, theoretical calculations revealed the existence of two conformers depending on the position of the isopropenyl group (axial and equatorial) and 24 rotamers (12 equatorials and 12 axials). The study of the H-bonded dimers revealed great complexity in the conformational landscape with a total of 36 structures studied. Herein, from a reliable assignment of the IR and Raman spectra and with help from the study of the VCD spectrum of the title compound, the most stable rotamers of the H-bonded complexes have been detected experimentally in the liquid and solid phases. Additionally, natural bond orbitals (NBO) analysis indicates an electronic delocalization between the two subunits in the dimer. The IR, Raman, and VCD are helpful and complementary techniques to characterize flexible systems, such as terpenes, which present several conformers and H-bonded aggregates.

R-(−)-camphorquinone is a bicyclical terpenoid with many usages and application in different fields. Different experimental and theoretical works reveal that there is only one stable conformer of this chiral chemical species in agreement to the sterical restriction that the bicycle introduces. In the current work, from a complete assignment of the vibrational IR and Raman spectra, we are able to explain the VCD spectrum of the title compound. The recorded spectra of R-(−)-camphorquinone in different phases have been analyzed and compared: the first one in CCl4 solution, the second one using Nujol and Fluorolube suspensions and the third one using thin films. Finally, to study the coupling between the two C=O stretching normal modes, a NBO analysis is performed. The present work reveals that IR, Raman and VCD, combined with quantum chemical calculations, are helpful complementary techniques to characterize chiral systems, as terpenes, in different phases.

A conformational study of diethyldichlorosilane and the elucidation of the gas-phase molecular structures of its four conformers have been performed using the combined approach of gas-phase electron diffraction and computational techniques. Moreover, the Raman spectrum of the liquid and the IR spectra of the gas and liquid phases have been recorded and thoroughly analyzed on the basis of the scaled quantum-mechanical force field methodology. The results of the vibrational assignment have given spectroscopic evidence of the presence of the different conformers in the samples. Copyright c � 2009 John Wiley & Sons, Ltd.

Plausible structures of the titanium tetramethoxide trimer were optimized at the B3LYP/6-31+G * level. From the four types of structures of the Ti 3 O 12 cage found earlier for the Ti(OH) 4 trimer only two isomers were found as energy minima on the Ti 3 (OMe) 12 potential energy surface. One isomer ( I ), belonging to the C i point group, is built from three interconnected titanium oxide tetrahedra with a linear arrangement of titanium atoms. This structure have a titanium oxide skeleton similar to that of Ti 3 (OH) 12 . The other isomer ( II ), of C 2 symmetry, is built by edge sharing TiO 6 groups. Theoretical IR spectra of these isomers are compared with reported experimental IR spectra of solid titanium tetramethoxide and newly obtained Raman spectra of commercial powders. It was shown that the number and position of observed bands in the CO stretching region of the IR spectra of the so-called modification A of solid titanium tetramethoxide are in a good agreement with the predicted vibrational spectrum of trimer I . The equilibrium structure and IR and Raman spectra were also obtained for the Ti 4 (OMe) 16 tetramer. The comparison of the predicted vibrational spectrum with the experimental IR spectra of modification B as well as of the Raman spectrum of solid titanium tetramethoxide allows us to confirm the tetrameric structure of this modification and to propose the similar structure for commercial samples.

S-(+)-carvone (5-isopropenyl-2-methylcyclohex-2-en-1-one) is the primary component in the oil of caraway. Different experimental and theoretical works reveal that there are two possible conformers in which the isopropenyl group can be in equatorial or axial position. For each one, three rotamers were found theoretically, with the equatorial rotamers around 95% of the whole statistical population. In the current work, from a complete assignment of the IR and Raman spectra and the results obtained from the study of the VCD spectrum of the title compound, the three most stable rotamers have been detected experimentally in the liquid phase for the first time. The present work reveals that IR, Raman and VCD are helpful complementary techniques to characterize flexible systems, as terpenes, which present several conformers.

In this study 2-(2′-furyl)-4,5-1H-dihydroimidazole (1) was prepared and then characterized by infrared, Raman, and multidimensional nuclear magnetic resonance (NMR) spectroscopies. The crystal and molecular structures of 1 were determined by X-ray diffraction methods. The density functional theory (DFT) and second-order Moller–Plesset theory (MP2) with Pople's basis set show that there are two conformers for the title molecule that have been theoretically determined in the gas phase, and that only one of them, conformer I, is present in the solid phase. NMR spectra observed for 1 were successfully compared with the calculated chemical shifts at the B3LYP/6-311++G** level theorized for this conformer. The harmonic vibrational frequencies for the optimized geometry of the latter conformer were calculated at the B3LYP/6-311++G** level in the approximation of the isolated molecule. For a complete assignment of the IR and Raman spectra in the solid phase of 1, DFT calculations were combined with Pulay´s scaled quantum mechanics force field (SQMFF) methodology to fit the theoretical frequency values to the experimental ones. Copyright © 2009 John Wiley & Sons, Ltd.

A conformational study in the liquid phase of the terpene (R)-(+)-limonene has been carried out, revealing the presence of three conformers. For this task, experimental vibrational techniques, such as IR, Raman, and VCD spectroscopies, together with quantum chemical calculations, have been used. Our study reveals that a previous vibrational analysis is desirable to achieve a thorough analysis of the VCD spectrum as well as that these three experimental techniques are complementary to characterize flexible systems, which present several conformers.

S-(-)-Perillaldehyde (4-isopropenylcyclohex-1-ene-1-carbaldehyde) is a secondary metabolite and an atmospheric pollutant obtained from the oxidation of other terpenes, as limonene and alpha-pinene, among others. For the first time, a study of the molecular structure and the infrared and Raman spectra of this chemical is presented. Theoretical calculations reveal the existence of two conformers depending on the position of the isopropenyl group (axial and equatorial) and twelve rotamers (six equatorials and six axials), being three of these equatorial rotamers the most stable (ca. 93%). A complete and reliable assignment of the IR and Raman spectra of the title compound is made, taking into account these three last rotamers, and the results are used to carry out a detailed interpretation, for the first time to our knowledge, of the VCD spectrum of this compound in the 1500-900 cm (-1) region.

We have accomplished a reliable assignment of the vibrational spectra of the ionic species potassium trimethylsilanolate, which is unstable towards hydrolysis and self-condensation, by means of the combined use of experimental data and theoretical density functional theory (DFT) calculations. We report the first record of the Raman spectrum of the pure solid. Additionally, we have newly recorded its IR spectrum in Nujol mull and for the first time in Fluorolube mull, completing the experimental data available in the literature about this chemical species. Further, in order to discuss the convenience of including the counterion in the model used for the quantum-mechanical calculations of its vibrational spectra, we have compared the performance of three different theoretical models, namely, the isolated trimethylsilanolate anion, a theoretical monomer of potassium trimethylsilanolate and a simplified ionic cluster model based on its crystalline structure. Copyright © 2007 John Wiley & Sons, Ltd.

Conformational studies of triethylchlorosilane (TECS) and triethylbromosilane (TEBS) and the elucidation of their gas phase molecular structures have been accomplished by the combined use of theoretical (ab initio and density functional theory) calculations and experimental data from gas phase electron diffraction experiments. Additionally, analysis of the experimental features observed in the IR and Raman spectra recorded for both compounds has allowed us to propose a complete description of the vibrational spectra of both compounds, including an explanation of certain bands, which can only be correctly assigned when more than one conformer is considered to be present.

The molecular geometry for trimethylsilylisocyanate ((CH3)3SiNCO) has been calculated at MP2 and DFT/B3LYP and DFT/B3PW91 methods, and using the 6-31G*, 6-311G**, 6-311++G**, cc-pVDZ and cc-pVTZ basis sets. The equilibrium structure of the molecule, linear or bent as concerns the -SiNCO moiety, was found to rely on the method employed. The potential energy surface of -SiNC bending has been investigated by quantum mechanical ab initio calculations at MPn (n = 2-4) and QCISD(T) levels of theory with the cc-pVTZ basis set. This large amplitude bending motion (the υ24 mode) was determined to be very anharmonic, with a low barrier to linearity of the SiNCO skeleton of ∼4-25 cm-1. New vapour and liquid IR, liquid Raman spectra and, for first time, INS spectrum have been recorded, and a complete vibrational assignment has been performed. INS data have allowed to assign two modes at 674 cm-1 and 141 cm-1 which, so far, have been considered as silent, i.e. A2, since previous authors have used a frame of C3v symmetry for this system. The intermolecular interactions show to have little effect on the torsional region (below 250 cm-1 in INS spectrum) and the isolated-molecule approximation works well in that region. A normal coordinate analysis has been carried out by scaling the force fields calculated at MP2/6-311++G** and B3LYP/cc-pVDZ levels of theory using the scaled quantum mechanical force field (SQMFF) methodology. In order to get the best possible agreement between calculated and observed vibrational wavenumbers, the scale factors were refined by least squares yielding a final r.m.s. of ≈7 cm-1. © 2006 Elsevier B.V. All rights reserved. Fil: Fernández Liencres, M.P.. Universidad de Jaén; España Fil: Navarro, A.. Universidad de Jaén; España Fil: Ben Altabef, Aida. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentina. Universidad Nacional de Tucumán; Argentina Fil: López González, J. J.. Universidad de Jaén; España Fil: Fernández Gómez, M.. Universidad de Jaén; España Fil: Kearley, G.J.. Delft University of Technology; Países Bajos

The fully optimized equilibrium structure of isochroman has been obtained from DFT calculations by using the hybrid B3LYP and B3PW91 functionals in combination with different basis sets (6-31G∗, 6-311G∗∗ and 6-311++G∗∗). Due to the absence of any experimental geometry data for isochroman, the optimized molecular structure has been compared to those of other compounds like naphthalene, benzene, cyclohexane, tetralin, 2H-pyran and chroman. The vapor, liquid, and solution (CCl 4 and CS 2 ) infrared (IR) and liquid Raman spectra have been recorded. The harmonic force field generated with B3LYP/6-31G∗, given in terms of the natural internal coordinates, has been scaled by the recommended scale factors by Rauhut and Pulay, using their multiple scaling (SQM) force field procedure. In order to get the best possible fitting between the calculated and experimental frequencies, the scale factors were refined by a linear least squares procedure obtaining a final rms of 7.5 cm −1 . Furthermore, supposing a Lorentzian band contour, the infrared spectrum of isochroman has been simulated using the theoretical and scaled force fields. On the basis of the frequencies and infrared intensities calculated from the refined SQM force field, the first vibrational assignment of the normal modes of the individual isochroman molecule is presented, having resulted the infrared intensity calculation decisive in this case for assigning the fundamentals in the low energy region where the most of the uncertainties appeared. In addition, a new method has been developed to characterize the similarity between the experimental and calculated spectra: the inspection of their scalar product, yielding the best result for isochroman in the case of scaled force fields.

NH-Indazoles in solid phase usually form NHN hydrogen bonds between positions 1 and 2, which determine the secondary structure, forming dimers, trimers, or catemers (chains). Thus, the difficulty of the experimental analysis of the structure of the family of 1H-indazoles is clear. We have outlined a complete strategy by using different techniques of vibrational spectroscopy that are sensitive (VCD) and not sensitive (IR, FarIR, and Raman) to the chirality together with quantum chemical calculations. We have studied the chiral structure of (4S,7R)-campho[2,3-c]pyrazole both in solution (CCl4) and in the solid phase (crystal). This compound crystallizes as a chiral trimer (LABHEB), with the monomer also being chiral. Herein, Far-IR, IR, and Raman spectra in solution and in the solid state are assigned using the support of B3LYP/6-31G(d) and B97D/6-31+G(d,p) calculations of (4S,7R)-campho[2,3-c] pyrazole monomers, dimers, and trimers, these last cyclamers being partially and fully optimized. Later, analysis of the vibrational circular dichroism (VCD) spectra allowed us to determine the chiral self-assembly of (4S,7R)-campho[2,3- c]pyrazole crystals (LABHEB). In the crystal, only the trimers are present while in solution, the monomer predominates. We have highlighted the importance of the analysis of the low frequency region (700-25 cm-1) in the FT-Raman and Far-IR spectra, because it provides relevant information in order to confirm the presence of the trimers in the solid phase. © 2014 Elsevier Ltd. All rights reserved.

S-(+)-carvone (C10H14O, 5-isopropenyl-2-methylcyclohex-2-en-1-one) and R-(+)-limonene (C10H16, 4-isopropenyl-1-methylcyclohexene) have been characterized in the gas phase using a Fourier transform microwave spectrometer coupled to a supersonic molecular beam. Two conformers—with the isopropenyl group in the equatorial position—have been detected for each compound and described by a set of molecular parameters including the principal rotational constants and the quartic centrifugal distortion parameters. Quantum chemical calculations indicate that a third conformer might not be observed due to relaxation processes in the jet. The gas phase results are compared with the liquid phase IR-Raman-VCD spectra.

A survey of the Cambridge Crystallographic Database reveals that there are 17 1H-indazoles forming dimers (7), trimers (4) and catemers or chains (6). Amongst the catemers there is one centrosymmetric compound and five non-centrosymmetric ones that crystallize in chiral helices, either M or P, including indazole itself, whose structure has been determined anew. An explanation will be provided for how an achiral molecule crystallizes in a chiral space group. The second part of the paper is devoted to the use of Vibrational Circular Dichroism (VCD) for determining the absolute configuration of a crystal of indazole. This previously needs the complete assignment of its IR and Raman spectra in solution and in the solid-state based on B3LYP/6-31G(d) calculations of indazole dimers and trimers, which are already chiral. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012.

R-(+)-Pulegone is a natural monoterpene obtained from the essential oils of a variety of plants. It is used in flavouring agents, perfumery and aromatherapy. In this work, a study of the molecular structure and the infrared and Raman spectra of this chemical is presented. Theoretical calculations reveal the existence of two conformers depending on the position of the methyl group (axial and equatorial), being the equatorial conformer the most stable. A complete and reliable assignment of the IR and Raman spectra of the title compound is made, and the results are used to carry out a detailed interpretation of the VCD spectrum of this compound in the 4000-900 cm(-1) region. Finally, the influence of the solvent in the VCD bands (intensity and sign) has been tested comparing the neat liquid spectrum with the VCD spectra recorded with four solvents.

S -(–)-perillaldehyde (C 10 H 14 O) has been characterized in the gas phase using a Fourier transform microwave spectroscopy experiment in a supersonic molecular beam. Two conformers − with the isopropenyl group in the equatorial position − have been detected and described by a set of molecular parameters including the principal rotational constants and the quartic centrifugal distortion parameters. Quantum chemical calculations indicate that a third conformer might not be observed due to relaxation processes in the jet. The gas phase results are compared with the liquid phase IR–Raman–VCD spectra. Our study shows that gas phase spectroscopy is a powerful tool for characterizing monoterpenes.

We report a theoretical study of the molecular structure of the triethylsilanol molecule and a thorough conformational analysis of the species following the Boltzmann's distribution law. The vibrational spectra of the title molecule have been assigned by means of the combined use of experimental data obtained from IR and Raman spectra and theoretical DFT calculations with the subsequent implementation of the SQMFF methodology. The role of hydrogen bonding in the shifting of the vibrational bands of the silanol group in the spectra of the liquid phase is discussed using a model of triethylsilanol dimer.

The gas-phase molecular structure of iodotrimethylsilane (ITMS) has been determined from electron diffraction data. Infrared and Raman spectra have been completely assigned. The experimental work is supported by ab initio HF and MP2 calculations for the gas-phase structure determination and DFT(B3LYP) calculations, combined with Pulay's SQM method, for the vibrational spectra data. © the Owner Societies 2006. Fil: Montejo, Manuel. Universidad de Jaén; España Fil: Hinchley, Sarah L.. University of Edinburgh; Reino Unido Fil: Ben Altabef, Aida. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán; Argentina Fil: Robertson, Heather E.. University of Edinburgh; Reino Unido Fil: Ureña, Francisco Partal. Universidad de Jaén; España Fil: Rankin, David W. H.. University of Edinburgh; Reino Unido Fil: López González, Juan J.. Universidad de Jaén; España

S-(-)-Limonene oxide (4-isopropenyl-1-methyl-7-oxabicyclo[4.1.0]heptane) is a secondary metabolite and an atmospheric pollutant product of oxidation of other terpenes, such as limonene and alpha-pinene, among others. For the first time, a theoretical study of the molecular structure and a theoretical and experimental analysis of the infrared and Raman spectra of this chemical species are presented. Theoretical calculations reveal the existence of two conformers depending on the position of the isopropenyl group (axial and equatorial) and twelve rotamers (six equatorials and six axials), with the six equatorial ones as the most stable (around 97%) on the basis of Boltzmann's distribution law. In the current work, from a reliable assignment of the IR and Raman spectra and with the help from the study of the VCD spectrum of the title compound, five rotamers have been detected experimentally in the liquid phase. The present work reveals that IR, Raman and VCD are helpful complementary techniques to characterize flexible systems, as terpenes, which present several conformers.