Equatorial Conformers Research Articles

Fourier transformation microwave spectroscopy of the methyl glycolate–H2O complex

The rotational spectrum of one conformer of the methyl glycolate–H2O complex has been measured by means of the pulsed jet Fourier transform microwave spectrometer. The observed a- and b-type transitions exhibit doublet splittings due to the internal rotation of the methyl group. On the other hand, most of the c-type transitions exhibit quartet splittings arising from the methyl internal rotation and the inversion motion between two equivalent conformations. The spectrum was analyzed using parameterized expressions of the Hamiltonian matrix elements derived by applying the tunneling matrix formalism. Based on the results obtained from ab initio calculation, the observed complex of methyl glycolate–H2O was assigned to the most stable conformer of the insertion complex, in which a non-planer seven membered-ring structure is formed by the intermolecular hydrogen bonds between methyl glycolate and H2O subunits. The inversion motion observed in the c-type transitions is therefore a kind of ring-inversion motion between two equivalent conformations. Conformational flexibility, which corresponds to the ring-inversion between two equivalent conformations and to the isomerization between two possible conformers of the insertion complex, was investigated with the help of the ab initio calculation.

Theoretical study on the anomeric effect in α-substituted tetrahydropyrans and piperidines

Conformational effects, including some controversial examples, have been reported in this work for 2-substituted tetrahydropyrans and piperidines, and for the respective protonated compounds [substituent = F, OH, OCH3, NH2, NHCH3 and N(CH3)2]. Hyperconjugation plays a major role in most cases, either due to endo or exo-anomeric interactions, especially when nitrogen is the electron donor to an antiperiplanar σ* orbital. This interaction also seems to contribute for the Perlin and reverse fluorine Perlin-like effects, which are related to the relative magnitude of 1JC,H and 1JC,F coupling constants, respectively, in axial and equatorial conformers. However, the preference for an equatorial conformation appears when a hydrogen or methyl group of the substituent faces the ring, increasing the steric repulsion, even if concomitant with a hyperconjugative interaction in the axial isomer, such as for the well-known 2-aminotetrahydropyran. Unlike some reports in the literature, the gas phase 2-hydroxypiperidine experiences the herein called reverse anomeric effect, although the highly stabilizing nN → σ*C-O interaction in the axial isomer. Overall, steric effects should be taken into account when deciding for the normal or reverse anomeric effects as determinant factors of the stereochemical control of carbohydrate-like molecules.

Bis(3,5-dimeth-oxy-2-{[2-(pyridin-2-yl)ethyl-imino-κN]-meth-yl}phenolato-κO)bis-(dimethyl sulfoxide)-manganese(III) perchlorate methanol 0.774-solvate.

The title compound, [Mn(C16H17N2O3)2(C2H6OS)2]ClO4·0.774CH3OH, comprises a central octa-hedrally coordinated MnIII cation, with two bidentate Schiff base ligands occupying the equatorial positions and two dimethyl sulfoxide (DMSO) ligands occupying the axial positions. There are two independant cations in the asymmetric unit, with the MnIII atoms of both cations being positioned on crystallographic centers of inversion. The perchlorate anion is disordered over two equivalent conformations, with occupancies of 0.744 (3) and 0.226 (3). In addition, there is a methanol solvent mol-ecule in the crystal lattice that is too close to the minor component of the perchlorate anion to be present simultaneously and thus it was refined to have the same occupancy as the major component of this anion. There is a Jahn-Teller distortion which results in Mn-ODMSO axial bond lengths of 2.2365 (12) and 2.2368 (12) Å in the two cations. In the crystal, inter-molecular π-π stacking between the non-coordinating pyridine rings of each cation is observed. This π-π stacking, along with extensive O-H⋯O hydrogen bonding and C-H⋯O inter-actions, link the components into a complex three-dimensional array.

Conformational impact of structural modifications in 2-fluorocyclohexanone

2-Haloketones are building blocks that combine physical, chemical and biological features of materials and bioactive compounds, while organic fluorine plays a fundamental role in the design of performance organic molecules. Since these features are dependent on the three-dimensional chemical structure of a molecule, simple structural modifications can affect its conformational stability and, consequently, the corresponding physicochemical/biological property of interest. In this work, structural changes in 2-fluorocyclohexanone were theoretically studied with the aim at finding intramolecular interactions that induce the conformational equilibrium towards the axial or equatorial conformer. The interactions evaluated were hydrogen bonding, hyperconjugation, electrostatic and steric effects. While the gauche effect, originated from hyperconjugative interactions, does not appear to cause some preferences for the axial conformation of organofluorine heterocycles, more classical effects indeed rule the conformational equilibrium of the compounds. Spectroscopic parameters (NMR chemical shifts and coupling constants), which can be useful to determine the stereochemistry and the interactions operating in the series of 2-fluorocyclohexanone derivatives, were also calculated.

Stereoelectronic Interactions as a Probe for the Existence of the Intramolecular α-Effect.

The first systematic study of the intramolecular α-effect, both in the stable ground-state structures and in the high-energy intermediates, was accomplished using the anomeric effect as an internal stereoelectronic probe. Contrary to the expectations based on the simple orbital mixing model, the lone pairs in a pair of neutral directly connected heteroatoms are not raised in energy to become stronger donors toward adjacent σ- and π-acceptors. Instead, the key n(X-Y)→σ*C-F interactions (X,Y = O,N) in the "α-systems" (both acyclic and constrained within a heterocyclohexane frame) are weaker than nX→σ*C-F interactions in "normal" systems. Surprisingly, polar solvent effects increase the apparent magnitude of α-effect as measured via increase in the anomeric stabilization. This behavior is opposite to the solvent dependence of normal systems where the anomeric effect is severely weakened by polar solvents. This contrasting behavior reflects the different balance of electrostatic and conjugative interactions in the two types of anomeric systems: the α-systems suffer less from the unfavorable orientation of bond dipoles in the equatorial conformer, a destabilizing electrostatic effect that is shielded by the polar environments. A weak α-effect is brought to life when the buttressing α-heteroatom bears a negative charge. However, electrostatic components mask the role of stabilizing orbital interactions. In contrast, the increased electron demand in carbocations and related electron-deficient TS- like structures does not lead to activation of the α-effect. As a consequence, we observed that ethers are better radical- and cation-stabilizing groups than peroxides. The latter finding should have significant implications for understanding the mechanistic complexity associated with the interaction of carbonyl compounds with hydroperoxides and H2O2 in acidic media, as such reactions involve α-cationic intermediates.

1,N6-α-hydroxypropanoadenine, the acrolein adduct to adenine, is a substrate for AlkB dioxygenase.

1,N6-α-hydroxypropanoadenine (HPA) is an exocyclic DNA adduct of acrolein - an environmental pollutant and endocellular oxidative stress product. Escherichia coli AlkB dioxygenase belongs to the superfamily of α-ketoglutarate (αKG)- and iron-dependent dioxygenases which remove alkyl lesions from bases via an oxidative mechanism, thereby restoring native DNA structure. Here, we provide in vivo and in vitro evidence that HPA is mutagenic and is effectively repaired by AlkB dioxygenase. HPA generated in plasmid DNA caused A → C and A → T transversions and, less frequently, A → G transitions. The lesion was efficiently repaired by purified AlkB protein; the optimal pH, Fe(II), and αKG concentrations for this reaction were determined. In vitro kinetic data show that the protonated form of HPA is preferentially repaired by AlkB, albeit the reaction is stereoselective. Moreover, the number of reaction cycles carried out by an AlkB molecule remains limited. Molecular modeling of the T(HPA)T/AlkB complex demonstrated that the R stereoisomer in the equatorial conformation of the HPA hydroxyl group is strongly preferred, while the S stereoisomer seems to be susceptible to AlkB-directed oxidative hydroxylation only when HPA adopts the syn conformation around the glycosidic bond. In addition to the biochemical activity assays, substrate binding to the protein was monitored by differential scanning fluorimetry allowing identification of the active protein form, with cofactor and cosubstrate bound, and monitoring of substrate binding. In contrast FTO, a human AlkB homolog, failed to bind an ssDNA trimer carrying HPA.

Synthesis and NMR spectroscopic conformational analysis of benzoic acid esters of mono- and 1,4-dihydroxycyclohexane, 4-hydroxycyclohexanone and the -ene analogue – The more polar the molecule the more stable the axial conformer

para-Substituted benzoic acid esters of cyclohexanol, 1,4-dihydroxycyclohexane, 4-hydroxy-cyclohexanone and of the corresponding exo-methylene derivative were synthesized and the conformational equilibria of the cyclohexane skeleton studied by low temperature 1H and 13C NMR spectroscopy. The geometry optimized structures of the axial/equatorial chair conformers were computed at the DFT level of theory. Only one preferred conformation of the ester group was obtained for both the axial and the equatorial conformer, respectively. The content of the axial conformer increases with growing polarity of the 6-membered ring moiety; hereby, in addition, the effect of sp2 hybridization/polarity of C(4)=O/C(4)=CH2 on the present conformational equilibria is critically evaluated. Another dynamic process could be studied, for the first time in this kind of compounds.

Intramolecular inversions, structure and conformational behavior of gaseous and liquid N-cyanopiperidine. Comparison with other 1-cyanoheterocyclohexanes

The molecular structure and intramolecular inversions of N-cyanopiperidine (CNP) were studied by various quantum chemical methods and using synchronous gas electron diffraction/mass spectrometry (GED/MS) and IR spectroscopy. The contribution of the equatorial conformer was found GED 52(6), IR 60(6), B3LYP 77, B3LYP-D3 67, M062X 59, MP2 54%. Interpolation using CCSD(T)-F12/CBS predicts Eax–Eeq = 0.26 kcal/mol. The NBO analysis shows a strong conjugation of the nitrogen atom lone pair with the triple bond making the r(N–CCN) = 1.355(3) Å distance as short as a typical sesquilateral bond.A low energy barrier for the Eq→Ax transition of 1.0–2.3 kcal/mol in CNP leads to difficulties in NMR conformational ratio studies. This leaves the GED method almost as the only experimental method to study both structural and conformational properties.Conformational properties of the related compounds are found to depend on the X–CCN bond distance and conjugation between the CN group and the lone pair on the heteroatom. The contribution of the axial form of 1-cyano-heterocyclohexanes increases in the series of heteroatoms X in the cyclohexane ring: N→C→Si→P.

Conformational Flexibility of Limonene Oxide Studied By Microwave Spectroscopy.

Monoterpenoids are biogenic volatile organic compounds that play a major role in atmospheric chemistry by participating in the formation of aerosols. In this work, the monoterpenoid (R)-(+)-limonene oxide (C10 H16 O) was characterized in the gas phase by Fourier-transform microwave spectroscopy in a supersonic jet. Five conformers of limonene oxide, four equatorial and one axial considering the configuration of the isopropenyl group, were unambiguously identified from analysis of the rotational spectrum. The observed conformers include cis and trans forms, which are stabilized by a subtle balance of hydrogen bonds, dispersive interactions, and steric effects. Estimated conformational relative abundances surprisingly reveal that the abundance of the axial conformer is similar to that of some of the equatorial conformers. In addition, the potential energy surface was extensively explored by using density functional theory and ab initio methods.

Solvent, temperature and concentration effects on the optical rotatory dispersion of (R)-3-methylcyclohexanone

Optical rotatory dispersion (ORD) spectra are reported for isolated and solvated (R)-3-methylcyclohexanone (R-3MCH) in 10 solvents, of wide polarity range, and over the spectral range 350–650 nm. Sample concentration effects on ORD spectra of R-3MCH were also recorded and investigated over widely varying concentrations from 2.5 × 10−3 to 2.5 × 10−1 g/mL where an observed sensitivity of optical rotation (OR) to incident light wavelength at low concentrations is correlated to solvent effects. Temperature effects were also studied by recording ORD spectra over the temperature range 0–65 °C in toluene. Recorded specific OR was plotted against various solvent parameters, namely, dipole moment, polarity, refractive index and polarizability to probe solvent effects. Furthermore, solvent effects were studied by incorporating Kamlet's and Taft's solvent parameters in the multi-parametric linear fitting. Theoretically, ORD spectra and populations of optimized geometries of equatorial and axial conformers of R-3MCH were calculated in the gas and solvated phases. All theoretical calculations were performed employing the polarizable continuum model using density functional theoretical and composite scheme (G4) methods with aug-cc-pVTZ and aug-cc-pVDZ basis sets. Net ORD spectra of R-3MCH were generated by the Boltzmann-weighted sum of the contributions of the dominant conformers. Upon comparing theoretical and experimental ORD spectra, a very good agreement is observed for the ORD spectra in the gas phase and high polarity solvents compared to relatively lesser agreement in low polarity solvents.

A Systematic Analysis of 2 Monoisocentric Techniques for the Treatment of Multiple Brain Metastases.

In this treatment planning study, we compare the plan quality and delivery parameters for the treatment of multiple brain metastases using 2 monoisocentric techniques: the Multiple Metastases Element from Brainlab and the RapidArc volumetric-modulated arc therapy from Varian Medical Systems. Eight patients who were treated in our institution for multiple metastases (3-7 lesions) were replanned with Multiple Metastases Element using noncoplanar dynamic conformal arcs. The same patients were replanned with the RapidArc technique in Eclipse using 4 noncoplanar arcs. Both techniques were designed using a single isocenter. Plan quality metrics (conformity index, homogeneity index, gradient index, and R50%), monitor unit, and the planning time were recorded. Comparison of the Multiple Metastases Element and RapidArc plans was performed using Shapiro-Wilk test, paired Student t test, and Wilcoxon signed rank test. A paired Wilcoxon signed rank test between Multiple Metastases Element and RapidArc showed comparable plan quality metrics and dose to brain. Mean ± standard deviation values of conformity index were 1.8 ± 0.7 and 1.7 ± 0.6, homogeneity index were 1.3 ± 0.1 and 1.3 ± 0.1, gradient index were 5.0 ± 1.8 and 5.1 ± 1.9, and R50% were 4.9 ± 1.8 and 5.0 ± 1.9 for Multiple Metastases Element and RapidArc plans, respectively. Mean brain dose was 2.3 and 2.7 Gy for Multiple Metastases Element and RapidArc plans, respectively. The mean value of monitor units in Multiple Metastases Element plan was 7286 ± 1065, which is significantly lower than the RapidArc monitor units of 9966 ± 1533 ( P < .05). For the planning of multiple brain lesions to be treated with stereotactic radiosurgery, Multiple Metastases Element planning software produced equivalent conformity, homogeneity, dose falloff, and brain V12 Gy but required significantly lower monitor units, when compared to RapidArc plans.

DFT study of molecular structures and relative stabilities of 1,2,7-thiadiazepane 1,1-dioxide and 1,2,7-thiadiazepane 1-oxide

The structures and energies of 1,2,7-thiadiazepane 1,1-dioxide and the axial and equatorial conformers of 1,2,7-thiadiazepane 1-oxide were calculated using the hybrid density functional B3LYP with the cc-pVDZ basis set. The results obtained explain the lower stabilities of equatorial conformers compared to the axial analogs and the lower stabilities of sulfones compared to sulfoxides.

A theoretical conformational study on the structural parameters involved in the ring strain of exo-unsaturated four-membered heterocycles, Y = CCH2CH2X

ABSTRACTThe effect of ring-puckering angle on the structural parameters (bond lengths and angles) involved in the ring strain of a series of four-membered heterocycles (1–16) was theoretically demonstrated by using the ab initio methods MP2 and HF, and the DFT methods PBE1PBE, B3LYP, SVWN5 with 6-31+G(d,p) as basis set. The results revealed that the bonds within the ring (C–X and C–C) are the most sensitive to puckering angle changes. The variation of the C–X and C=Y bond lengths as function of puckering angle are determined by a balance between the 1,3 repulsive interactions and the electronic nature of the heteroatoms X and Y. Particularly, for azetidines and phosphetanes, the C–X and C=Y bond lengths exhibit a major increase at axial conformations. In general, the C–C bond length decreases with the puckering angle for all heterocycles. While the heteroatom–H bonds (in the ring skeleton) are very sensitive to geometric changes, exhibiting an increasing behaviour for equatorial conformations and a decreasing behaviour for axial conformations highly puckered (ϕ > −20°). The C–X–C angle decreases monotonically with the puckering angle, increasing the Baeyer strain on the studied molecules. Finally, all methods predicted a similar behaviour for the studied parameters as function of the puckering angle, although some smaller differences in the predictions of their respective values, especially at HF level, were observed.

Hyperconjugative interactions are the main responsible for the anomeric effect: a direct relationship between the hyperconjugative anomeric effect, global hardness and zero-point energy

The correlations between the global hardness (η), hyperconjugative anomeric effect, Pauli exchange-type repulsions, electrostatic model associated with dipole–dipole interaction and structural parameters in 2-fluorotetrahydropyran, -thiopyran, -selenopyran (1–3) and their chloro- (4–6) and bromo-analogs (7–9) were investigated by means of the conventional and range-corrected functionals and natural bond orbital (NBO) interpretation. By deletion of the HC-exo-AE and HC-endo-AE, the equatorial conformations of compounds 1–9 become more stable than their corresponding axial forms, revealing that anomeric relationships in compounds 1–9 have the hyperconjugative anomeric effect origins while the electrostatic model associated with dipole–dipole interaction does not play a determining role on the variations of the anomeric relationships in these compounds. The anomeric relationships in compounds 1–3 have no Pauli exchange-type repulsions origin, but it has a significant impact on the conformational preferences in compounds 4–6 and 7–9. A canonical molecular orbital interpretation was conducted to investigate the correlations between the linear combinations of natural bond orbitals in the HOMOs, LUMOs and the global hardness (η) values. There is a direct relationship between the hyperconjugative anomeric effect, global hardness (η) and zero-point energies in compounds 1–3, 4–6 and 7–9. The harder axial conformations with the greater hyperconjugative anomeric effect and zero-point energy values are more stable than their corresponding equatorial forms.

Influence of oxygenation in cyclic hydrocarbons on chain-termination reactions from R + O2: tetrahydropyran and cyclohexane

Multiplexed photoionization mass spectrometry (MPIMS) is used to determine branching fractions of conjugate alkenes from R+O2 oxidation reactions for cyclohexane (c-C6H12) and tetrahydropyran (c-C5H10O), a lignocellulosic-derived oxygenated biofuel. Because conjugate alkene formation is coincident with the formation of HO2, the results reveal the temperature- and pressure-dependent influence of the oxygen heteroatom on chain-termination propensity. The experiments were conducted using Cl-initiated oxidation at 10 and 1520Torr and from 500 to 700K, and ab initio calculations of bond energies, saddle point energies, and rate coefficients of unimolecular decomposition of α-tetrahydropyranyl were conducted to complement the experiments.Relative to the initial radical concentration [R]0 the trend in conjugate alkene branching fraction exhibits monotonic positive temperature dependence in both cyclohexane and tetrahydropyran, except for the latter species at 10Torr where increasing the temperature to 700K caused an appreciable decrease. The decrease in the branching fraction with increasing temperature in tetrahydropyran oxidation occurs because ring-opening rates of α-tetrahydropyranyl radicals, enabled by weak C–O bond dissociation energies, exceed rates of O2-addition. Ring-opening rate coefficients for α-tetrahydropyranyl, computed from stationary points at the CCSD(T)-F12a/cc-PVDZ//M06-2X/6-311++G** level of theory, confirm that ring-opening at 700K is favorable and higher oxygen concentrations are required for O2-addition rates to be significant. With increased temperature and lower [O2], α-tetrahydropyranyl radicals preferentially undergo unimolecular decomposition into the linear radical C˙H2(CH2)3CHO. Conjugate alkene branching fractions measured at 1520Torr for both cyclohexane and tetrahydropyran followed monotonic positive temperature dependence. The change in the tetrahydropyran trend at 1520 Torr relative to the 10Torr measurements is ascribed to the increase in oxygen concentration mitigating ring-opening reactions of the initial R radicals.In contrast to the results at higher temperature, where ring-opening of tetrahydropyranyl radicals interrupts R+O2 chemistry and reduces the formation of conjugate alkenes, branching fractions measured below 700K were higher in tetrahydropyran compared to cyclohexane at 10Torr. The difference suggests that the ether group renders chain-termination pathways more-facile. Saddle point energy calculations on the surfaces of equatorial ROO conformers reveal that the barrier height to direct HO2 formation from α-tetrahydropyranylperoxy is lower by ca. 5kcal/mol compared to cyclohexylperoxy at the CBS-QB3 level of theory, which facilitates low-temperature chain-termination.

N-substituted akyl- and nonalkylpiperidines: Equatorial, axial or intermediate conformations?

Detailed quantum chemical calculations for a series alkyl- and nonalkyl-derivatives were performed continuing a systematic study of N-substituted piperidines. Three groups have been proposed to sort out the compounds distinguishing from each other by preference of the substituent’s position: (a) adopting exclusively equatorial position (alkylpiperidines); (b) with no exceptional priority of any of the conformers; (c) a peculiar group for which the terms ‘equatorial and axial’ are not applicable – the nitrogen bond configuration is planar or nearly planar (formyl, carbonyl, etc.). Geometry, pathways and barriers for nitrogen and ring inversions were calculated. Most of the MP2 calculations predict higher axial form contribution as compared with those by DFT-B3LYP.

Crystal structures of 4-methyl-2-oxo-2H-chromene-7,8-diyl di-acetate and 4-methyl-2-oxo-2H-chromene-7,8-diyl bis-(pent-4-ynoate).

In the structures of the two title coumarin derivatives, C14H12O6, (1), and C20H16O6, (2), one with acetate and the other with pent-4-ynoate substituents, both the coumarin rings are almost planar. In (1), both acetate substituents are significantly rotated out of the coumarin plane to minimize steric repulsions. One acetate substituent is disordered over two equivalent conformations, with occupancies of 0.755 (17) and 0.245 (17). In (2), there are two pent-4-ynoate substituents, the CC group of one being disordered over two positions with occupancies of 0.55 (2) and 0.45 (2). One of the pent-4-ynoate substituents is in an extended conformation, while the other is in a bent conformation. In this derivative, the planar part of both pent-4-ynoate substituents deviate from the coumarin plane. The packing of (1) is dominated by π-π stacking involving the coumarin rings and weak C-H⋯O contacts link the parallel stacks in the [101] direction. In contrast, in (2) the packing is dominated by R 2 (2)(24) hydrogen bonds, involving the acidic sp H atom and the oxo O atom, which link the mol-ecules into centrosymmetric dimers. The bent conformation of one of the pent-4-ynoate substituents prevents the coumarin rings from engaging in π-π stacking.

Conformational analysis of N-methylformamide in ground S0 and excited S1 and T1 electronic states

For conformers of the N-methylformamide (HCONHCH3) molecule, calculations of equilibrium geometry parameters, harmonic vibration frequencies, energy differences and potential barriers to conformational transitions were performed in the ground (S0) and lowest excited singlet (S1) and triplet (T1) electronic states. In the S0 state, the molecule exists in trans and cis stable conformations (having Cs symmetry). Our calculations show that the electronic excitations T1←S0 and S1←S0 cause changes in the structure of conformers: both HCON and HNCC fragments become pyramidal and rotate around the CN bond. As a result, in each excited electronic state under consideration, there are 12 minima forming six pairs of equivalent conformers separated by relatively small potential barriers. One- and two-dimensional potential energy surface sections corresponding to different intramolecular large-amplitude motions were calculated using the MP2/aug-cc-pVTZ (S0) and CASPT2/cc-pVTZ (S1 and T1) methods. Anharmonic vibrational problems for large-amplitude motions were solved, and the corresponding frequencies were estimated.

3-Trimethylsilylcycloalkylidenes. γ-Silyl vs γ-Hydrogen Migration to Carbene Centers.

A series of γ-trimethylsilyl-substituted carbenes have been studied experimentally and by computational methods. In an acyclic system, 1,3-trimethylsilyl migration successfully competes with 1,3-hydrogen migration to the carbene center. The behavior of cyclic 3-trimethylsilyl-substituted carbenes contrasts with that of the acyclic system. Only 1,2-hydrogen migration processes are observed in the five-membered ring due to the high barrier to 1,3-hydrogen migration. In the cyclohexyl system, a small amount of a cyclopropane derived from 1,3-hydrogen migration occurs, as shown by a labeling study. In the cycloheptyl carbene system, a labeling study again showed that 1,3-hydrogen migration to the carbene center leads to the major product. Computational studies suggest that the cyclic carbenes all have lower energy conformations where the trimethylsilyl group is in a pseudo equatorial conformation where it cannot migrate to the carbene center. Computational studies also suggest that cyclohexyl and cycloheptyl carbene systems are slightly stabilized by a rear lobe interaction of the Si-C bond with the carbene center.

Vibrational assignments and conformer stability determination of cyclobutyldichlorosilane by variable temperature Raman spectra in krypton solution

The infrared spectrum (3100–300cm−1) in the gas phase and Raman spectrum (3100–150cm−1) of the liquid of cyclobutyldichlorosilane (c-C4H7SiHCl2) have been recorded. Variable temperature (−143°C to −123°C) studies of the Raman spectra (3100–300cm−1) dissolved in liquid krypton have been carried out. From these data, the experimental stabilities of the conformer have been determined to be Eq-g>Ax-t>Eq-t>Ax-g. The enthalpy difference between Eq-g and Ax-t has been determined from band pairs to be 85±10cm−1 (1.01±0.11kJmol−1) with the Eq-g conformer the more stable form. The enthalpy difference between Eq-g and Eq-t is 116±43cm−1 (1.39±0.52kJmol−1) and the enthalpy difference between Eq-g and Ax-g has been determined to be 138±42cm−1 (1.66±0.51kJmol−1) with the Eq-g conformer as the more stable form. The percentage of the equatorial gauche conformer is estimated to be 47% at ambient temperature. To support the spectroscopic study, ab initio calculations by the Møller–Plesset perturbation method to second order MP2(full) and density functional theory calculations by the B3LYP method have been carried out. The infrared intensities, Raman activities, vibrational frequencies and band contours have been predicted from MP2(full)/6-31G(d) calculations and these theoretical values are compared to the experimental ones when available. The conformational stabilities have been predicted from theoretical calculations with basis sets up to 6-311+G(2d,2p) from both MP2(full) and density functional theory calculations by the B3LYP method. The results are discussed and compared to the corresponding properties of some related molecules.