Conformational preference of the silyl group. Ab initio and molecular mechanics studies

Cho, Soo Gyeong; Rim, One Kwon; Kim, Yoon Seok

doi:10.1016/0166-1280(95)04461-2

Cited by 8 publications

(7 citation statements)

References 53 publications

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“…The energy barriers are slightly higher in n -butane, however. The very similar conformational properties of n -butane and 1 are consistent with the similar enthalpy differences between axial and equatorial conformers of methyl- and silylcyclohexane. , …”

Section: Discussionsupporting

confidence: 66%

“…The very similar conformational properties of n-butane and 1 are consistent with the similar enthalpy differences between axial and equatorial conformers of methyl-and silylcyclohexane. 26,27 In 2, the enthalpy difference ∆H°between anti and gauche form is very small (0.14 (18) kcal mol -1 ) but still positive. This value is reproduced correctly by all four QC methods, which also predict slightly positive values.…”

Section: Discussionmentioning

confidence: 97%

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Gas Phase Structures and Conformational Properties of 1-Silabutane and 2-Silabutane

Arnason

Oberhammer

2002

J. Phys. Chem. A

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The molecular structures of 1-silabutane 1 and 2-silabutane 2 have been determined by gas electron diffraction (GED). The conformational equilibrium of 1 and 2 was studied experimentally in the gas phase (GED) and by quantum chemical (QC) calculations (HF with 6-31G* basis sets, MP2 with 6-31G* and cc-pVTZ basis sets, and B3LYP with 6-311G* basis sets). The potential function for internal rotation around the central C-C bond in 1 resembles that for n-butane, whereas the rotation around the Si-C bond in 2 has much lower energy barriers. The experimental relative enthalpies ∆H°(gauche-anti) are 0.76(10) and 0.14(18) kcal mol -1 for 1 and 2, respectively. The enthalpy difference for 2 is reproduced within the experimental uncertainties by all four QC methods. Only the MP2 method with a large basis set reproduces the enthalpy difference for 1 correctly. Taking the different multiplicities of anti and gauche conformers into account, the conformational composition of 1 was found to be 65(5)% anti and 35(5)% gauche. The conformational composition of 2 was found to be 43(9)% anti and 57(9)% gauche.

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Section: Discussionsupporting

confidence: 66%

Section: Discussionmentioning

confidence: 97%

Gas Phase Structures and Conformational Properties of 1-Silabutane and 2-Silabutane

Arnason

Oberhammer

2002

J. Phys. Chem. A

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“…26 Cho et al have compared calculated A values for the methyl and silyl groups. 27 They report A values of 2.14 kcal mol -1 (CH 3 ) and 1.90 kcal mol -1 (SiH 3 ) from ab initio calculations, whereas MM3 calculations resulted in 1.78 kcal mol -1 (CH 3 ) and 1.16 kcal mol -1 (SiH 3 ). The authors explained the lower A value of the silyl group compared with that of the methyl group by the longer SisC bond (1.904 Å) compared to the CsC bond (1.534 Å), which makes the axial SiH 3 sterically less unfavorable than the axial methyl group.…”

Section: Introductionmentioning

confidence: 99%

Conformational Properties of 1-Silyl-1-Silacyclohexane, C₅H₁₀SiHSiH₃: Gas Electron Diffraction, Low-Temperature NMR, Temperature-Dependent Raman Spectroscopy, and Quantum Chemical Calculations

et al. 2010

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The molecular structure of axial and equatorial conformers of 1-silyl-silacyclohexane, C(5)H(10)SiHSiH(3), and the thermodynamic equilibrium between these species were investigated by means of gas electron diffraction (GED), dynamic nuclear magnetic resonance (DNMR), temperature-dependent Raman spectroscopy, and quantum chemical calculations (CCSD(T), MP2 and DFT methods). According to GED, the compound exists as a mixture of two conformers possessing the chair conformation of the six-membered ring and C(s) symmetry and differing in the axial or equatorial position of the SiH(3) group (axial = 57(7) mol %/equatorial = 43(7) mol %) at T = 321 K. This corresponds to an A value (free energy difference = G(axial) - G(equatorial)) of -0.17(15) kcal mol(-1). A low-temperature (13)C NMR experiment using SiD(4) as a solvent resulted in an axial/equatorial ratio of 45(3)/55(3) mol % at 110 K corresponding to an A value of 0.05(3) kcal mol(-1), and a DeltaG(#) value of 5.7(2) kcal mol(-1) was found at 124 K. Temperature-dependent Raman spectroscopy in the temperature range of 210-300 K of the neat liquid, a THF solution, and a heptane solution indicates that the axial conformer is favored over the equatorial one by 0.26(10), 0.23(10), and 0.22(10) kcal mol(-1) (DeltaH values), respectively. CCSD(T)/CBS and MP2/CBS calculations in general predict both conformations to have very similar stability and are, thus, in excellent agreement with the DNMR result but in a slight disagreement with the GED and Raman results. Two DFT functionals, that account for dispersion interactions, M06-2X/pc-3 and B2PLYP-D/QZVPP, deviate from the high-level coupled cluster and MP2 calculations by only 0.1 kcal mol(-1) on average, whereas B3LYP/pc-3 calculations greatly overestimate the stability of the equatorial conformer.

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“…A different effect is observed when X ) CH 3 , because the barrier becomes lower than in the corresponding carbon derivative: 2,3 this behavior has been interpreted 2,3 as being due to a consistent decrease in steric effects in the rotational maximum of type B in the molecule containing silicon owing to the CsSi being longer than the CsC bond distance. Reduced steric effects in silicon compounds with respect to the analogous carbon derivatives have been reported 14 for the conformational behavior of cyclohexyl derivatives as well. The X group in the CH 2 SiX 3 rotor affects the hyperconjugative character of the CsSi bond 3 , becoming smaller when X ) Cl with respect to X ) H and CH 3 .…”

Section: Introductionmentioning

confidence: 96%

The Rotational Barriers of Groups Containing Silicon in Substituted Benzenes. A Theoretical Approach to the Silicon Substituent Effect

Taddei

1998

J. Chem. Inf. Comput. Sci.

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The potential energy profile for a number of derivatives of benzene substituted with the SiH 3 , SiH 2 CH 3 , and CH 2 SiX 3 (X ) H, F, Cl, CH 3 ) groups was calculated at ab initio (HF/6-31G*//HF/6-31G*) level, and the energy barriers were estimated. The rotational barrier is low for the molecules with silicon directly bonded to the phenyl ring, but higher values are found for the CH 2 SiX 3 groups, which depend on X as well. The hyperconjugative effect of the substituents was estimated from the natural bond orbital (NBO) theory of donor acceptor properties: the SiH 2 CH 3 group was found to be electron-acceptor in character, and the CH 2 SiX 3 were found to be electron-donor groups. The rotational barrier of these molecules is mainly determined by hyperconjugation, steric effects being smaller than in the analogous carbon derivatives. The SisH and SisC bonds display an electron-acceptor character of similar magnitude when silicon is attached to the phenyl ring, but the SisC bond has a prevailing donor character when carbon is bonded to the phenyl ring.

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Conformational preference of the silyl group. Ab initio and molecular mechanics studies

Cited by 8 publications

References 53 publications

Gas Phase Structures and Conformational Properties of 1-Silabutane and 2-Silabutane

Gas Phase Structures and Conformational Properties of 1-Silabutane and 2-Silabutane

Conformational Properties of 1-Silyl-1-Silacyclohexane, C₅H₁₀SiHSiH₃: Gas Electron Diffraction, Low-Temperature NMR, Temperature-Dependent Raman Spectroscopy, and Quantum Chemical Calculations

The Rotational Barriers of Groups Containing Silicon in Substituted Benzenes. A Theoretical Approach to the Silicon Substituent Effect

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Conformational preference of the silyl group. Ab initio and molecular mechanics studies

Cited by 8 publications

References 53 publications

Gas Phase Structures and Conformational Properties of 1-Silabutane and 2-Silabutane

Gas Phase Structures and Conformational Properties of 1-Silabutane and 2-Silabutane

Conformational Properties of 1-Silyl-1-Silacyclohexane, C5H10SiHSiH3: Gas Electron Diffraction, Low-Temperature NMR, Temperature-Dependent Raman Spectroscopy, and Quantum Chemical Calculations

The Rotational Barriers of Groups Containing Silicon in Substituted Benzenes. A Theoretical Approach to the Silicon Substituent Effect

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Conformational Properties of 1-Silyl-1-Silacyclohexane, C₅H₁₀SiHSiH₃: Gas Electron Diffraction, Low-Temperature NMR, Temperature-Dependent Raman Spectroscopy, and Quantum Chemical Calculations