Chlorosilanes: Development and application of MM2 force field parameters

Abstract

The geometries, relative conformational energies, and dipole moments of mono and polychlorosilanes have been calculated using ab initio molecular orbital (MO) theory. Calculations at the HF/3-21G(*) level, with the exception of dipole moments, give reasonable agreement with experimental data. A new MM2 force field for chlorosilanes, which includes terms for bond length shortening and bond angle compression due to the attachment of electronegative C1 atoms, has been developed on the basis of experimental and ab initio results. The new force field is generally successful in predicting structural parameters, but is unable to reproduce the dipole moments of several model systems. While dipole moment predictions are not the authors' main interest, this failure defines a shortcoming in the MM2 method. The new parameters have been applied to problems in the prediction of stereochemistries of cyclic systems, and compared with experimental results where data are available.

Intrinsic conformational preferences of and an anomeric‐like effect in 1‐substituted silacyclohexanes

“…Similarly, there is a slight quantitative discrepancy between our values for 2 (Δ E MP2, Δ E BestEst. = +0.40 kcal mol −1 and Δ E = +0.34 kcal mol −1 ) versus Δ E from MM2 calculations (+0.635 kcal mol −1 ) 6.…”

“…Conformational analysis of silanes was prevalent in the 1970–1990s in order to develop and optimize molecular mechanics force fields for silicon containing compounds. These force fields were built to gain a better understanding of the stereochemical effects that silicon imparts on the molecule 3–8. The conformational analysis of the chair, boat, twist boat, and sofa conformations of silacyclohexane has been examined by quantum mechanical methods to determine interconversion pathways, structural parameters, and relative energies.…”

“…For example, 1‐cholorsilacyclohexane was examined in 1989 by Cho et al in order to test recently developed force fields for silicon. This MM2 study determined that the axial chair conformation of 1‐chlorosilacyclohexane was more stable than the corresponding equatorial conformer by 0.635 kcal mol −1 6. In 2002, Arnason et al examined cyclohexane, silylcyclohexane, and 1‐methyl‐1‐silacyclohexane by gas phase electron diffraction (GED), low‐temperature NMR, and quantum chemical calculations to determine the conformational behavior of the aforementioned ring systems 12.…”

Ab Initio Study of Chlorosilanes: Dipole Moments and Charge Distributions

“…During the course of these studies, we observed unusual outcomes in various geometric features, which arise probably due to strong polarization of chlorosilane derivatives. Furthermore, we found that most of the ab initio calculations including HF/6-31G* substantially overestimate experimental dipole moments 4a. These abnormal results are somewhat surprising because a HF/6-31G* calculation is generally accepted to furnish reasonably good values of dipole moments in a variety of molecules including some silicon containing compounds .…”

“…Their electronic natures have not been explored thoroughly yet, even though they have been applied widely in synthetic organic chemistry . We were involved in the development of molecular mechanics (MM2) parameters for chlorosilanes some years ago and focused mainly on molecular structures and conformational energies to identify a stable conformer among various diastereomers in alkyl substituted chlorosilacyclohexane derivatives 4a. During the course of these studies, we observed unusual outcomes in various geometric features, which arise probably due to strong polarization of chlorosilane derivatives.…”