Ab initio calculation of 1H - 29Si coupling constants in organoalkoxysilanes

PHYS 573

Stephen E. Rankin, srankin@engr.uky.edu, Department of Chemical & Materials Engineering, University Of Kentucky, 177 Anderson Hall, Lexington, KY 40506-0046 and Jyothirmai Ambati, Jyothirmai.Ambati@uky.edu, Chemical and Materials Engineering, University of Kentucky, 177 Anderson Hall, Lexington, KY 40506.
Despite their apparent simplicity, organoalkoxysilane compounds and their hydrolyzed derivatives sometimes show surprises in their NMR properties. For example, the series of hydrolyzed methyltrimethoxysilane derivatives CH3(OH)x(OCH3)4-xSi, show a nonlinear 29Si chemical shift trend with respect to x.[T.M. Alam and M. Henry, Phys. Chem. Chem. Phys. 2000 2: 23] While these trends can be surprising, methodology has been established for partial charge and ab initio calculations of 29Si chemical shifts. However, the best methodology for the calculation of scalar coupling constants for 29Si and 1H has not been as clearly established. We present the results of coupling constant calculations for a variety of organoalkoxysilanes and their hydrolyzed derivatives, and show that the 6-31G basis set provides good agreement of 2JSi-H and 3JSi-H with experiment when calculations are performed with B3LYP method under Gaussian03. We use this method to help to explain the surprisingly complex coupling pattern between methylene protons and silicons in R3SiCH2CH2-SiR3.
 

PHYS Poster Session - Computational Spectroscopy and Reaction Dynamics
7:30 PM-10:00 PM, Wednesday, April 9, 2008 Morial Convention Center -- Hall A, Poster

Division of Physical Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008