Comparison of the electron diffraction and ab initio structures of neopentane and di-tert-butyl methane

by Siam, Khamis S.; Ewbank, John David; Schäfer, Lothar

The molecular structures of neopentane (NP) and di-tert-butyl methane (DTBM) were determined by ab initio gradient geometry refinements on the 4-21G level. The structure calculated for DTBM is in agreement with the steric deformations previously inferred by an experimentally undetermined electron diffraction analysis. The average C-C bond distance is stretched by 0.008 Aring from the neopentane reference value (experimental value 0.008 Aring). The central C-C-C bond angle is opened to the extreme value of 124.2deg (experimental value 125-128(6)deg). The methyl carbons in adjacent t-butyl groups are twisted away from the perfectly staggered positions by 11.6-16.5deg (experimental value 15+or-6deg). Calculated average C-H and C-C bond distances (rg) are 1.118(10) Aring and 1.536(3) Aring, respectively, for NP (experimental values 1.114(8) Aring and 1.537(3) Aring); and 1.118(10) Aring and 1.544(3) Aring, respectively, for DTBM (experimental values 1.122(15) Aring and 1.545(5) Aring). Calculated results for DTBM provide important structural trends, including significant differences in individual C-H and C-C bond distances, and asymmetry of t-butyl and methyl groups, not established experimentally.

Journal
Journal of Molecular Structure-Theochem
Volume
137
Issue
1-2
Year
1986
Start Page
155
ISBN/ISSN
2210-2728; 0166-1280
DOI
10.1016/0166-1280(86)80094-X