Electron Diffraction Study of the Structures of Ethane and Deuteroethane

Abstract

An electron diffraction structure determination for ethane and deuteroethane has been carried out to study the magnitudes of primary and secondary deuterium isotope effects on bond lengths. Mean parameters and estimated standard errors for C₂H₆ were r_g(C–H) = 1.1122±0.0012 Å, l_g(C–H) = 0.0760±0.0010 Å, r_g(C–C) = 1.5340±0.0011 Å, l_g(C–C) = 0.0496±0.0010 Å, and ∠CCH = 111.0±0.2°. Corresponding parameters for C₂D₆ were r_g(C—D) = 1.1071±0.0012 Å, l_g(C—D) = 0.0668±0.0010 Å, r_g(C–C) = 1.5323±0.0011 Å, l_g(C–C) = 0.0517±0.0010 Å and ∠CCD = 111.0±0.2°. Shrinkage corrections have not been made for bond angles. A primary deuterium isotope effect of 0.0050±0.0006 Å was found for the carbon hydrogen bond. A possibly significant secondary effect was observed in which the C–C length in ethane exceeded that in deuteroethane by Δr_g(1) = 0.0016±0.0007 Å. Some aspects of secondary isotope effects are discussed briefly.