ChemInform Abstract: CH Stretching Frequencies and Bond Strengths, and Methyl Group Geometry in CH3CXO Compounds (X: H, Me, F, Cl, Br, I, CN, OMe) and CH3CH2CN.

Abstract

Abstract Infrared spectra in the CH stretching region are reported for CHD 2 CXO and CH 3 CXO compounds, where X = F, Cl, Br, I, CN, OMe, and for CHD 2 CD 2 CN and CD 3 CHDCN. In all the carbonyl compounds except the iodide the two out-of-plane CH bonds in the methyl group are significantly weaker than the in-plane one. Differences in CH bond length of up to 0.006 A are predicted, which are considered to be more reliable than the available microwave data. The separations of v as CH 3 and v CHD 2 , frequencies are compatible with a strong angular asymmetry (∠H s CH a ≠ ∠H a CH a ) in the acetyl compounds. The gauche and trans effects of halogen on v CH is are similar, but larger, than those in alkyl halides. In ethyl cyanide, the methyl CH bonds are identical in strength. The α and β substituent effects from the CN group fall into no simple pattern.