Infrared spectra, methyl group structure and internal rotation in some methy - metal compounds

Abstract

Recent and current work on spectra in the CH and CD stretching regions of methyl-metal compounds is reviewed. Free internal rotation with CH force constant variation is found in MMe 3 (M  Ga, Tl) and MMe(CO) 5 (M  Mn, Re) compounds, studied in the gas phase. From solution measurements, no such rotation occurs in CpMMe(CO) 3 (M  Cr,Mo,W) and Cp 2MMe 2 (M  Ti,Zr,Hf), in most of which each methyl group contains two types of CH bond. In each d-subgroup, ν is CH decreases with increasing atomic number, while δ sCH 3 increases. The reverse occurs from Ga to Tl. r oCH values are predicted. There is evidence for the breakdown of the ν is CH/∠HCH correlation, especially in MeTiCl 3 where several features point to an unusual structure of the methyl group.