Spectra and structure of small ring compounds. XXXVI. 2‐methyl‐1,3‐dioxolane; 2‐methyl‐1,3‐dioxolane‐d4; 2‐methyltetrahydrofuran; and methylcyclopentane

Abstract

AbstractThe infrared spectra of solid, liquid and gaseous 2‐methyl‐1,3‐dioxolane, 2‐methyl‐1,3‐dioxolane‐d4, 2‐methyltetrahydrofuran, and methylcyclopentane were recorded from 4000 to 33 cm−1. The Raman spectra were also recorded and depolarization values were measured for 2‐methyl‐1,3‐dioxolane and methylcyclopentane. The fundamental vibrations of each compound have been assigned on the basis of group frequency correlations, isotopic shifts, and band intensities as well as depolarization values when applicable. The barrier hindering internal rotation of the methyl group has been calculated to be 3.5, 3.6, and 4.2 kcal mole−1 for 2‐methyl‐1,3‐dioxolane, 2‐methyltetrahydrofuran, and methylcyclopentane, respectively. The pseudorotational ring vibration was observed at 58 and 56 cm−1 for gaseous 2‐methyl‐1,3‐dioxolane and 2‐methyltetrahydrofuran, respectively. This implies a barrier to pseudorotation of the order of 1.3 kcal mole−1 for 2‐methyl‐1,3‐dioxolane and 2‐methyl‐tetrahydrofuran. The pseudorotational mode could not be observed for methylcyclopentane, even at maximum pressure‐path length condition.