Microwave studies of three alkylbenzenes: Ethyl, <i>n</i>-propyl, and <i>n</i>-butylbenzene

Abstract

The rotational spectra of ethyl, n-propyl, and n-butylbenzene have been observed and analyzed using a high-resolution Fourier transform microwave spectrometer. Only one stable conformation was found for ethylbenzene, in agreement with previous results from Caminati et al. [Mol. Phys. 74, 885 (1991)]. The high sensitivity of the technique allows observation of the rotational spectra of the six C13 isotopes of ethylbenzene in natural abundance. The structural analysis indicates that the dihedral angle between the ethyl group and the ring plane is 88.7°±0.9°. Two conformers have been found for n-propylbenzene as predicted by ab initio calculations while four of the five theoretically predicted conformers [Dickinson et al., J. Chem. Soc., Faraday Trans. 93, 1467 (1997)] have been found for n-butylbenzene.