Gas-phase conformational distributions for the 2-alkylalcohols 2-pentanol and 2-hexanol from microwave spectroscopy

Chirped-pulse and cavity Fourier-transform microwave spectrometers were used to record rotational spectra arising from four conformational structures of 2-pentanol and 14 conformations of 2-hexanol. Each conformer's rotational spectrum consists of 10-89 transitions, making the microwave spectra of the alkylalcohols very congested. Assignments of the spectra to conformational structures were made by comparison of the experimental moments of inertia and dipole-selection-rule intensities to predictions from ab initio (MP2/6-311++G∗∗) model structures. The all-anti configurations of 2-pentanol and 2-hexanol were calculated to have the lowest energies and gave rise to the strongest signals. Spectra were observed from conformers up to 4 kJ mol−1 above these minimum energy structures.