Knowledge Bank

Far infrared spectra of solid $C2HA3OH,C2H3OD$, and $C2D3OD$ have been obtained and used to assign the observed frequencies in terms of transitory and rotational lattice vibrations. With the aid of the crystal analysis and the spectra of the liquids, these vibrations can also be interpreted in terms of hydrogen bond motions. Based on the ethanol results, vibrational assignments have been made for the observed low frequency modes of a number of alkyl alcohols. In many cases the intramolecular vibrations of the hydrocarbon chains can be distinguished from the intermolecular hydrogen bond vibrations by comparison to the assigned low frequencies of alkyl acids. For the solid alcohols the lattice vibrations can again be related to hydrogen bond motions. Some of these hydrogen bond vibrations, notably the hydrogen bond stretching mode, fall at different frequencies for different compounds. These shifts will be discussed in terms of molecular structure, mixing of vibrations, hydrogen bond strength, and relation to the OH stretching frequency.