HYDROGEN-BONDING AND PHASE-TRANSITIONS OF A GROUP OF ALCOHOLS DERIVEDFROM 2,2-DIMETHYLPROPANE

A group of alcohols with the general formula (CH3)(4-x)C(CH2OH)(x) (x = 1,2,3,4), all of which are forming plastic crystalline phases, were investigated by vibrational spectroscopy and thermal analysis in order to determine their hydrogen bonds in the different crystal phases and the melts. Additional structural information was obtained from IR spe ctra of solutions in carbon tetrachloride as well as in low temperatur e argon matrices. The alcohols have strong hydrogen bonds forming laye rs in the crystals. At the phase transition from the crystal to the pl astic crystalline state the OH stretching bands shift to higher wavenu mbers and a considerable band broadening occurs in the vibrational spe ctra. Further heating gives no additional increase in the half bandwid th of the melt spectra. The observations from the vibrational spectra agree with the enthalpies, which are high for the phase transitions be tween the anisotropic crystals and the plastic phase crystals (dependi ng on the number of OH groups), but very low for the melting. The data reveal that the hydrogen bonds become weaker in the plastic crystalli ne phases and in the melts. The larger rotational freedom in the plast ic crystalline state and the melts leads to more than one spectroscopi cally distinguishable conformer for all the investigated alcohols exce pt 2,2-dimethyl-1-propanol.