MESOPHASES OF ALKYLAMMONIUM SALTS .5. HEAT-CAPACITIES OF SYMMETRICAL HALIDES WITH ALKYL CHAINS LONGER THAN ETHYL

The heat capacities of tetra-n-alkylammonium bromides and iodides in t he solid state have been measured from 130 K through their respective transitions and fitted at low temperatures to two THETA temperatures, using group vibrations computed from the vibrational spectra and the T arasov analysis, as developed for linear macromolecules. The compounds analyzed were (C3H7)4NBr, (C4H9)4NBr, (C5H11)4NBr, (C6H13)4NBr, (C7H1 5)4NBr, (C8H17)4NBr, (C10H21)4NBr, (C12H25)4NBr, (C16H33)4NBr, (C18H37 )4NBr, (C3H7)4NI, (C4H9)4NI, (C5H11)4NI, (C6H13)4NI, (C7H15)4NI, and ( C12H25)4NI. The total vibrational contribution to the heat capacity is thus, derived and compared to the experimentally measured heat capaci ty over the whole temperature range. Positive deviations of the measur ed heat capacity from the calculation occur already below room tempera ture, implying the existence of large-amplitude, nonvibrational motion in the solid state, as suggested before by solid-state C-13 NMR analy sis. Quantitative information on the entropy of disordering generated outside of the transition ranges is derived and agrees with the entrop y deficits predicted by the analysis of the first-order transitions. A n addition scheme is developed for the heat capacity of the methylene groups in these compounds, that is similar to the paraffins.