55320-68-8

Deuterium and carbon-13 NMR of specifically labeled benzenehexoyl hexa-n-hexanoate in the various solid-state phases are reported.The spectra exhibit dynamic line shapes which change discontinuously at the phase transitions.The results are interpreted in terms of sequential "melting" of the side chains on going from the low-temperature solid phases IV, III, etc., toward the liquid.In phase IV the molecules are very nearly static, except for fast rotation of the methyl groups about their C3 axes.The results in phase III were quantitatively interpreted in terms of a two-site isomerization process ivolving simultaneous rotation by 95 deg about C1-C1 and transition from gtg to g'g't (or equivalently g'tg' to ggt) for the rest of the chain.The specific rate of this reaction at 0 deg C is ca. 1E5 s-1.In phase II additional chain isomerization processes set-in which were, however, not analyzed quantitatively.Further motional modes, involving reorintation of whole chains about their Car-O bonds, appear on going to phase I.In all solid phases the benzene ring remains static.

Metastable molecular ions of hexanoic acid (1) decompose unimolecularly to C2H5. and protonated methacrylic acid (5-H+)(92percent rel. abund.).Investigation of the mechanism reveals that 1) the branched cation radical 11 must be regarded as the essential intermediate in the course of the rearrangement/dissociation reaction and 2) the process commences with intramolecular hydrogen transfer from either C-3 or C-5 to the ionized carbonyl oxygen ("hidden" hydrogen migration).Hydrogen transfer from C-4, which would correspond to the well-known McLafferty rearrangement, is of no importance in the C2H5.-elimination from 1.The same conclusion applies for various alternative mechanisms, as for example a SRi type reaction, 1 -> 2-H+.The gas phase chemistry of the cation radical of 1, and in particular the hydrogen exchange processes between the methylene groups C-2/C-3 and C-5/C-6, is in surprisingly close correspondence to the chemistry of free alkyl radicals. - The syntheses of various 13C and 2H-labelled model compounds are described.