Isomeric ion-neutral complexes generated from ionized 2-Methylpropanol and n-Butanol: the effect of the polarity of the neutral partner on complex-mediated reactions.

ABSTRACT

Photoionization was used to characterize the energy dependence of C3H 7 (+) , C3H 6 (+) , CH3OH 2 (+) and CH2=OH(+) formation from (CH3)2)CHCH2OH(+•) (1) and CH3CH2CH2CH2OH(+•) (2). Decomposition patterns of labeled ions demonstrate that close to threshold these products are primarily formed through [CH 3 (+) CHCH3 (•)CH2OH] (bd3) from 1 and through [CH3CH2CH2 (•)CH2=OH(+)] (9) from 2. The onset energies for forming the above products from 1 are spread over 85 kJ mol(-1), and are all near thermochemical threshold. The corresponding onsets from 2 are in a 19 kJ mol(-1) range, and all except that of CH2=OH(+) are well above their thermochemical thresholds. Each decomposition of 3 occurs over a broad energy range (> 214 kJ mol(-1)), This demonstrates that ion-permanent dipole complexes can be significant intermediates over a much wider energy range than ion-induced dipole complexes can be. H-exchange between partners in the complexes appears to be much faster than exchange by conventional interconversions of the alcohol molecular ions with their distonic isomers. The onsets for water elimination from 1 and 2 are below the onsets for the complex-mediated processes, demonstrating that the latter are not necessarily the lowest energy decompositions of a given ion when the neutral partner in the complex is polar.