Intramolecular hydrogen migrations in ionized aliphatic alcohols. Barton type and related rearrangements

Molecular orbital calculations at the unified G2(MP2, SVP) level of theory have been used to examine the energy barrier for 1,n-hydrogen atom migratio ns in ionized aliphatic alcohols [H(CH2)(n-1)OH](.+) --> [(CH2)(n-1)OH2](.) (n = 2-5). A complementary set of experimental and theoretical data confi rm that this approach leads to results accurate to within a few kJ mol(-1). The better stability of distonic ions [(CH2)(n-1)OH2](.+) with respect to their classical homologs [H(CH2)(n-1)OH](.+) is clearly demonstrated by the calculations; it amounts to similar to 30 kJ mol(-1). Critical energies of 106, 90, 76, and 19 kJ mol(-1) are calculated for n = 2, 3, 4, and 5, resp ectively. A lowering of the barrier height is observed when considering the energy barrier for 1,5 hydrogen atom migrations in ionized systems with re spect to the neutral equivalent, i.e. the Barton rearrangement. (C) 2000 El sevier Science B.V.