Intramolecular hydrogen migrations in ionized aliphatic alcohols. Barton type and related rearrangements
Abstract
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 migrations in ionized aliphatic alcohols [H(CH2)(n)-1)OH]*+ ? [(CH2)(n)-1OH2]*+ (n = 2-5). A complementary set of experimental and theoretical data confirm 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 ~30 kJ mol-1. Critical energies of 106, 90, 76, and 19 kJ mol-1 are calculated for n = 2, 3, 4, and 5, respectively. A lowering of the barrier height is observed when considering the energy barrier for 1,5 hydrogen atom migrations in ionized systems with respect to the neutral equivalent, i.e. the Barton rearrangement. (C) 2000 Elsevier Science B.V.