Quantitative 2H NMR spectroscopy

Abstract

The selectivity of deuterium distribution between the nonequivalent positions in 3 carene (1), 4 α acetyl 2 carene (2), and 4 (1 hydroxyethyl) 2 carene (3) has been measured by 2 H { 1 H} NMR spectroscopy at the natural abundance of deuterium. These "H/D isotope portraits" were shown to be typical of terpenes and terpenoids produced in plants via the biosynthetic DXP pathway. The mechanism of acylation of 1 was studied by the density functional theory method (PBE functional, TZ2p basis set). The six membered ring in com pound 1 is planar. However, the endo attack of electrophiles on this ring is more favorable both kinetically and thermodynamically. It was shown both experimentally and theoretically that the elimination of a hydrogen atom in the second reaction step proceeds stereoselectively at the C(2) atom from the anti position with respect to the three membered ring and occurs with pronounced nucleophilic assistance from the carbonyl group.