The regioselectivity in FeO+- and FeO2+-mediated hydroxylation reactions of 2-methylbutane that involves primary (1°), secondary (2°), and tertiary (3°) carbon atoms is discussed from theoretical calculations at the B3LYP DFT level. The energetics for four kinds of hydroxylation reactions of 2-methylbutane that lead to primary, secondary, and tertiary alcohols in a two-step concerted mechanism and in a radical mechanism are calculated and analyzed. With respect to H atom abstraction, a concerted mechanism via the four-centered transition state C⋯H⋯O-Fe is energetically more favorable than a radical mechanism via the linear transition state C⋯H⋯O-Fe in most cases, except for a case generating a tertiary carbon radical intermediate. The regioselectivity in the concerted mechanism prefers a secondary C-H bond dissociation and declines in the order 2° > 1° > 3°, whereas the regioselectivity in the radical mechanism prefers a tertiary C-H bond dissociation and declines in the order 3° > 2° > 1°. The kinetic isotope effects (KIEs) for the H atom abstraction from 2-methylbutane are analyzed on the basis of the transition state theory. Computed kH/kD values in the concerted mechanism do not show site dependence, while those in the radical mechanism have significant site dependence, the order of kH/kD values being 1° > 2° > 3°.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry