Enhanced H-atom abstraction from pinonaldehyde, pinonic acid, pinic acid, and related compounds: theoretical study of C–H bond strengths
Abstract
The experimentally observed rate of the pinonaldehyde + OH reaction is substantially higher than expected from established structure activity relationships (SARs). In this study the C–H bond strengths in pinonaldehyde and in related, structurally similar compounds are investigated theoretically using B3LYP-DFT/6-31G(d,p). We find bond strengths in agreement with the literature values for smaller reference compounds, except for the abstraction of hydrogens from the exocyclic CH2 group, which has a significantly lower bond strength due to strain-enhanced hyperconjugation. The rate constant for H-abstraction from this group in pinonaldehyde is estimated at 8 × 10−12 cm3 molecule−1 s−1. The C–H bond strengths of the two tertiary hydrogens on the carbons in the four-membered ring are found to have normal values, in contrast to the high
values for secondary hydrogens in (substituted)