Analysis of Conformational Preferences in Caffeine.

ABSTRACT: High level DLPNO-CCSD(T) electronic structure calculations with extended basis sets over B3LYP-D3 optimized geometries indicate that the three methyl groups in caffeine overcome steric hindrance to adopt uncommon conformations, each one placing a C-H bond on the same plane of the aromatic system, leading to the C-H bonds eclipsing one carbonyl group, one heavily delocalized C-N bond constituent of the fused double ring aromatic system, and one C-H bond from the imidazole ring. Deletion of indiscriminate and selective non-Lewis orbitals unequivocally show that hyperconjugation in the form of a bidirectional -CH3 ⇆ aromatic system charge transfer is responsible for these puzzling conformations. The structural preferences in caffeine are exclusively determined by orbital interactions

SUBMITTER: Gomez S 

PROVIDER: S-EPMC8949453 | biostudies-literature | 2022 Mar

REPOSITORIES: biostudies-literature