The role of hyperconjugation in the unusual conformation of thymine: a natural bond orbital analysis

Publication date: Available online 13 March 2018 Source:Computational and Theoretical Chemistry Author(s): Emerson Rengifo, Sara Gómez, Julio C. Arce, Frank Weinhold, Albeiro Restrepo The diketo conformation of thymine inferred from a high-level ab initio calculation, where one of the C–H bonds of the methyl group lies in the ring plane eclipsing another C–H bond instead of the polar C=O bond, seems unexpected on the grounds of an analysis in terms of steric hindrance and long–distance inductive interactions. To assess the causes of such conformation, we carried out a natural bond orbital analysis. We found that charge delocalization (hyperconjugation), associated mainly with vicinal σ C - H - CH 3 → σ C - C ∗ ring and σ C - H - CH 3 → π C - C ∗ ring interactions, strongly favors the observed conformation. Graphical abstract

Source: Computational and Theoretical Chemistry - March 14, 2018 Category: Chemistry Source Type: research