| Autor: |
Francisco CB; Department of Chemistry, State University of Maringá, 5790, Maringá 87020-900, Brazil.; Department of Chemistry, University of Toronto, 3359, Mississauga L5L-1C6, Canada., Fernandes CS; Department of Chemistry, State University of Maringá, 5790, Maringá 87020-900, Brazil., Franco Dourado F; Department of Chemistry, State University of Maringá, 5790, Maringá 87020-900, Brazil., Gauze GF; Department of Chemistry, State University of Maringá, 5790, Maringá 87020-900, Brazil., Rittner R; Chemistry Institute, University of Campinas, 6154, Campinas 13083-970, Brazil., Prosser RS; Department of Chemistry, University of Toronto, 3359, Mississauga L5L-1C6, Canada., Basso EA; Department of Chemistry, State University of Maringá, 5790, Maringá 87020-900, Brazil. |
| Abstrakt: |
The conformational features of α-halopropiophenones were investigated to understand the influence of α-halogens on conformation through hyperconjugative interactions, electrostatics, and steric factors. Using NMR, C-H scalar coupling constants were measured in different solvents, revealing a pattern in the conformational equilibria, which we validated by computational means. This behavior arises largely from hyperconjugative effects with the exception of the fluoro-derivatives, which are also influenced by steric and electrostatic interactions. In all cases, the contribution to hyperconjugation of the α-halo ketones is driven by the oxygen lone pair (rather than the C-X bond), which donates electron density to the adjacent C-C bonds. Additionally, C-C α bond rotation generates distortions in the side chain, responsible for destabilization, thus affecting system conjugation. These structural features identified for the α-halo ketones are also reflected in their reactivity, which is distinct from that expected for nucleophilic addition. |
