Computational exploration of α-lactone rearrangements and the cyclic halonium zwitterion from bromination of acrylate anion in water: Implicit vs. explicit solvation

Abstract In memory of Jonathan Williams, a valued colleague incisive intellect (and regarded by undergraduates as ‘the better-looking Prof. Williams’ in the Department). Bromomethyloxiranone has much larger repertoire molecular acrobatics than previously recognised: conformational isomerism, degenerate rearrangement that exchanges O atoms α-lactone ring, and epimerisation, all which occur with lower barriers dyotropic to more stable β-lactone. DFT calculations (B3LYP/6-31 + G∗) implicit solvation (PCM) water predict cyclic bromonium zwitterion (formally derived from addition Br+ acrylate anion) be transition structure but QM/MM simulations, combining same method explicit many MM molecules using dynamics obtain free-energy profiles surfaces, reconfirms status an intermediate.