Free-energy surfaces for liquid-phase reactions and their use to study the border between concerted and nonconcerted α, β-elimination reactions of esters and thioesters

Yongho Kim, Jerry R. Mohrig, Donald G. Truhlar

Research output: Contribution to journalArticlepeer-review

60 Scopus citations

Abstract

Distinguishing between the concerted second-order mechanism for I-eliminations and nonconcerted mechanisms with discrete carbanion intermediates is very difficult experimentally, but the ability of quantum chemistry to find stationary points of the free-energy surface in liquid-phase solutions, even for complex reagents, provides a new tool for elucidating such mechanisms. Here we use liquid-phase density functional theory calculations to find transition states and intermediates on the free-energy surfaces of four base-initiated α, β-eliminations of acetoxy and mesyloxy esters and their analogous thioesters. The geometries, free energies, and charge distributions of these structures support a stepwise irreversible first-order elimination from a conjugate base (E1cBI) mechanism with acetoxy ester 3, acetoxy thioester 4, and mesyloxy thioester 6. However, mesyloxy ester 5, which has an excellent nucleofuge and a less-acidic proton, follows a concerted but asynchronous E2 mechanism with an E1cB-like transition state. The anti transition state is more favorable than the syn one, even for the poorer nucleofuge and more-acidic thioesters. The article includes a general scheme for describing liquid-phase reactions in terms of free-energy surfaces.

Original languageEnglish (US)
Pages (from-to)11071-11082
Number of pages12
JournalJournal of the American Chemical Society
Volume132
Issue number32
DOIs
StatePublished - Aug 18 2010

Fingerprint Dive into the research topics of 'Free-energy surfaces for liquid-phase reactions and their use to study the border between concerted and nonconcerted α, β-elimination reactions of esters and thioesters'. Together they form a unique fingerprint.

Cite this