1.The Walden cycle revisited: a computational study of competitive ring closure to alpha- and beta-lactones.
Buchanan JG1, Diggle RA, Ruggiero GD, Williams IH. Chem Commun (Camb). 2006 Mar 14;(10):1106-8. Epub 2006 Feb 1.
The text-book Walden cycle which interconverts the stereochemical configurations of chlorosuccinic and malic acids involves a beta-lactone intermediate in preference to an alpha-lactone intermediate because the O(nuc) C Cl angle in the transition structure for the former (174 degrees) is more favourable than that for the latter (139 degrees), as determined by PCM(epsilon = 78.4)/B3LYP/6-31+G* calculations; the smaller ring-strain energy of the beta-lactone contributes little to the reactivity difference.