The text-book Walden cycle which interconverts the stereochemical configurations of chlorosuccinic and malic acids involves a β-lactone intermediate in preference to an α-lactone intermediate because the Onuc C Cl angle in the transition structure for the former (174°) is more favourable than that for the latter (139°), as determined by PCM(ε = 78.4)/B3LYP/6-31+G* calculations; the smaller ring-strain energy of the β-lactone contributes little to the reactivity difference.
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