The standard enthalpy of formation ΔH○f,298 for hydroxyoxiranone is estimated as -377 ± 10 kJ mol-1 by means of ab initio molecular orbital calculations at the QCISD(T)(full)/6-311G(2df,p)//MP2(full)/6-311G(d,p) level of theory, corresponding to a conventional ring strain energy of 104 kJ mol-1. The hydroxy substituent on Cα stabilizes the α-lactone by 65 kJ mol-1 with concomitant elongation of the bond from Cα to the endocyclic oxygen On. There is a much larger stabilization (205 kJ mol-1) by the hydroxy substituent upon the zwitterion obtained by heterolysis of the Cα-On bond, and upon the carbene obtained by decarboxylation of the zwitterion. The relative energies of the α-lactone, zwitterion and carbene have been determined by MP2(fc)/6-31+G(d) calculations in vacuo and with the IPCM method for aqueous solvation. Solvation by this continuum method preferentially stabilizes the zwitterion, although at the IPCM-MP2(fc)/6-31+G(d) level the a-lactone is still 21 kJ mol-1 lower in energy than the zwitterion.
|Number of pages||6|
|Journal||Journal of the Chemical Society. Perkin Transactions 2|
|Publication status||Published - 1 Jan 1997|
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