THE ENOLS OF ACETIC-ACID AND METHYL ACETATE

We have determined the heat of formation of 1,1 -dimethoxyethene, Delt a H-f(l) = -75.56 +/- 0.87 kcal mol(-1), by measuring the heat of hydr olysis. The heat of vaporization, 8.47 +/- 0.10 kcal mol(-1), was esti mated from the boiling points at various pressures. The standard entro py of gaseous 1,1-dimethoxyethene, 82.02 +/- 2. cal deg(-1) mol(-1), w as calculated using frequencies obtained by MO calculations at the 6-3 1G* level. The free energy of transfer, 1.02 +/- 1, was estimated by additivity with allowance for a distant polar interaction. Thus the fr ee energy of formation in aqueous solution, Delta G(f)(aq) = -37.07 +/ - 1.48 kcal mol(-1), could be calculated. The free energies of hydroly sis for enol ethers appear to be insensitive to structure; we used an average value and so calculated the values of the free energies of for mation of the enols of acetic acid and methyl acetate, -67.90 +/- 1.67 and -52.48 +/- 1.53 kcal mol(-1), respectively. These values are in g ood agreement with other recent evaluations. This method should be app licable to related enols.