Calculation of the pKa values of alcohols from .sigma. constants and from the carbonyl frequencies of their esters

Abstract

in the second 0.870. In accordance with Student's criterion a probability of the coincidence of these mean values is below 0.01. Moreover in the correlations employing , the reaction sets of different authors under equivalent or very like conditions lead to the same correlation parameters. For example, sets 2, 4, and 6, respectively, yield p 1.07, 1.09, and 1.05 and pK°= 0.87, 0.98, and 1.00. Sets 3 and 5 give p 1.90 and 1.66, and pK°= 5.93 and 6.17. Differences in these values do not exceed the mean deviations. The correlation with Charton's method gives substantially different parameters. The sets 2, 4, and 6 give h = 2.31, 0.23, and 3.02, a = -6.83, -4.78, and -3.78, ß = -3.02, -4.05, and -0.62, respectively. The sets 3 and 5 give h = 7.99 and 7.26, a = -13.30 and -12.18, ß = 0.44 and -4,80. There is obviously no physical sense in these differences. Thus the Charton correlations, although giving satisfactory results, may lead to serious errors when analyzing the substituent effects on the properties of organophosphorus compounds. This danger may be avoided by using the constants.The correlation of with and using eq 7gives approximately linear dependence with the de-

The enol content of simple carbonyl compounds: an approach based upon pKa estimation

“…However, since the largest ApKa for a substituent (chloro) is 1.4, and the difference in ApKa between cis-and trans-chloro seems unlikely to be a large fraction of this, the error will not be prohibitively large. For R, the effect on the en01 pKa is-assumed to be the same as for the effect upon the alcohol pKa in 11, which is estimated using the correlation with o* of Takahashi et al (13). The ApKa values and related data are contained in Table 3 which has been deposited within the Depository of Unpublished Data.…”

“…We have presented in recent been done in the past 12). taking advantage of the work described in the earlier papers (7, lo), we 'Alfred P. Sloan Fellow, 1975-1979 can generate a correlation between rate and equilib- (13). We have extended this approach to give estimates of the pKa of enols.…”

The enol content of simple carbonyl compounds: a thermochemical approach

“…For other enols, the pK, values were estimated niaking the following two assumptions: for substituents on the [3 carbon of the enol the effect of the substituent is the same as for substitution a t the or-tho position of a phenol; for substituents at the a position of an enol the effect of the substituent is the same as for a saturated alcohol. Substituent effects were calculated from the observed pK, values for ortho-substituted phenols (19) and from the linear free energy relationship shown to hold for alcohol pK, values (20).…”

The mechanism of hydrolysis of 2-hydroxyethanesulfonyl chloride: the intermediacy of 1,2-oxathietane 2,2-dioxide (β-sultone)

“…The pKa of 1 may be estimated by the method of Takahashi et al (22) to be about 13.2; this makes 1 a distinctly stronger acid than water (pKa 15.7) and hence the transfer of the hydroxyl proton in 1 to hydroxide prior to cyclization a favoured process.…”