Table 5. Hammett sigma constants.

Ethanol concentration	ρa	Sigma constant
		m-Allyl		p-Allyl		m-Propenyl		p-Propenyl
Wt %
0	1.000	−0.056	0.004b	−0.116	0.004b	−0.038	0.006b	−0.277	0.023b
12.2	1.128	−.062	.006	−.105	.003	− .036	.006	−.302	.035
25.2	1.266	−.092	.008	−.113	.006	−.043	.002	−.187	.013
44.1	1.465	−.079	.003	−.081	.003	−.048	.006	−.111	.009
64.8	1.578	−.068	.010	−.072	011	−.034	.009	−.121	.019

^aCalculated from ρ = 1.000 + 0.628 Y_, where Y_, which is a characteristic parameter of carboxylate-carboxylic acid equilibria, was obtained by interpolation of the values given by Grunwald and Berkowitz [6].

^bStandard error of the mean $\frac{\sqrt{S_{p{K}_{\text{H}}}^2+S_{p{K}_S}^2}}{\rho }$ where $S_{\overline{p}{K}_H}$ is the standard error of the mean for benzoic acid and $S_{\overline{p}{K}_S}$ is the corresponding value for the substituted benzoic acid.