Question

(d) pka value of p-chlorobenzoic acid is 3.98 and
that of benzoic acid is 4.19.Calculate sigma for
p-chlorobenzoic acid.​

Answer 1

Answer:

Sigma for p-Chlorobenzoic acid is σ = 0.0223

Explanation:

Substituent constant is also Known as HAMMETT CONSTANT. It is a measure of the electronic effect of replacing H by Substituent. it is denoted by σ (sigma) .

$\sigma = \log(\frac{KH}{KR} )$

here,

KR and KH = Dissociation constant of substituted acids and unsubstituted acids.

$\sigma = \log(\frac{4.19}{3.98} )\\\sigma = 0.0223$

Conclusion : sigma for p-Chlorobenzoic acid = 0.0223