Explain why carboxylic acids behave as acids. Discuss briefly the effects of electron withdrawing and donating substituents on acid strength of carboxylic acids.

Explain why carboxylic acids behave as acids. Discuss briefly the effe

1.	Explain why carboxylic acids behave as acids. Discuss briefly the effects of electron withdrawing and donating substituents on acid strength of carboxylic acids.
Answer» Solution :Acidic nature of acids : (i) Acid molecule IONISES to produce `H^(+)` ions in solution. (ii) The carboxylate anion is stabilised by resonance. HENCE the CLEAVAGE of `-COOH` bond to release `H^(+)` is favoured, thereby making it to behave as acids. (iii) Any factor that weakens the `-COOH` bond will facilitate the cleavage to release `H^(+)` more easily. The degree of ionisation is increased and acid becomes relatively a STRONGER acid. (iv) When the following acids are compared, `CH_(3)-overset(CH_(3))overset(\|)(CH)-COOHltCH_(3)-CH_(2)COOHltCH_(3)COOHltHCOOHltClCH_(2)COOH` Their strength varies as the above order. (v) Methyl group is a +I group (electron pair repelling group). Acid strength decreases with increasing number of electron repelling substituent attached to the `alpha` - carbon atom. The +I effect is felt in increasing the strength of the -OH bond and the cleavage to form `H^(+)` becomes difficult. Hence they are weaker acid than formic acid (HCOOH) which does not have +I methyl group. (vi) Acid strength increases with INCREASE in electronegativity of substituents. This effect weaknens the -O-H bond there by facilitating the removal of `H^(+)` from - OH group. This acid becomes stronger than formic acid.