Ionic species are stailised by the dispersal of charge. Which of the following carboxylate ion is the most stable ?

Options

A. `CH_(3) - overset(O)overset(||)(C) - O^(-)`
B. `Cl - CH_(2) - overset(O)overset(||)(C) - O^(-)`
C. `F - CH_(2) - overset(O)overset(||)(C) - O^(-)`
D.

Answer

D

Explanation

In all the given carbocations, the negative is dispersed which stabilises these carbocations. Here, the negative charge is dispersed by two factors i.e., `+R`-effect of the carboxylate ion (conjugation) and `I-`effect of the halogens.
These effects are shown below in the carbocations




As it is clearly evident from the above structure, that `+R-`effect is common in all the four structures, therefore, overall dispersal of negative charge depends upon the number of halogen atoms and electronegativity. Since, F has the highest electronegativity and two F-atoms are present in options (d0, thus, dispersal of negative charge is maximum in option (d)
Note In above structure (a), methyl group `(CH_(3))` increases the density on C-atom.