Ionic species are stabilised 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 charge is dispersed which stabilises these carbocations. Here, the negative charge is dispersed by two factors, i.e., +Reffect 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 structures, 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 option (d), thus, dispersal of negative charge is maximum in option (d).