Question

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

पर्याय

• \[\begin{array}{cc}
  \phantom{...}\ce{O}\\
  \phantom{...}||\\
  \ce{CH3 - C - O}
  \end{array}\]

• \[\begin{array}{cc}
  \phantom{........}\ce{O}\\
  \phantom{........}||\\
  \ce{Cl - CH2 - C - O}
  \end{array}\]

• \[\begin{array}{cc}
  \phantom{........}\ce{O}\\
  \phantom{........}||\\
  \phantom{.}\ce{F - CH2 - C - O}
  \end{array}\]

• \[\begin{array}{cc}
  \phantom{}\ce{F}\phantom{......}\ce{O}\\
  \phantom{}\backslash\phantom{......}||\\
  \phantom{......}\ce{CH - C - O}\\
  \phantom{}/\phantom{.......}\\
  \ce{F}\phantom{.........}
  \end{array}\]

Answer 1

\[\begin{array}{cc}
\phantom{}\ce{F}\phantom{......}\ce{O}\\
\phantom{}\backslash\phantom{......}||\\
\phantom{......}\ce{CH - C - O}\\
\phantom{}/\phantom{.......}\\
\ce{F}\phantom{.........}
\end{array}\]

Explanation:

The stabilisation of carboxylate ion depends on dispersal of negative charge. The negative charge is dispersed by two factors, i.e., +R effect of the carboxylate ion and inductive effect of the halogens. In all the above structures, +R effect is common but halogen atoms are different. Therefore, dispersal of negative charge depends upon halogen atoms. F is most electronegative, in structure two F atoms are present and more dispersal of negative charge is there.