Question

Which of the following group(s) is/are only meta-directing?

• A. $-Cl$
  
• B. $-CH=C{H}_2$
  
• C. $-CHO$
  
• D. $-COOH$

Answer 1

Answer: (C), (D)

$-COOH$

Although halogens are deactivating by -I effect, they are ortho- and para-directing due to +R effect. $-CH=C{H}_2$ can show +R effect and donates its $\pi e^{-}$ to the benzene and stabilises intermediate $\sigma$ - complex and thus can act as ortho-para directing.and thus, it is ortho- and para-directing.

($-CHO$) and ($-COOH$) are electron withdrawing group. They shows both -R effect and -I effect and decrease the electron density at ortha and para position relative to meta position. Thus, it deactivates the ortho and para position and the substitution takes place at meta position.

Therefore, (c) and (d) are meta directing group.