Question

Which of the following groups exhibit the highest $-I$ effect?

• A. $-CHO$
• B. $-CH=NH$
• C. $-CH=C{H}_2$
• D. Both (a) and (b) above

Answer 1

The correct option is A $-CHO$

Among the three groups, $-CHO$ group has a polar $-C=O$ bond and $-CH=NH$ group has a polar $-C=N$ bond while $-CH=C{H}_2$ group is non polar because the electronegativity difference between two carbon atoms is zero.
The high electronegativity of $O$ atom makes the $-CHO$ group more electron-withdrawing due to the generation of more partial positive charge on the respective $C$ atom.

Therefore, $-CHO$ group will show the highest $-I$ effect.