Question

Choose the correct $-I$ effect order for halogens when attached to a carbon chain:

• A. $-I>-Br>-Cl>-F$
• B. $-F>-Cl>-Br>-I$
• C. $-Cl>-F>-Br>-I$
• D. $-I>-Br>-F>-Cl$

Answer 1

The correct option is B $-F>-Cl>-Br>-I$

The halogens when attached to a less electronegative element like C , are electron withdrawing in nature.
More the electronegativity of the halogen group attached , more is the electron withdrawing nature.
Consequently, more is the $-I$ effect shown by that particular halogen group.
Electronegativity order is :
$F>Cl>Br>I$

Since Iodine is the least electronegative element among the halogen groups given, so it will show the least $-I$ effect.
$-I$ effect order is :
$-F>-Cl>-Br>-I$