Question

Which of the following group shows maximum $+I$ effect?

• A. $-N{H}^{-}$
• B. $-C{H}_2^{-}$
• C. $-O^{-}$
• D. All the three groups show similar $+I$ effect.

Answer 1

The correct option is B $-C{H}_2^{-}$

For $+I$ effect :
More the electronegativity of the atom, more is the tendency of that atom to hold the elctrons to itself, i.e. it will have a lesser tendency to be an electron donating group.
Lesser the tendency to donate electrons , lesser is the $+I$ effect.
Among $C,N,O$ , oxygen has the highest electronegativity followed by nitrogen and then carbon.
So, $+I$ effect follows the order :

$-C{H}_2^{-}>-N{H}^{-}>-O^{-}$

Theory:
$+I$ effect order of some groups :
$-\stackrel{-}{C}{H}_2>-\stackrel{-}{N}H>-O^{-}>-CO{O}^{-}>-C{R}_3>-CH{R}_2>-C{H}_{2}R>-C{D}_3>-C{H}_3>-T>-D>-H$