$$ - C{H_3}$$ is the best nucleophile because carbon is least electronegative among the given options. The order is $${H_3}\overline C > \overline N {H_2} > \overline O H > {F^ - }$$
52.
The compound which gives the most stable carbonium ion on dehydration is :
A
\[C{{H}_{3}}\underset{\begin{smallmatrix}
|\,\,\,\,\, \\
C{{H}_{3}}
\end{smallmatrix}}{\mathop{-CH-}}\,C{{H}_{2}}OH\]
B
\[C{{H}_{3}}\underset{\begin{smallmatrix}
| \\
\,\,\,\,C{{H}_{3}}
\end{smallmatrix}}{\overset{\begin{smallmatrix}
\,\,\,\,C{{H}_{3}} \\
|
\end{smallmatrix}}{\mathop{-C-}}}\,OH\]
C
\[C{{H}_{3}}C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}OH\]
D
\[C{{H}_{3}}\underset{\begin{smallmatrix}
|\,\,\,\,\, \\
OH\,\,
\end{smallmatrix}}{\mathop{-CH-}}\,C{{H}_{2}}-C{{H}_{3}}\]
NOTE : The order of stability of carbonium ion is tertiary > secondary > primary > methyl
Tertiary carbonium ions ( formed in B ) are more stable because of electron repelling ( $$ + I$$ effect ) nature of $$C{H_3}$$ group due to which the $$+ve$$ harge gets dispersed and also due to hyperconjugation.
53.
Most stable carbocation among the following is :
$$– I$$ group destablises carbocation and since inductive effect decreases with increasing length of carbon chain. Therefore (b) is the correct option.
58.
The general formula $${C_n}{H_{2n}}{O_2}$$ could be for open chain
The most stable carbocation is $$t-alkyl$$ carbocation. The order of stability of $$alkyl$$ carbocation is $$ter - alkyl > \sec - alkyl > pri - alkyl > CH_3^ + $$ carbocation.
This stability order is described with the help of hyperconjugation and inductive effect. On the basis of hyperconjugation, $${\left( {C{H_3}} \right)_2}\mathop C\limits^ + H$$ shows six resonating structures due to the presence of six $$\alpha {\text{ - }}C - H$$ bonds, shows nine resonating structures due to the presence of nine $$\alpha {\text{ - }}C - H$$ bonds.
Greater the $$\alpha \,H - atom$$ greater will be the hyper conjugation resonating structure and therefore, greater will be the stability.
$$\mathop C\limits^ + {H_3}$$ does not show the property of resonance while $$C{H_3} - \mathop C\limits^ + {H_2}$$ shows three resonating strictures due to presence of three $$\alpha {\text{ - }}C - H$$ bonds. Hence, larger number of resonating structures are possible in (B), so it is most stable. The above order of stability is also explained with the help of $$(+)$$ $$I$$ - effect of $$ - C{H_3}$$ group. More the number of $$ - C{H_3}$$ group more will be tendency to displace the electrons towards positively charged carbon of carbocation. Thus, positive charge is decreased or compensated and stability of carbocation is increased.
60.
The blue compound formed in the positive test for nitrogen with Lassaigne solution of an organic compound is
A
$$N{a_4}\left[ {Fe{{\left( {CN} \right)}_5}\left( {NOS} \right)} \right]$$
B
$$N{a_3}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$$
C
$$Fe{\left( {CN} \right)_3}$$
D
$$F{e_4}{\left[ {Fe{{\left( {CN} \right)}_6}} \right]_3}$$