CBSE 2026 · Region 3 · Set 3 · Q28 · 3 marks
Give reasons for the following :(a)Haloalkanes react with KCN to form alkyl cyanides, while with AgCN , they form isocyanides.(b)
is more reactive towards $\displaystyle \mathrm{S}_{\mathrm{N}} 2$ displacement as compared to
(c)Grignard reagents should be prepared under anhydrous conditions.
Give reasons for the following :
(a)
Haloalkanes react with KCN to form alkyl cyanides, while with AgCN , they form isocyanides.
(b)
is more reactive towards $\displaystyle \mathrm{S}_{\mathrm{N}} 2$ displacement as compared to
(c)
Grignard reagents should be prepared under anhydrous conditions.
Marking-scheme solution
(a)
Because the bond in KCN is ionic and the attack takes place mainly
through carbon atom while in AgCN being covalent, the attack is mainly
from nitrogen atom.
(b)
Because C in
is $\displaystyle 1$° whereas in
is $\displaystyle 2$°
which offer steric hindrance to Nucleophile.
(c)
Because in presence of moisture, Grignard Reagent forms Hydrocarbon
(alkane).
Haloalkanes and HaloarenesChemical Reactions of Haloalkanes and HaloarenesUnderstandshort_answermedium
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CBSE Class 12 Chemistry past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.