Question
Alkanes and alkenes do not react with lithium amide. Give reason.
✓
Answer
i. The sp hybrid carbon atom in terminal alkynes is more electronegative than the $sp^2$ carbon in ethene or the $sp^3$ carbon in ethane.
ii. Due to high electronegative character of carbon in terminal alkynes, hydrogen atom can be given away as proton $(H^+)$ to very strong base as shown in the reactions below.
+
ii. Further, since s-character decreases from $sp$ to $sp^2$ to $sp^3$ carbon atom, the relative acidity of alkanes, alkenes and alkynes is in the following order: $H – C = C – H > H_2C = CH_2 > H_3C – CH_3$
Hence, alkenes and alkanes do not react with lithium amide.
ii. Due to high electronegative character of carbon in terminal alkynes, hydrogen atom can be given away as proton $(H^+)$ to very strong base as shown in the reactions below.
+
ii. Further, since s-character decreases from $sp$ to $sp^2$ to $sp^3$ carbon atom, the relative acidity of alkanes, alkenes and alkynes is in the following order: $H – C = C – H > H_2C = CH_2 > H_3C – CH_3$
Hence, alkenes and alkanes do not react with lithium amide.
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