What is the enthalpy change for the isomerization reaction: CH 2 =CH-CH 2 -CH=CH 2 (A) → CH 2 =CH-CH=CH-CH 3 (B) (reagent: NaNH 2 , Δ) Magnitude of resonance energies of A and B are 20 and 50 kJ/mol,

Question

What is the enthalpy change for the isomerization reaction:

CH₂=CH-CH₂-CH=CH₂ (A) → CH₂=CH-CH=CH-CH₃ (B) (reagent: NaNH₂, Δ)

Magnitude of resonance energies of A and B are 20 and 50 kJ/mol, respectively. A and B contain identical bonds (same Kekulé bond inventory), so their bond-enthalpy contributions are equal.

TestHub · Accepted Answer

The isomerization keeps the same number and type of bonds (2 C=C, 2 C-C, 8 C-H on both sides), so the bond-enthalpy parts cancel. Only resonance stabilization changes: ΔH = RE A - RE B = 20 - 50 = -30 kJ. This is option (d).

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