Order of bond energy in furan, pyrolle and thiophene

[Krushnaraj Pandya]

Homework Statement

A bromo-methyl group is attached adjacent to the N,O and S atoms respectively in furan, pyrolle and thiophene, find correct order of bond energy required for heterolytic cleavage of CBr bond forming carbocation

2. The attempt at a solution
Lone pairs participate in resonance in all three, so I thought the only different thing is the elctronegativity of the atoms. Since Oxygen>Nitrogen>Sulphur in EN furan would be most unstable since it'd try to pull electrons from the already positive carbon so its bond energy should be highest, then pyrolle's then thiophene but this is incorrect. I'd appreciate some help, thank you

 

[Krushnaraj Pandya]

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