Dissociatin enthalpies of methane, ethane and ethylene are respectively 400, 680 and 540 kcal mol^(-1). Calculate sigmaC - H,sigma C -C and pi C - C bond energies.

Dissociatin enthalpies of methane, ethane and ethylene are respectivel

1.	Dissociatin enthalpies of methane, ethane and ethylene are respectively 400, 680 and 540 kcal mol^(-1). Calculate sigmaC - H,sigma C -C and pi C - C bond energies.
Answer» Solution :Methane has four `sigmaC - H` bonds. `=400/4 = 100` `sigmaC - H` bond energy kcal `mol^(-1)` Ethane has six `SIGMA C - H` bonds and one `sigma C - C`bond. `sigma C- C` bond energy `= 680-(6 xx 100)` `= 80 k CAL mol^(-1)`. Ethylene has four `sigmaC - H` bonds one `sigma C -C` bond and one `PI C - C` bond. `:. pi C - C` bond energy `= 540 - [(4 xx 100) + 80]` `=60 kcal mol^(-1)`