given bond energy of carbon- carbon,carbon =carbon are 373.98, 410.87,631.72 kJ delta H OF BENZENE is -5506kJ calculate the RESONANCE ENERGY OF BENZENE ??

ALSO TELL THE STRATEGY OF SOLVING THE JEE PAPER

Dear student,

The resonance energy of benzene can be determined by comparing the enthalpies of hydrogenation of benzene and cyclohexene. If benzene did have the hypothetical 'cyclohexatriene' structure (the Kekulé structure), then it would be expected to have an enthalpy of hydrogenation that is three times that of cyclohxene.

The enthalpy of hydrogenation of cyclohxene is -121 kJ mol^-1, providing a theoretical value of -363 kJ mol^-1 for Kekulé benzene with its three separate carbon-carbon double bonds.

In fact, the actual enthalpy of hydrogenation of benzene is only -209 kJ mol^-1. Therefore, 154 kJ mol^-1 of energy less than might have been expected is evolved. This is the energy that must have been expended in overcoming the additional stability conferred upon the benzene ring, owing the delocalisation of electrons. It is called the resonance energy or delocalisation energy.

In general, substances in which electrons are fairly evenly distributed over the entire or part of the molecules tend to be more stable and less reactive than those in which electrons are localised. This is because the polarity of chemical bonds is kept to a minimum, making bond breaking more difficult.