Question

6. Delocalization energy, DE, can be defined as the difference between the calculated value for the total pi-electron energy and "the sum of its parts". For example, DE for 1,3-butadiene Er(calculated) ET for two ethylenes; for benzene, its Er(calculated) - Er for three ethylenes, etc. (note that the total pi- energy for each ethylene is 2a + 2B) (a) Given that the eigenvalues for benzene are: a +2B and a B, calculate DE for benzene (b) One often reads that benzene is stabilized by 36 kcal/mol due to the delocalization. Knowing this determine the value of the resonance integral, B. Show your work.

Answer 1

NOte fiut of all you Ahauld Fnow that benzehe uh alUenant ludcaban, nanig that foi each HMO (tuckel molocula cHBÄAl) witfh eneng there an HMO uith eher d-p Now, HOw to fird uhethen a bon 0 het- 9 0 ah altenrant hydbio hydbto carbon Ah atehant hydolbon which thera o two Aes of Cobon one w staied CoxbCh and other i unitemed abon, ard gtauted corbons muU borded only a planer tenjugate hydtalorbon, u to untatied Corboiand vite-vea. Thu, codiestondingto there wiu the given ehengy lavel d+Barddt2B als0°d-Bard -28 eneqy lovels (eigan value)) úh the benzehe. Si nce s a Lavels wil be- hagactrive humber,thus oder of these enogg d-2Bd-A Pd+2p. kept aw given molacule, Aso, you should know if we starding which wiu be ch Aame haight wiu have Mame ehergy. thus Siugle Netex,the 'd'atam), then the humber ofc Gh a d-2p d-B Note: Eloctren filliu. AdA i take plate from Lower eneryy lwels d-B d-2p d-p メ+p huigha Thuy,Total reenerqy of behzenez 2ott2)ltp) +2 (d+p) = [6o +B8= ET humbecfe un that ehegyNOw, we have, Lovel DE = E (altuladed- f7 for thaee ellylete uride Gal+Bp-3(2+ 2) Fumberof etylene units 28

Giveh DE fo benzene we have Calculated DE - 2 A 36 K Callmol Thu), 2B36 KCalrol B-18KCallm