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Unformatted text preview: 2/6/2012 Why is pyrrole unreactive in the Diels-Alder reaction? Which reactant, A or B, has the higher activation energy? Nmethylpyrrole A B Ea(B) Ea(A)
energy reaction Why is pyrrole unreactive in the Diels-Alder reaction? D Cl Furan (B) is more reactive in the Diels-Alder reaction than pyrrole (A). Why? Nmethylpyrrole A furan B Which reactant, A or B, is more stabilized by resonance? Cyclic conjugation results in unusual stability. A B 1 2/6/2012 Cyclic conjugation results in unusual stability. Why do three double bonds in a ring have so much more resonance stabilization than two? How can the stability due to cyclic conjugation be measured? A. Infrared spectroscopy B. NMR spectroscopy C. Ultraviolet spectroscopy D. Heats of Hydrogenation
energy A. 50 kJ/mol B. 8 kJ/mol C. 152 kJ/mol D. 208 kJ/mol What is the resonance stabilization of benzene? Heats of Hydrogenation Does resonance theory predict cyclobutadiene to be stabilized by resonance? (A) yes (B) no A. 50 kJ/mol B. 8 kJ/mol C. 152 kJ/mol D. 208 kJ/mol energy What is the resonance stabilization of cyclohexadiene? Does molecular orbital theory predict the stabilization of conjugated -systems? (A) yes (B) no A. 50 kJ/mol B. 8 kJ/mol C. 152 kJ/mol D. 208 kJ/mol energy 2 2/6/2012 Using six p-orbitals how many molecular orbitals are there for the benzene -system ? How many electrons are in the benzene -system? A 1 D 6 B 2 E 12 C 4 F 18 A 1 D 6 B 2 E 12 C 4 F 18 Which of the following molecular orbitals is highest in energy? A B C benzene -system D E F Which of the following molecular orbitals has the same energy as B? energy energy How many electrons are in the benzene -system? What is the E for ethylene in energy units of ?
http://www.ic.sunysb.edu/Class/orgchem/ A 0 B 2 C 4 D 6 E 8 p-orbital -bond A B C
energy benzene -system 2 number of electrons D E F E(ethylene) = 2
energy 3 2/6/2012 What is the predicted E for benzene in energy units of if there were no resonance stabilization? p-orbital -bond A 0 B 2 C 4 D 6 E 8 0.0
energy benzene -system 2 Predicted E (benzene)= 3(2) = 6 What is the delocalization (resonance) energy for benzene in energy units of ?
delocalization energy = E(benzene) E3(ethylene) = 8(benzene) - 6(ethylene) = 2 A 0 B 2 C 4 D 6 E 8 0.0
energy ethylene -system benzene -system
E = 4 E = 2(2) E (total) = 8 2 Predicted E (benzene)= 3(2) = 6 4 ...
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