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Special_Topic_G - P1 PBU/OVY JWDD052-G P2 PBU/OVY QC...

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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Hamilton JWDD052-G JWDD052-Solomons-v3 June 1, 2007 19:28 G SPECIAL TOPIC Electrocyclic and Cycloaddition Reactions SOLUTIONS TO PROBLEMS G.1 According to the Woodward-Hoffmann rule for electrocyclic reactions of 4 n π -electron systems (Section G.2A), the photochemical cyclization of cis, trans -2,4-hexadiene should proceed with disrotatory motion . Thus, it should yield trans -3,4-dimethylcyclobutene: hv disrotatory H H CH 3 CH 3 + enantiomer cis , trans -2,4-Hexadiene trans -3,4-Dimethylcyclobutene H CH 3 CH 3 H G.2 (a) CH 3 CH 3 H 3 C H H CH 3 200 ° C ( + ) ( + ) - - ( + ) ( + ) ( + ) ( + ) ( - ) ( - ) ( - ) ( - ) H CH 3 H CH 3 CH 3 H 3 C ψ 2 of a hexadiene (Section G.2A) (b) This is a thermal electrocyclic reaction of a 4 n π -electron system; it should, and does , proceed with conrotatory motion. G.3 hv disrotatory heat conrotatory H CH 3 CH 3 H trans, trans -2,4-Hexadiene cis -3,4-Dimethylcyclobutene cis, trans -2,4-Hexadiene CH 3 H CH 3 H H H CH 3 H 3 C 505
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Hamilton JWDD052-G JWDD052-Solomons-v3 June 1, 2007 19:28 506 SPECIAL TOPIC G Here we find that two consecutive electrocyclic reactions (the first photochemical, the
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