Chapter_7

Organic Chemistry

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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Hamilton JWDD052-07 JWDD052-Solomons-v3 June 2, 2007 10:27 7 ALKENES AND ALKYNES I: PROPERTIES AND SYNTHESIS. ELIMINATION REACTIONS OF ALKYL HALIDES SOLUTIONS TO PROBLEMS 7.1 (a) ( E )-1-Bromo-1-chloro-1-pentene or ( E )-1-Bromo-1-chloropent-1-ene (b) ( E )-2-Bromo-1-chloro-1-iodo-1-butene or ( E )-2-Bromo-1-chloro-1-iodobut-1-ene (c) ( Z )-3,5-Dimethyl-2-hexene or ( Z )-3,5-Dimethylhex-2-ene (d) ( Z )-1-Chloro-1-iodo-2-methyl-1-butene or ( Z )-1-Chloro-1-iodo-2-methylbut-1-ene (e) ( Z ,4 S )-3,4-Dimethyl-2-hexene or ( Z ,4 S )-3,4-Dimethylhex-2-ene (f) ( Z ,3 S )-1-Bromo-2-chloro-3-methyl-1-hexene or ( Z ,3 S )-1-Bromo-2-chloro-3-methylhex-1-ene 7.2 (a),(b) CH 2 CH 3 CHCH CHCH 3 CCH 2 CH 3 CH 3 CH 3 CH 3 CHCH 2 CH 3 CH 3 CH 3 CHCH 2 CH 3 CH 3 CH 2 Δ H ° = 119 kJ mol 1 Δ H ° = 127 kJ mol 1 2-Methyl-1-butene (disubstituted) 3-Methyl-1-butene (monosubstituted) CH 3 C CH 3 CH 3 CHCH 2 CH 3 CH 3 Δ H ° = 113 kJ mol 1 2-Methyl-2-butene (trisubstituted) H 2 Pt pressure H 2 Pt pressure H 2 Pt pressure (c) Yes, because hydrogenation converts each alkene into the same product. 100
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Hamilton JWDD052-07 JWDD052-Solomons-v3 June 2, 2007 10:27 ALKENES AND ALKYNES I: PROPERTIES AND SYNTHESIS 101 (d) CH 2 CCH 2 CH 3 CH 3 CH 3 CHCH CH 3 CH 2 >> CHCH 3 CH 3 C CH 3 (trisubstituted) (disubstituted) (monosubstituted) Notice that this predicted order of stability is conFrmed by the heats of hydro- genation. 2-Methyl-2-butene evolves the least heat; therefore, it is the most stable. 3-Methyl-1-butene evolves the most heat; therefore, it is the least stable. (e) CH 2 CHCH 2 CH 2 CH 3 1-Pentene cis -2-Pentene trans -2-Pentene H 3 C CH 2 CH 3 C H H C H 3 C C H CH 2 CH 3 H C (f) Order of stability: trans -2-pentene > cis -2-pentene > 1-pentene 7.3 (a) 2,3-Dimethyl-2-butene would be the more stable because the double bond is tetra- substituted. 2-Methyl-2-pentene has a trisubstituted double bond. (b) trans -3-Hexene would be the more stable because alkenes with trans double bonds are more stable than those with cis double bonds. (c) cis -3-Hexene would be more stable because its double bond is disubstituted. The double bond of 1-hexene is monosubstituted. (d) 2-Methyl-2-pentene would be the more stable because its double bond is trisubstituted. The double bond of trans -2-hexene is disubstituted. 7.4 The location of IR absorptions between 600 cm 1 and 1000 cm 1 due to out-of-plane bending of alkene C—H bonds can be the basis of differentiation. (a) 2-Methyl-2-pentene, 800 cm 1 2,3-Dimethyl-2-butene, no alkene C—H bonds (b) cis -3-Hexene, 650–750 cm 1 trans -3-Hexene, 960 cm 1 (c) 1-Hexene, 900 cm 1 and 1000 cm 1 cis -3-Hexene, 650–750 cm 1 (d) trans -2-Hexene, 960 cm 1 2-Methyl-2-pentene, 800 cm 1 7.5 KOEt EtOH heat (trisubstituted, more stable) (monosubstituted, less stable) (a) Major product Minor product Br
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Hamilton JWDD052-07 JWDD052-Solomons-v3 June 2, 2007 10:27 102 ALKENES AND ALKYNES I: PROPERTIES AND SYNTHESIS Br KOEt EtOH heat (tetrasubstituted, more stable) (disubstituted,
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Chapter_7 - P1 PBU/OVY JWDD052-07 P2 PBU/OVY QC PBU/OVY T1...

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