07+ - P1: PBU/OVY JWCL234-07 P2: PBU/OVY QC: PBU/OVY T1:...

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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Bind Rite JWCL234-07 JWCL234-Solomons-v1 December 8, 2009 21:37 CONFIRMING PAGES 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 Order of increasing stability << 7.3 (a), (b) Δ H ° = 119 kJ mol 1 Δ H ° = 127 kJ mol 1 2-Methyl-1-butene (disubstituted) 3-Methyl-1-butene (monosubstituted) 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. 106
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Bind Rite JWCL234-07 JWCL234-Solomons-v1 December 8, 2009 21:37 CONFIRMING PAGES ALKENES AND ALKYNES I: PROPERTIES AND SYNTHESIS 107 (d) >> (trisubstituted) (disubstituted) (monosubstituted) H H H H H 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) 1-Pentene cis -2-Pentene trans -2-Pentene H H H H H H H (f) Order of stability: trans -2-pentene > cis -2-pentene > 1-pentene 7.4 (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. 7.5 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 7.6 most less least Br NaOEt EtOH, 55 ° C
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Bind Rite JWCL234-07 JWCL234-Solomons-v1 December 8, 2009 21:37 CONFIRMING PAGES 108 ALKENES AND ALKYNES I: PROPERTIES AND SYNTHESIS 7.7 heat + (trisubstituted, more stable) (monosubstituted, less stable) (a) Br + (tetrasubstituted, more stable) (disubstituted, less stable) (b) Major product Minor product Major product Minor product Br OK OH heat OK OH 7.8 t -BuOK in t -BuOH 7.9
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This note was uploaded on 10/20/2011 for the course CHEMISTRY ES110 taught by Professor Te.li during the Spring '11 term at Central Texas College.

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07+ - P1: PBU/OVY JWCL234-07 P2: PBU/OVY QC: PBU/OVY T1:...

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