CONJUGATION IN ALKADIENES AND ALLYLIC SYSTEMS 239 (d) Addition of hydrogen chloride to allyl bromide proceeds in accordance with Markovnikov's rule H,C=CHCH, Br CH3 CHCH, Br Allyl bromide 1- Bromo-2-chloropropane (e) Addition of bromine to allyl bromide gives 1, 2, 3-tribromopropane H,C=CHCH, Br BrChChChaB Allyl bromide 1, 2, 3-Tribromopropane (f) Nucleophilic substitution by hydroxide on allyl bromide gives allyl alcohol H,C=CHCH.Br HC=CHCH.OH Allyl bromide Allyl alcohol (g) Alkylation of sodium acetylide using allyl bromide gives the desired 1-penten-4-yne H, C=CHCH. Br NaC=CH, HC=CHCHCECH Allyl bromide 1-Penten-4-yne (h) Sodium-ammonia reduction of 1-penten-4-yne reduces the triple bond but leaves the double bond intact. Hydrogenation over Lindlar palladium could also be used H_C=CHCH2 C=CH or H Lindlar Pd H2C=CHCH,CH-CH2 L4-Pentadiene 10.23 (a) The desired allylic alcohol can be prepared by hydrolysis of an allylic halide. Cyclopent can be converted to an allylic bromide by free-radical bromination with N-bromosuccinim NBS peroxides OH Cyclopentene 3-Bromocyclopentene 2-Cyclopenten-l-o (b) Reaction of the allylic bromide from part(a) with sodium iodide in acetone converts it to the 3-lodocyclopentene Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website(d) Addition of hydrogen chloride to allyl bromide proceeds in accordance with Markovnikov’s rule. (e) Addition of bromine to allyl bromide gives 1,2,3-tribromopropane. ( f ) Nucleophilic substitution by hydroxide on allyl bromide gives allyl alcohol. (g) Alkylation of sodium acetylide using allyl bromide gives the desired 1-penten-4-yne. (h) Sodium–ammonia reduction of 1-penten-4-yne reduces the triple bond but leaves the double bond intact. Hydrogenation over Lindlar palladium could also be used. 10.23 (a) The desired allylic alcohol can be prepared by hydrolysis of an allylic halide. Cyclopentene can be converted to an allylic bromide by free-radical bromination with N-bromosuccinimide (NBS). (b) Reaction of the allylic bromide from part (a) with sodium iodide in acetone converts it to the corresponding iodide. 3-Bromocyclopentene 3-Iodocyclopentene Br NaI acetone I NBS heat, peroxides H2O Na2CO3 Br OH Cyclopentene 2-Cyclopenten-1-ol 3-Bromocyclopentene Na, NH3 1,4-Pentadiene H2C CHCH2CH CH2 1-Penten-4-yne H2C CHCH2C CH or H2, Lindlar Pd H2C CHCH2Br NaC CH Allyl bromide 1-Penten-4-yne H2C CHCH2C CH H2C CHCH2Br Allyl bromide Allyl alcohol H2C NaOH CHCH2OH H2C CHCH2Br Allyl bromide 1,2,3-Tribromopropane BrCH2CHCH2Br Br2 Br H2C CHCH2Br Allyl bromide 1-Bromo-2-chloropropane CH3CHCH2Br HCl Cl CONJUGATION IN ALKADIENES AND ALLYLIC SYSTEMS 239 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website