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Dehydrohalogenation of 3-bromohexane gives a mixture of cis-2-hexene and trans-2-hexene. How can this mixture be converted to pure (a) cis-2-hexene? (b) trans-2-hexene? |
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Answer» Solution :Relatively pure alkenes (geometric ISOMERS) are prepared by stereoselective reduction of ALKYNES. <BR> (a) Hydrogenation of 2-hexyne with Lindlar.s catalyst gives cis-2-hexene. `CH_3CH=CHCH_2CH_2CH_3overset(Br_2)rarrCH_3underset(Br)underset(|)CH-underset(Br)underset(|)CHCH_2CH_2CH_3overset(2NaNH_2)rarr`  (b) Reduction with Na in liquid `NH_3` gives the trans PRODUCT. 
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