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Primary alkyl halide C_(4)H_(9)Br(a) reacted with alcoholic KOH to give compound (b). Compound (b) is reacted with HBr to give (c) which is an isomer of (a). When (a) is reacted with sodium metal, it gives a compound (d), C_(8)H_(18)which is different from the compound formed when n-butyl bromide is reacted with sodium. Give the structural formula of (a) and write the equations for all the reactions. |
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Answer» SOLUTION :Two primary ALKYL halideshaving the molecular formula, `C_(4)H_(9)Br `are `underset("n -Butyl bromide") (CH_(3)CH_(2)CH_(2)CH_(2)Br) "and " underset("Isobutyl bromide") (CH - overset(CH_(3)) overset(|) CH - CHBr) ` Compound (a) when reacted with Na metal gives a compound (d) with molecular formula `C_(8)H_(18) `which is different from the compound obtained when n-butyl bromide is reacted with Na metal. THEREFORE, (a) must be isobutyl bromide and compound (d) must be 2, 5- dimethylhexane. `underset("n-Butylbromide "(1^(@))) (2CH_(3)CH_(2)CH_(2)Br ) + Na underset(-2NaBr) overset("Wurtz reaction ") to underset("n -octane") (CH_(3)CH_(2)CH_(2)CH_(2)CH_(2)CH_(2) CH_(2)CH_(3))underset("Isobutyl bromide (a) "(1^(@))) (CH_(3) - overset(CH_(3)) overset(|) CH - CH_(2)Br ) + 2Na underset(-2 NaBr) overset("Wurtz reaction ") to underset("2, 5- Dimethylhexane") (CH_(3) - overset(CH_(3))overset(|) CH - CH_(2) - CH_(2) - overset(CH_(3)) overset(|) CH - CH_(3)) ` With the identification of (a) and (d) , other compounds i.e., (B) and (c ) can be identified as under : `underset((a)) underset ("Isobutyl chloride ") (CH_(3) - overset(CH_(3)) overset(|) C= CH_(2)Br )underset("Dehydrohalogenation ") overset(KOH (alc), Delta ) tounderset((b)) underset("2 - METHYL -1-propane") (CH_(3) - overset(CH_(3)) overset(|) C = CH_(2)) ` Thus, (b) is 2 - methyl -1- propene. The compound (b) on treatment with HBr gives compound (c ) in accordance with Markovnikov.s rule . Therefore , compound (c ) is tert - butyl bromide which is an isomer of compound (a) i.e., isobutyl bromide . `underset("2 - Methyl -1-propene ") (CH_(3) - overset(CH_(3)) overset(|) C = CH_(2)) underset("Markovnikov addition ") overset("HBr") to underset(["an isomer of compound (a) "]) underset("tert -Butyl bromide (c )") (CH_(3) - underset(Br) underset(|) overset(CH_(3)) overset(|) C = CH_(3)) ` Thus , (a) is isobutyl bromide, (b) is 2- methyl -1- propene, (c ) is tert - butylbromide and (d) is 2 , 5 - dimethylhexane. |
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