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Explain dehydrohalogenation reaction. |
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Answer» SOLUTION :Elimination reaction (ordehydrohalogenation reaction ) : <BR> This is a reaction in which two atoms or groups are removed from the aduacent carbon atoms (`alpha-beta` positions ) in the (organic ) molecule forming unsaturated COMPOUND. Explanation : When an alkyl halide is heated with alcoholic solution of KOH an alkene is formed DUE to removal of H and halogen X atoms from the adjacent carbon atoms (`alpha-beta` positions ) and this elimination reaction is called dehydrohalogenation reaction. `-overset(overset(H)(|beta))underset(|)(C)-overset(overset(H)(|alpha))underset(|)(C)-underset(("alc."))(KOH)overset(triangle)(rarr)-underset(|)(C)=underset(|)(C) -+KX+H_(2)O` For example, `{:(overset(beta)(CH_(3))-overset(alpha)(CH_(2))-Br + ,KOH overset(triangle)(rarr),H_(2)C=CH_(2)+KBr+H_(2)O),("ethyl bromide","(alc.)","isobutylene"):}` Thertiary butyl bromide when heated with alcoholic solution of potassium hydroxide forms isobutylene. `CH_(3)-overset(overset(CH_(3))(alpha|beta))underset(underset(Br)(|))(C)-CH_(3)+underset(("alc."))(KOH)overset(triangle)(rarr)underset("isobutylese")(CH_(3)-)overset(overset(CH_(3))(|))(C)=CH_(2)+KBr+H_(2)O` If by elimination reaction, two isomers are formed than more stable SYMMETRICAL alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms is formed to a greater extent giving major product. For example : `underset("2-Bromobutane")(CH_(3)-CH_(2)-CHBr)-CH_(3) + underset("alc.")(KOH)overset(triangle)(rarr)` `{:(Ch_(3)- CH=CH,-CH_(3)+,CH_(3)-CH_(2)-CH=CH_(2)+KBr+H_(2)O), ("but-2-ene(80%)",,"but-1-ene(20%)"),("(major product)",,"(minor product)"):}` |
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