For the following reactions: (a) CH3CH2CH2Br + KOH(alc) -> CH3CH=CH2 + KBr + H2O (b) CH3CHBrCH2CH3 + KOH(aq) -> CH3CH(OH)CH2CH3 + KBr (c) C6H10(cyclohexene) + Br2 -> trans-1,2-dibromocyclohexane Which of the following statements is correct?

Correct answer: (B) (B) a is elimination, b is substitution and c is addition reaction. In (a) alcoholic KOH removes HBr from CH3CH2CH2Br giving the alkene — a -elimination (dehydrohalogenation). In (b) aqueous KOH supplies OH^- which replaces Br to give the alcohol — a nucleophilic substitution. In (c) Br2 adds across the C=C of cyclohexene to give the vicinal dibromide — electrophilic addition. So a = elimination, b = substitution, c = addition.

NEET 2016 Phase 1 · ChemistryPrevious Year Question

For the following reactions: (a) $CH X_{3} CH X_{2} CH X_{2} Br + KOH (alc) CH X_{3} CH = CH X_{2} + KBr + H X_{2} O$ (b) $CH X_{3} CHBrCH X_{2} CH X_{3} + KOH (aq) CH X_{3} CH (OH) CH X_{2} CH X_{3} + KBr$ (c) $C X_{6} H X_{10} (cyclohexene) + Br X_{2}$ trans-1,2-dibromocyclohexane Which of the following statements is correct?

Answer: (B) (B) a is elimination, b is substitution and c is addition reaction. In (a) alcoholic $KOH$ removes $HBr$ from $CH X_{3} CH X_{2} CH X_{2} Br$ giving the alkene — a $β$ -elimination (dehydrohalogenation).

A.(A) a and b are elimination reactions and c is addition reaction
B.(B) a is elimination, b is substitution and c is addition reaction✓
C.(C) a is elimination, b and c are substitution reactions
D.(D) a is substitution, b and c are addition reactions

Correct Answer

(B) (B) a is elimination, b is substitution and c is addition reaction

Solution & Explanation

In (a) alcoholic $KOH$ removes $HBr$ from $CH X_{3} CH X_{2} CH X_{2} Br$ giving the alkene — a $β$ -elimination (dehydrohalogenation). In (b) aqueous $KOH$ supplies $OH X^{-}$ which replaces $Br$ to give the alcohol — a nucleophilic substitution. In (c) $Br X_{2}$ adds across the C=C of cyclohexene to give the vicinal dibromide — electrophilic addition. So a = elimination, b = substitution, c = addition.

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For the following reactions: (a) CHX3​CHX2​CHX2​Br+KOH(alc)​CHX3​CH=CHX2​+KBr+HX2​O (b) CHX3​CHBrCHX2​CHX3​+KOH(aq)​CHX3​CH(OH)CHX2​CHX3​+KBr (c) CX6​HX10​(cyclohexene)+BrX2​​ trans-1,2-dibromocyclohexane Which of the following statements is correct?

Solution & Explanation

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