IIT-JEE 2010 · Paper 1 · Chemistry Q3

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ChemistrySingle correct+3 / -1Question 3 of 84

The synthesis of 3-octyne is achieved by adding a bromoalkane into a mixture of sodium amide and an alkyne. The bromoalkane and alkyne respectively are

\ce{BrCH2CH2CH2CH2CH3}

and

\ce{CH3CH2C#CH}

\ce{BrCH2CH2CH3}

and

\ce{CH3CH2CH2C#CH}

\ce{BrCH2CH2CH2CH2CH3}

and

\ce{CH3C#CH}

\ce{BrCH2CH2CH2CH3}

and

\ce{CH3CH2C#CH}

Answer and worked solution

Official answer: D

Target. 3-Octyne is $\ce{CH3CH2-C#C-CH2CH2CH2CH3}$ : an ethyl and an n-butyl group on the triple bond.

Route. $\ce{NaNH2}$ deprotonates a terminal alkyne, and the acetylide does $\mathrm S_\mathrm N2$ on a primary bromide. So use but-1-yne, $\ce{CH3CH2C#CH}$ , and 1-bromobutane, $\ce{BrCH2CH2CH2CH3}$ .

(D)

Topics:Alkynes SN1 and SN2

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IIT-JEE 2010 · Paper 1, Chemistry question 3