Q47 of 51 Page 169

In the following questions a statement of assertion (A) followed by a statement of reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A) : Among isomeric pentanes, 2, 2-dimethylpentane has highest boiling point.


Reason (R) : Branching does not affect the boiling point.


(i) Both A and R are correct and R is the correct explanation of A.


(ii) Both A and R are correct but R is not the correct explanation of A.


(iii) Both A and R are not correct.


(iv) A is not correct but R is correct.


(iii) Both A and R are not correct.

Explanation – Long chain hydrocarbon have higher boiling point than branched chain.


If branching increases than it decrease the boiling point. Branching decreases the surface area of alkanes due to this force of attraction between the molecule decreases. If we apply heat in branch chain hydrocarbon molecule it will separate easily due low molecular attraction. So, branch chain molecule boil easily than long chain.


More from this chapter

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45

In the following questions a statement of assertion (A) followed by a statement of reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A) : Toluene on Friedal Crafts methylation gives o– and p–xylene.


Reason (R) : CH3- group bonded to benzene ring increases electron density at o– and p– position.


(i) Both A and R are correct and R is the correct explanation of A.


(ii) Both A and R are correct but R is not the correct explanation of A.


(iii) Both A and R are not correct.


(iv) A is not correct but R is correct.


 46

In the following questions a statement of assertion (A) followed by a statement of reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A) : Nitration of benzene with nitric acid requires the use of concentrated sulphuric acid.


Reason (R) : The mixture of concentrated sulphuric acid and concentrated nitric acid produces the electrophile, NO2+ .


(i) Both A and R are correct and R is the correct explanation of A.


(ii) Both A and R are correct but R is not the correct explanation of A.


(iii) Both A and R are not correct.


(iv) A is not correct but R is correct.


 48

An alkyl halide C5H11Br (A) reacts with ethanolic KOH to give an alkene ‘B’, which reacts with Br2 to give a compound ‘C’, which on dehydrobromination gives an alkyne ‘D’. On treatment with sodium metal in liquid ammonia one mole of ‘D’ gives one mole of the sodium salt of ‘D’ and half a mole of hydrogen gas. Complete hydrogenation of ‘D’ yields a straight chain alkane. Identify A,B, C and D. Give the reactions involved.

 49

896 mL vapour of a hydrocarbon ‘A’ having carbon 87.80% and hydrogen 12.19% weighs 3.28g at STP. Hydrogenation of ‘A’ gives 2-methylpentane. Also ‘A’ on hydration in the presence of H2SO4 and HgSO4 gives a ketone ‘B’ having molecular formula C6H12O. The ketone ‘B’ gives a positive iodoform test. Find the structure of ‘A’ and give the reactions involved.