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 Multiple Choice QuestionsMultiple Choice Questions

11.

Assertion : The major products formed by heating C6H5CH2OCH, with HI are C6H5CH2I and CH3OH.

Reason : Benzyl cation is more stable than methyl cation.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


A.

If both assertion and reason are true and reason is the correct explanation of assertion

C6H5CH2OCH2 H+  C6H5CH+2 +CH3OH

                                I-C6H5CH2I

This can be explained on the basis of SN1 mechanism, the carbonium ion produced being benzylium ion, since this type is more stable than alkylium ion.


12.

Which of the following compound gives iodoform test?

  • CH3CN

  • CH3OH

  • CH3COCH3

  • C6H5OH


C.

CH3COCH3

Compounds containing CH3CO group give the iodoform test. The reaction is

CH3CO-CH3 + 3I2 +NaOH CHI3 + HCOONa + H2O

                                           iodoform (yellow ppt)

Hence, only acetone gives the iodoform test.


13.

Among the following the dissociation constant is highest for

  • C6H5OH

  • C6H5CH2OH

  • CH3CCH

  • CH3NH3+Cl


D.

CH3NH3+Cl

CH3N+H3Cl- is a salt which can be completely ionized in aqueous solution.


14.

Strongest nucleophile is

  • RNH2

  • ROH

  • C6H5O-

  • CH3O-


D.

CH3O-

CH3O- is stronger nucleophilic reagent because methyl group increase the electron density on oxygen, since it show +I effect.


15.

The major product formed in the following reaction is

  • (CH3)2CH-CH2OCH3

  • CH3-CH(OCH3)-CH2CH3

  • CH3-C(CH3)=CH2

  • (CH3)2-C-OCH3- CH3


D.

(CH3)2-C-OCH3- CH3

In the above reaction, alkyl halide is 1°. It always gives substitution reaction by SN2/E-2 mechanism.

E.g. with (CH3)3C-O-. It gives mainly elimination reaction and involves carbocation intermediate, i.e.primary carbocation. It rearranges itself to form tertiary carbocation. It is mainly because of the stability of a charged system which is increased by dispersal of the charge. Stability of carbocation is 3° > 2° > 1°. Rearrangement can be done in 2 ways- 

Therefore,

 


16.

Assertion : 2-bromobutane on reaction with sodium ethoxide in ethanol gives 1-butene as a major product.

Reason : 1-butene is more stable than 2-butene.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


D.

If both assertion and reason are false.

2-bromobutane on reaction with sodium ethoxide in ethanol gives 2-butene as a major product.

This is according to Saytzeffs rule i.e. the predominant product is the most substituted alkene. 2-butene is more stable than 1-butene due to presence of large number of hyperconjugating structures in 2-butene.


17.

SN2 mechanism is involed in the following substitution :

  • CH3-CH2-Cl + OH-

  • (CH3)2-C(Cl)-CH3-OH-

  • (CH3)2-C-Cl + OH-

  • CH3-CH2-(CH3)C(Cl)-CH3 + OH-


A.

CH3-CH2-Cl + OH-

Primary halide undergoes alkaline hydrolysis through SN2 mechanism .


18.

Arrange the hydra - acids of halogens in increasing order of acidity .

  • HF < HCl < HBr < HI

  • HI < HBr < HCl < HF

  • HF < HBr < HI <HCl

  • HF < HI < HBr < HCl


A.

HF < HCl < HBr < HI

Hydra - acids of halogens in increasing order of acidity :

HF < HCl < HBr < HI

As the strength of hydrogen bonding decreases in the order of :

HF > HCl > HBr > HI


19.

IUPAC name of 

CH3CH2C(Br)=CH-Cl is :

  • 2 - bromo - l - chloro butene - 1

  • 1 - chloro - 2 - bromo - butene

  • 3 - chloro - 2 - bromo butene - 2

  • none of these


A.

2 - bromo - l - chloro butene - 1

CH3CH2C(Br)=CH-Cl

2 - bromo - 1 - chloro butene - 1


20.

The major product obtained on treatment of CH3CH2CH(F)CH3 with CH3O/CH3OH is

  • CH3CH2CH(OCH3)CH3

  • CH3CH = CHCH3

  • CH3CH2CH = CH2

  • CH3CH2CH2CH2OCH3


B.

CH3CH = CHCH3

According to Saytzeff's rule, the major product will be the one that contains more number of substituents around the double bond. Therefore, the correct answer is CH3CH = CHCH3.