Previous year Questions (2016-20) - Hydrocarbons Notes | EduRev

Q.1. Consider the following reactions
(I) (CH₃)₃CCH(OH)CH₃ 
(II) (CH₃)₃CHCH(Br)CH₃ 
(III) (CH₃)₂CHCH(Br)CH₃ 
(IV)
Which of these reaction(s) will not produce Saytzeff product?    (2020)
(1) (I), (III) and (IV)
(2) (IV) only
(3) (III) only
(4) (II) and (IV)
Ans. (3)
The reaction involved is:
(I)

(II)

(III)

(IV)

Since, the base used in reaction (III) is bulky, so it will abstract the hydrogen from less hindered carbon atom and will not form Saytzeff alkene.

Q.2. Consider the following reactions:
(I)
(II)
(III)
(IV)
Which of these reactions are possible?    (2020)
(1) (I) and (II)
(2) (I) and (IV)
(3) (II), (III) and (IV)
(4) (II) and (IV)
Ans. (4)
The possible reactions of benzene are:

Reaction (II):

Reaction (IV):


Q.3. The major products A and B in the following reactions are    (2020)

(1)
(2)
(3)
(4)
Ans. (4)
The reaction involved is



Q.4. The major product [B] in the following sequence of reaction is    (2020)

(1)
(2)
(3)
(4)
Ans. (3)
The reaction involved is


Q.5. In the following sequence of reactions, the maximum number of atoms present in molecule ‘C’ in one plane is _______.

(A is a lowest molecular weight alkyne)    (2020)
Ans. (13)
The reaction involved is

The molecular formula of toluene is C₇H₈, thus, the total number of atoms in toluene is 13.

Q.6. The correct order of heat of combustion for following alkadienes is    (2020)
(i)
(ii)
(iii) +
(1) (I) < (II) < (III)
(2) (I) < (III) < (II)
(3) (III) < (II) < (I)
(4) (II) < (III) < (I)
Ans. (1)
We know
Heat of combination of alkene ∝ 1/Stability of alkene
Since, trans-alkene is more stable than the cis-alkenes. Hence, the correct order of heat of combustion of the given dienes is: (I) < (II) < (III).

Q.7. The major product (Y) in the following reactions is    (2020)

(1)
(2)
(3)
(4)
Ans. (4)
The reaction involved is


Q.8. In the following reaction, A is    (2020)

(1)
(2)
(3)
(4)
Ans. (1)
The reaction involved is


Q.9. The number of sp² hybrid orbitals in a molecule of benzene is    (2020)
(1) 24
(2) 6
(3) 18
(4) 12
Ans. (3)
The number of sp² hybridized orbitals in benzene is 6 × (1 s-orbital + 2 p-orbitals) = 18 orbitals.


Q.10. The major product obtained in the following conversion is:    (2019)

(1)
(2)
(3)
(4)
Ans: (1)


Q.11. The major product of the following reaction is:    (2019)

(1)
(2)
(3)
(4)
Ans. (4)


Q.12. The major product of the following reaction is:    (2019)

(1)
(2)
(3)
(4)
Ans. (4)


Q.13. The major product of the following reaction is:    (2019)

(1) CH₃CH = C = CH₂
(2)
(3) CH₃CH = CHCH₂NH₂
(4) CH₃CH₂C ≡ CH
Ans. (4)


Q.14. Which one of the following alkenes when treated with HCI yields majorly an anti Markovnikov product?    (2019)
(1) CH₃O — CH = CH₂ 
(2) Cl — CH = CH₂ 
(3) H₂N — CH = CH₂ 
(4) F₃C — CH = CH₂
Ans. (4)


Q.15. The major product of the following reaction is:    (2019)

(1) CH₃CD(I)CHD(Cl)
(2) CH₃CD(Cl)CHD(I)
(3) CH₃CD₂CH(Cl)(I)
(4) CH₃C(I)(Cl)CHD₂ 
Ans. (4)

Both additions follow Markovnikov’s rule.

Q.16. The major product(s) obtained in the following reaction is/are:    (2019)

(1)
(2)
(3)
(4)

Ans. (1)


Q.17. The major product of the following addition reaction is    (2019)

(1)
(2)
(3)
(4)
Ans. (2)


Q.18. But 2-ene on reaction with alkaline KMnO₄ at elevated temperature followed by acidification will give:    (2019)
(1)
(2) one molecule of CH₃CHO and one molecule of CH₃COOH
(3) 2 molecules of CH₃COOH
(4) 2 molecules of CH₃CHO
Ans. (3)


Q.19. Consider the following reaction:    (2019)

'A' is:
(1) CH ≡ CH
(2) CH₃ - C ≡ C - CH₃
(3) CH₃- C = CH
(4) CH₂ = CH₂
Ans. (3)
 

Q.20. The trans-alkenes are formed by the reduction of alkynes with:    (2018)
(1) H₂ – Pd/C, BaSO₄ 
(2) NaBH₄ 
(3) Na/liq. NH₃ 
(4) Sn-HCl  
Ans. (3)
Na/Liq. NH₃ reduces alkynes into transalkene (trans addition).

Q.21. The major product of the following reaction is:    (2018)

(1)
(2)
(3)
(4)
Ans. 2


Q.22. Which of the following compounds will most readily be dehydrated to give alkene under acidic condition?    (2018)
(1) 4-Hydroxypentan-2-one 
(2) 3-Hydroxypentan-2-one 
(3) 1-Pentanol 
(4) 2-Hydroxycyclopentanone 
Ans. (1)
 will most readily be dehydrated to give conjugated alkene.

Q.23. Which of the following, upon treatment with tert-BuONa followed by addition of bromine water, fails to decolourize the colour of bromine?    (2017)
(1)
(2)
(3)
(4)
Ans. (1)

The above product does not have any C = C or C ≡ C bond, so, it will not give Br₂-water test.

Q.24. 3-Methyl-pent-2-ene on reaction with HBr in presence of peroxide forms an addition product. The number of possible stereoisomers for the product is    (2017)
(1) Six
(2) Zero
(3) Two
(4) Four
Ans. (4)

Since product (X) contains two chiral centres and it is unsymmetrical. 
So, its total stereoisomers = 2² = 4. 

Q.25. Which of the following compounds will not undergo Friedel Craft's reaction with benzene?    (2017)
(1)
(2)
(3)
(4)
Ans. (1)
Formation of carbocation is not possible in case of CH₂ = CHCl

Q.26. The major product of the following reaction is:    (2017)

(1)
(2)
(3)
(4)
Ans. (1)




Q.27. The product of the reaction given below is:    (2016)

(1)
(2)
(3)
(4)
Ans. (2)


Q.28. Fluorination of an aromatic ring is easily accomplished by treating a diazonium salt with HBF₄. Which of the following conditions is correct about this reaction?    (2016)
(1) Only heat
(2) NaNO₂/Cu
(3) Cu₂O/H₂O
(4) NaF/Cu
Ans. (1)


Q.29. Bromination of cyclohexene under conditions given below yields:    (2016)

(1)
(2)
(3)
(4)
Ans. (4)

It is free radical substitution reaction.