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CBSE class XII Chemistry Important Questions

Q. 1. Among the isomeric alkanes of molecular formula C5H12, identify the one that on photochemical chlorination yields (i) A single monochloride (ii) Three isomeric monochlorides. ( 1 mark)
Q. 2. While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason. (1 mark)

Q. 3. With the help of an example discuss the stereo chemistry involved in SN1 and SN 2 mechanism. (2 marks)
Q. 4. Explain Saytzeff rule by taking suitable examples. (2 marks)
Q. 5. Draw the structures of all isomeric alcohols of molecular formula C5H12O and give their IUPAC names. Classify these isomers of alcohols as primary, secondary and tertiary alcohols. ( 2 marks)
Q. 6. Nitro group increases the reactivity of chlorobenzene when attched to o and p- position but not at meta position? Explain? Write the mechanism also. (3 marks)
Q. 7. Account for the following. ( 3 marks)
  1. It is necessary to avoid even traces of moisture from a Grignard reagent.
  2. Chloroform is stored in closed dark coloured bottles completely filled.
  3. The carbon– oxygen bond length in phenol is slightly less than that in methanol.
Q8. (a) Explain the fact that in aryl alkyl ethers (i) the alkoxy group activates the benzene ring towards electrophilic substitution and (ii) it directs the incoming substituents to ortho and para positions in benzene ring. (2 marks)
(b) Arrange the following compounds in increasing order of their acid strength: (1 mark)
Propan-1-ol, 2,4,6-trinitrophenol, 3-nitrophenol, 3,5-dinitrophenol, phenol, 4-methylphenol
Q. 9. Give equations of the following reactions: (3 marks)
  1. Preparation of Sec-Butyl alcohol from ethanal
  2. Preparation of Phenol from Aniline.
  3. Treating phenol with chloroform in presence of aqueous NaOH.
Q. 10. How will you distinguish between the following: (3 marks)
  1. Propanoic acid and propanal
  2. Ethanal and Benzaldehyde
  3. Pentan-3-one and Pentan-2-one
Q. 11. How will you bring about the following conversions in not more than two steps. (5 marks)
    1. Propanone to Propene
    2. Benzene to m-Nitroacetophenone
    3. Chlorobenzene to benzoic acid
    4. Propanoic acid to propene
    5. Propyne to propan-2-ol

Q. 12. Explain the following with the help of suitable examples: (5 marks)
(a) Limitation of Williamsons synthesis (b) Stephen reaction. (c) Hell-Volhard-Zelinsky reaction (d) Aldol Condensation (e) Wolff-Kishner reduction.
Q. 13.(a) An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (C) on dehydration gives but-1-ene. Write equations for the reactions involved (b) Predict the products formed when cyclohexanecarbaldehyde reacts with following reagents.
  1. PhMgBr and then H3O+ (ii) Tollens’ reagent
Q. 14. Primary alkyl halide C4H9Br (a) reacted with alcoholic KOH to give compound (b). Compound (b) is reacted with HBr to give (c) which is an isomer of (a). When (a) is reacted with sodium metal it gives compound (d), C8H18 which is different from the compound formed when n-butyl bromide is reacted with sodium. Give the structural formula of (a) and write the equations for all the reactions.
(ii) Out of C6H5CH2Cl and C6H5CHClC6H5, which is more easily hydrolysed by aqueous KOH.

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