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Chemistry Paper-2 2021 — CSS Past Paper

FEDERAL PUBLIC SERVICE COMMISSION

COMPETITIVE EXAMINATION-2021

FOR RECRUITMENT TO POSTS IN BS-17
UNDER THE FEDERAL GOVERNMENT

CHEMISTRY, Paper-2

TIME ALLOWED: THREE HOURS
PART-I(MCQS): MAXIMUM 30 MINUTES
PART-I (MCQS) MAXIMUM MARKS = 20
PART-II MAXIMUM MARKS = 80

NOTE:

  • (i) Part-II is to be attempted on the separate Answer Book.
  • (ii) Attempt ONLY FOUR questions from PART-II. ALL questions carry EQUAL marks.
  • (iii) All the parts (if any) of each Question must be attempted at one place instead of at different places.
  • (iv) Candidate must write Q. No. in the Answer Book in accordance with Q. No. in the Q.Paper.
  • (v) No Page/Space be left blank between the answers. All the blank pages of Answer Book must be crossed.
  • (vi) Extra attempt of any question or any part of the attempted question will not be considered.

PART-II

Q. No. 2.

(a) Describe factors that influence keto-enol tautomerization. Elaborate the statement with the help of examples. (10)

(b) Assign “R- or **S” configuration on each of the chiral centres of the given compounds. (10) (20)

Chemistry, Paper 2, Q 2 b, CSS 2021
Chemistry, Paper 2, Q 2 b, CSS 2021

Q. No. 3.

Give the products expected (if any) when ethylbenzene reacts under following conditions: (02 marks each)

(i) Br, in CCI4 (dark) ( In)

(ii) 1-1N0,1-1,S0,

(iii) Conc. 11:SO,

(iv)

0 c2HiA-ci .A1C1,(1 I equi, ). then H2O

(v) Alkaline KMnO4

 

(b) Account for the following: (05 marks each) (10) (20)

(i) Intramolecular II-bonding is stronger than intermolecular H-bonding

(ii) Control of nucleophilic substitution reaction over elimination reactions

Q. No. 4.

(a) Write down reagents, reaction conditions and important steps for the following conversions: (10)

(i) Chlorobenzene to 2,4-dinitrophenyl hydrazine

(ii) Pyridine, to 2-ammo pyridine

(b) Write a note that substituents on aromatic rings dictate reactivity and orientation of the incoming electrophile in electrophilic aromatic substitution reactions. (10)

Q. No. 5.

Draw detailed mechanisms for:

(i)

Chemistry, Paper 2, Q 5 a, CSS 2021
Chemistry, Paper 2, Q 5 a, CSS 2021

(ii)

Chemistry, Paper 2, Q 5 b, CSS 2021
Chemistry, Paper 2, Q 5 b, CSS 2021

(iii)

Chemistry, Paper 2, Q 5 c, CSS 2021
Chemistry, Paper 2, Q 5 c, CSS 2021

(iv)

Chemistry, Paper 2, Q 5 d, CSS 2021
Chemistry, Paper 2, Q 5 d, CSS 2021

(v)

Chemistry, Paper 2, Q 5 e, CSS 2021
Chemistry, Paper 2, Q 5 e, CSS 2021

Q. No. 6.

Account for the following: (05 marks each)

(I) In DNA. a guanine residue reacts with electrophiles predominantly at the 7 and 3 positions of the ring system (see below). Suggest an explanation for this.

Chemistry, Paper 2, Q 6 a, CSS 2021
Chemistry, Paper 2, Q 6 a, CSS 2021

(ii) Outline the synthesis of following compound:

Chemistry, Paper 2, Q 6 b, CSS 2021
Chemistry, Paper 2, Q 6 b, CSS 2021

(iii) A Grignard reagent that is a key intermediate in an industrial synthesis of vitamin A can be synthesized in the following way:

Chemistry, Paper 2, Q 6 c, CSS 2021
Chemistry, Paper 2, Q 6 c, CSS 2021

What are the structures of compounds A and C? The acid catalysed rearrangement of A to B takes pl.

(iv) What are compounds A and B in the reaction given below? Compound B has a strong IR absorption band in the 1650-1730 cm-I region and a broad strong band in the 3200 3550 cm’ region. (20)

Chemistry, Paper 2, Q 6 d, CSS 2021
Chemistry, Paper 2, Q 6 d, CSS 2021

Q. No. 7.

Explain the following: (04 marks each) (20)

(i) How can ER be used to help interpret NMR spectra?

(ii) What are diastereotopic protons? Explain with examples.

(iii) Determine the structure for a compound with formula C61-14N204 with following 1H-NMR data: 8.761(114), 8.38 dd (2H), 7.97 1(1H)

(iv) Assign chemical shifts of each proton in the above structure.

(v) Why 13C-NMR is less sensitive than IH-NMR?

Q. No. 8.

Answer following questions: (04 marks each) (20)

  • (i) Comment if glycogenesis is anabolic or catabolic. Write down all steps involve in glycogenesis.
  • (ii) Describe endergonic and endergonic reactions
  • (iii) Write a note on anionic and cationic surfactants.
  • (iv) Comment if waste glass can be used for cement production.
  • (v) What is the chemical composition of nucleic acids and their biological significance?

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