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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2023 · Paper I

Q5(c). Geometry and hybridisation of carbon in cytosine and thymine

Question

Assign a geometry and hybridization to each carbon atom present in the cytosine and thymine nucleotide bases.

Answer in brief

Cytosine: C2, C4, C5, C6 are all sp², trigonal planar; thymine: the four ring carbons are sp², trigonal planar, and the methyl carbon is sp³, tetrahedral.

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As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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Topic notes: VSEPR, hybridisation and Bent's rule, with every Civil Services, IFoS and Geo-Scientist PYQ →

Covershybridisationcytosinethyminepyrimidine basessp2 carbonnucleobases

All parts of Question 5