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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper I covers inorganic chemistry.

UPSC Combined Geo-Scientist, Mains · 2018 · Mains Paper I

Q1(i). Borazine and benzene

Question

Draw the structure of borazine. With the help of its reaction with HCl, explain why chemical properties of borazine are quite different from those of benzene.

Answer in brief

Borazine is a planar alternating B–N six-membered ring, B₃N₃H₆; its polar B–N bonds undergo addition of HCl, unlike benzene under ordinary conditions.

Key points

  • Each B and each N initially bears one H. Nitrogen-to-boron π donation gives partial delocalisation, but it is less uniform than in benzene because the…
  • B is electrophilic and N is relatively electron rich.
  • Chloride attaches to B and the added hydrogen to N.

The full model answer

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.

Model answer to Q1(i), 2018 Mains Paper I: solution pages 5 and 6
Solution pages 5 and 6 of 17
Read the whole 2018 solution2018 question paper

CoversBorazinebenzeneBoron–nitrogen compounds

All parts of Question 1