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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 · 2021 · Paper I

Q6(a). Bonding in cyclic phosphazene, benzene and borazine

Question

How does the bonding in cyclic phosphazene differ from that of benzene and borazine?

Answer in brief

Benzene and borazine have a pπ–pπ ring π bond (complete and aromatic in benzene, polar and partial N → B in borazine); in cyclic phosphazene the π bond is dπ–pπ and stops at each P, giving three P–N–P islands without a ring current.

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Topic notes: main group chemistry: boranes, borazine, phosphazenes, silicates, silicones, interhalogens, xenon and sulfur–nitrogen compounds, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverscyclic phosphazeneborazinedπ–pπ bondingDewar island modelaromaticityinorganic benzene

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