Bond Fission And Reaction Intermediates
When a covalent bond breaks so that both shared electrons leave with one atom forming oppositely charged ions, what type of cleavage has occurred?
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Solution
Heterolytic fission
Covalent bonds can break in two fundamental ways, and recognising them is central to predicting reaction intermediates. In heterolytic fission the bonding pair of electrons departs entirely with one of the two atoms, generating a cation on the electron-poor atom and an anion on the electron-rich atom; this is favoured in polar bonds and polar solvents. Homolytic fission is incorrect because there each atom retains one electron, producing neutral free radicals rather than ions. A pericyclic shift describes a concerted cyclic electron reorganisation, not a simple bond break, so it is wrong. A sigmatropic rearrangement is a specific concerted migration and again does not describe ionic cleavage. The formation of oppositely charged ions is the defining signature of heterolysis, which gives rise to carbocations and carbanions studied in NCERT. Plausibility check: charge separation into a positive and a negative fragment can only arise when the electron pair is kept by one atom, confirming heterolytic fission.
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About This Question
- Subject
- chemistry
- Chapter
- some basic principles of organic chemistry
- Topic
- bond fission and reaction intermediates
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
Heterolytic fission
Covalent bonds can break in two fundamental ways, and recognising them is central to predicting reaction intermediates. In heterolytic fission the bonding pair of electrons departs entirely with one of the two atoms, generating a cation on the electron-poor atom and an anion on the electron-rich atom; this is favoured in polar bonds and polar solvents. Homolytic fission is incorrect because there each atom retains one electron, producing neutral free radicals rather than ions. A pericyclic shift describes a concerted cyclic electron reorganisation, not a simple bond break, so it is wrong. A sigmatropic rearrangement is a specific concerted migration and again does not describe ionic cleavage. The formation of oppositely charged ions is the defining signature of heterolysis, which gives rise to carbocations and carbanions studied in NCERT. Plausibility check: charge separation into a positive and a negative fragment can only arise when the electron pair is kept by one atom, confirming heterolytic fission.
This easy difficulty chemistry question is from the chapter some basic principles of organic chemistry, covering the topic of bond fission and reaction intermediates. It appeared in the 2025 exam.
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