Exams › JEE Advanced › Chemistry

Which of the following groups can act both as an electron-pair donor (+R) and as an electron-pair acceptor (-R) in resonance, depending on the situation?

1. -NO2
2. -CH=CH2 (vinyl)
3. -CHO
4. -NH2

Correct answer: -CH=CH2 (vinyl)

Solution

A vinyl group (-CH=CH2) and similar unsaturated/conjugating groups can either donate or withdraw electrons through resonance depending on what they are attached to: attached to an electron-deficient site they donate pi electrons, while attached to an electron-rich site they can withdraw. Pure +R groups like -NH2 only donate, and pure -R groups like -NO2 and -CHO only withdraw.

Related JEE Advanced Chemistry questions

• When N₂ is converted to N₂⁺, what happens to the bond dissociation energy of the N–N bond, and when O₂ is converted to O₂⁺, what happens to the bond dissociation energy of the O–O bond?
• In which of these ions is pπ–dπ bonding absent?
• What is the VSEPR formula for the chlorine trifluoride molecule?
• Consider the following molecules: CO2, SO2, and H2O. Arrange them in ascending order of their dipole moments.
• Which of the following occurrences is primarily influenced by hydrogen bonding?
• When two 1s atomic orbitals (one from each atom) combine to form molecular orbitals, which of the following statements is correct?

⚔️ Practice JEE Advanced Chemistry free + battle 1v1 →