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Question 55


How many compounds among the following compounds show inductive, mesomeric as well as hyperconjugation effects?

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Correct Answer: 4

Solution

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  • 5-methylhex-3-en-2-one (Top, 2nd): The carbonyl group pulls electrons, and the isopropyl group provides +I and hyperconjugation through its alpha-hydrogen to the alkene.
  • 1-isopropyl-2-nitrobenzene (Bottom, 1st): The group shows. The isopropyl group shows +I and has one alpha-hydrogen that can participate in hyperconjugation with the benzene ring.
  • 1-acetyl-2-methylcyclohex-1-ene (Bottom, 4th): The acetyl group is in conjugation with the double bond -M and -I. The methyl group on the double bond provides hyperconjugation and +I.
  • 5-methylhex-3-en-2-one :This molecule contains an alpha,beta-unsaturated carbonyl system. The pi-bond of the alkene is in conjugation with the pi-bond of the carbonyl group. Because oxygen is highly electronegative, it pulls the electron density toward itself through the conjugated system. This is a -M effect. Electronegativity difference can account for Inductive effect. In this molecule, the isopropyl group is attached directly to the sp^2 carbon of the double bond. The carbon atom in the isopropyl group that is directly attached to the alkene is the alpha-carbon. It has one alpha-hydrogen. This hydrogen can delocalize its sigma-bond electrons into the pi-system of the alkene, stabilizing the molecule.

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