Question:medium

Identify the species from following that exhibits no bond resonance.

Show Hint

Always associate the phrase "no bond resonance" instantly with hyperconjugation. Look for carbocations, alkenes, or free radicals possessing alpha-hydrogens, as they are classical structural examples that display this electronic behavior.
Updated On: Jun 11, 2026
  • $\mathrm{CH_3CH_2Br}$
  • $\mathrm{\overset{(+)}{C}H_2CH_3}$
  • $\mathrm{CH_3CH_2NO_2}$
  • $\mathrm{C_6H_6}$
Show Solution

The Correct Option is B

Solution and Explanation

Step 1: Decode the term.
No bond resonance is the older name for hyperconjugation, the delocalisation of $\sigma$ electrons of a $\mathrm{C-H}$ bond into an adjacent empty p-orbital or $\pi$ system.
Step 2: State the requirement.
It needs at least one $\alpha$-hydrogen on an $sp^3$ carbon sitting next to an electron-deficient or unsaturated $sp^2$ centre such as a carbocation, radical or alkene.
Step 3: Test $\mathrm{CH_3CH_2Br}$.
This is fully saturated with no vacant p-orbital or adjacent $\pi$ system, so no hyperconjugation.
Step 4: Test the ethyl carbocation.
$\mathrm{\overset{(+)}{C}H_2CH_3}$ has an $sp^2$ cationic carbon with an empty p-orbital, and the neighbouring $\mathrm{CH_3}$ supplies three $\alpha$ C-H bonds that delocalise into it. This is exactly no bond resonance.
Step 5: Test the remaining options.
$\mathrm{CH_3CH_2NO_2}$ is saturated with no such acceptor orbital, and benzene shows ordinary $\pi$-$\pi$ resonance, not hyperconjugation.
Step 6: Conclude.
The species showing no bond resonance is the ethyl carbocation, option (B).
\[ \boxed{\mathrm{\overset{(+)}{C}H_2CH_3}} \]
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