Question

Which of the following groups does not show (+R) effect?

• A. -NH\(_2\)
• B. -NHCO\(_2\)R
• C. -CN
• D. -NR

Hint:

The (-CN) group is electron-withdrawing, meaning it does not exhibit the (+R) resonance effect, unlike groups with lone pairs like -NH\(_2\) or -OCH\(_3\).

Answer 1

The Correct Option is C

Step 1: Understanding (+R) effect.
The (+R) effect, or the +M effect, involves the donation of electron density through resonance, which is typically seen in groups that have lone pairs on heteroatoms (such as -OH, -NH\(_2\), -OCH\(_3\)).
Step 2: Analyzing the options.
(A) -NH\(_2\): The amino group (-NH\(_2\)) shows the (+R) effect due to the lone pairs on nitrogen.
(B) -NHCO\(_2\)R: The -NHCO\(_2\) group shows the (+R) effect due to nitrogen's lone pairs.
(C) -CN: The -CN group is electron-withdrawing through resonance (not donating), so it does not show the (+R) effect.
(D) -NR: Similar to -NH\(_2\), -NR shows the (+R) effect due to lone pairs on nitrogen.
Step 3: Conclusion.
The correct answer is (C) -CN, as it does not show the (+R) effect.