Question

Which of the following shows -R effect?

• A. \(-\text{CN}\)
• B. \(-\text{OCOCH}_3\)
• C. \(-\text{OCH}_3\)
• D. \(-\text{Cl}^-\)

Hint:

To recognize the -R effect, look for groups with lone pairs that can donate electron density through resonance, such as -CN.

Answer 1

The Correct Option is A

The -R effect refers to the resonance electron-donating effect. It is typically observed when groups with lone pairs of electrons, such as -CN (cyanide), donate electron density through resonance to the attached carbon. This makes the group a resonance donor, and the effect is called the -R effect (negative resonance effect). - -CN: The cyanide group is a strong electron-withdrawing group via induction, but it also has a resonance donation of electrons, showing -R effect. - \(\text{OCOCH}_3\): This group can show both electron-withdrawing and electron-donating effects but is more commonly an electron-withdrawing group via induction. Thus, the correct answer is -CN.