Question

What does a negative value of $\sigma$ signify for a substituent?

• A. It is electron donating
• B. It is electron withdrawing
• C. It is neutral
• D. It is hydrophobic

Answer 1

The Correct Option is A

Step 1: Understanding the Hammett Sigma Parameter - The Hammett sigma ($\sigma$) parameter is a measure of the electronic effects of substituents on a benzene ring. - It is used in linear free energy relationships (LFER) and in the Hammett equation to predict reaction rates and equilibrium positions.

Step 2: Interpretation of $\sigma$ Values - Positive $\sigma$ values correspond to electron-withdrawing groups (EWG), which stabilize a positive charge on the benzene ring and reduce electron density. - Negative $\sigma$ values correspond to electron-donating groups (EDG), which increase electron density on the ring, making it more reactive toward electrophiles.

Step 3: Selecting the Correct Answer - Since a negative $\sigma$ value indicates an electron-donating substituent, the correct answer is: It is electron donating (Option A).