Question

Refer to the electrostatic potential maps on p. 368 to answer the following questions:

a. Why is the bottom part of the electrostatic potential map of pyrrole blue?

b. Why is the bottom part of the electrostatic potential map of pyridine red?

c. Why is the center of the electrostatic potential map of benzene more red than the center of the electrostatic

potential map of pyridine?

Short answer

a)The nitrogen atom (the atom at the bottom of the epm) in pyrrole has a partial positive charge because it donates electron by resonance into the ring.

b) The nitrogen atom (the atom at the bottom of the epm) in pyridine can't donate electrons by resonance, it withdraws electrons from the ring inductively because it is the most electronegative atom in the molecule. thus this nitrogen is electro rich.

c) The relatively electronegative nitrogen atom in pyridine withdraws electrons from the ring.

Step-by-step solution

Resonance structures

Resonance structures of pyridine

Final answer

a)The nitrogen atom (the atom at the bottom of the epm) in pyrrole has a partial positive charge because it donates electron by resonance into the ring.

b) The nitrogen atom (the atom at the bottom of the epm) in pyridine can't donate electrons by resonance, it withdraws electrons from the ring inductively because it is the most electronegative atom in the molecule. thus this nitrogen is electro rich.

c) The relatively electronegative nitrogen atom in pyridine withdraws electrons from the ring.