[eglaud]

In the picture attached, why is the nitrogen on carbon 3 sp3 hybridized? My professors explanation is "Only the NH2 nitrogen is sp3. The other nitrogens are bonded to sp2 carbons, so they will be sp2 so that the lone pairs can participate in resonance with the adjacent C=O groups." Is carbon 4 not an sp2 carbon as well? Thanks.

[Dan]

Is carbon 4 not an sp2 carbon as well?

Yes, but the NH₂ is not bonded to C4, it's bonded to C3.

[FAN7OM]

Is carbon 4 not an sp2 carbon as well?

Yes, but the NH₂ is not bonded to C4, it's bonded to C3.

Why is the NH2 on C3 Sp3 hybridized, when the NH2 has only 3 substituents? is what OP is asking.

[eglaud]

Is carbon 4 not an sp2 carbon as well?

Yes, but the NH₂ is not bonded to C4, it's bonded to C3.

You're right, I just looked right past that. There can't be resonance there to make it sp2 (it's still sp3 because of the l.p.'s) because the others are one bond closer to a double bond. Thanks!