SUPER helpful. thank you so much for uploading this, you've really helped me a lot :)

@mevansthechemist

5 жыл бұрын

Glad to hear it! :-)

Hello! Thank you for such a helpful video! May I please know what you mean by the heteroatom on a resonance-donating group cannot be involved in a Pi bond and must have a p orbital that can house its lone pair (2:54)?

@mevansthechemist

4 жыл бұрын

This essentially means that the atom must not already be involved in a pi bond. For example, -N=R is not an electron-donating group even though nitrogen has a lone pair, because the lone pair is in a hybrid orbital, not a p orbital. Nitrogen's p orbital is involved in a pi bond to R. The hybrid orbital has no net overlap with an adjacent pi system, so the lone pair isn't really "donated" to it-it's isolated from it. Contrast this situation with the amino group in (B), starting around 4:00. Replacing -NR2 with -N=R removes the donating ability of the nitrogen.

Why with electrophile (increasing of electrophilic properties) of molecule B we are talking about LUMO, but not HOMO?

Why Cl, Br and F are not withdraw electrons? And benzene define them like withdrawing groups. Someone help me please

@mevansthechemist

2 жыл бұрын

Cl, Br, and F are pi (resonance) donors but sigma (inductive) acceptors. For these very electronegative elements, the inductive withdrawal is much stronger than the resonance donation effect, making them electron-withdrawing groups overall. Benzene is a rather ambiguous case but, IIRC, is withdrawing based on its Hammett constant. Check out my series of videos on Hammett substituent parameters and LFERs for more information about this-it is possible to provide experimental support for whether a group is donating or withdrawing.

Group OH is electron-donating?

@mevansthechemist

2 жыл бұрын

By resonance, yes. OH and OR are inductively withdrawing.