Comments on: Hidden Hydrogens, Hidden Lone Pairs, Hidden Counterions

By: Alen

Alen — Mon, 26 Sep 2016 11:51:47 +0000

Hi James,

I really like your site, it is very informative. However, I didnt notice any topics on hydrogen bonding and I was wondering if you could try answering my somewhat peculiar question. Is it possible to get a hydrogen bonding between a hydroxy (R-OH) group and alkoxide (R-O-) group if pKa values of both are somewhat similar or if they differ greatly? or do we get a simple proton transfer reaction?

To be more specific, I have a material which has alkoxide functionality on the surface and I am wondering if an alcohol (phenol) could form a stronger H-bond in comparison to the material with hydroxyl functionality?

Cheers

By: Robert Grossman

Robert Grossman — Thu, 06 Aug 2015 19:54:19 +0000

Thanks for the kind words. The resonance structure rule is Meier’s rule, named after my colleague Mark Meier, who says, “When in doubt, draw in all the lone pairs, and then draw resonance structures until the cows come home.” The “cows come home” part is very important.

By: Chemjobber

Chemjobber — Wed, 28 Sep 2011 12:57:51 +0000

4th! on Grossman’s rule. A very useful thought, early in the book.

[I bumped into him at NOS 2003 literally. I excused myself, looked at his name tag and said, “I have your book — it’s great!” He’s terribly modest.]

By: azmanam

azmanam — Wed, 29 Jun 2011 16:25:24 +0000

3rd for Grossman’s rule and the resonance rule in his book (I don’t know if he attributes it to himself or someone else):

The 2nd best resonance structure usually defines a molecules reactivity.
-It explains Markovnikov’s rule, Electrophilic Aromatic Substitution, enolate chemistry…

By: James

James — Wed, 29 Jun 2011 02:23:11 +0000

In reply to Texascarbon. since 2 people have mentioned it I'll have to do a post on Grossman's rule. thanks for the input.

By: Texascarbon

Texascarbon — Tue, 28 Jun 2011 23:49:03 +0000

Grossmans rule is super useful. It also helps prevent that accidental dropping of carbons. Whenever I tutor I always encourage addingin everything to help avoiding mistakes.

By: James

James — Tue, 28 Jun 2011 20:42:55 +0000

In reply to Stewie Griffin. that *is* effective, thanks for bringing it to my attention. I have the Grossman book but don't recall the rule. Thanks!

By: Stewie Griffin

Stewie Griffin — Tue, 28 Jun 2011 14:47:01 +0000

With regards to hidden hydrogens, don’t forget “Grossman’s Rule” (named by Robert Grossman in his “Art of Writing Reasonable Organic Reaction Mechanisms” book) which basicallys says “When you’re stuck, draw in the implicit hydrogens near the reactive sites”.
It’s amazingly effective, especially when students first encounter acid mediated reactions (like 1,2-shifts) where they may forget there’s a hydrogen that can move.

By: Egon Willighagen

Egon Willighagen — Tue, 28 Jun 2011 08:11:25 +0000

Nice overview. Now, I think the challenge with respect to lone pairs lies in the various coordinate systems for particularly S and P… PH3 has how many lone pairs, and how many has H2S. Or that R2S=O has a lone pair. That is less known. What about phosphors and sulphurs with more neighbors. This atom typing is one source of pain in the cheminformatics software, the Chemistry Development Kit (and others too, of course).