Comments on: Evaluating Resonance Structures With Negative Charges

By: BJ

BJ — Fri, 26 Jun 2020 14:58:11 +0000

One last question: Based on the last point on hybridization, is it safe to say we cannot use hybridization to determine stability between resonance forms?

By: BJ

BJ — Fri, 26 Jun 2020 14:36:38 +0000

Ah! I may have figured this out. Correct me if I am wrong, but isn’t the fact that the those negative charges are able to participate in resonance mean that we can ignore the alpha effect? When looking back at Klein’s explanation the lone pairs that were adjacent to each other could not move via resonance, hence, it is my suspicion that when dealing with inductive effects we need only worry about the alpha effect if the electrons in the negative charge are unable to move via resonance.

By: BJ

BJ — Fri, 26 Jun 2020 14:23:18 +0000

When discussing the inductive effect, why would those EWG directly adjacent to the negative charge stabilize it?As you stated in your note 1 there would be some repulsion,however, I read in Klein’s Organic Chemistry I:Translating the Basic Concepts that a lone pair adjacent to a lone pair is called the “alpha effect” which is a destabilizing effect.

By: James Ashenhurst

James Ashenhurst — Fri, 15 Nov 2019 15:44:28 +0000

In reply to Mili Litvajova. Yes there should be! This is in line to be fixed.

By: Mili Litvajova

Mili Litvajova — Sat, 31 Mar 2018 09:28:03 +0000

Hi James,
I love your blogs! What a great way to refresh my org chem!
I was just thinking, regarding Note 2 where you discuss hybridization, shouldn’t there be a H in alkene? e.g. -CH3 < -CH=CH2 < -C triple bond CH

By: Ryan Peterson

Ryan Peterson — Sat, 16 Jul 2016 20:07:00 +0000

In the bottom example why is the nitrogen on the right considered to be sp2 when the Hybridization rule is Number of attached atoms (2 in this case, hydrogen and nitrogen) and 2 lone pairs. 2 plus 2 is 4 orbitals or sp3?

By: Sarmistha

Sarmistha — Sat, 23 Nov 2013 04:13:38 +0000

In reply to James Ashenhurst. Point taken. :-)

By: James Ashenhurst

James Ashenhurst — Sat, 23 Nov 2013 03:42:01 +0000

In reply to Sarmistha. Look at the figure drawn. Is there an aromatic ring drawn anywhere? No. It is an isopropyl group. If an aromatic group was there, then, yes, the diazonium form would be more stable, because the diazo form disrupts aromaticity. But an aromatic group is NOT drawn. It is an alkyl diazo compound. Very different. I don't understand why aromatic rings are being brought up in this discussion.

By: Sarmistha

Sarmistha — Sat, 23 Nov 2013 02:06:42 +0000

Thanks for your response. What I meant to say was that C(-)-N=N(+) is the more unstable form of the Diazonium ion that has a resonance structure with the triple bonded one in which the latter predominates. Aqueous solution of these Diazonium ions have sufficient stability between 0-10 deg C that may be used as intermediates in a variety of Nucleophilic substitution reactions. For instance if water is the only nucleophile available for reaction phenols are formed in good yield. So by way of comparison in the same aryl group where Diazonium salts find mention in literature I thought of the structure comparison as the correct way to look at it.
As an aside I am highly appreciative of your initiatives for rendering very useful insights into the rather complicated field of organic chemistry as well as your prompt responses to any debates that may arise in understanding the subtle nuances in conceptual thinking which nevertheless enriches the learning process in a significant way. Please keep it up!

By: James Ashenhurst

James Ashenhurst — Fri, 22 Nov 2013 20:13:52 +0000

In reply to Sarmistha.

Incorrect. The structure C(-)-N=N(+) that the comment suggests would have less than a full octet on the terminal nitrogen, which is extremely unstable. The diazo resonance form C=N=N(-) makes a very significant contribution, indeed the major one, which distinguishes it from ARYL diazo salts,in which only the triple-bonded nitrogen form [“diazonium”] is significant. The physical properties of alkyl diazo compounds differ considerably from that of aryl diazonium salts – ethyl diazo acetate for example is a liquid that can be (carefully) distilled, whereas one would be extremely foolish to heat an aryl diazonium salt (let alone an alkyl diazonium salt).
Diazomethane is not an alkyl diazonium salt. It only becomes one once protonated, whereby it readily loses nitrogen.