Comments on: Degrees of Unsaturation (or IHD, Index of Hydrogen Deficiency)

By: Apurva

Apurva — Sat, 21 Sep 2024 03:46:33 +0000

I read that in Dewar benzene, the middle C1-C4 linkage in not sigma bond but 2p-2p pi bond (special type of pi without sigma).

By: Daksh Mishra

Daksh Mishra — Thu, 23 Mar 2023 09:27:08 +0000

In compound R-NO2 (suppose R is an aliphatic saturated compound), will the degree of unsaturation be 1 or 1.5? Shouldn’t we take DU equal to 1.5 due to resonance between the negative charge of oxygen atom and the double bond?
Which one is correct? Sorry to ask a silly question.

By: Samuel

Samuel — Mon, 25 Jul 2022 15:33:05 +0000

I have been struggling with using IHD to deduce a structural fromula from a spectrum graph.
Your explanation has help me a lot.
Thank you.

By: James Ashenhurst

James Ashenhurst — Tue, 08 Feb 2022 20:15:50 +0000

In reply to Thenard Rinmann. That is very clever! To be a fair question, however, it should specify the counter-ions. For sodium oxalate, Na+ would be the same as H+ and provide an answer of 2 for C2O4Na2

By: James Ashenhurst

James Ashenhurst — Tue, 08 Feb 2022 20:14:01 +0000

In reply to Bhavya garg. No, it's done on an atom-by-atom basis

By: Suparna Bhattacharjee

Suparna Bhattacharjee — Fri, 10 Dec 2021 18:41:43 +0000

First problem to be solved using simultaneous equations in two variables.
A hydrocarbon contains only two elements, viz C and H. Let the formula be CxHy.
Given IHD= 6.
Substitute in IHD formula and get the first simultaneous equation as
2x+2+-y= 6
Atomic weights of C=12 and H=1. Substitute to calculate formula weight and get 2nd equation in two variables
12x + y = 284.
solve for x and y

By: Bhavya garg

Bhavya garg — Fri, 30 Jul 2021 00:29:12 +0000

Sir is there any subtraction or for functional group?

By: James Ashenhurst

James Ashenhurst — Fri, 22 May 2020 16:35:21 +0000

In reply to Chris G..

Hi Chris – This is a post about structure determination.

The usefulness of IHD is that it is a value you can calculate from the molecular formula without knowing anything else about the structure (the molecular formula can be obtained from techniques like elemental analysis, high-resolution mass spectrometry, etc.)

That’s why I say it’s one of the first calculations to make when you’re dealing with a molecule of unknown structure.

If you already know the structure, then IHD isn’t really going to help you

By: Chris G.

Chris G. — Thu, 21 May 2020 18:55:07 +0000

If we’re given the structure of the molecule, can’t we just calculate degrees of unsaturation by the formula:

IHD = #rings + #double bonds + 2#triple bonds

If we only have the molecular formula, this formula isn’t helpful. But if we have the structure, isn’t this formula more simple?

By: Thenard Rinmann

Thenard Rinmann — Mon, 11 May 2020 12:12:35 +0000

I once came a cross a question,
which spoke of degrees of unsaturation for,
the oxalate ion, not the acid, beware.
The answer spoke of degrees 3, not 2,
as the anionic oxygens could pick up a H2 too,
I’d like to know if this accepted and right,
Pray do clear my plight!