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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: mass on April 05, 2008, 06:02:02 AM

Title: Double bond equivalents
Post by: mass on April 05, 2008, 06:02:02 AM
How many double bond equivalents are there in each of the following molecules?
C6H1206. Whats the method so I can do the rest of the questions by myself.
Title: Re: Double bond equivalents
Post by: Astrokel on April 05, 2008, 07:20:29 AM
Quote from: mass on April 05, 2008, 06:02:02 AM
How many double bond equivalents are there in each of the following molecules?
C6H1206. Whats the method so I can do the rest of the questions by myself.

You should recognize C6H1206 is glucose.

http://campus.northpark.edu/biology/cell/carbohydrates.html

Hope this helps

Kelvin  ;D
Title: Re: Double bond equivalents
Post by: sjb on April 05, 2008, 07:33:08 AM
GIYF, try http://www.google.com/search?q=double+bond+equivalents

C6H12O6 is not always glucose, mind.

It could be any of Allose, Altrose, Glucose, Mannose, Gulose, Idose, Galactose, Talose, Psicose, Fructose, Sorbose, Tagatose (and that's just the straight chain hexoses) - the principle is the same though.
Title: Re: Double bond equivalents
Post by: mass on April 05, 2008, 09:51:52 AM
can one of you take me through the method rather than just point me towards google. Thanks.
Title: Re: Double bond equivalents
Post by: sjb on April 05, 2008, 10:24:15 AM
OK, on the first page of google (from where I'm sitting), I see

http://en.wikipedia.org/w/index.php?title=Degree_of_unsaturation

It says
Quote
The formula for degree of unsaturation is
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fmath%2F4%2F2%2F5%2F425ff9794459a35ebc797c830a861911.png&hash=a740ec7d96674f88ea611ff4d46f15aa9e09c6e7)
 
where C is the numbers of carbon atoms, H is the numbers of hydrogen atoms, X is the numbers of halide atoms, and N is the numbers of nitrogen atoms. Do not count group VI elements such as oxygen and sulfur atoms (but count H groups attached to oxygen atoms, such as hydroxyl groups). Halogen atoms (F, Cl, Br, I) count as H atoms for degree of unsaturation calculations.


Let's apply that to Pencillin G. This has the formula C16H18N2O4S.

Doing the calculation, you can see that there are (2x16 + 2 - 18 + 2)/2 or 9 degrees of unsaturation (or double bond equivalents) in the molecule.

Looking at the actual structural formula, (https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fthumb%2F7%2F7c%2FPenicillin-G.png%2F180px-Penicillin-G.png&hash=a92d8cc9cec3d1f374ca520767ec486062cb8d67), you can see the benzyl ring (making 4) the amides (an further 2), the carboxylic acid (1) and the 5:4 fused rings (an extra 2), total 9 as predicted by the DBE formula.

Can you now have a go at your formula?