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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: 113zami on July 27, 2008, 01:55:43 PM

Title: HNMR--H types
Post by: 113zami on July 27, 2008, 01:55:43 PM

http://i274.photobucket.com/albums/jj243/113zami/hnmr.jpg

I don't understand why A and B are different types of hydrogens, they should be the same ( and thus give 1 HNMR signal) since the atoms they're connected to are the same all the way to the other end of the molecule
please explain, thanks

Title: Re: HNMR--H types
Post by: Borek on July 27, 2008, 02:04:54 PM

No rotation around double bond.

Title: Re: HNMR--H types
Post by: g-bones on August 01, 2008, 07:55:06 PM

a and b are different because one methyl group is cis to a hydrogen and trans to a methyl group (making them closer in space to a hydrogen than a methyl group) and vice versa.  they will have different signals because they are seeing two different environments.  the guy above me is right in that there is no rotation about the double bond so they are stuck in two different environments. 

hope this helps

Title: Re: HNMR--H types
Post by: 113zami on August 03, 2008, 04:45:10 PM

ha ha thanks g-bones make sense now, I was wondering wat rotation had to do with it