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Topic: Enantiomers and IR  (Read 3784 times)

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Offline agugliotta

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Enantiomers and IR
« on: February 02, 2016, 10:02:00 PM »
In regard to infrared and isomers (enantiomers in particular), can FTIR distinguish these molecules?  For example, if an IR absorbance spectrum for an unidentified drugs hits on l-amphetamine hydrochloride, does this mean that is a definitive id of the unknown drug? or could the unknown be d-amptheramine hydrochloride also?  .. what about cocaine enantiomers? Thank you!

I know IR is designed to give structural information, but I wasn't sure about isomers. Thanks.

Offline Doc Oc

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Re: Enantiomers and IR
« Reply #1 on: February 03, 2016, 09:46:53 AM »
Enantiomers have the same physical traits so they are not distinguishable by IR.

Offline Babcock_Hall

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Re: Enantiomers and IR
« Reply #2 on: February 03, 2016, 11:09:31 AM »
I agree with Doc Oc, but I will point out one possible exception.  Enantiomers are not distinguishable, unless they are in a chiral environment.  I would predict that if you dissolved each enantiomer in in S-2-butanol (for example) they might be distinguishable, but I don't know how practical such an experiment would be.

Offline Corribus

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Re: Enantiomers and IR
« Reply #3 on: February 03, 2016, 12:44:59 PM »
You can also use FTIR/VCD to distinguish between enantiomers.

See Ito et al, JACS 1979 101, 2, 496-498. http://pubs.acs.org/doi/abs/10.1021/ja00496a045

A general description of VCD can be found here.

https://en.wikipedia.org/wiki/Vibrational_circular_dichroism
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline agugliotta

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Re: Enantiomers and IR
« Reply #4 on: February 03, 2016, 09:55:19 PM »
Thank you all!  So ultimately, with using FTIR, you wouldn't know which stereoisomer is present (i.e. l or d-amphetamine) as it could really be either one.

Thank you again.

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