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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Chaste on October 29, 2010, 10:22:45 PM

Title: Is there a way to use NMR to determine the position of substituents in a benzene
Post by: Chaste on October 29, 2010, 10:22:45 PM

Hi,

as above. I wanna know if para, ortho, meta positions can be inferred from proton NMR or by other means? like IR or???

Title: Re: Is there a way to use NMR to determine the position of substituents in a benzene
Post by: MissPhosgene on October 29, 2010, 10:42:13 PM

Yes. Use 1H and 13C NMR.

Title: Re: Is there a way to use NMR to determine the position of substituents in a benzene
Post by: Chaste on October 30, 2010, 02:52:35 AM

Sorry  , do you mind elaborating how carbon 13 nmr can determine its positions?

Title: Re: Is there a way to use NMR to determine the position of substituents in a benzene
Post by: Doktor Nadon on November 01, 2010, 06:27:29 PM

I don't know about ortho and meta, but for para there is a very typical pattern that appears in H NMR.

Here is an example.

http://chemistry.umeche.maine.edu/CHY251/Hnmr-2.html

On the left you can see the two symmetric doublets, which represent the two pairs of electrons which are equivalents in the para substituted aryl.

Title: Re: Is there a way to use NMR to determine the position of substituents in a benzene
Post by: ATMyller on November 02, 2010, 05:43:40 AM

From IR spectrum you can easily determine the benzene subsititution from 2000-1600 cm-1 range (benzene fingers). And not only orto, meta, para substitutions, but tri and tetra substitued as well. Penta and hexa substitued are a bit difficult to distinquish thou.