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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: astein16 on March 18, 2012, 01:37:54 PM

Title: Question about the 1H NMR Spectrum for 2,5-dichloronitrobenzene
Post by: astein16 on March 18, 2012, 01:37:54 PM

Ok, so I know that there will be three peaks observed and I know the multiplicity, I just need some help figuring out the order. I know that the hydrogen directly in between the chlorine and the nitro group will be furthest downfield and will be most deshielded.
My question is: even though it seems like a very reasonable assumption that the hydrogen that is vicinal to one of the chlorines and is 3 bonds away from the nitro group (the hydrogen bonded to carbon 3) would be more deshielded than the hydrogen bonded to carbon 4, but since the nitro group is an electron withdrawing group, would it act as an ortho-para deactivator, thus making the hydrogen on carbon 4 be more deshielded in actuality?

Title: Re: Question about the 1H NMR Spectrum for 2,5-dichloronitrobenzene
Post by: orgopete on March 19, 2012, 02:42:08 PM

Without thinking about where the hydrogens should appear, the multiplicity should allow you to determine which is which. You have three signals. If they are sufficiently separated and the para coupling constant is zero, then you should have a large ortho coupling (6-7 Hz), a small meta coupling (1-2 Hz), and a signal with an ortho and meta coupling.