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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: electrogeek on December 16, 2020, 06:31:39 AM

Title: Solvents and Coalescence in NMR
Post by: electrogeek on December 16, 2020, 06:31:39 AM

Hi everyone,

I have been given this question below:

"The methyl groups of N,N-dimethylacetamide coalesce at a higher temperature in a 1H NMR spectrum run
in DMSO or acetone solution than they do in cyclohexane solution. Why? (Assume the low temperature
spectra in the solvents are identical)."

My thinking was that both DMSO and acetone are polar solvents compared to cyclohexane, and so interactions with the amide group affects the rate of rotation about the C-N bond, leading to the observed effect in the 1H NMR. But I wasn't sure whether this is correct or is there something else that the solvent is doing?

Title: Re: Solvents and Coalescence in NMR
Post by: Babcock_Hall on December 16, 2020, 12:55:31 PM

I think that your answer is not unreasonable, but I also think that you could be more specific in your discussion of the types of interactions that occur.