[Mitsunobo]

Good day to all of you and thanks for taking time to read this post.

I protected my product with Cbz and got very broad peaks after protection but once I epoxidized the compound, the nmr spectra turned well again.

I am thinking of heating it to get a better spectra or changing nmr solvent. I want to know what you guys think of a good way to go about this.

[g-bones]

hmm, did you just take one nmr of the one with broad peaks? perhaps the shim wasn't that great or it was too concentrated? try shimming by hand and keeping it to a pipet tip full of product and a good amount on nmr solvent.  there is no harm in trying a different solvent though.

[Markov]

The N-CBS  (and also N-Boc) is a carbamate. In carbamates, as in amides, the rotation around the N-C bond is often slow enough to be noticed on the NMR time scale, causing broadening of the peaks or sometimes resulting in two sets of signals (i.e. a mixture of so-called rotamers).
This may also show in the 13C spectrum.


You may be able to prove that this is the case by recording NMR spectra at higher temperatures. If, at some higher temperature, the signals get sharp again, or collapse into one set of signals, this means that the rotation has been speeded so much that the NMR can lo longer distinguish between the two rotameric forms.

This said, I cannot see any obvious explanation why you would get sharp peaks after the epoxidation step. But rotamerism is in my experience more of the kind that it sometimes shows in the NMR and sometimes not.

Good luck!

[Mitsunobo]

Thanks for your input guys. The concentration of my sample is fine. Once I get my results, I'll post it here for future reference.