Hi

Well, it depends on the exact structure of your products, but as a general comment, a good NMR analysis can give you a lot of information. For example, small differences in the chemical shift can help you to ascertain whether you have the E or the Z isomer. Particularly, the experiment that can be more helpful in this case is a NOESY. So, before using X-ray, I would do some NMR experiments, 1D (1H, 13C and heteroatoms if present) and 2D (COSY, HSQC, HMBC and NOESY). Hopefully, all this information should help you to differentiate between them,  

If you still can´t differentiate between isomers, X-ray diffraction is indeed a good option. If you had problems obtaining crystals from your products (after trying several times with different solvents), you could try preparing some derivatives with bromo and/or nitro substituents in the aryl rings. This should facilitate the obtention of crystals.

I hope you find this helpful.

Best regards,

i did 1H & 13C NMR . in 1H-NMR there is a singlet signal for CH=N  at 9-9.5 ppm. there is no adjacent coupling protons, so, will NOESY NMR will deterimine if it is E or Z ?

i uploaded the chemical structure im working on.

Hi

If you try to make a molecular model of the Z-isomer of this molecule you will observe that there is a severe steric clash, so most probably you are generating the E-isomer. And a NOESY experiment should indeed help you confirming that.

I'm not an expert in that, but as quick qualitative explanation, NOESY is based on the Nuclear Overhauser Effect, which affects atoms which are in close proximity in space, even if they are separated by many bonds (and thus you will not see any coupling between them in the 1D 1H-NMR spectrum and COSY).

So, for the E-isomer you should observe a cross peak between the triazole NH proton and the imine N=CH proton. It is recommendable to do also a COSY, and compare it to the NOESY, since the NOESY will have most of the cross peaks of the COSY plus the few cross peaks of the atoms coupled by space.

In summary, if you see the cross peak it will be unambiguous evidence that you have the E-isomer. If you don't, you will have to look for other alternatives to confirm that you are generating the E-isomer.

Good luck!

This depends, in case of  e.g. 5-( 2- pyridylazomethine) ability to form M complexes is a good proof for Z isomer. Otherwise in general NOESY and COSY are the most reliable tool before trying X-ray crystallography.

Thanks alot prof. adel 

Aldimines normally do exist in E configuaration