Dear all,

I have a question concerning a 2D-1H/1H-NOESY NMR of a two-compound mixture.

The compounds in question are two atropoisomers which are present in a roughly 2:1 ratio (the phenomenon of atropisomerism is known for these compounds:

- Kingo, U. et al., Chemistry Letters 1999, 28 (1), 63-64

- Göstl, R. et al., Chemistry – A European Journal 2012, 18 (45), 14282-14285

- Uchida, K. et al., Journal of Molecular Structure: THEOCHEM 2002, 579(1), 115-120

- Goldberg, A. et al., The Journal of Physical Chemistry A 2003, 107 (25), 4982-4988).

Having examined the corresponding 1H, 13C, COSY, HSQC and HMBC- spectra I could elucidate the connectivites of the major compound present (in CD2Cl2 @ 280 K, concentration roughly 50 mM). To ascertain which of the two possible atropoisomers is the major compound at hand I have recorded a 2D-NOESY spectrum and the result is shown in the attachment. What you see there are the crosspeaks between the aliphatic protons (namely the allylic protons of a 1,2-cyclopentene moiety and the methylene of two attached 2-ethyl-hetar-1-yl systems in 1,2-position of the cyclopentene).

Now the strange thing I noticed are the crosspeaks e.g. between the dublett at 7.81 ppm to the multipletts at 3.05 and 2.90 ppm since HSQC clearly tells me that these latter two multipletts clearly correspond to the minor species. Along those lines, the crosspeaks between the three multipletts at around 7.55 to 7.65 ppm to the multiplett at 3.25 ppm should also not be possible since the former downfield multipletts clearly belong to the minor species (as elucidated by heteronuclear coupling).

The question I have is now the following:

Has anyone of you experienced similar artifacts in 2D-NOESY spectra?

Best regards and I'm looking forward to your ideas

EDIT: Could it be that the mixing time was too long and that this is why I see correlations between the isomers?