[Robin]

Hi there, Ive been doing a series of thionation reactions, converting lactams to thiolactams,  and I've noticed something pretty peculiar. For all of my compounds the thionation significantly de-shields the protons adjacent to it, particularly those directly bonded to the thiolactam at the N position. C NMR of the thiolactams also clearly shows that these carbons are significantly more deshielded than their carbonyl counterparts (typically 170ppm for C=O and almost 200 for C=S).

Does anybody have any ideas as to why this would be? I would have assumed based on electronegativity that Thioketons are less de-shielding than carbonyls?

Thanks for everything!

[orthoformate]

Hi there, Ive been doing a series of thionation reactions, converting lactams to thiolactams,  and I've noticed something pretty peculiar. For all of my compounds the thionation significantly de-shields the protons adjacent to it, particularly those directly bonded to the thiolactam at the N position. C NMR of the thiolactams also clearly shows that these carbons are significantly more deshielded than their carbonyl counterparts (typically 170ppm for C=O and almost 200 for C=S).

Does anybody have any ideas as to why this would be? I would have assumed based on electronegativity that Thioketons are less de-shielding than carbonyls?

Thanks for everything!

Your reasoning makes perfect sense to me, I would have thought exactly as you did. I think if you post this in the organic spectroscopy child board you will catch an experts attention and hopefully get some good information.

The organic spectroscopy child board is in a link at the top of the Organic Chemistry Forum page.

good luck!