# DCC coupling of N-hydroxysuccinimide and 2,2-dimethoxyacetic acid

I am forming N-hydroxysuccinimide ester (1) by DCC coupling with N-hydroxysuccinimide and 2,2-dimethoxyacetic acid using distilled THF as solvent.

What I see on $$\ce{^1H}$$-NMR is three major singlets: $$\delta~\pu{4.840 ppm}~(1\ce{H}),$$ $$\delta~\pu{3.432 ppm}~(7.26\ce{H}),$$ $$\delta ~\pu{2.731 ppm}~(6.36\ce{H})$$ and some impurities.

While the chemical shifts are well-aligned with theoretical predictions (in my opinion), integration ratios do not quite make sense. I wish I could purify it to have a clearer NMR spectrum and see whether I actually have the desired product, but I don't think my ester will stay stable in silica in column chromatography. Any suggestions?

• Maybe take or get an NMR of the reagents and theoretical side products and see if there can be any overlap with the signals you see. I'm not sure I understand what your doubt is, though. NMR integration is not always very precise, especially for acidic protons. – user6376297 Jun 10 '19 at 15:17
• What is your next reaction with this product? – Waylander Jun 10 '19 at 15:18
• @user6376297 I have already taken the NMR of 2,2-Dimethoxy Acetic acid: $\delta \: \pu{4.867 ppm}$ (1H) and $\delta \: \pu{3.4615 ppm}$ (6.6H) (c.f. $\delta \: \pu{4.840 ppm}$ (1H) and $\delta \: \pu{3.432 ppm}$ (7.26H) in my product NMR) Not sure whether I can argue that peaks have 'shifted' in the product NMR – chemrese Jun 11 '19 at 3:37

If peaks for "some impurities" are appear around $$\delta \: \pu{1.8 ppm}$$, I assume you have residual THF in your crude product. The other multiplet of THF is probably burried under $$\delta \: \pu{3.43 ppm}$$ resonance. That would confirmed by your impurity integration, which should be equal to 1H unit equivalence. If I'm right, your 6.36H unit equivalence is actually overlap one of $$\ce{CH3}$$-resonance and one of $$\ce{CH2}$$-resonance.
On the other hand, the two resonances at $$\delta \: \pu{3.43 ppm}$$ and $$\delta \: \pu{2.73 ppm}$$ would very well be representing two $$\ce{CH3}$$-groups and (two $$\ce{CH2}$$-groups + part of THF impurity), respectively, as well.