A level chemistry

Hi when we add d20 to a hydrogen nmr to remove the oh and the nh groups are the oh groups removed as they have an extra proton? Can someone explain?

Reply 1

Fruit Face

Yes and no. OH/NH peaks are removed when added D2O, yes. However D2O doesn't have extra protons, but rather extra neutrons.

The H from OH is transferred to one of the lone pairs of O in D2O, forming an alkoxide ion and HD2O+.
The alkoxide ion will react with unreacted D2O to reform the alcohol [plus and OD-], except the group is now OD and not OH.

HD2O and OD- will just get lost into normal equilibrium with water (H2O or D2O), so we don't have to worry about them.

i.e.

CH3CH2OH + D2O -> CH3CH2O- + HD2O+

CH3CH2O- + D2O -> CH3CH2OD + OD-

[no OH peaks produced because there is no OH, but rather OD]

I don't think we need to know why OH/NH peaks are removed when we add D2O at A level, but there's the little explanation if anyone else is curious.

If anyone else has anything I may have missed/wrote that doesn't seem right, please say !