What is the effect of hydrogen bonding on NMR?
Answers
Explanation:
Hydrogen bonding is well known to cause large changes in chemical shift values– this is evident if you look up the chemical shift of an alcohol in a data-book (for an aliphatic alcohol this is anywhere between 0.5 and ca. 6.0 ppm depending on solvent/concentration), where a large range of values are given.[1]
In general, formation of hydrogen bonds causes shifts to move to a higher frequency (higher ppm) due to deshielding.[2] In itself this is counter-intuitive, as in a hydrogen bonding interaction the H is actually receiving electron density from the donor atom (and therefore should be shielded). In the case of NMR however, the actual electron density isn’t whats causing this, but rather the field set up from the presence of the interaction.[#]
Intramolecular vs intermolecular hydrogen bonding