An Investigation of Weak CH···O Hydrogen Bonds in Maltose Anomers by a Combination of Calculation and Experimental Solid-State NMR Spectroscopy

Two-dimensional 1H−13C MAS-J-HMQC solid-state NMR spectra of the two anomeric forms of
maltose at natural abundance are presented. The experimental 1H chemical shifts of the CH and CH2
protons are assigned using first-principles chemical shift calculations that employ a plane-wave pseudopotential approach. Further calculations show that the calculated change in the 1H chemical shift when
comparing the full crystal and an isolated molecule is a quantitative measure of intermolecular C−H···O
weak hydrogen bonding. Notably, a clear correlation between a large chemical shift change (up to 2 ppm)
and both a short H···O distance (<2.7 Å) and a CHO bond angle greater than 130° is observed, thus
showing that directionality is important in C−H···O hydrogen bonding.