Two-dimensional H-1-C-13 MAS-J-HMQC solid-state NMR spectra of the two anomeric forms of maltose at natural abundance are presented. The experimental H-1 chemical shifts of the CH and CH2 protons are assigned using first-principles chemical shift calculations that employ a plane-wave pseudo-potential 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-(HO)-O-... weak hydrogen bonding. Notably, a clear correlation between a large chemical shift change (up to 2 ppm) and both a short (HO)-O-... distance (< 2.7 angstrom) and a CHO bond angle greater than 1301 is observed, thus showing that directionality is important in C-(HO)-O-... hydrogen bonding.