Nuclear Quadrupole Double Resonance in DL-Proline

1 7 0 nuclear quadrupole resonance spectra have been measured in an l v O enriched polycristalline sample of DL-proline with the help of 1 H l v O nuclear quadrupole double resonance technique. The results show the presence of eight chemically inequivalent oxygen sites corresponding to four inequivalent proline molecules in the unit cell. The oxygen sites may be grouped into two sets of four sites. One set with the short proton-oxygen distances belongs to the C O • • • H groups whereas the other with the long proton-oxygen distances to the C = O groups.