CHARGE-DENSITY IN CRYSTALLINE CITRININ FROM X-RAY-DIFFRACTION AT 19 K

For the fungal metabolite citrinin, C13H14O5, the total experimental e lectron distribution rho(r) and its Laplacian del(2) rho(r) have been obtained from an extensive set (36 564 measurements) of single-crystal X-ray diffracted intensities at a temperature of 19 +/- 2 K. Relevant steps in data collection and processing are reported. The resulting 7 698 independent intensity data have been analysed with a multipole (ps eudoatoms) formalism. The topological properties of rho(r) have been d etermined according to the quantum theory of atoms in molecules. CC an d CO bond path lengths have been obtained by numerical integration; th eir values are found to be well correlated with those of the electron density at the bond critical points. Topological features have been us ed to characterize the extension of the conjugated system of the molec ule, and to confirm the stability of its rings, particularly the two f ormed by intramolecular H bonds. Maps of del(2) rho(r) are presented, showing details in the valence charge distribution and providing a ver y sensitive tool for analysing dependence of the density on the model adopted to interpret X-ray data. The known chemical reactivity of the molecule towards nucleophiles at a Csp(2) atom is confirmed by the sha pe of the molecular reactive surface (the zero envelope of del(2) rho( r)).