Absolute configuration determination of the anti-head-to-head photocyclodimer of anthracene-2-carboxylic acid through cocrystallization with L-prolinol.

The absolute configuration has been established of the enantio­pure anti-head-to-head cyclo­dimer of anthracene-2-car­boxy­lic acid (AC) cocrystallized with l-propinol and di­chloro­methane [systematic name: (S)-2-(hy­droxy­meth­yl)pyrrolidin-1-ium (5R,6S,11R,12S)-8-carb­oxy-5,6,11,12-tetrahydro-5,12:6,11-bis­([1,2]benzeno)­dibenzo[a,e][8]annulene-2-carboxyl­ate di­chloro­methane monosolvate], C5H12NO+·C30H19O4−·CH2Cl2. In the crystal structure, the AC dimer inter­acts with l-prolinol through a nine-membered hydrogen-bonded ring [R22(9)], while the di­chloro­methane mol­ecule is incorporated to fill the void space. The absolute configuration determined in this study verifies a recent assignment made by comparing theoretical versus experimental circular dichroism spectra.