Experimental and Calculated CPL Spectra and Related Spectroscopic Data of Camphor and Other Simple Chiral Bicyclic Ketones

UV, circular dichroism (CD), fluorescence and circularly polarized luminescence (CPL) spectra were recorded for a set of four related [2.2.1] bicyclic compounds ((1S,4S)-and (1R,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one, namely (1S)- and (1R)-camphor
(1), (1S,4R)-4,7,7-trimethylbicyclo[2.2.1]hept-5-en-2-one, (1S)-dehydro-epicamphor (2), (1S,4S)-1,7,7-trimethylbicyclo[2.2.1]heptane-2,5-dione, (1S)-5-oxocamphor (3), (1S,4R)- and (1R,4S)-
1,7,7-trimethylbicyclo[2.2.1]heptane-2,3-dione, (1S)- and (1R)-camphorquinone (4)) and a set
of three related [2.2.2] bicyclic compounds (1S,4S)-bicyclo[2.2.2]octan-2,5-dione (saturated
diketone (5)), (1R,4R)-bicyclo[2.2.2]oct-7-en-2,5-dione (unsaturated diketone (6)), ((1S,4S)-
bicyclo[2.2.2]oct-7-en-5(S)-ol-2-one (which we refer to as unsaturated hydroxy-ketone (7)). For
the latter three compounds also mid-IR vibrational circular dichroism (VCD) spectra were
recorded and are presented. Time-Dependent Density Functional (TD-DFT) calculations provide
a satisfactory interpretation of both absorption and emission chiroptical spectra and permit
insight into ground and excited state electronic properties. We discuss the applicability of the
octant rule or of other approximated models to rationalize the observed sign of the CPL.