Upon reaction in vitro with calf thymus DNA, the two pairs of enantiomeric benzo(c)phenanthrene 3,4-diol-1,2-epoxides (in which the epoxide oxygen is either cis or trans to the benzylic hydroxyl group) derived from the enantiomeric benzo(c)phenanthrene trans-3,4-dihydrodiols have previously been shown to bind covalently to deoxyguanosine and deoxyadenosine residues with exceptionally high efficiency relative to epoxide hydrolysis. In order to identify the chemical structures of the adducts formed (one cis and one trans addition product derived from the reaction of each of the four configurationally isomeric diol epoxides with either deoxyguanosine or deoxyadenosine), these adducts have been prepared and compared to the adducts derived from DNA. The stereochemistry (cis or trans addition to the epoxide) for each adduct was deduced from the /sup 1/H-NMR spectrum of its pentaacetate ester. A combination of NMR spectroscopy, chemical stability considerations and pH titration established the site of substitution as the exocyclic nitrogen of guanine or adenine. A correlation was observed between R-absolute configuration at C/sub 1/ of the benzo(c)phenanthrene moiety and negative ellipticity for the major CD band (approx.250-260 nm) exhibited by these adducts.