CN versus NN bond cleavage selectivity in the chemisorption of diazirine on Cu(110) and copper films was studied using temperature-programmed desorption and X-ray photoelectron spectroscopy. Dissociative adsorption occurs at or below 124 K, yielding XPS spectra characteristic of atomic nitrogen and species containing CN bonds. The TPD spectra show that the decomposition products rearrange or recombine, leading to high-temperature N-2 and C2N2 desorption. In combination, these results show that dissociative adsorption of diazirine on Cu(110) involves totally selective NN bond scission. Results for the adsorption of diazirine on copper films deposited at 107 K also show that dissociative adsorption occurs through selective NN bond scission. Furthermore, the fact that similar dissociation chemistry is observed for both the atomically rough films and the single-crystal surface implies that the selective NN bond scission should be interpreted in terms of electronic structure. The selective chemistry on copper is interpreted with reference to previous results for Pd(110), where both CN and NN bond scission were observed. An analysis based on the match between the molecular frontier orbitals and the metal valence band structure suggests that the pi-sigma bonding interactions in the:chemisorption of diazirine are antisynergistic. The observed surface decomposition of diazirine is compared to data from the organometallic literature for the interaction of diazirine compounds with metal complexes.