To address this question, we carried out DFT calculations on trifluoromethyl phenyl diazirine. We found that the lowest unoccupied molecular orbital (LUMO) was centred mostly on the diazirine group (Fig. ), while both the highest occupied molecular orbital (HOMO) and the HOMO-2 extended across the aromatic ring and onto the diazirine unit. The HOMO-1 (not shown) was localized to the benzene ring.