The work described in this thesis investigates the inter- and intra-molecular trapping of heterocyclic N-nitrenes in order to gain a better understanding of the mechanism of such trapping. The range of heterocyclic N-nitrenes known to exhibit the effect termed "secondary orbital interaction" was extended to include quinazolinonylnitrenes and enzimidazolylnitrenes. When these groups of compounds are substituted in the 2-position by a chiral substituent, they bring about chiral induction in the formation of asymmetrical aziridines from the N-nitrene addition to mono-substituted alkenes. The quinazolinonylnitrenes readily add intramolecularly to alkenes and arenes and one alkyne. The intramolecular addition reaction has been shown to proceed in a stepwise fashion via a dipolar seven-membered ring intermediate. However, despite good yields in intramolecular addition, when the nitrene is offered a trap which allows "secondary orbital interaction" during the transition state of the intermolecular addition, up to 100% of the nitrene is diverted to an intermolecular pathway. The importance of the "secondary" orbital interaction, due to its ability to lower the transition state energy of the concerted mechanism is thus emphasised.