Chemistry Reference
In-Depth Information
theoretical methods, particularly theoretical methods capable of describing patho-
logical cases for theory such as open-shell singlet diradical configurations that are
prevalent in many experimentally observed nitrenes.
This chapter focuses on the roles that theory and computation have played in this
collaborative effort to unravel the complex chemistry and properties of nitrenes and
their excited-state precursors. For overviews of nitrene chemistry that focus pre-
dominantly on experimental studies, see Chapter 1 and previous reviews.
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The first part of this chapter describes the structure and electronic states of
nitrenes. This section includes descriptions of the possible electronic states that
can be adopted by nitrenes, and how substituents affect the relative energies and
character of these electronic states. How substituents influence the electronic
states of the singlet nitrenes has been shown to be important, since the nature
of the singlet electronic state exerts a strong influence over which subsequent
nitrene decay pathways will be favored. Included in this section is a discussion
of computational methods that have been used to compute these properties,
while emphasizing the difficulties associated with modeling open-shell singlet
nitrenes.
The second part of this chapter describes the role of computation and theory in
understanding the reactivity and decay channels of the singlet nitrene—the central
species in nitrene chemistry. This discussion is followed by an overview of the
different precursors of nitrenes, with a particular focus on the structural and
electronic characteristics of the most common nitrene precursor, the azide moiety.
After this section, we describe the photochemistry of different azides in light of
recent experimental and theoretical results. Finally, this chapter concludes with a
review of an exciting new area of study in the investigation of nitrenes and its primary
precursors, azides, which is a collaborative partnership between ultrafast laser
spectroscopy and computational studies of excited-state precursors of nitrenes
that give insights into the dynamics of the excited species and how the excited
state surfaces of the photo-precursors connect with the surfaces of the nascent
nitrenes.
2.2 STRUCTURAL AND ELECTRONIC PROPERTIES OF NITRENES
2.2.1 The Electronic Landscape of Nitrenes
Nitrenes can adopt a number of different electronic states of singlet or triplet
multiplicity. Common electronic states of nitrenes are shown in Figure 2.1, with the
nitrene nitrogen depicted as adopting
sp
-hybridization. As detailed in later sections,
each different electronic configuration of a nitrene potentially opens up a distinct
landscape of chemical reactivity for the reactive species. For instance, triplet nitrenes
typically have clear and distinct reactivity from singlet nitrenes. More subtly,
different singlet electronic configurations of nitrenes often lead to different reaction
pathways being favored. Indeed, the nature of the electronic state adopted by the
nitrene powerfully influences its ultimate reactivity.
