ReactiVity of the Benzoylnitrene Radical Anion
6
,7
described previously.22,23 Benzoylnitrene and phenylnitrene anions
were generated by 70 eV electron ionization of neutral precursors,
benzoylazide and phenylazide. The anions were carried by helium
labeling experiments involving biological macromolecules and
in photoresist technology.4
,8
Studies have also been carried out on nitrene anions.
Phenylnitrene anion, generated by electron ionization of phenyl
3
buffer gas (0.400 Torr, flow [He] ) 190 STP cm /s) through the
9
,10
10
flow tube, where they were allowed to undergo ion-molecule
reactions with the neutral reagent vapors added through fixed
reagent inlets. The reactions were monitored by the loss of reactant
ion and formation of product anion. The ions generated in the flow
tube were cooled to ambient temperature by the helium buffer gas
and sampled through a 1 mm orifice into a low-pressure triple-
quadrupole mass filter where they were analyzed. Reaction rate
constants were measured by monitoring the intensity of the reactant
azide,
exhibits both free radical and anionic behavior, as
the proton-transfer reaction with 1,1,1-trifluoroacetone and the
radical displacement reaction with propionoaldehyde demon-
strate its anionic and free-radical character, respectively. In
addition, studies reported by McDonald et al.9 show that
phenylnitrene anion can undergo 1,2- and 1,4-addition reactions
with various R,â-unsaturated compounds, a reaction useful in
synthetic organic chemistry.11 Most significantly, nitrene anions
,11
22
ion as a function of the neutral reagent flow. The reaction
12-14
efficiency, eff, is given by eff ) kobs/kcoll, where k is the collision
have been used in photodetachement
and photoelectron
to determine thermochemical properties
coll
spectroscopic studies1
5,16
rate constant, calculated by using the average dipole orientation
24
(ADO) method.
of nitrenes.
Materials. Benzoylazide25 and phenylazide26 were synthesized
Unlike simple alkyl- or arylnitrenes, acylnitrenes are predicted
to have singlet (or nearly singlet) ground states, because the
singlet states can be stabilized by resonance (eq 2). B3LYP
by literature procedures. Unless otherwise indicated all the other
reagents were used as received. Helium was purified through a
liquid nitrogen trap containing molecular sieves. Gas purities are
17
1
8
calculations carried out on benzoylnitrene by Gritsan et al.
as follows: He (99.995%), NO (99%), NO
CO (99.999%), and CS (99%). Caution: Azides are potentially
2 2
(99%), SO (99%),
and photolyses studies of naphthoyl and substituted benzoyl
azides studies confirm that the acylnitrenes have singlet ground
states.1
2
2
explosive and should be handled with proper precautions. However,
we have not encountered any problems in this work.
9,20
Computational Studies. Electronic structure calculations (B3LYP)
were carried out with Gaussian 98W27 and QChem. All molecules
were fully optimized with the 6-31+G* basis set. Frequency
28
calculations were also carried out at the same level. NPA
calculations2
9-31
were carried out to study the charge distribution
of the molecules.
Recently we reported the formation of benzoylnitrene radical
anion, 1 , by electron ionization of benzoylazide (eq 3). In
Results and Discussion
1) Electronic Structure of 1 . The benzoylnitrene radical
-
21
-
(
our first study, we described the determination of the thermo-
-
anion can be envisioned as arising from adding an extra electron
to the triplet state of benzoylnitrene. The two singly occupied
orbitals in triplet benzoylnitrene are represented in Figure 1.
The a′′ orbital is a carboxylate-like π orbital, whereas the a′
orbital is a σ-like orbital localized on the nitrogen. Two
electronic states of the anion are created by adding an electron
to either one of the orbitals in the triplet. Adding an electron to
chemical properties of 1 and related species. In this work, we
report the bimolecular reactivity of the ion and provide a
description of its electronic structure.
2
the a′′ orbital creates the A′ state, which is best described as
having a delocalized (carboxylate-like) anion and a localized,
(
18) Gritsan, N. P.; Pritchina, E. A. MendeleeV Communi. 2001, 3, 85-
Experimental Section
1
5
2
24.
(19) Autrey, T.; Schuster, G. B. J. Am. Chem. Soc. 1987, 109, 5814-
All gas-phase ion/molecule reactions were carried out at room
temperature in a flowing afterglow triple-quadrupole apparatus
820.
(20) Pritchina, E. A.; Gritsan, N. P.; Bally, T. Russ. Chem. Bull. Int. Ed.
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(
(
(
1
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