Structure, vibrational spectroscopy, and photochemistry of 5-phenoxy-1-phenyltetrazole in argon and nitrogen cryomatrices

Article abstract of DOI:10.1139/cjc-2015-0025

The molecular structure, infrared spectra, and photochemistry of 5-phenoxy-1-phenyltetrazole (5PPT) isolated in argon and N₂ cryogenic matrices were investigated by infrared spectroscopy and theoretical calculations (DFT(B3LYP)/6-311++G(d,p)).

Full text of DOI:10.1139/cjc-2015-0025

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
1
ARTICLE
Structure, vibrational spectroscopy, and photochemistry of
5-phenoxy-1-phenyltetrazole in argon and nitrogen
cryomatrices
A. Borba, L.I.L. Cabral, R. Fausto, and M.L.S. Cristiano
Abstract: The molecular structure, infrared spectra, and photochemistry of 5-phenoxy-1-phenyltetrazole (5PPT) isolated in argon
and N2 cryogenic matrices were investigated by infrared spectroscopy and theoretical calculations (DFT(B3LYP)/6-311++G(d,p)).
Calculations yield two dissimilar minima on the potential energy surface of the molecule, both being eightfold degenerate by
symmetry and belonging to the C1 symmetry point group. Extensive analysis of the potential energy landscape of the molecule
was performed. Upon consideration of the zero-point vibrational correction to the energy, the calculations predict that the
higher energy minimum shall relax barrierlessly to the lower energy form, leading to conclude that the compound exists in a
single conformer in the gas phase. Accordingly, a single conformer was observed and fully characterized spectroscopically upon
isolation of the monomer of the compound in argon and nitrogen cryomatrices. UV-laser irradiation (␭ = 250 nm) of matrix-
isolated 5PPT leads to photocleavage of the tetrazole ring, with release of N2 and formation of the corresponding carbodiimide.
Key words: tetrazole, 5-aryloxytetrazole, molecular structure, infrared spectra, UV-induced N2 photoelimination.
Résumé : La structure moléculaire, les spectres infrarouges et la photochimie de 5-phénoxy-1-phényltétrazole (5PPT) isolé dans
des matrices cryogéniques de l’argon et de N2 ont été étudiés par spectroscopie d’infrarouges et calculs théoriques (DFT(B3LYP)/
6-311++G(d,p)). Les calculs donnent deux minima différents sur la surface d’énergie potentielle de la molécule, les deux étant de
huit fois dégénéré par symétrie et appartenant au groupe de points de symétrie C1. Une analyse approfondie du paysage d’énergie
potentielle de la molécule a été effectuée. Après examen des corrections du point zéro de vibration a` l’énergie, les calculs
prédisent que le minimum d’énergie plus élevée doit détendre sans barrière a` la forme d’énergie plus faible, ce qui permet de
conclure que le composé existe comme un seul conformère dans la phase gazeuse. En effet, un seul conformère a été observé, et
caractérisé entièrement par spectroscopie, après l’isolement du monomère du composé dans des cryomatrices de l’argon et
d’azote. Irradiation de 5PPT isolé en cryomatrice de l’argon avec laser UV (␭ = 250 nm) conduit a` photoclivage de l’heterocicle
tetrazole avec sortie de N2 et production de la carbodiimide correspondante.
Mots-clés : tetrazole, 5-aryloxytetrazole, structure moléculaire, spectres infrarouges, photoélimination de N2.
ether (3) (Scheme 1, bond a). On the other hand, in ether 3, bond b
(Scheme 1) is comparatively strong due to delocalization of the
Introduction
Tetrazole1 and derivatives remain a topic of intense research.
The wide interest in this class of compounds derives mainly from
their relevant applications in major areas, such as in medicine,2
agriculture,3 the automobile industry,4 imaging technology,5 and
coordination chemistry6 and also as high-energy materials.7 In
drug design, 5-substituted tetrazoles are often used as a metabol-
ically stable bioisosteric replacement for the carboxylic acid
moiety8 and 1,5-disubstituted tetrazoles act as a mimic for the
cis-amide bond.9
unshared electron pair on oxygen towards the electron-withdrawing
heterocycle. This methodology for hydrogenolysis makes use of
hydrogen donors, thus avoiding the use of molecular hydrogen,
and the catalyst is easily filtered off and may be reused. The leav-
ing group leads to formation of water-soluble tetrazolone (5)
(Scheme 1).16
The photochemistry of tetrazoles, in solution and isolated in
cryogenic matrices, has been reviewed.17,18 Generally, irradiation
of tetrazoles in the UV spectral region leads to cleavage of the
tetrazole ring. The photofragmentation pattern and the structure
and stability of the photoproducts obtained are determined by the
chemical nature and conformational flexibility of the substitu-
ents. If the molecule exhibits tautomerism, tautomer-selective
photochemistry may take place.19–21
Additionally, tetrazoles play a major role in synthesis. Due to
the strong electron-withdrawing properties of the heterocycle,
5-chloro-1-phenyltetrazole10 (1) (Scheme 1) has been used as deri-
vatising agent for alcohols. The resulting tetrazolyl ethers proved
to be excellent intermediates for reductive cleavage of the C–O
bond catalysed by transition metals in phenols11,12 and in allylic,13
benzylic,14 and naphthylic alcohols.15 Etherification weakens the
C–O bond of the original alcohol so that hydrogenolysis occurs
easily and selectively across the longer bond in the tetrazolyl
The structural features that render tetrazolyl ethers excellent
substrates for transfer hydrogenolysis may also influence their
photochemistry. Among 1,5-disubstituted tetrazoles, 5-aryloxy-1-
phenyltetrazoles appear to be especially interesting, since the
Received 12 January 2015. Accepted 7 April 2015.
A. Borba and R. Fausto. Department of Chemistry, University of Coimbra, P-3004-535 Coimbra, Portugal.
L.I.L. Cabral and M.L.S. Cristiano. CCMAR and Department of Chemistry and Pharmacy, F.C.T., University of Algarve, P-8005-039 Faro, Portugal.
Corresponding author: M.L.S. Cristiano (e-mail: mlscristiano@gmail.com).
This article is part of a Special Issue entitled “Advances and Applications in Physical Organic Chemistry” based on contributed papers from the 22nd International Conference
on Physical Organic Chemistry (Ottawa, Canada, 2014).
Can. J. Chem. 93: 1–10 (2015) dx.doi.org/10.1139/cjc-2015-0025
Published at www.nrcresearchpress.com/cjc on 21 April 2015.

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
2
Can. J. Chem. Vol. 93, 2015
Scheme 1. Tetrazolyl ethers 3 as intermediates for catalytic transfer hydrogenolysis of alcohols 2.
central oxygen links an aromatic and an electron-withdrawing
heteroaromatic system. Reported crystal structures for a repre-
sentative library of aryloxy and naphthoxy tetrazoles22 reveal
that, as expected, the central ether linkage (3) (Scheme 1) is much
shorter on the tetrazolyl ether side (C–O b around 132 pm) than on
the aryl or naphthyl side (O–C a around 143 pm), with C–O–C bond
angles around 117°. As may be deduced from crystallographic anal-
ysis, in these heteroaromatic ethers the ether oxygen appears to
show an approximate sp2 hybridization22 and is strongly conju-
gated with the tetrazolyl ring system, but not with that of the
phenyl or naphthyl substituent. The X-ray analyses also show that
the plane of the naphthyl or aryl ring is nearly perpendicular to
that of the tetrazolyl system.
Although the structure of aryloxy tetrazoles is well character-
ized in the condensed phase, there is no information regarding
their structure for the isolated molecule situation. Furthermore,
the photochemistry of 5-aryloxy tetrazoles has not been investigated.
In this work, we discuss our recent findings on the monomeric
structure and UV-induced photochemistry of 5-phenoxy–1-phenyl
tetrazole (5PPT) (3) (Scheme 1; R = Ph), isolated in solid argon and
N2 cryomatrices. In this 1,5-disubstituted tetrazole, both substitu-
ents bear aromatic character and may, in principle, conjugate
with the tetrazole ring. The interpretation of the experimental
results was assisted by extensive DFT(B3LYP)/6-311++G(d,p) calcu-
lations on the structures of 5PPT and of putative photoproducts.
Matrix preparation, infrared spectroscopy, and UV
irradiation experiments
For preparing the low-temperature matrices, a solid sample of
5PPT was sublimated (at ϳ325 K) using a pyrex minioven placed in
the vacuum chamber of the cryostat (APD Cryogenics close-cycle
helium refrigeration system with a DE-202A expander). The vapor
of the compound was deposited together with a large excess of
inert gas (argon N60 or nitrogen N50, both obtained from Air
Liquide) onto a cold (14–20 K) CsI subtrate. The temperature was
controlled and measured using a diode sensor connected to a
Scientific Instruments digital temperature controller (model
9659) to within 1 degree. In the matrix isolation annealing exper-
iments, the temperature was varied in steps of 3° until ϳ25 K.
The IR spectra (4000–400 cm−1) were collected with 0.5 cm−1
spectral resolution using a Nicolet 6700 fourier transform infra-
red spectrometer equipped with a deuterated triglycine sulphate
detector and a Ge/KBr beamsplitter. Modifications of the sample
compartment of the spectrometer were made to accommodate
the cryostat head and allow an efficient purging of the system by
a continuous stream of dry air to avoid interference from atmo-
spheric water and CO2.
The UV irradiation (␭ = 250 nm) of the matrices was carried out
through the outer quartz window of the cryostat, with the fre-
quency doubled signal beam of the Quanta-Ray MOPO-SL pulsed
(10 ns) optical parametric oscillator (FWHM ϳ 0.2 cm−1, repetition
rate 10 Hz, pulse energy ϳ1.0 mJ) pumped by a Nd:YAG laser.
Experimental section
Computational methods
Chemicals and apparatus
The quantum chemical calculations were performed with the
Gaussian 09 suite of programs23 at the DFT(B3LYP)24–26 level of
approximation using the 6-311++G(d,p) basis set.27 Structures were
optimized using the geometry direct inversion of the iterative
subspace method,28 with the nature of the obtained stationary
points being checked by inspection of the corresponding Hessian
matrix. Potential energy profiles for internal rotation were calcu-
lated by performing relaxed scans on the B3LYP/6-311++G(d,p)
potential energy surface along the relevant coordinates. The
transition state structures for conformational conversions were
obtained using the synchronous transit-guided quasi-Newton
method.29
All chemicals were used as purchased. Solvents for extraction
were of technical grade. When required, solvents were freshly
distilled from the appropriate drying agents before use. Analytical
TLC was performed with silica gel 60 F254 plates. Melting points
were recorded on a Stuart Scientific SMP3 melting point appara-
tus and are uncorrected. Mass spectra were obtained on a VG
7070E mass spectrometer by electron ionization at 70 eV. NMR
(400 MHz) spectra were obtained on a Bruker AM-400 spectrome-
ter using TMS as the internal reference (␦ = 0.0 ppm). The 1H NMR
spectrum for 5PPT is provided as supporting information (Fig. S1)
(see Supplementary material section).
Preparation of 5-phenoxy-1-phenyltetrazole (5PPT)
The B3LYP/6-311++G(d,p)-calculated vibrational frequencies were
scaled by 0.978 and the resulting frequencies, together with the
calculated intensities, were used to simulate the spectra shown
in the figures. In these simulations, the absorptions were broad-
ened by Lorentzian profiles (fwhm = 5 cm−1) centered at the calcu-
lated (scaled) frequencies using the SYNSPEC software.30 Note that
the peak intensities in the simulated spectra (shown in units of
“relative intensity”) differ from the calculated intensities (in
km mol−1) because they were set to satisfy the condition that the
integrated band area in the simulated spectrum corresponds to
the calculated infrared intensity. The theoretical normal modes
were analyzed by carrying out the potential energy distribution
calculations performed according to a procedure described in the
literature.31,32 The set of internal coordinates used in the potential
Phenol (630 mg, 6.65 mmol) was added to a suspension of NaH
(520 mg, 2.16 mmol) in dry THF (20 mL) in anhydrous conditions.
The mixture was stirred for 3 h at room temperature under N2.
Then, a solution of 5-chloro-1-phenyltetrazole 1 (1 g, 5.4 mmol) in
dry THF (20 mL) was added and the final mixture was stirred
overnight. Evaporation of the solvent followed by extraction with
DCM (30 mL), washing of the organic layer with 2 mol L–1 HCl
(10 mL) and water (2 × 30 mL), and evaporation of combined or-
ganic extracts led to a solid. Recrystallization from ethanol–DCM
(2:1) yielded the required crystalline product (1.06 g, 4.48 mmol,
83% yield), mp 116–118 °C. 1H NMR (400 MHz, CDCl3) ␦: 7.24 (t, 1H,
J = 7.1 Hz), 7.37 (td, 4H, J = 7.9 Hz, J = 15.9 Hz), 7.45 (d, 1H, J = 7.4 Hz),
7.51 (t, 2H, J = 7.6 Hz), 7.74 (d, 2H, J = 8.1 Hz).
Published by NRC Research Press

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
Borba et al.
3
Fig. 1. Structures of the 5PPT minimum energy forms and adopted
atom numbering scheme. The three internal rotational degrees of
freedom of the molecule are indicated by the arrows. The
C18–O17–C5–N1 dihedral angle in forms 1 and 2 is approximately 178°
and 169°, respectively. The geometries about the bonds A and C are
discussed in detail in the text (see also Figs. 2 and 3).
Fig. 2. B3LYP/6-311++G(d,p) potential energy map describing the
change in the potential energy (zero-point uncorrected energy values) as a
function of the C6–N1 and C18–O17 torsional coordinates. The map was
built with the driving coordinates fixed at values differing by 20°
and by optimizing all of the remaining coordinates. The positions of
the minima are indicated.
The dihedral angle around the C6–N1 bond (A in Fig. 1) defines
the relative orientation of the phenyl substituent and tetrazole
rings. The calculations show that in the two minimum-energy
structures, the planes of these two rings make an angle of approx-
imately 30° (36° in form 1 and 32° in 2). The value of the angle
between the planes of these two rings is largely determined by the
balance among three factors: (i) steric repulsions between the two
substituents on the tetrazole ring (phenyl and phenoxyl), which
favor a nonplanar geometry, (ii) conjugation of the ␲-electron
systems of both rings, favoring their coplanarity, and (iii) weak
intramolecular hydrogen-bond-like interaction between the
ortho-hydrogen atoms of the phenyl ring and the negatively
charged O17 and N2 atoms located at the tetrazole side of the
molecule, with the C7–H12···N2 and C11–H16···O17 interactions being
expected to favor noncoplanar and coplanar arrangements of the
two rings, respectively. It is interesting to note that the C7–H12···N2
and C11H16···O17 H-bond distances are somewhat shorter in 2 than
in 1 (259 and 247 pm, respectively, versus 263 and 254 pm), indi-
cating that these two weak hydrogen-bond-type interactions in
the higher energy minimum 2 are slightly stronger than in the
more stable form 1. The angle between the planes of the phenyl
and tetrazole rings is smaller in form 2 than in form 1 and the
orientation of the phenyl group of the phenoxyl substituent rela-
tively to the tetrazole ring is also different in the two forms. The
approximate coplanarity of the tetrazole and phenoxyl moieties
in form 1 clearly imposes a stronger steric hindrance to the copla-
narity of the phenyl substituent of the tetrazole ring compared
with the more skewed arrangement of the tetrazole and phenoxyl
moieties present in form 2 (see Fig. 1).
energy distribution analysis was defined following the recom-
mendations of Pulay et al.33
Results and discussion
Geometries and energies
The 5PPT molecule has three torsional degrees of freedom, cor-
responding to internal rotations around the C6–N1 (A in Fig. 1),
O17–C5 (B), and C18–O17 (C) bonds (Fig. 1). All low-energy structures
of the molecule were found to exhibit a conformation about the
O17–C5 bond approximately trans (i.e., with the two phenyl groups
of the molecule pointing to opposite directions). On the other
hand, the alternative cis orientation brings the two phenyl groups
in close spatial proximity, resulting in strong steric repulsions
and considerably large energies. The conformational space of the
molecule is then essentially determined by the arrangements
around the C6–N1 (A) and C18–O17 (C) bonds, which are related with
the orientation of each one of the phenyl groups relatively to the
tetrazole ring.
The search on the B3LYP/6-311++G(d,p) potential energy surface
of the molecule revealed the existence of two different minima, 1
and 2 (Fig. 1), both being eightfold degenerate by symmetry and
belonging to the C1 symmetry point group. According to the
calculations, the energy difference between the two different
minima amounts to 1.14 kJ mol−1 (zero-point corrected energy
difference; 1.31 kJ mol−1 if counted from the bottom of the poten-
tial wells), with the lower energy minimum having a slightly
larger dipole moment (5.30 versus 5.23 D in 2). A potential energy
map showing the location of the two forms as a function of the
conformationally relevant C6–N1 and C18–O17 torsional coordi-
nates is shown in Fig. 2. Figure 3 shows the relaxed potential
energy profiles for rotation about the C6–N1 and C18–O17 bonds,
corresponding roughly to the cuts in the potential energy map
indicated in Fig. 2 by the horizontal and perpendicular broken
lines.
In form 1, the two transition states for rotation of the phenyl
group (about C6–N1), one corresponding to the structure with
coplanar tetrazole (TS1) and phenyl rings and the other to a geom-
etry where these rings are perpendicular (TS2), have energies
higher than the minimum energy structure of 2.30 and 4.35 kJ mol−1,
respectively (see Fig. 3, trace II). The higher energy of the transi-
tion state bearing the two rings perpendicular, compared with
that where the two rings are coplanar, results from the lack of
Published by NRC Research Press

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
4
Can. J. Chem. Vol. 93, 2015
Fig. 3. B3LYP/6-311++G(d,p) calculated potential energy profiles for internal rotation of the phenyl groups (trace I, belonging to the phenoxyl
substituent; trace II, directly connected to the tetrazolyl moiety). These potential energy profiles were calculated by incrementing the value of
the scanned coordinate in steps of 5° and letting all other coordinates relaxito their optimal values. In all geometries along the potential
energy profile (I), the conformations about the C6–N1 and O17–C5 axes optimize to approximately 30° and 180°, respectively, while along the
potential energy profile II, the conformations about the C18–O17 and O17–C5 axes both optimize to approximately 180°. Horizontal broken lines
indicate the zero-point levels for the two minimum energy structures.
␲-electron delocalization between the two rings in the first case.
Nevertheless, it shall also be stressed that the conjugation be-
tween the phenyl and tetrazole rings is reduced. This can be con-
cluded not only by taking into account the small energy
difference between the energies of the two transition states TS1
and TS2 but also by considering the length of the C6–N1 bond
(142.7 pm), which does not differ too much from a typical C–N
single bond in alkylamines (within the 145–147 pm range),34 and
differs very much from a typical double bond (for instance, like
that found in methylenimine, H2C=NH: 127.3 pm).35 In simple
diazines (pyrazine, pyrimidine, and pyridazine), where the CN
bond lengths have a bond order of approximately 1.5, conjugated
system, the bond lengths are approximately 133.5 pm,36–38 i.e.,
also considerably shorter than the C6–N1 distance in 5PPT.
Internal rotation around the C18–O17 bond (C in Fig. 1) deter-
mines the relative orientation of the phenyl ring of the phenoxyl
substituent and the tetrazole ring. This internal rotation corre-
sponds to the most flexible coordinate of the molecule and is
essentially the one distinguishing the two minima. In the lowest
energy form 1, the two rings are nearly coplanar (the planes of the
two rings make an angle smaller than 10°), which ensures both a
more relevant ␲-electron delocalization and a favorable geometry
for establishment of a stabilizing intramolecular hydrogen bond
interaction (C–H28···N4; see Fig. 1). The hydrogen bond distance
(H28···N4) is 225 pm, i.e., considerably shorter than the sum of the
van der Waals radii of hydrogen and nitrogen atoms (ϳ275 pm).
On the other hand, in the higher energy structure 2, this interac-
tion does not exist, since the tetrazole ring and the phenyl ring of
the phenoxyl substituent are significantly deviated from copla-
narity (the angle between the planes of the two rings is ϳ80°).
Considering that the C–H28···N4 intramolecular hydrogen bond is
the main interaction distinctive of the two forms, one can roughly
estimate the strength of such an interaction in form 1 as being of
the order of magnitude of the energy difference between the two
forms, i.e., ϳ1–2 kJ mol−1.
Table 1. B3LYP/6-311++G(d,p)-calculated bond lengths (pm) and angles
(°) around the central ether linkage in tetrazolyl ethers 5MPP,39
5EPT40, and 5PPT.
Structural parameter
Molecule
O−Ct
Ca−O
C−O−C
Ca−O−C−N(ph)
5MPT
5EPT
5PPT
132.4
132.3
132.7
144.7
146.0
140.4
115.4
115.7
125.2
177.0
176.6
178.1
Note: Subscripts “t” and “a” designate the tetrazolyl and aryl/alkyl substitu-
ents, respectively.
conclude that it relaxes barrierlessly to 1. In practical terms, this
result shows that 5PPT has actually only one conformer in the gas
phase (form 1), which one can expect to be also the sole species
present in the low-temperature matrices investigated in this study
(see below).
The calculated bond lengths and angles around the central
ether linkage in 5PPT are compared with corresponding data pre-
viously obtained by our groups for 5-methoxy-1-phenyltetrazole
(5MPT)39 and 5-ethoxy-1-phenyltetrazole (5EPT)40 (Table 1). In all of
these compounds, the tetrazole ring and the heavy atom skeleton
of the second ether substituent are preferentially oriented in a
near coplanar fashion, with the latter pointing in the opposite
direction relatively to the phenyl substituent of the tetrazole
(Ca–O–C–N(Ph)). These data are in keeping with results obtained
from crystallographic analysis of a library of aryloxy- and
naphthoxytetrazoles.22 As mentioned in the Introduction section,
due to the electron-withdrawing nature of the tetrazole ring, for
all ethers the central ether linkage is much shorter on the
tetrazolyl ether side (O–Ct around 132 pm) than on the aryl or alkyl
side (Ca–O ranging from 140 to 146 pm). The constancy of the O–Ct
bond length in the three compounds demonstrates that the ex-
tent of electron delocalization associated with the tetrazole ring
and the ether oxygen atom lone-electron pair is not significantly
influenced by the nature of the second ether substituent (either it
being alkyl or aryl). On the other hand, the Ca–O bond is consid-
erably shorter in 5PPT than in the two alkyl ethers, as could be
expected considering that the carbon atom is hybridized sp2 and
also the likely existing electron delocalization involving the aryl
fragment and the oxygen atom lone-electron pairs.
The potential energy profile for rotation about the C18–O17
bond, shown in Fig. 3 (trace I), reveals that the energy barriers
separating the higher energy minimum 2 from the most stable
form 1 are very low, amounting only to 0.09 and 0.24 kJ mol−1 (TS3
and TS4, respectively) The calculated (scaled) frequency of the
torsion around the C18–O17 bond for form 2 is 16.8 cm−1, which
yields a zero-point energy for this mode at the minimum
(0.10 kJ mol−1), which surpasses the energy barrier of 0.09 kJ mol−1
taken from the bottom of the potential well. This means that form
2 does not in fact correspond to a stable structure, since upon
taking into account the zero-point energy correction, one can
C–O–C bond angles range from 115° in the alkoxytetrazoles to
125° in phenoxytetrazole. The larger angle observed in phenoxy-
tetrazole results from both the more relevant steric hindrance
between the tetrazole and phenyl moiety of the phenoxyl sub-
Published by NRC Research Press

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
Borba et al.
5
Fig. 4. Comparison of the infrared spectra of monomeric 5PPT isolated in argon and nitrogen matrices (15 K) with the B3LYP/6-311++G(d,p)-
calculated spectrum of the compound. The calculated spectrum was simulated using Lorentzian functions with a full-width-at-half-maximum
of 5 cm−1 with frequencies scaled by 0.978.
stituent and the higher sp2-type hybridization character exhibited
by the ether oxygen atom in this compound.
substantially affected by the nature of the substituent at position
1, and some differ considerably among the three compounds.
Among the most intense bands in the IR spectra of 5PPT associ-
ated with modes originated mainly in this group (␯(N=C), ␯(N=N),
␯(N–N=), ␯(C–N), ␯(N–N), and ␦(T-ring 2)), the two CN stretching
modes appear to be the most sensitive to the nature of the sub-
stituent connected to position 1 of the tetrazole ring. For example,
Infrared spectra of matrix-isolated 5PPT
The infrared spectra of the matrix-isolated 5PPT in argon and
nitrogen matrices are presented in Fig. 4 together with the B3LYP/
6-311++G(d,p)-predicted spectrum of the compound (form 1). The
experimental spectra exhibit considerable site-splitting (espe-
cially in case of the most intense bands associated with more polar
molecular fragments, which can be expected to be more sensitive
to the local environment), revealing that the 5PPT molecules
occupy multiple matrix sites, in both the argon and nitrogen
matrices. Annealing experiments showed that the different local
environments shall have very similar stability, since the observed
band components resulting from site-splitting do not experience
intensity changes upon temperature variation, i.e., no site conver-
sions could be induced in an efficient way within the range of
temperatures investigated (15–25 K).
As can be seen in Fig. 4, despite the splitting observed in the
bands of the experimental spectra, the agreement between these
spectra and the calculated one is very good, enabling a full, reli-
able assignment of the experimental bands. The assignments are
provided in Table 2 (see supporting information Table S1for defi-
nition of coordinates).
Belonging to the C1 symmetry point group, the 5PPT molecule
has 78 fundamental vibrations, all of them expected to be active in
the infrared. In agreement with the spectral data previously ob-
tained for 5MPT and 5EPT,39,40 the IR spectrum of 5PPT may be
considered as formed by three groups of bands associated respec-
tively with the vibrational modes of the phenyl group, tetrazolyl
ring, and phenoxyl substituent. The bands comprised in the first
group appear in the spectrum of 5PPT at nearly the same frequen-
cies observed for 5MPT39 and 5EPT.40 This result indicates that the
nature of the substituent in position 5 of the the tetrazole ring has
a minor influence on the internal potential of the phenyl group
linked to position 1. Such a finding is in consonance with the
conclusions extracted above based on structural and energetic
data for the three compounds.
the ␯(N=C) vibration appears as a doublet at 1299/1298 cm−1 in
40
5EPT and
at 1572/1571 cm−1 in 5MPT39 and as a multiplet cen-
tered at approximately 1450 cm−1 in 5PPT (see Table 2).
The effects of the nature of the substituent on the C–O stretch-
ing vibrations closely follow the trends extracted from the struc-
tural data discussed above: the ␯(CT-ring–O) frequency is similar in
the three compounds (1567/1565/1553 cm−1 in 5EPT,40 1489 cm−1 in
5MPT,39 and 1551/1545/1542/1532 cm−1 in 5PPT), while the fre-
quency of the ␯(O–Ca) (subscript “a” standing for aryl or alkyl)
vibration is much higher in the case of 5PPT (1200/1198/1193 cm−1),
where the O–Ca bond is much shorter, than in 5MPT (746 cm−1)39
and 5EPT (903/901/900/886/885 cm−1).40
UV-laser-induced photochemistry of matrix-isolated 5PPT
It has been shown17,18,41,42 that the preferred reaction occurring
upon subjecting tetrazoles to UV irradiation corresponds to mo-
lecular nitrogen extrusion, with formation of several different
isomeric species, which include the diazirine, nitrilimine, cyanamide,
and carbodiimide (Scheme 2). In general, nitrilimine and diazirine
species are short lived under photolysis conditions because they
quickly convert into the photostable isomeric carbodiimide or,
less frequently, cyanamide.41,42
Upon UV laser irradiation (␭ = 250 nm) (see supporting informa-
tion Fig. S2 the UV absorbance spectrum of 5PPT) of the monomer
of 5PPT isolated in argon, the infrared spectrum of the compound
lost intensity, while new bands developed, indicating that the
compound underwent a photochemical transformation. Figure 5
presents the difference spectrum obtained by subtracting the
spectrum of the deposited matrix from that recorded after
70 min of UV irradiation. In the figure, a theoretical difference
spectrum is also plotted, where the bands pointing down corre-
spond to the reactant (5PPT) and those pointing up to N-phenoxy-
N=-phenylcarbodiimide. Among the possible photoproducts, this
In contrast with the vibrations belonging to the phenyl sub-
stituent, the tetrazole ring vibrations are, as one could anticipate,
Published by NRC Research Press

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
6
Can. J. Chem. Vol. 93, 2015
Table 2. Proposed assignments for the IR spectra of 5PPT isolated in argon and nitrogen matrices, B3LYP/6-311++G(d,p)-calculated spectrum for
the compound (form 1), and results of normal coordinate analysis.
Observed
Calculated
IR
Description
␯(C−H)b
Argon matrix
Nitrogen matrix
Frequency
intensity
Potential energy distribution
1
3119/3116/3115
3107
3087/3084
3080
3075/3078
3055
3043/3044
3122/3119
3105
3087
3084
3078
3166.4
3143.4
3140.7
3129.0
3123.6
3121.0
3112.8
3109.9
3102.6
3100.7
1606.9
1604.4
1597.5
1593.5
1534.6
1498.9
1485.7
1459.9
1454.2
1429.9
1339.6
1324.8
1324.2
1306.8
1299.5
1281.1
1187.4
1175.5
1163.2
1159.0
1154.0
1103.3
1090.6
1080.1
1067.7
1044.9
1024.6
1015.7
995.6
15.3
1.1
0.5
S26(99)
S16(54) + S17(38)
S15(90)
S27(63) + S29(24)
S17(41) + S18(39) + S16(15)
S28(75) + S29(19)
S19(94)
␯(C−H)a 2=
␯(C−H)a 1
␯(C−H)b 2=
␯(C−H)a 2=
␯(C−H)b 2==
␯(C−H)a 3==
␯(C−H)b 3==
␯(C−H)a 3=
␯(C−H)b 3=
␯(Phb-ring 4)
␯(Pha-ring 2)
␯(Pha-ring 4)
␯(Phb-ring 2)
␯(C−O)
3.9
14.7
17.3
9.1
9.6
0.0
3054
3043
S30(89)
3030/3027/3025
3031/3027
S18(52) + S16(31) + S17(16)
S29(57) + S27(33) + S28(10)
S23(35) + S21(27)
S10(62) + S47(19)
S12(63) + S46(10)
S21(26) + S23(30) + S52(11)
S7(38) + S3(34)
S45(49) + S13(29) + S6(10)
S50(61) + S24(32)
0.1
0.3
1605
1601
1599/1597/1595
1606
1602
1597
15.1
16.0
41.3
623.1
75.9
160.2
4.8
47.4
174.7
41.9
2.4
4.6
11.8
5.8
67.6
133.0
2.4
61.2
1.3
16.1
33.7
27.8
5.6
45.8
5.2
15.4
7.8
0.1
1.4
0.1
2.9
1.4
1551sh/1545/1542/1532sh
1513sh/1510/1509
1494
1474
1544
␦(C−H)a 2
1513sh/1512/1509/1502sh
1494
1470
␦(C−H)b
2
␦(C−H)b 3
␦(C−H)a 3
␯(N=C)
S25(27) + S51(26)
1469
S14(30) + S46(26) + S44(10)
S4(31) + S6(12) + S3(10)
S1(63) + S44(20)
S44(53) + S11(15)
S49(62) + S22(13)
1460/1456/1451/1444/1442/1431
1339sh/1336/1334sh
1321
1460/1455/1451/1450/1442/1430sh
1338sh/1337/1334
1323
␯(N=N)
␦(C−H)a 1
␦(C−H)b 1
␯(Phb-ring 3)
␯(Pha-ring 3)
␦(T-ring 1)
␯(O−C)
␦(C−H)a 4
␦(C−H)b 4
␦(C−H)a 5
1297
1290
1284
S22(61) + S49(16)
1288/1285/1283/1282
1305/1303/1301
1200/1198/1193
1179
1171/1169/1167/1164/1162
1160/1159
S11(69) + S1(14) + S44(10)
S3(22) + S6(18) + S22(15) + S36(11)
S52(28) + S8(25) + S21(13)
S47(76) + S10(24)
1311/1305/1300sh
1201/1195
1182
1168/1665
1161
S52(31) + S53(19) + S8(14)
S48(65) + S11(13) + S46(12)
S53(48) + S52(16) + S51(10) + S22(10)
S5(24) + S2(15) + S14(11) + S46(11)
S37(35) + S2(31) + S14(10)
S25(48) + S51(34) + S53(10)
S14(30) + S37(25) + S46(14) + S5(11)
S13(40) + S45(21) + S5(12)
S24(50) + S50(23) + S20(15)
S9(29) + S38(29) + S13(17)
S38(49) + S9(48)
␦(C−H)b
␯(N−N== )
5
1121/1120/1118/1116
1100/1098/1095/1094/1089
1121
1097/1096
␦(T-ring 2)
␯(Phb-ring 6)
␯(Pha-ring 6)
␯(Pha-ring 5)
␯(Phb-ring 5)
␯(Pha-ring 1)
␦(Pha-ring 1)
␦(Phb-ring 1)
␥(C−H)a 4
1072/1071
1049
1029/1028/1026
1021
1073
1049
1029sh/1026
1021
1006
1007
994.8
983.5
978.6
976.7
S41(62) + S20(33)
S56(25) + S71(25) + S70(22) + S72(14)
S2(26) + S37(19) + S4(11) + S77(10)
S77(21) + S59(17) + S2(11)
S58(27) + S72(25) + S70(18) + S69(15)
+ S73(14)
␯(C−N)
␯(N−N)
␥(C−H)a 2
978/977
960
978/976
n.o.
964.8
0.1
␥(C−H)b
␥(C−H)a 1
␥(C−H)b
␯(Phb-ring 1)
1
n.o.
914/909
960.8
910.6
905.5
857.5
0.2
3.7
6.4
S75(33) + S61(24) + S74(13) + S78(12)
S73(29) + S69(28) + S71(25) + S57(11)
S78(29) + S76(25) + S74(24) + S60(13)
S36(21) + S20(20) + S8(13) + S41(12)
912sh/910
907/905/902
866/864/863/862/860/859/
855sh/853/851/850sh
795
5
907/905sh
863/860/858/854/853/852sh/848
24.0
␥(C−H)a 4
␥(C−H)b 4
␥(C−H)a 3
␥(C−O)
801/794/788
828.6
824.9
756.2
752.4
744.7
706.3
692.8
683.3
682.2
678.6
625.5
615.2
611.2
0.1
0.2
38.4
57.1
26.3
8.9
11.6
10.6
29.3
17.0
0.9
S73(29) + S69(27) + S70(23) + S72(20)
S74(35) + S76(26) + S77(20) + S75(17)
S71(33) + S66(21) + S72(10)
S76(22) + S68(13)
S76(35)
S55(45) + S65(31) + S54(20)
S54(43) + S56(26)
S59(34) + S75(12) + S77(10)
S56(16) + S59(16) + S54(14)
S40(36) + S64(12) + S36(11)
S43(39) + S32(14)
S39(83)
S42(86)
759
762
756/755/752
743/734/730sh
719/717
699
687sh/686/685
761/759sh
745/739/737/732
722
699
689/688/687
␥(C−H)b 3
␶(T-ring 1)
␶(Pha-ring 1)
␥(C−H)b 2
␶(Phb-ring 1)
␦(Pha-ring 3)
␦(Phb-ring 3)
␦(Pha-ring 2)
␦(Phb-ring 2)
680/679sh
630
614
682sh/680/679sh
n.o.
n.o.
n.o.
0.3
0.4
Published by NRC Research Press

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
Borba et al.
7
Table 2 (concluded).
Observed
Calculated
IR
Description
Argon matrix
Nitrogen matrix
Frequency
intensity
Potential energy distribution
␥(C−N)
␶(Phb-ring 2)
524
493
521
490
520.4
492.6
10.2
7.1
S67(31) + S57(13) + S33(12) + S43(10)
S68(57) + S60(20) + S76(57)
Note: Wavenumbers (scaled by 0.978) in cm−1, calculated intensities in km mol−1. ␯, bond stretching; ␦, bending; ␥, rocking; ␶, torsion; Pha-ring, phenyl ring;
Phb-ring, phenyl ring of the phenoxyl substituent; T-ring, tetrazole ring; n.o., not observed; sh, shoulder. Calculated data for spectral region not experimentally
investigated (description: frequency (cm−1) (IR intensity (km mol−1); potential energy distribution: ␥(N−N): 458.6 [3.9] S34(22) + S33(11) + S43(11) + S66(11), ␶(Phb-ring 3): 411.7
[0.0] S61(70), ␶(Pha-ring 3): 407.5 [0.2] S58(71), ␯(N−C): 369.3 [1.8] S40(19) + S35(18) + S6(17), ␶(T-ring 2): 343.6 [1.5] S65(22) + S57(17) + S55(10), ␦(Phb−O): 305.5 [4.0] S35(24) + S36(11) +
S7(10), ␦(Pha−N): 277.8 [0.9] S55(25) + S65(22) + S34(16), ␶(Pha-ring 2): 223.3 [0.7] S60(28) + S57(10), ␦(O−C−N): 211.9 [0.1] S60(23) + S57(15) + S32(10), ␦(C−O−Phb): 155.6 [2.5]
S
S
31(36) + S35(16) + S33(12) + S34(10), ␥(C−N): 103.3 [0.8] S65(65), ␦(C−N): 63.9 [0.8] S33(26) + S32(15) + S31(12), ␶(Pha−N): 43.3 [0.8] S63(65) + S62(15), ␶(C−O): 29.1 [0.0] S62(51) +
64(39) + S63(16), ␶(Phb−O): 12.9 [0.5] S64(65) + S62(28).
Scheme 2. Possible photoproducts of tetrazole ring N2 photoelimination. 1, carbodiimide; 2, cyanamide; 3, diazirine; 4, nitrilimine
(propargylic (4a) and allenic (4b) forms).
Fig. 5. (A) Calculated difference infrared spectrum (carbodiimide minus 5PPT) and (B) experimental difference spectrum (UV-irradiated argon
matrix, ␭ = 250 nm, 70 min minus deposited matrix). See text for an explanation of the observed smearing of intensity of experimental bands
of the carbodiimide at approximately 1200 and 885 cm−1
.
Published by NRC Research Press

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
8
Can. J. Chem. Vol. 93, 2015
Table 3. Proposed assignments for the carbodiimide photoproduct and calculated (B3LYP/6-311++G(d,p))-calculated IR spectrum for this molecule.
Calculated
Calculated
Approximate
description
Approximate
description
␯
IR intensity
Observed ␯
␯
IR intensity
Observed ␯
␯CH
3152.8
3129.7
3125.5
3121.8
3118.2
3112.9
3104.9
3104.4
3097.5
3096.5
2112.6
1.8
6.6
9.0
14.1
22.0
9.9
2.2
12.0
1.6
1.7
1040.9
3098
␥CH
979.5
962.9
962.5
950.2
909.9
885.7
880.9
826.6
815.1
0.0
0.1
0.2
0.0
4.4
168.8
7.2
0.3
64.1
0.0
5.9
n.o.
n.o.
n.o.
n.o.
n.o.
902/899
3074
␯N−O
␥CH
3053
3036
812
785
␦CNO, ␦CCC
␥CH
␦CNC, ␦CCC
812.4
778.4
␯NCN as.
␯CC
2286/2257/2236/2164/2149/2138/2135/
2130/2128/2127/2118/2040/2024
1602/1600/1597/1594/1590
1600.6
1598.0
1594.5
1585.0
1490.4
1481.3
1454.6
1449.7
1383.2
1321.9
1318.6
1305.0
1294.6
1206.2
1171.9
1157.0
1156.6
1151.9
1126.1
1076.1
1075.5
1021.4
1020.3
995.1
19.0
1.1
␥CH
759.6
742.7
684.9
683.2
644.2
617.4
613.1
606.0
560.8
515.7
498.5
465.2
410.9
409.8
403.6
348.1
288.0
221.1
203.2
158.5
99.7
51.4
68.4
32.6
23.7
67.4
4.2
771/761
753/751
691
192.3
10.3
29.4
195.4
2.5
2.9
14.4
0.9
␶ ring
␦CH
1502/1489/1486/1481
␦CCC
␦NCN
␶ ring
655
638/634
n.o.
n.o.
1395/1390/1383
1318
1.4
72.3
31.2
11.0
9.8
0.8
0.0
0.1
0.7
19.1
0.3
0.0
4.8
0.9
4.1
0.6
0.3
0.3
␯NCN s.
␦CH
583/578
n.i.
␦CCC
␶ ring
8.1
1.6
1288
␯CC
␯C−O
␦CH
10.5
289.6
3.0
31.3
2.7
13.6
13.5
11.0
7.7
␦CCN
Skeletal
␥CN
␥CO
Skeletal
1262/1249/1241/1222/1216
n.o.
1166/1161
1153/1146
1127
1074
1056
1027
␯C−N
␦CH
␯CC
2.4
17.5
0.7
74.3
31.8
18.4
13.6
␶C−O
␶Ph−N
␶N−O
␦CCC
n.o.
n.o.
989.9
1.8
0.4
Note: Calculated frequencies (␯ (cm−1)) scaled by 0.978; IR intensities in km mol−1. ␯, bond stretching; ␦, bending; ␥, rocking; ␶, torsion; Ph, phenyl ring; as.,
antisymmetric; s., symmetric; n.o., not observed; n.i. not investigated.
is the one whose characteristic spectrum better matches the spec-
trum of the photoproduced species. The comparison of the cal-
culated infrared spectra of the other putative photoproducts
(specifically, the isomeric nitrilimine, diazirine, and cyanamide;
see Scheme 2 and Fig. S3) with that of the observed photoproduct
allowed us to safely discard them as contributors to the observed
spectrum.
A strong indication supporting the identification of the carbo-
diimide as the observed product of photolysis of 5PPT is the pres-
ence in the spectrum of the characteristic intense and structured
band centered at ϳ2133 cm−1, exhibiting satellite bands centered
at ϳ2250 and ϳ2230 cm−1 (see Fig. 5; top panels), which is a very
characteristic spectroscopic signature of carbodiimides (␯N=C=N
antisymmetric stretching).41–44 In the studied low-frequency re-
gion between 1650 and ϳ600 cm−1, the predicted spectrum for the
carbodiimide fits also rather well the experimental spectrum of
the photoproduct (see Table 3 for proposed assignments), with
two notable exceptions: the calculations predict the ␯C–O and
␯N–O stretching modes of the molecule to appear as relatively
intense bands at approximately 1206 and 886 cm−1, respectively,
while no prominent bands are observed at these frequencies in
the experimental spectrum. However, a broad band spreading
from 893 to 905 cm−1 is indeed observed in the experimental
spectrum, which can be correlated with the ␯N–O vibration of the
carbodiimide, while in the 1215–1265 cm−1 range, the experimen-
tal spectrum presents a series of at least five low-intensity bands
that one can assign to the ␯C–O vibration. The main reason for the
observed intensity smearing of the ␯C–O and ␯N–O bands shall be
ascribed to the fact that these two vibrations are very much sen-
sitive to the molecular conformation about the N–O bond of the
molecule. The ␶N–O torsional coordinate is in fact extremely flex-
ible, the calculated vibrational frequency for this mode being only
13.5 cm−1. This result correlates with a very flat ␶N–O torsional
potential, leading to large amplitude torsional movements even if
one restricts the movement to the zero vibrational level, and also
to a rather slow vibration compared with the ␯C–O and ␯N–O
stretching modes. This band intensity smearing phenomenon has
been observed in other molecules exhibiting low frequency, large
amplitude torsional vibrations, e.g., azobenzene,45 and dimeth-
yloxalate.46 For the considered carbodiimide, calculations of the
vibrational frequencies along the ␶N–O torsion,47 for values of the
torsional angle deviated from the equilibrium geometry within
60°, showing that in the studied spectral region, only three vibra-
tions with large enough predicted IR intensity (above 5 km mol−1)
have frequencies that are significantly influenced by the torsional
angle. These are precisely the ␯C–O and ␯N–O modes plus the
␯N=C=N antisymmetric stretching (which, as mentioned above, is
a broad band and does also exhibit quite pronounced satellite
Published by NRC Research Press

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
Borba et al.
9
(5) Koldobskii, G. I.; Ostrovskii, V. A.; Poplavskii, V. S. Khim. Geterot. Soed. 1981,
10, 1299.
(6) Gaponik, P. N.; Voitekhovich, S. V.; Ivashkevich, O. A. Russ. Chem. Rev. 2006,
75, 507. doi:10.1070/RC2006v075n06ABEH003601.
(7) Stierstorfer, J.; Tarantik, K. R.; Klapötke T. M. Chem. Eur. J. 2009, 15, 5775.
doi:10.1002/chem.200802203.
(8) Herr, R. J. Bioorg. Med. Chem. 2002, 10, 3379. doi:10.1016/S0968-0896(02)00239-0.
(9) May, B. C. H.; Abell, A. D. J. Chem. Soc., Perkin Trans. 1 2002, 172. doi:10.1039/
B109128J.
(10) Bugalho, S. C. S.; Lapinski, L.; Cristiano, M. L. S.; Frija, L. M. T.; Fausto, R. Vib.
Spectrosc. 2002, 30, 213. doi:10.1016/S0924-2031(02)00028-0.
(11) Hussey, B. J.; Johnstone, R. A. W.; Entwistle, J. D. Tetrahedron 1982, 38, 3775.
doi:10.1016/0040-4020(82)80091-4.
(12) Johnstone, R. A. W.; Wilby, A. H.; Entwistle, I. D. Chem. Rev. 1985, 85, 129.
doi:10.1021/cr00066a003.
bands, in line with the present interpretation). For these three
modes, the calculated frequency shifts are 20, 30, and 27 cm−1,
respectively, which are considerably larger than the mean abso-
lute shift for all of the remaining 52 modes lying in the probed
spectral region, which is smaller than 5 cm−1.
It is also interesting to note that the carbodiimide is, among the
isomeric molecules shown in Scheme 2, the species having the
lowest energy. According to the performed B3LYP/6-311++G(d,p)
calculations on all of those molecules, the carbodiimide is 1.69,
54.13, and 55.02 kJ mol−1 more stable than its isomeric cyanamide,
nitrilimine, and diazirine, respectively. This is an additional argu-
ment in favor of the observation of the carbodiimide as the final
product of photolysis of 5PPT.
(13) Cristiano, M. L. S.; Johnstone, R. A. W.; Price, P. J. J. Chem. Soc. Perkin Trans. 1
1996, 1453. doi:10.1039/P19960001453.
(14) Araújo, N. C. P.; Brigas, A. F.; Cristiano, M. L. S.; Frija, L. M. T.;
Guimarães, E. M. O.; Loureiro, R. M. S. J. Mol. Catal. A 2004, 215, 113. doi:10.
1016/j.molcata.2003.12.033.
(15) Frija, L. M. T.; Cristiano, M. L. S.; Guimarães, E. M. O.; Martins, N. C.;
Loureiro, R. M. S. S.; Bickley, J. F. J. Mol. Catal. A 2005, 242, 241. doi:10.1016/
j.molcata.2005.08.022.
(16) Gómez-Zavaglia, A.; Reva, I. D.; Frija, L. M. T.; Cristiano, M. L. S.; Fausto, R.
J. Photochem. Photobiol., A 2006, 179, 243. doi:10.1016/j.jphotochem.2005.08.
021.
(17) Frija, L. M. T.; Ismael, A.; Cristiano, M. L. S. Molecules 2010, 15, 3757. doi:10.
3390/molecules15053757.
(18) Frija, L. M. T.; Cristiano, M. L. S.; Gómez-Zavaglia, A.; Reva, I.; Fausto, R.
J. Photochem. Photobiol., C 2014, 18, 71. doi:10.1016/j.jphotochemrev.2013.09.
001.
(19) Gómez-Zavaglia, A.; Reva, I. D.; Frija, L. M. T.; Cristiano, M. L. S.; Fausto, R.
J. Phys. Chem. A 2005, 109, 7967. doi:10.1021/jp0517706.
(20) Gómez-Zavaglia, A.; Reva, I.; Frija, L. M. T.; Cristiano, M. L. S.; Fausto, R. J. Mol.
Struct. 2006, 786, 182. doi:10.1016/j.molstruc.2005.08.019.
(21) Ismael, A.; Cristiano, M. L. S.; Fausto, R.; Gómez-Zavaglia, A. J. Phys. Chem. A
2010, 114, 13076. doi:10.1021/jp109215q.
(22) Alves, J. A. C.; Barkley, J. V.; Brigas, A. F.; Johnstone, R. A. W. J. Chem. Soc.,
Perkin Trans. 2 1997, 669. doi:10.1039/A607912A.
(23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.;
Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.;
Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.;
Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.;
Tomasi, J.; Cossi, M.; Rega, N.; Millam, M. J.; Klene, M.; Knox, J. E.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;
Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.; Foresman, J. B.;
Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision D.01; Gaussian, Inc.:
Wallingford, CT, 2009.
(24) Becke, A. D. Phys. Rev. A 1988, 38, 3098. doi:10.1103/PhysRevA.38.3098.
(25) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785. doi:10.1103/
PhysRevB.37.785.
(26) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200. doi:10.1139/p80-
159.
(27) Frisch, M. J.; Head-Gordon, M.; Pople, J. A. Chem. Phys. Lett. 1990, 166, 281.
doi:10.1016/0009-2614(90)80030-H.
(28) Császár, P.; Pulay, P. J. Mol. Struct. 1984, 114, 31. doi:10.1016/S0022-2860(84)
87198-7.
Conclusions
5-Phenoxy-1-phenyltetrazole was isolated in argon and N2 cryo-
genic matrices and its molecular structure, conformational
landscape, vibrational signature, and photochemistry were inves-
tigated by infrared spectroscopy and theoretical calculations
(DFT(B3LYP)/6-311++G(d,p)). Two different minima were located on
the potential energy surface of the molecule, both being eightfold
degenerate by symmetry and belonging to the C1 symmetry point
group. However, consideration of zero-point vibrational energy
allowed concluding that the higher energy minimum shall relax
barrierlessly to the lower energy form so that in the gas phase, the
compound exists in a single conformer. These theoretical predic-
tions were confirmed by the experimental results, with only one
conformer of 5PPT contributing to the infrared spectra of the
compound isolated in argon and N2 matrices. Structural details of
the different conformations and intramolecular interactions op-
erating in 5PPT were used to understand the conformational pref-
erences of the compound.
The infrared spectra of 5PPT in the studied matrices were fully
assigned and interpreted with help of normal coordinate analysis.
UV laser irradiation (␭ = 250 nm) of matrix-isolated 5PPT was
found to lead to photocleavage of the compound to the corre-
sponding carbodiimide accompanied by N2 release. Relevant
characteristics of the experimental spectrum of the observed pho-
toproduct, specifically the intensity smearing noticed in the ␯N–O
and ␯C–O spectral regions, were interpreted based on the effect of
the low-frequency, large-amplitude ␶N–O mode in this compound.
Supplementary material
Supplementary material is available with the article through
the journal Web site at http://nrcresearchpress.com/doi/suppl/
10.1139/cjc-2015-0025. Supporting information: Figure S1 with the
1H NMR spectrum of 5PPT in CDCl3, Fig. S2 with the UV-visible
spectra of 5PPT in ethanol, Fig. S3 with calculated infrared spectra
for considered possible products resulting from photoelimination
of N2 from 5PPT, and Table S1 with the definition of the internal
coordinates used in the normal modes analysis calculations per-
formed on 5PPT.
(29) Peng, C.; Schlegel, H. B. Isr. J. Chem. 1994, 33, 449.
(30) Irikura, K. K. Program SYNSPEC; National Institute of Standards and
Technology: Gaithersburg, MD.
(31) Keresztury, G.; Jalsovszky, G. J. Mol. Struct. 1971, 10, 304. doi:10.1016/0022-
2860(71)87090-4.
(32) Rostkowska, H.; Lapinski, L.; Nowak, M. J. Vib. Spectrosc. 2009, 49, 43. doi:10.
1016/j.vibspec.2008.04.012.
(33) Pulay, P.; Fogarasi, G.; Pang, F.; Boggs, J. E. J. Am. Chem. Soc. 1979, 101, 2550.
doi:10.1021/ja00504a009.
(34) Batista de Carvalho, L. A. E.; Teixeira-Dias, J. J. C.; Fausto, R. Struct. Chem.
1990, 1, 533. doi:10.1007/BF00674129.
(35) Pearson, R.; Lovas, F. J. Chem. Phys. 1977, 66, 4149. doi:10.1063/1.434490.
(36) Cradock, S.; Purves, C.; Rankin, D. W. H. J. Mol. Struct. 1990, 220, 193. doi:10.
1016/0022-2860(90)80109-W.
Acknowledgements
The authors gratefully acknowledge Fundação para a Ciência e
a Tecnologia (FCT), Portugal (Projects PEst-OE/QUI/UI0313/2014
and PEst-C/MAR/LA0015/2014, cofunded by QREN-COMPETE-UE),
and CCMAR for financial support. A.B. and L.C. acknowledge
FCT and CCMAR, respectively, for the award of a postdoctoral
grant (reference SFRH/BPD/66154/2009) and a research fellowship.
(37) Fernholt, L.; Römming, C. Acta Chem. Scand. 1978, 32, 271. doi:10.3891/acta.
chem.scand.32a-0271.
(38) Bormans, B. J. M.; de With, G.; Mijlhoff, F. C. J. Mol. Struct. 1977, 42, 121.
doi:10.1016/0022-2860(77)87035-X.
References
(1) Bugalho, S. C. S.; Maçôas, E. M. S.; Cristiano, M. L. S.; Fausto, R. Phys. Chem.
Chem. Phys. 2001, 3, 3541. doi:10.1039/b103344c.
(2) Mohite, P.-B.; Bhaskar, V. H. Int. J. PharmTech Res. 2011, 3, 1557.
(3) Sandmann, G.; Schneider, C.; Boger, P. Z. Naturforsch. C 1996, 51, 534.
(4) Zhao-Xu, C.; Heming, X. Int. J. Quantum Chem. 2000, 79, 350. doi:10.1002/1097-
461X(2000)79:6<350::AID-QUA3>3.3.CO;2-K.
(39) Gómez-Zavaglia, A.; Reva, I. D.; Frija, L. M. T.; Cristiano, M. L. S.; Fausto, R.
J. Photochem. Photobiol., A 2006, 180, 175. doi:10.1016/j.jphotochem.2005.10.012.
(40) Frija, L. M. T.; Reva, I. D.; Gómez-Zavaglia, A.; Cristiano, M. L. S.; Fausto, R.
J. Phys. Chem. A 2007, 111, 2879. doi:10.1021/jp068556h.
Published by NRC Research Press

Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
10
Can. J. Chem. Vol. 93, 2015
(41) Bégué, D.; Qiao, G. G.; Wentrup, C. J. Am. Chem. Soc. 2012, 134, 5339. doi:10.
1021/ja2118442.
(42) Nunes, C. M.; Araújo-Andrade, C.; Fausto, R.; Reva, I. J. Org. Chem. 2014, 79,
3641. doi:10.1021/jo402744f.
(43) King, S. T.; Strope, J. H. J. Chem. Phys. 1971, 54, 1289. doi:10.1063/1.1674967.
(44) Pagacz-Kostreva, M.; Mucha, M.; Weselski, M.; Wierzejewska, M. J. Photochem.
Photobiol. A 2013, 251, 118. doi:10.1016/j.jphotochem.2012.10.023.
(45) Duarte, L.; Fausto, R.; Reva, I. Phys. Chem. Chem. Phys. 2014, 16, 16919. doi:10.
1039/C4CP00240G.
(46) Lopes, S. B.; Lapinski, L.; Fausto, R. Phys. Chem. Chem. Phys. 2002, 4, 5952.
doi:10.1039/B206270B.
(47) The ␶N–O mode does not mix with others, so that optimization of geometry
of the molecule for different values of this coordinate leads to vanishing
forces on atoms along all of the remaining coordinates, thus making mean-
ingful the vibrational calculations for geometries other than the equilib-
rium geometry.
Published by NRC Research Press