Reversible Photoisomerization among Triplet Amino Naphthylnitrene, Triplet Diimine Biradical, and Indazole: Matrix-Isolation IR Spectra of 8-Amino-1-naphthylnitrene, 1,8-Naphthalenediimine, and 1,2-Dihydrobenz[cd]indazole

Article abstract of DOI:10.1021/acs.jpca.7b00154

Reaction mechanisms of nitrene, one of the most famous biradicals, have been frequently studied, and many spectral data have been obtained so far. In the present study, the experimental IR spectra of triplet 8-amino-1-naphthylnitrene (³ANN), a triplet diimine biradical 1,8-dihydro-1,8-naphthalenediimine (³DND), and 1,2-dihydrobenz[cd]indazole (DBI), which are produced in the UV photolysis of 1,8-diaminonaphthalene in an Ar matrix and identified by a combination method of IR spectroscopy and DFT quantum chemical calculations, are first reported. ³ANN is found to change to DBI by hydrogen-atom migration with bond making between the two nitrogen atoms upon visible-light irradiation (λ > 580 nm) with its backward reaction caused by 350 nm irradiation. In addition, ³ANN isomerizes to ³DND by 700 nm irradiation, while its backward reaction occurs upon 500 nm irradiation. The wavelength dependences of these photoisomerizations are explained in terms of their electronic transition energies estimated by time-dependent DFT calculations. It is concluded that the novel reversible photoisomerization system among ³ANN, ³DND, and DBI is totally different from the well-known photoisomerization between phenylnitrene and a seven-membered cyclic compound.

Full text of DOI:10.1021/acs.jpca.7b00154

Article
pubs.acs.org/JPCA
Reversible Photoisomerization among Triplet Amino
Naphthylnitrene, Triplet Diimine Biradical, and Indazole: Matrix-
Isolation IR Spectra of 8‑Amino-1-naphthylnitrene, 1,8-
Naphthalenediimine, and 1,2-Dihydrobenz[cd]indazole
Takuya Okamura, Nobuyuki Akai,* and Munetaka Nakata*
Graduate School of Bio-Applications and Systems Engineering (BASE), Tokyo University of Agriculture and Technology, 2-24-16
Naka-cho, Koganei city, Tokyo 184-8588, Japan
S
* Supporting Information
ABSTRACT: Reaction mechanisms of nitrene, one of the most famous biradicals, have been
frequently studied, and many spectral data have been obtained so far. In the present study, the
experimental IR spectra of triplet 8-amino-1-naphthylnitrene (3ANN), a triplet diimine biradical
1,8-dihydro-1,8-naphthalenediimine (3DND), and 1,2-dihydrobenz[cd]indazole (DBI), which are
produced in the UV photolysis of 1,8-diaminonaphthalene in an Ar matrix and identified by a
combination method of IR spectroscopy and DFT quantum chemical calculations, are first
3
reported. ANN is found to change to DBI by hydrogen-atom migration with bond making
between the two nitrogen atoms upon visible-light irradiation (λ > 580 nm) with its backward
3
3
reaction caused by 350 nm irradiation. In addition, ANN isomerizes to DND by 700 nm
irradiation, while its backward reaction occurs upon 500 nm irradiation. The wavelength
dependences of these photoisomerizations are explained in terms of their electronic transition
energies estimated by time-dependent DFT calculations. It is concluded that the novel reversible
3
3
photoisomerization system among ANN, DND, and DBI is totally different from the well-
known photoisomerization between phenylnitrene and a seven-membered cyclic compound.
3
Scheme 1. Reversible Photoisomerization among ANN,
INTRODUCTION
■
3DND(2), and t-DBI
Nitrenes are important intermediates in chemical organic
reactions, and many researchers have conducted to exper-
imentally identify various nitrenes usually produced by
photolysis or pyrolysis of the corresponding azido com-
pounds.1−4 One of the simplest nitrene is well-known
phenylnitrene, which shows a unique reversible photoisomeri-
zation; phenylnitrene changes to azacyclrohepta-1,3,5,6-tet-
raene, a seven-membered ring compound, by 485 nm
irradiation with its backward reaction by 334 nm irradiation.5,6
The reversible photoinduced isomerization has been frequently
investigated so far,7−9 and some analogous systems have been
found; for example, 1-naphthylnitrene reversibly isomerizes to
the corresponding azirine and a seven-membered cyclic
ketenimine.10 However, besides the above phenylnitrene
systems, fewer reversible photoisomerization systems including
nitrenes have been reported.1,3
In this study, novel reversible photoinduced isomerization
systems among a triplet nitrene, 8-amino-1-naphthylnitrene
(3ANN), a triplet biradical, 1,8-dihydro-1,8-naphthalenediimine
(3DND), and 1,2-dihydrobenz[cd]indazole (DBI) without the
corresponding azirine and seven-membered cyclic ketenimine
(7-CK) were fortuitously found in the photolysis of 1,8-
diaminonaphtharene (DAN) isolated in an Ar matrix, as shown
in Scheme 1. One may try to synthesize 3ANN by photolysis of
the corresponding azide, 8-amino-1-azidonaphthalene, as a
standard photoproduction process, but we happened to find
3
that ANN was produced in the photolysis of DAN upon UV
irradiation to yield a new cyclic compound, DBI, in analogous
to the photolysis of 1,2-diaminobenzene to yield 5,6-diimino-
1,3-cyclohexatriene and 7,8-diazabicyclo[4.2.0]octa-1,3,5-tri-
ene.11,12 Here, the observed matrix-isolation IR spectra of
3
3
new three species, ANN, DND and DBI, are reported, and
Received: January 6, 2017
Revised: February 7, 2017
Published: February 14, 2017
© XXXX American Chemical Society
A
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Table 1. Observed and Calculated Wavenumbers (in cm−1)
of t-DBI
then their photoisomerization mechanisms are discussed based
on the experimental results with the aid of time-dependent
density functional theory (TD-DFT) calculations.
a
obsd
calcd
b
v
abs
2.5
v
int
9.9
assignment
EXPERIMENTAL AND CALCULATION METHODS
̃
̃
■
3346
3339
3468
3463
3144
3133
1639
1629
1601
1388
1342
1333
1164
1014
893
v(N−H)
The combination method of matrix-isolation IR spectroscopy
with DFT calculation was used. A small amount of DAN
(Tokyo Chemical Industry) evaporated at 302 K with excess
pure Ar gas was deposited onto a CsI plate at ca. 15 K. All IR
spectra of samples isolated in matrices were measured with an
FT-IR spectrophotometer (Jeol, JIR-7000); the accumulation
number of 100 and the spectral resolution of 0.5 cm−1. A
superhigh-pressure mercury lamp was used as a light source to
induce photoreactions through some shorter-wavelength cutoff
filters. Other experimental details were reported elsewhere.11,12
All calculations including optimized structures and predicted IR
spectral patterns were performed using unrestricted B3LYP
functional with a 6-31++G(d,p) basis set on Gaussian09W.13
3.2
17.1
12.2
19.5
32.7
23.5
44.0
22.1
13.3
8.8
v(N−H)
v(C−H)
v(C−H)
v(C−C)
v(C−C)
v(C−C)
1635
1633
1591
1385
1342
1328
1161
1017
849
7.6
10.9
13.2
13.7
0.9
v(C−C) + δ(N−H)
v(C−C) + δ(N−H)
δ(N−H)
6.9
7.4
5.5
δ(C−H)
v(N−N)
2.0
24.5
6.2
3.3
δip(CCC)+δ(N−H)
δoop(C−H)
v(ring)
841
3.9
838
13.5
35.4
24.1
823
4.2
811
RESULTS AND DISCUSSION
■
809/811
763
15.9
798
δoop(ring)
Upon UV irradiation (λ > 300 nm) for 15 min, DAN isolated in
an Ar matrix multiply yielded chemical species. The measured
IR spectrum was slightly complicated as shown in Figure S1 in
the Supporting Information, and it was hard to identify the
photoproducts clearly. When the matrix sample was exposed to
visible light (λ > 580 nm) for 270 min following the UV
preirradiation (λ > 300 nm), a simple IR spectral change due to
the photoconversion of one photoproduct was measured
(Figure 1). The measured spectrum of the product in the
100
776
100
δoop(N−H)
δoop(C−H)
δoop(C−H)
δip(ring) + δ(N−H)
δip(CNNC)
v(ring)
757
37.0
28.2
9.8
725
707
662
641
620
51.6
5.3
728
712
6.6
666
8.7
17.3
15.5
642
22.7
6.6
619
δoop(ring)
a
Estimated at the B3LYP/6-31++G(d,p) level using a scaling factor of
0.98. Vibrational modes with relative intensities less than 5 are
omitted, but given in Table S1. Symbols of v and δ represent
b
stretching and bending modes, and the subscripts of ip and oop
represent in-plane and out-of-plane modes, respectively.
wavenumbers are consistent with the corresponding theoretical
values for t-DBI, although the band calculated at 757 cm−1 may
be missed by overlapping with the strongest band at 763 cm−1.
Thus, our initial purpose to measure the IR spectrum of a new
species DBI was accomplished successfully.
We recognized more interesting phenomenon in the
difference spectrum shown in Figure 1, i.e., the decreasing
bands were not assigned to the reactant, DAN, but to an
3
unexpected photoproduct ANN, which was confirmed by a
comparison of the observed spectral pattern with the calculated
spectral pattern (Figure 1). The intense decreasing bands
observed at 3509/3500, 1604 cm−1 were assigned to the
characteristic NH2 asymmetric stretching and C-NH2 stretching
mode of 3ANN. The both bands observed at 806 and 720 cm−1
were assigned to the out-of-plane ring bending modes, which
were very close to the reported intense bands in this region of
1-naphthylnitrene.10 The calculated wavenumbers of 3ANN
were consistent with the corresponding observed values
satisfactorily (Table 2). We also found the backward isomer-
Figure 1. (a) Difference spectrum obtained by isomerization from
3ANN to t-DBI upon visible-light irradiation (λ > 580 nm) following
the UV preirradiation (λ > 300 nm). (b) Simulated spectrum
composed of the calculated spectral patterns for 3ANN in the
downside and t-DBI in the upside, obtained at the B3LYP/6-31+
+G(d,p) level using a scaling factor of 0.98.
upside resembles the calculated spectral pattern of t-DBI rather
than that of c-DBI. The notations of t and c represent trans and
cis conformations around the N−N bond for the two hydrogen
atoms bonded to the nitrogen atoms, respectively. Our DFT
calculations showed that t-DBI is more stable than c-DBI by
23.8 kJ mol−1. The increasing bands at 3339, 763, and 725 cm−1
were assignable to the N−H stretching, the N−H bending and
the C−H bending modes of t-DBI, respectively, but not of c-
DBI, (see Figure S2). A comparison of the observed and
calculated wavenumbers is shown in Table 1 with their
vibrational modes. It is found that most of the observed
3
ization from t-DBI to ANN upon UV irradiation (λ > 350
3
nm). The existence of the triplet nitrene ANN has been
previously reported in the photolysis of 8-amino-1-azidonaph-
thalene by ESR study14 but its IR spectrum and reversible
photoisomerization have not been known so far.
3
The nitrene ANN showed one more interesting photo-
isomerization upon visible-light irradiation. A new triplet
3
3
biradical DND was produced from ANN by the secondary
irradiation (λ > 700 nm) after the prephotolysis of DAN by 300
nm irradiation, as shown in Figure 2. Three stable
B
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Table 2. Observed and Calculated Wavenumbers (in cm−1)
3
of ANN
a
obsd
calcd
v
abs
v
int
assignment
v(N−H)
v(N−H)
v(C−H)
v(C−H)
̃
̃
3509/3500
3320
20.7
11.0
3623
3446
3141
3136
1622
1520
1489
1457
1352
1331
1320
1256
1207
1072
1031
791
18.7
12.2
9.1
Figure 3. Optimized structures of 3ANN, 3DND(2), and t-DBI
calculated at the B3LYP/6-31++G(d,p) level. Bond lengths (in Å) of
C−N, O−H, and N−N are written; other bond lengths are given in
Figure S4.
6.2
1604
100
100
v(C−NH2)
v(C−C)
1514/1512
1486/1482
1455
9.7
5.5
9.2
9.3
v(C−C) + v(C−N)
v(C−C) + v(C−N)
v(C−C) + δip(N−H)
v(C−C) + δip(N−H)
v(C−C) + v(C−N)
v(C−C) + δip(N−H)
v(C−C) + δip(N−H)
δip(ring)
and S4). The bands observed at 3279, 1143, 823, and 672/669
cm−1 in Figure 2 satisfactorily corresponded to the calculated
values of 3401, 1140, 809, and 666 cm−1, respectively, which
were assigned to the N−H stretching, the in-plane N−H/C-H
bending, the out-of-plane ring bending and the out-of-plane
17.3
2.0
12.3
3.2
1346
1321
14.7
5.1
12.6
12.3
8.2
1311
1256/1253
1206
14.1
4.3
3
N−H bending modes of DND(2), respectively. The band at
7.5
3387 cm−1 was assigned to a combination band. A comparison
of the observed wavenumbers of 3DND(2) with the
corresponding calculated ones is summarized in Table 3. The
1073
9.6
4.5
1024
2.5
4.6
δip(ring)
806
44.0
12.4
49.3
22.8
1.7
δoop(ring)
743
738
δoop(C−H)
δoop(ring)
Table 3. Observed and Calculated Wavenumbers (in cm−1)
of DND(2)
720
717
21.4
3
a
See the captions in Table 1. All the calculation results are given in
Table S2.
a
obsd
calcd
v
abs
1.9
v
int
6.3
assignment
combination
̃
̃
3387
3279
3067
1550
1519
1385
1351
1342
1178
1143
1074
1042
823
1.2
1.4
3401
3139
1550
1524
1386
1354
1335
1161
1140
1073
1038
809
v(N−H)
v(C−H)
v(C−C)
v(C−C)
v(C−C−N)
δip(N−H)
δip(N−H) + δip(C−H)
δip(N−H)
δip(N−H) + δip(C−H)
δip(ring)
13.3
6.2
7.0
2.5
10.8
19.0
5.4
3.3
3.9
6.4
10.3
5.5
5.7
37.6
16.1
17.3
34.4
22.0
10.8
35.6
δip(CCC) + δip(C−H)
δoop(ring)
100
672/669
650
78.8
11.0
666
100
6.6
δoop(N−H)
δip(ring)
Figure 2. (a) Dfference spectrum obtained by isomerization from
3ANN to 3DND(2) upon visible-light irradiation (λ > 700 nm)
following the UV preirradiation (λ > 300 nm). (b) Simulated spectrum
composed of the calculated spectral patterns for 3ANN in the
downside and DND(2) in the upside, obtained at the B3LYP/6-31+
+G(d,p) level using a scaling factor of 0.98.
646
a
See the captions in Table 1. All the calculation results are given in
Table S3.
3
3
3
backward reaction from DND(2) to ANN upon visible-light
irradiation (λ > 500 nm) was also confirmed. In addition, the
photoisomerization from DND(2) to t-DBI upon 600 nm
3
3
conformations of DND are possible in association with the
relative direction of the two imino groups, as shown in Scheme
1. It is interesting that a simulated spectrum for the most stable
conformer DND(1), having one hydrogen bond between the
irradiation was also confirmed (Figure S5). However, the
backward reaction from t-DBI to 3DND(2) was not induced by
any light used in the present study.
3
hydrogen atom in one imino group and the nitrogen atom in
the other imino group, was inconsistent to the observed one
(see Figure S3). In contrast to this fact, the second stable
conformer 3DND(2) reproduced the difference spectrum
satisfactorily, as shown in Figure 2, where the simulated
spectrum is composed of the calculated spectral patterns of
It must be explained that no bands of the most stable
3
3
conformer DND(1) and the third stable conformer DND(3)
were observed upon 700 nm irradiation. One possibility is the
3
3
conversion from DND(1) to ANN through the hydrogen-
atom tunneling, where the transition barrier height, 52.3 kJ
mol−1, is too high for the thermal conversion at such low-
3
3ANN in the downside and DND(2) in the upside.
3
temperature condition. On the other hand, DND(3) could
3
The biradical DND(2) has a feature of double interaction
immediately isomerize to DBI, because the geometrical
structures of the both species are similar to each other.
between the hydrogen atom of one •N−H group and the
nitrogen atom in the other •N−H group, as shown in Figure 3,
where the two imino groups twist from a quasi-planar
3
However, the energy of DBI is predicted to be about 150 kJ
3
mol−1 higher than DND(3). Thus, we remove the possibility
3
3
3
naphthalene part (see the side view of DND(2) in Figures 3
of the isomerization from DND(3) to DBI on the triplet
C
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3
potential surface. Another possibility is that DND(3) changes
to 3DND(1), where the barrier height from 3DND(3) to
concluded that the photon energies required for the photo-
reaction processes were explainable in terms of triplet−triplet
transition energies estimated by TD-DFT calculations.
3DND(1) is 27.3 kJ mol−1, and then DND(1) changes to
3
3ANN by the tunneling,4,15−17 resulting in the detection of only
the bands due to 3DND(2), although we have no more
experimental evidence on this assumption.
ASSOCIATED CONTENT
■
S
* Supporting Information
3
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jpca.7b00154.
The triplet nitrene ANN with a quasi-planar structure is
more stable than the singlet one ANN by 92.9 kJ mol−1
1
(Figure 4). The low triplet−triplet transition energies were
Comparison of the observed IR spectra with those of the
other isomers, their optimized structures, and all
wavenumbers theoretically estimated by the B3LYP/6-
31++G(d,p), and a complete ref 13 (PDF)
AUTHOR INFORMATION
Corresponding Authors
*(N.A.) E-mail: akain@cc.tuat.ac.jp. Telephone: +81-42-388-
7344.
■
*(M.N.) E-mail: necom816@cc.tuat.ac.jp. Telephone: +81-42-
388-7349.
ORCID
Nobuyuki Akai: 0000-0002-5722-4596
Figure 4. Relative energies of possible photoproducts obtained by the
DFT calculations at the B3LYP/6-31++G(d,p) level, where triplet
states are drawn by blue lines. Since the relative energies of the lowest
triplet states for t-DBI, c-DBI, 7CK, and azirine are estimated to be
146.78, 210.07, 103.89, and 269.38 kJ mol−1, respectively, they are out
of range on this scale.
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
estimated by the TD-DFT calculation to be 692, 621, and 437
nm, which are consistent with the experimental results on the
photoinduced isomerization observed in the present study;
ACKNOWLEDGMENTS
This work was supported by a JSPS KAKENHI grant, Number
16K05644.
■
3
3ANN changed to DND(2) by 700 nm irradiation and to t-
DBI by 580 nm irradiation, implying that the former
isomerization occurs through the first electronic transition
state, while the latter isomerization occurs through the second
one.
REFERENCES
■
(1) Tomioka, H. Versatile Reaction Undergone by Carbenes and
Nitrenes in Noble Gas Matrices at Cryogenic Temperatures. Bull.
Chem. Soc. Jpn. 1998, 71, 1501−1524.
(2) Gritsan, N. P.; Platz, M. S. Kinetics, Spectroscopy, and
Computational Chemistry of Arylnitrenes. Chem. Rev. 2006, 106,
3844−3867.
(3) Li, H.; Wu, Z.; Li, D.; Zeng, X.; Beckers, H.; Francisco, J. S. A
Singlet Thiophosphoryl Nitrene and Its Interconversion with Thiazyl
and Thionitroso Isomers. J. Am. Chem. Soc. 2015, 137, 10942−10945.
(4) Nunes, C. M.; Knezz, S. N.; Reva, I.; Fausto, R.; McMahon, R. J.
Evidence of a Nitrene Tunneling Reaction: Spontaneous Rearrange-
ment of 2-Formyl Phenylnitrene to an Imino Ketene in Low-
Temperature Matrixes. J. Am. Chem. Soc. 2016, 138, 15287−15290.
(5) Chapman, O. L.; LeRoux, J. P. 1-Aza-1,2,4−6-cycloheptatetraene.
J. Am. Chem. Soc. 1978, 100, 282−285.
The low triplet−triplet transition energies of 3DND(2) were
estimated to be 596, 523, and 467 nm. Our experimental results
3
showed the photoinduced isomerization from DND(2) to t-
DBI by 600 nm irradiation, and to 3ANN by 500 nm
irradiation, respectively. We conclude that the former and the
latter correspond to the first (596 nm) and the second (523
nm) calculated transitions. In addition, our DFT calculations
summarized in Figure 4 can explain the fact that a seven-
membered cyclic ketenimine (7CK) and azirine were
undetected in the photolysis of DAN, because they are less
stable than t-DBI by more than 130 kJ mol−1.
(6) Chapman, O. L.; Sheridan, R. S.; LeRoux, J. P. Photochemical
Interconversion of Phenylnitrene and the Isomeric Pyridylmethylenes.
J. Am. Chem. Soc. 1978, 100, 6245−6247.
(7) Hayes, J. C.; Sheridan, R. S. The IR Spectrum of Triplet
Phenylnitrene. On the Origin of Didehydroazepine in Low Temper-
ature Matrices. J. Am. Chem. Soc. 1990, 112, 5879−5881.
(8) Burdzinski, G. T.; Middleton, C. T.; Gustafson, T. L.; Platz, M. S.
Solution Phase Isomerization of Vibrationally Excited Singlet Nitrenes
to Vibrationally Excited 1,2-Didehydroazepine. J. Am. Chem. Soc. 2006,
128, 14804−14805.
(9) Inui, H.; Sawada, K.; Oishi, S.; Ushida, K.; McMahon, R. J. Aryl
Nitrene Rearrangements: Spectroscopic Observation of a Benzazirine
and Its Ring Expansion to a Ketenimine by Heavy-Atom Tunneling. J.
Am. Chem. Soc. 2013, 135, 10246−10249.
(10) Maltsev, A.; Bally, T.; Tsao, M.-L.; Platz, M. S.; Kuhn, A.;
Vosswinkel, M.; Wentrup, C. The Rearrangements of Naphthylni-
CONCLUSIONS
■
3
3
IR spectra of ANN, DND(2), and t-DBI produced in the
photolysis of DAN in an Ar matrix were first measured in the
present experiment. By a comparison of the DFT calculations
3
with the observed spectra, the conformations of DND(2) and
t-DBI were determined; the former is the second stable
conformer having feature intramolecular interaction in the two
imino groups twisted from a quasi-planar naphthalene part; the
latter is the more stable conformer having trans positions in
association with two hydrogen atoms in the NH groups. The
prototype isomerization systems from ANN to DND(2) and
to t-DBI were found, which was contrast to the well-known
reversible isomerization between triplet naphthylnitrenes and
the corresponding seven-membered ring compounds.10 It was
3
3
D
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Article
trenes: UV/Vis and IR Spectra of Azirines, Cyclic Ketenimines, and
Cyclic Nitrile Ylides. J. Am. Chem. Soc. 2004, 126, 237−249.
(11) Akai, N.; Kudoh, S.; Nakata, M. UV Photolysis of 1,4-
Diaminobenzene in a Low-Temperature Argon Matrix to 2,5-
Cyclohexadiene-1,4-diimine via 4-Aminoanilino Radical. J. Phys.
Chem. A 2003, 107, 6725−6730.
(12) Ujike, K.; Akai, N.; Kudoh, S.; Nakata, M. Photoisomerization
and Photocyclization of 3,5-Cyclohexadiene-1,2-diimine and Its
Methyl-substituted Derivatives in Low-Temperature Argon Matrices.
J. Mol. Struct. 2005, 735−736, 335−342.
(13) 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. et al.; Gaussian 09W, Revision C.01; Gaussian,
Inc.: Wallingford CT, 2009. The complete author list is given in the
Supporting information.
(14) Platz, M. S.; Carrol, G.; Pierrat, F.; Zayas, J.; Auster, S. Some
Observations of Various 1,8 Naphthoquinodimethane Biradicals by
Electron Spin Resonance Spectroscopy. Tetrahedron 1982, 38, 777−
785.
(15) Nanbu, S.; Sekine, M.; Nakata, M. Hydrogen-Atom Tunneling
in Isomerization Around the C-O Bond of 2-Chloro-6-fluorophenol in
Low-Temperature Argon Matrixes. J. Phys. Chem. A 2011, 115, 9911−
9918.
(16) Henkel, S.; Huynh, Y.; Neuhaus, P.; Winkler, M.; Sander, W.
Tunneling Rearrangement of 1-Azulenylcarbene. J. Am. Chem. Soc.
2012, 134, 13204−13207.
(17) Halasa, A.; Lapinski, L.; Reva, I.; Rostkowska, H.; Fausto, R.;
Nowak, M. J. Three Conformers of 2-Furoic Acid: Structure Changes
Induced with Near-IR Laser Light. J. Phys. Chem. A 2015, 119, 1037−
1047.
E
DOI: 10.1021/acs.jpca.7b00154
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