Chlorodifluoroacetyl isocyanate, ClF2CC(O)NCO: Preparation and structural and spectroscopic studies

Article abstract of DOI:10.1021/jp3096055

Chlorodifluoroacetyl isocyanate, ClF₂CC(O)NCO, was prepared by the reaction of ClF₂CC(O)Cl with excess of AgNCO. The colorless compound melts at -83 °C and the vapor pressure follows the equation ln p = -3868.3 (1/T) + 10.89 (p [Atm], T [K]) in the range -38 to +22 °C, extrapolated bp ca. 82 °C. It has been characterized by IR (gas phase, Ar matrix), liquid Raman, ¹⁹F and ¹³C NMR, gas UV-vis spectrum, photoelectron spectroscopy (PES), photoionization mass spectrometry (PIMS), and gas electron diffraction (GED). The matrix photochemistry has been studied and the conformational properties of ClF₂CC(O)NCO have been analyzed by joint application of vibrational spectroscopy, GED, and quantum chemical calculations. Two conformers were detected in gaseous and liquid phases, in which the C-Cl bond adopts a gauche orientation with respect to the C=O group, whereas this group can be in syn or anti orientation with respect to the N=C bond of the NCO group. An enthalpy difference δHexp° = 1.3 ± 0.2 kcal mol^-1 between the most stable syn-gauche and the less stable anti-gauche form was derived using the van't Hoff equation, which is in reasonable agreement with the computed difference of δH° = 0.8 kcal mol^-1 (B3LYP/6-311+G(3df) approximation). The most significant gas phase structural parameters for gauche-syn ClF₂CC(O)NCO are r_e(NC=O) = 1.157(1) A, r_e(N=CO) = 1.218(1) A, r_e(N-C) = 1.378(9) A, r_e(C=O) = 1.195(1) A,_e(CNC) = 128.6(19)°. Photolysis of ClF ₂CC(O)NCO using an ArF excimer laser (193 nm) mainly yield ClF ₂CNCO along with some ClF₂CC(O)N nitrene. The valence electronic properties of the title compound were studied using the PES and PIMS. The experimental first vertical ionization energy of 11.54 eV corresponds to the ejection of a carbonylic oxygen lone pair electron.

Full text of DOI:10.1021/jp3096055

Article
pubs.acs.org/JPCA
Chlorodifluoroacetyl Isocyanate, ClF CC(O)NCO: Preparation and
2
Structural and Spectroscopic Studies
†
†
†
‡
‡,#
Luis A. Ramos, Sonia E. Ulic, Rosana M. Romano, Yury V. Vishnevskiy, Raphael J. F. Berger,
‡
§
§
∥
∥
Norbert W. Mitzel, Helmut Beckers, Helge Willner, Shengrui Tong, Maofa Ge,
,
†
́
and Carlos O. Della Vedova*
†CEQUINOR (UNLP-CONICET), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47
esq. 115, 1900 La Plata, Republica Argentina
r Anorganische Chemie und Strukturchemie, Universitat
Fachbereich C - Anorganische Chemie, Bergische Universitat Wuppertal, 42097 Wuppertal, Germany
State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences,
́
‡
§
∥
Lehrstuhl fu
̈
̈ ̈
Bielefeld, Universitatsstraße 25, 33615 Bielefeld, Germany
̈
Beijing 100190, China
*
S Supporting Information
ABSTRACT: Chlorodifluoroacetyl isocyanate, ClF CC(O)-
2
NCO, was prepared by the reaction of ClF CC(O)Cl with
2
excess of AgNCO. The colorless compound melts at −83 °C
and the vapor pressure follows the equation ln p = −3868.3
(
1/T) + 10.89 (p [Atm], T [K]) in the range −38 to +22 °C,
extrapolated bp ca. 82 °C. It has been characterized by IR (gas
1
9
13
phase, Ar matrix), liquid Raman, F and C NMR, gas UV−
vis spectrum, photoelectron spectroscopy (PES), photo-
ionization mass spectrometry (PIMS), and gas electron
diffraction (GED). The matrix photochemistry has been
studied and the conformational properties of ClF CC(O)-
2
NCO have been analyzed by joint application of vibrational spectroscopy, GED, and quantum chemical calculations. Two
conformers were detected in gaseous and liquid phases, in which the C−Cl bond adopts a gauche orientation with respect to the
CO group, whereas this group can be in syn or anti orientation with respect to the NC bond of the NCO group. An
−
1
enthalpy difference ΔH° = 1.3 ± 0.2 kcal mol between the most stable syn−gauche and the less stable anti-gauche form was
exp
−1
derived using the van’t Hoff equation, which is in reasonable agreement with the computed difference of ΔH° = 0.8 kcal mol
(
B3LYP/6-311+G(3df) approximation). The most significant gas phase structural parameters for gauche−syn ClF CC(O)NCO
2
are r (NCO) = 1.157(1) Å, r (NCO) = 1.218(1) Å, r (N−C) = 1.378(9) Å, r (CO) = 1.195(1) Å, ∠ (CNC) =
e
e
e
e
e
1
28.6(19)°. Photolysis of ClF CC(O)NCO using an ArF excimer laser (193 nm) mainly yield ClF CNCO along with some
2
2
ClF CC(O)N nitrene. The valence electronic properties of the title compound were studied using the PES and PIMS. The
2
experimental first vertical ionization energy of 11.54 eV corresponds to the ejection of a carbonylic oxygen lone pair electron.
INTRODUCTION
SNCO, CH OC(O)SNCO, OV(NCO) , ONNCO, N NCO,
3 3 3
■
FNCO, and CClF NCO (see refs 4−6 and references cited
2
Isocyanates, i.e., derivatives of the isocyanic acid, have a wide
range of applications, but also present very basic challenges.
They are precursors in the formation of polyurethane polymers
and thus have a variety of important technological applica-
therein). These contributions include preparation, chemical,
physical, and spectroscopic studies of the compounds. The
molecule ClC(O)NCO challenges the reliability of ab initio
7
1
,2
calculations. The conformational properties of the molecules
tions including adhesives, sealants and paints, and flexible and
rigid foams. However, fundamental aspects of the isocyanates
are also of interest. Off-axis substitution on a pseudohalogen of
the type azide, isothiocyanate, or isocyanate leads to interesting
spectroscopic consequences caused by splitting of the π
XC(O)NCO (X = F, Cl, Br, and CH ) are of interest: the syn
3
conformation in equilibrium with a lower concentration of the
anti form seems to be preferred for Cl, Br, and CH3
compounds, whereas for FC(O)NCO the anti rotamer (65%)
3
is the most stable form. Very few molecules provide vibrational
degeneration.
8
spectra so rich in information as FC(O)NCO.
Our fundamental studies on the bonding and properties of
isocyanates containing molecules has included a large series of
molecules: S(NCO) , FC(O)NCO, ClC(O)NCO, BrC(O)-
Received: September 27, 2012
Revised: November 1, 2012
Published: November 1, 2012
2
NCO, CH C(O)NCO, FSO NCO, ClSO NCO,
3
2
2
CF SO NCO, F NC(O)NCO, ClCH CH NCO, FC(O)-
3
2
2
2
2
©
2012 American Chemical Society
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Article
Another interesting result concerning isocyanates is the
mechanism of its UV photoevolution from carbonyl azides.
Carbonyl azides can photoevolve to two different products,
carbonyl nitrenes and the Curtius-rearranged isocyanate
Raman spectra of the neat liquid at room temperature were
measured in flame-sealed capillaries (3 mm o.d.) on a Bruker
RFS 106/S spectrometer, equipped with a 1064 nm Nd:YAG
laser, in the region from 4000 to 100 cm− using 2 cm of
1
−1
9
molecule. Our interest covers also the electronic characteristics
resolution.
of the isocyanates, see for instance the PES study of S(NCO)
(c). Matrix Isolation Experiments. For matrix isolation
2
10
and the results derived by using this spectroscopy. In the
present work we will combine all these studies to gain a detailed
understanding of the title species. Consequently, for chlorodi-
experiments ClF CC(O)NCO was diluted with argon in a ratio
2
of 1:2000 in a 1 L stainless-steel storage container. Small
amounts (∼0.2 mmol) of this mixture were deposited within 10
min onto the cold matrix support (16 K, Rh-plated Cu-block)
in a high vacuum. Temperature-dependent experiments were
carried out by passing the gaseous sample-Ar mixtures through
a quartz nozzle (1 mm i.d.), heated over a length of ∼10 mm
with a platinum wire (0.25 mm o.d.) prior to deposition on the
matrix support. The nozzle was held at 298 and 583 K.
Photolysis experiments were carried out with an ArF excimer
laser (Lambda-Physics 193 nm) and with a high-pressure
mercury lamp (TQ150, Heraeus) by conducting the light
through water-cooled quartz lenses combined with different cut
off filters (Schott).
fluoroacetyl isocyanate, ClF CC(O)NCO, we will report the
2
results from an interdisciplinary study including its preparation,
determination of physical properties, its IR (gas phase, Ar
1
9
13
matrix), liquid Raman, F and C NMR, gas UV−vis
spectrum, photoelectron spectroscopy (PES), photoionization
mass spectrometry (PIMS), and gas electron diffraction
(
GED). These data will be reciprocally linked and comple-
mented with results from computations to analyze its
conformational and photochemical behavior along the photo-
electron spectroscopy (PES) to determine molecular energy
levels of ClF CC(O)NCO in its valence region.
2
IR spectra of matrix isolated samples were recorded in a
reflectance mode on a Bruker IFS 66v/S spectrometer using a
transfer optic. An MCT detector and a KBr/Ge beam splitter
EXPERIMENTAL SECTION
■
Synthesis. Silver cyanate was prepared from AgNO and
−1
3
were used in the wavenumber range 5000 to 530 cm . For the
spectra with apodized resolutions of 0.25 cm− and 200 scans
1
KNCO, and ClF CC(O)Cl was prepared by chlorination of the
2
corresponding acid, ClCF C(O)OH, with PCl . ClF CC(O)-
2
5
2
were added. More details of the matrix apparatus are given
12
NCO was synthesized by the reaction of difluorochloroacetyl
elsewhere.
chloride, ClF CC(O)Cl, with excess of silver cyanate, AgNCO.
2
(d). UV Spectroscopy. A UV−visible spectrum of gaseous
For this purpose 1.2 g of ClF CC(O)Cl were distilled into an
2
ClF CC(O)NCO was recorded using a glass cell equipped with
2
evacuated 250 mL glass vessel provided with a Young valve and
.5 g of dry AgNCO. The reaction was carried out for 2 h at 20
C. The product was purified by trap-to-trap condensations
quartz windows (10 cm optical path length) and a Lambda
EZ210 UV/vis spectrometer (Perkin-Elmer). Measurements
were carried out in the spectral region from 190 to 700 nm with
1
°
−1
with traps held at −60, −100, and −196 °C. ClF CC(O)NCO
2
a sampling interval of 1.0 nm, a scan speed of 200 nm min ,
and a slit with of 2 nm.
remained in the trap at −60 °C together with a small amount of
difluorochloroacetyl chloride, which was further separated by
fractional distillation. The final yield was 60%.
13
19
(
e). NMR Spectroscopy. For C and F NMR spectra, pure
samples were flame-sealed in thin-walled 4 mm o.d. tubes and
placed into 5 mm NMR tubes. The NMR spectra were
recorded on a Bruker Avance 400 spectrometer at 100.6 and
376.5 MHz, respectively. The samples were held at 25 °C and
C D was used as an external lock and reference.
Instrumentation and Procedure. (a). General Proce-
dure. Volatile materials were manipulated in a glass vacuum
line equipped with a capacitance pressure gauge (221 AHS-
1
000, MKS Baratron, Burlington, MA), three U-traps and
6
6
valves with PTFE stems (Young, London, U.K.). The vacuum
line was connected to an IR cell (optical path length 200 mm,
Si windows 0.5 mm thick) placed in the sample compartment
of a Bruker Vector 25 FTIR spectrometer. This arrangement
allows to follow the course of the reactions and the purification
processes. The pure compound was stored in flame-sealed glass
ampules under liquid nitrogen in a long-term Dewar vessel. The
ampules were opened with an ampule key at the vacuum line,
an appropriate amount was taken out for the experiments, and
(f). Quantumchemical Calculations. DFT calculations were
13
14
performed using the program package GAUSSIAN 03. MP21
5
calculations have been carried out using the Firefly program.
The potential surface of internal rotations along the C2−C6
and C2−N3 in ClF CC(O)NCO bonds has been calculated at
2
16−19
the B3LYP/cc-pVTZ level of approximation
by optimizing
the molecular geometry with fixed torsion angles N3−C2−
C6−Cl7 and O1−C2−N3−C4 in range from 0 to 360 and step
size of 10° (see Figure 2). In this way four stable conformations
were found: gauche−syn, gauche−anti, syn−syn, and syn−anti
(see Figure 1). Using the B3LYP/6-31G(d) and MP2(full)/
aug-cc-pVTZ approximations full optimizations of all con-
formers were performed. Subsequent calculations of vibrational
frequencies proved that all these forms are true minima. The
obtained energies and geometrical parameters for gauche−syn
and gauche−anti conformers are given in Tables 1 and 3,
respectively.
11
then they were flame-sealed again. The vapor pressures of
samples were measured in a small vacuum line equipped with a
calibrated capacitance pressure gauge (MKS Baratron, AHS-
100) and a small sample reservoir in the temperature range
between −38 and +22 °C.
The melting point of ClF CC(O)NCO was determined in a
2
flame-sealed 6 mm glass tube placed in a transparent Dewar
vessel with cold ethanol. The temperature was increased at a
−1
rate of about 1 °C min starting at −100 °C. The solid melts
To assign the PES of ClF CC(O)NCO, we applied the
2
at −83 °C to a colorless liquid.
OVGF approach using the 6-311+G(d) basis set, which
(
b). Vibrational Spectroscopy. Infrared gas spectra were
includes correlation effects of the self-energy to the molecules
20
recorded on a Bruker Vector 25 spectrometer, with a resolution
to give accurate results of the vertical ionization energies.
of 2 cm− in the range from 4000 to 400 cm , using a glass cell
1
−1
Molecular orbital plots were generated using the Gauss View
with Si windows and optical path length of 200 mm.
program.
1
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The Journal of Physical Chemistry A
Article
were calculated for both gauche−syn and gauche−anti
conformers employing the B3LYP/6-31G(d) approximation.
The mean square amplitudes and vibrational corrections to the
equilibrium structure were calculated with the SHRINK
26−29
program.
Root mean square amplitudes were refined in
groups (see Tables S1 and S2). For this purpose the scale
factors (one per group) were used as independent parameters.
Thus, the ratios between different amplitudes in one group
were fixed at the theoretical values calculated from B3LYP/6-
3
1G(d) quadratic and cubic force fields.
RESULTS AND DISCUSSION
■
°
General Properties. Solid ClF CC(O)NCO melts at −83
2
C to a colorless liquid. The vapor pressure of the liquid was
measured over a temperature range between −38 and +22 °C.
Its temperature dependence can be described by the eq 1 from
Figure 1. Conformations of ClF CC(O)NCO calculated with the
B3LYP/6-31G(d) level of approximation.
2
which a boiling point of 82 °C was extrapolated. ClF CC(O)-
2
NCO is stable at room temperature.
ln p = −3868.3(1/T) + 10.89(p[Atm], T[K])
(1)
(
g). Photoelectron and Photoionization Mass Spectrosco-
19
py. The equipment used in this work has been described
previously.
spectrometer consists of two parts: the double-chamber UPS-II
machine and a time-of-flight mass spectrometer. The PES was
recorded in the double chamber UPS-II equipment with a
resolution of about 30 meV as indicated by the Ar ( P )
photoelectron band. Experimental vertical ionization energies
IPs) were calibrated by the simultaneous addition of a small
amount of argon and methyl iodide to the sample. Mass
analysis of ions was performed with the time-of-flight mass
analyzer mounted directly to the photoionization point. The
relatively soft ionization is provided by single-wavelength He(I)
radiation. The PE and PIM spectra can be recorded
subsequently within a few seconds under identical conditions.
The ambient temperature F NMR spectrum shows a singlet
2
1,22
The photoelectron and photoionization mass-
at δ = −65.8 ppm attributed to both fluorine atoms of the
1
3
ClCF group (Figure S1, Supporting Information). The
C
2
NMR spectrum exhibits two triplet signals at δ = 157.6 ppm
2
1
( J
= 37.3 Hz) and δ = 117.9 ppm ( J
= 301.5 Hz) and a
C−F
C−F
+
2
singlet at 131.4 ppm, corresponding to the carbon atoms of the
CO, ClCF2 and NCO groups, respectively (Figure S2,
Supporting Information). These values are in good agreement
3/2
(
30
with those reported for similar compounds. The UV−visible
spectrum of gaseous ClF CC(O)NCO (Figure S3, Supporting
2
Information) shows an absorption band at λmax = 256 nm
attributed to the n → π* transition located on the CO
carbonyl chromophore and a stronger absorption at λ = 197
max
nm, which could be due to the π → π* transition on this
chromophore, according to reports for similar molecules.
30
(
h). Gas Electron Diffraction. The electron diffraction
3
1
patterns were recorded on the heavily improved Balzers
Figures showing the UV−visible spectra of CClF C(O)NCS
2
23
6
3
Eldigraph KD-G2 gas-phase electron diffractometer at the
University of Bielefeld. The experimental details are presented
in Table 7. In total two images for each, the long and short
nozzle-to-plate distances, were measured on the Fuji BAS-IP
MP 2025 imaging plates. The plates with the diffraction
patterns were scanned using a calibrated Fuji BAS-1800II
scanner. The intensity curves (Figure S5) were obtained by
applying the method described earlier. Sector function and
electron wavelengths were estimated using the method
described in the literature, from benzene diffraction patterns,
recorded along with the substance under investigation.
and CClF C(O)N are included for comparison.
2
Computational chemistry. The presence of both, a
chlorine atom and an NCO group, in ClF CC(O)NCO raises
2
the possibility to adopt more than one orientation around the
C2−C6 and C2−N3 bonds (Figure 1). To evaluate the
expected conformational equilibrium, a potential energy surface
for the internal rotation about both bonds was calculated at the
B3LYP/cc-pVTZ level of theory (Figure 2). In addition a full
optimization of all possible conformers on the potential energy
24
25
surface of ClF CC(O)NCO was carried out using ab initio
2
(MP2) and DFT (B3LYP) levels of theory. Four conformers,
denoted as gauche−syn, gauche−anti, syn−syn, and syn−anti
(Figure 1), were found to correspond to minima over the
potential energy surface (Figure 2). The calculated energies of
In order to compute amplitudes of vibrations and curvilinear
corrections used in the gas-phase electron diffraction refine-
ments, analytical quadratic and numerical cubic force fields
a
Table 1. Calculated Relative Energies and Estimated Abundances of the ClF CC(O)NCO Conformers at 298, 478, and 583 K
2
B3LYP/6-31G(d)
g-a s-s
MP2(full)/aug-cc-pVTZ
g-s
s-a
g-s
g-a
s-s
s-a
ΔE, kcal/mol
0.00
0.00
0.87
0.84
1.42
1.11
6
1.81
1.46
3
0.00
0.00
0.13
0.27
1.23
1.03
5
1.21
1.18
4
ΔG°, kcal/mol
b
x , % (298 K)
73
18
56
35
b
x , % (478 K)
60
55
25
26
9
6
48
46
37
36
8
7
b
x , % (583 K)
11
8
10
8
a
b
g-s, g-a, s-s, and s-a denote the gauche−syn, gauche−anti, syn−syn, and syn−anti conformations, respectively. Calculated from ΔG° according to
the Boltzmann law at 298, 478, and 583 K.
1
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Figure 2. Potential surface for rotation along bonds C2−C6 and C2−
C3 calculated at the B3LYP/cc-pVTZ level of theory.
these rotamers and their estimated abundances at room
temperature are given in Table 1. The gauche−syn conformer
was predicted to be more stable than the gauche−anti form at
both levels of theory. The energy differences of the more stable
forms gauche−syn and gauche−anti, however, vary from 0.84
kcal mol− (B3LYP/6-31G(d)) to 0.27 kcal mol (MP2(full)/
aug-cc-pVTZ) (4.18 J = 1 cal). Thus, a contribution of more
than 15% of the gauche−anti conformer in the gas phase at 298
K can be estimated according the calculated Gibbs free energy
difference between the two forms. Additionally, the abundances
of both syn−syn and syn−anti conformers are less than 10%
according to the calculations.
1
−1
Figure 3. Upper trace: IR spectrum of ClF CC(O)NCO isolated in an
2
−1
argon matrix (1:2000) at 16 K (resolution: 0.25 cm ). Middle trace:
IR spectrum of gaseous ClF CC(O)NCO at 298 K (resolution: 2
2
−
1
cm ). Lower trace: Raman spectrum of liquid ClF CC(O)NCO at
298 K (resolution: 2 cm ). Band due to impurity is marked by an
asterisk.
2
−1
Vibrational Spectra. Gas-phase IR, argon matrix IR, and
liquid Raman spectra of ClF CC(O)NCO are shown in Figure
2
3
. The observed vibrational frequencies are listed in Table 2
and compared with the calculated frequencies of the two
possible conformers at the B3LYP/6-311+G(3df) level of
regions (see Figure 4 and Table 1 for the estimated populations
at 478 and 583 K).
theory. ClF CC(O)NCO has 21 fundamental vibrational
Accordingly, these matrix IR spectra revealed that the relative
intensity of the bands attributed to the gauche−anti
conformation increases with temperature, whereas the relative
intensity of the corresponding bands of the gauche−syn form
decreases. This indicates that gauche−syn is the most stable
conformer, but also tells that it is in equilibrium with another
less populated gauche−anti rotamer.
2
modes which are expected to be active in IR and Raman.
For this compound the most interesting vibrational
information appears in the carbonylic region. The position of
the CO stretching vibration can serve as conformational
sensor for the molecule. This mode can be assigned
straightforward to the strong signals at 1783 and 1761 cm−1
in the gas IR and liquid Raman spectra, respectively. A shoulder
at 1775 cm− in the Raman spectrum becomes also apparent.
As mentioned earlier in the computational section, two
rotamers with gauche−syn and gauche−anti orientations are
expected for the molecule. In such a case, the matrix-isolation
technique is particularly well suited for studying the conforma-
tional equilibrium, due to the sharpness of the IR absorption
The remaining vibrational bands were assigned by compar-
1
6,8,30
ison with reported data for related molecules.
Using the results from Figure 4 and including the spectrum
−
1
at 478 K an experimental ΔH° = 1.3 ± 0.2 kcal mol was
exp
derived using the van’t Hoff equation for the enthalpy
difference of these two rotamers with an estimated ΔS° =
0.10 cal K− mol (B3LYP/6-311+G(3df)).
1
−1
bands of species isolated in inert solid matrixes. ClF CC(O)-
Photolysis of ClF CC(O)NCO. The UV spectrum of
2
2
NCO was isolated in argon (1:2000) and deposited onto the
cold matrix support at 15 K. The recorded matrix IR spectrum
is shown in Figure 3 (upper trace). Relevant conformational
splitting were detected, in agreement with the results expected
from the Raman spectra and computational chemistry. In order
to confirm the presence of a conformational equilibrium, the
temperature dependence of the matrix IR absorptions for
equilibrium mixtures at 298 and 583 K were recorded in the
NCO antisymmetric, CO, NCO symmetric and CClF2
symmetric and antisymmetric normal modes of vibration
gaseous ClF CC(O)NCO is depicted in Figure S3 (Supporting
2
Information); it shows intense and weak absorptions at 197 and
256 nm, respectively, that are suitable to initiate UV photolysis
processes.
When the matrix containing ClF CC(O)NCO is irradiated
2
for 6 min with light of a wavelength longer than 225 nm no sign
of photoevolution was detected. However, 20 min of UV
irradiation with λ = 193 nm (ArF laser, 2 mJ) induced the
complete depletion of the IR bands of ClF CC(O)NCO. The
2
IR difference spectrum showing the spectral changes during
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−1
Table 2. Experimental and calculated frequencies (cm ) and assignments of the fundamental vibrational modes of
ClF CC(O)NCO
2
d
experimental
calculated
gauche−syn
a
b
c
e
mode
IR (gas)
IR (Ar matrix)
2260.2
256.1
1779.6
766.7
Raman (liquid)
gauche−anti
assignment
νas(NCO)
ν1
2269 vs
1783 s
2260
(8)
2335 (1333)
1815 (297)
1483 (260)
1243 (39)
1164 (198)
1048 (323)
919 (186)
788 (70)
2346 (1178)
2
ν2
ν3
ν4
ν5
ν6
ν7
ν8
1775 sh
1761
(76)
1834 (547)
1502 (116)
1228 (69)
1150 (158)
1047 (235)
911 (201)
738 (19)
ν(CO)
1
1457 sh
1457.6
1436.7
1252.6
1458
(39)
(34)
(21)
νs(NCO), ν(C−N)
ν(C−C), ν (CF )
1
431 m
1440 sh
1247
1244 w
1179 m
1057 s
933 s
as
2
1
241.3
1177.6
163.7
1057.6
046.5
930.9
25.8
1168
(6)
ν (CF )
as 2
1
1055 sh
1045
931
(17)
(21)
(10)
(11)
(31)
(14)
(15)
ν (CF ), ν(C−N)
s 2
1
ν (CF ), ν(C−N)
as
2
9
924 sh
781
785 w
717 w
624 w
782.8
ν(C−N), ν (CF ), δ(NCO)
s
2
7
37 sh
ν9
710.0
730
718 (86)
632 (41)
617 (10)
589 (9)
665 (18)
625 (22)
613 (52)
599 (13)
δ(CC(O)N)
δ(NCO)
ν10
ν11
ν12
624.8
599.0
627
(93)
(21)
(23)
(8)
δ(CF ), δ(NCO)
2
596
δ(NCO)
5
78.0
579
ν13
ν14
ν15
491 vw
494
493 (6)
421 (<1)
358 (2)
502 (3)
421 (<1)
366 (2)
δ(CF2)
431
(100)
(36)
ν(C−Cl), δ(CF2)
δ(CC(O)N)
369 sh
3
63
344
27
264
41
197
ν16
ν17
(13)
(19)
(8)
321 (<1)
239 (1)
338 (3)
263 (6)
ρ(CClF2)
ρ(CClF2)
3
2
(21)
(34)
ν18
ν19
ν20
ν21
188 (1)
98 (<1)
75 (1)
188 (1)
96 (1)
δ(CCN), δ(ClCC)
δ(CNC)
93 (<1)
25 (<1)
τ((O)C−NCO)
40 (<1)
τ(CClF −C(O))
2
a
b
c
Relative band intensities: s, strong; m, medium strong; w, weak; v, very; sh, shoulder. Only the most populated Ar-matrix sites are given. Relative
intensities based on the integrated band areas are given in the parentheses. sh, shoulder. B3LYP/6-311+G(3df) calculated IR frequencies (cm )
and intensities in parentheses (km mol ). ν, δ, ρ, and τ denote stretching, deformation, rocking, and torsion modes, respectively.
d
−1
−1
e
ArF laser photolysis is displayed in Figure 5 (lower trace). In
In order to describe the conformational behavior of
Figure 5 (upper trace) the photodecomposition of ClF CC-
ClF CC(O)NCO by means of the GED data the following
models were evaluated. The one-conformer model for the
2
2
6
(
O)N3 is shown for comparison. Apparently, the main
photochannels are almost the same. In the present study
gauche−syn, gauche−anti, syn−syn, and syn−anti gave total
both the formation of the nitrene, ClF CC(O)N, and
structural R factors of 5.8, 7.4, 9.7, and 11.5% respectively.
2
str
isocyanate, ClF CNCO, along with CO were obtained by
The refinement of the two-conformer model consisting of the
mixture of the gauche−syn and gauche−anti conformations
2
ArF laser photolysis of ClF CC(O)NCO. Assignments are
2
collected in Table 3.
Gas Electron Diffraction Analysis. Gas electron diffrac-
tion was used to determine the gas-phase structure of
gave R factor of 5.4% and 72(7)% of the gauche−syn form.
str
The next was the four-conformer model. The refinement of
ratios of all conformations leads to unstable solutions with very
high correlations between parameters. A stable solution was
obtained after fixing the relative abundance of both syn−syn
and syn−anti forms to 5%, whereas the ratio of the gauche−syn
and gauche−anti conformations were kept free to refine. This
ClF CC(O)NCO. The structural analysis was performed
2
3
3
employing the UNEX program. All refinements were
performed using two intensity curves simultaneously (provided
in Figure S4, Supporting Information), one from short and
another from long camera distance, which were obtained by
averaging independent intensity curves obtained in the
experiment. For the definition of the independent geometrical
parameters and their groups in least-squares refinements see
Table 4. The differences between values of parameters in one
group were kept fixed on the values taken from MP2(full)/aug-
cc-pVTZ calculations.
model gave larger R (5.8%) and a slightly worse agreement
str
regarding the radial distribution function (see Figure 6). Thus,
on the basis of electron diffraction data it is impossible to prove
the existence of syn−syn and syn−anti conformations in the gas
phase at the temperature of the experiment since their inclusion
in the model did not lead to any significant improvement of the
fit. Therefore, the two-conformer model with Rstr = 5.4% was
1
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Article
Figure 4. Ar matrix IR spectra (1:2000) in the regions of the ν (NCO), ν(CO), ν (NCO), ν (CF ), and ν (CF ) stretching fundamentals of an
as
s
s
2
as
2
equilibrium mixture of gauche−syn and gauche−anti ClF CC(O)NCO held at 298 K (black line) and at 583 K (red line) rapidly trapped in solid
2
argon at 16 K. Stick-style calculated spectra for the two conformers using the B3LYP/6-311+G(3df) level of approximation intensities weighted by
the conformer’s estimated populations at the two temperatures according Table 1 are also depicted.
is similar to those of H CC(O)NCO and FC(O)NCO, but
3
longer than that of ClC(O)NCO and shorter than that of
HNCO. This is surprising, as the isocyanate NC bond is of
similar length for all the compounds and much closer to the
different substituents. All C−N bonds between carbonyl group
and NCO unit are much shorter than a typical single N−C
bond (1.46 Å), the longest of this series is found for
H CC(O)NCO, whereas electronegative F, Cl, or Cl FC
3
2
substituents shorten this bonds.
Some variation is observed for the parameters describing the
angle of the almost linear NCO group at the central N-atom,
the angle C−N−C (or H−N−C in the case of HNCO). The
smallest value of 123.11(15)° is found for HNCO. All carbonyl
isocyanates have values of ≥125.9°, the maximum being
Figure 5. Lower trace: IR difference spectrum recorded before and
after 20 min of an excimer laser irradiation (λ = 193 nm) of Ar-matrix
isolated ClF CC(O)NCO. The IR bands of newly formed species
2
point upward while those of depleted ClF CC(O)NCO point
128.6(19)° for ClF CC(O)NCO.
2
2
downward. Uper trace: IR difference spectrum recorded before and
after 10 min of UV−visible irradiation (λ > 225 nm) of Ar-matrix
isolated ClF CC(O)N .
Photoelectron Spectra. Photoelectron spectroscopy
(PES) using He(I) radiation (21.2 eV = 58.4 nm) is an useful
technique to study the valence electronic structure of molecules
2
3
37−39
in combination with theoretical calculations.
The He(I)
finally chosen. Its refinement gives the results shown in Table 4.
The largest correlations were (i) −0.74 between parameters in
groups 10 and 11 and (ii) −0.72 between parameters in groups
photoelectron spectrum of ClF CC(O)NCO is shown in
2
Figure 7. Outer valence Green function (OVGF) calculations
were performed to obtain the ionization energies in order to
assign the PE spectrum. The experimental vertical ionization
2
and 5 (see Table 4).
The structural parameters obtained for ClF CC(O)NCO can
potentials (IP), theoretical vertical ionization energies (E ;
OVGF/6-311+G(d)), molecular orbitals (MO), and the
v
2
34
be compared to a number of related compounds, HNCO,
3
5
36
7
H CC(O)NCO, FC(O)NCO, and ClC(O)NCO, and a
corresponding characters of outer valence shells for ClF CC-
3
2
detailed listing of selected parameters is provided in Table 5.
(O)NCO are listed in Table 6. In accordance with the above
The length of the isocyanate CO bond in ClF CC(O)NCO
discussion on the structure of ClF CC(O)NCO its He(I)
2
2
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−1
Table 3. Observed Band Positions (cm ), Relative Intensities, and Assignments for the IR Bands of the Ar-Matrix Isolated
Photolysis Products of ClF CC(O)NCO (λ = 193 nm, 20 min) and ClF CC(O)N (λ > 225 nm, 10 min) at 15 K
2
2
3
IR (Ar matrix)
ClF CC(O)NCO
wavenumbers (cm−1)a
ClF CC(O)N
3
assignment
mode
2
2
wavenumbers (cm−1
2282.3 (100)
)
a
species
calculated
2359
b
2
2
1
1
1
1
1
1
1
1
281.1 (100)
ClF CNCO
vas(NCO)
2
c
142.8
CO
ν(CO)
815.4 (6)
1815.4 (3)
1463.0 (14)
1325.5 (1)
1166.5
ClF CC(O)N
ν(CN) S/ν(CO) T
vs(NCO)
1813 S/1564 T
1501
2
463.7 (12)
326.2 (2)
ClF CNCO
2
ClF CC(O)N
ν(CO) S/ν(CC) T
v (CF )
1326 S/1231 T
1167 S/1143 T
1156
2
165.6
ClF CC(O)N
2
as
2
156.5 (23)
138.6/1137.3 (8)
117.2 (<1)
001.3 (35)
1150.5 (19)
ClF CNCO
v (CF )
as 2
2
1138.6/1137.3 (6)
1116.0 (<1)
ClF CC(O)N
v (CF )
1150 S/1094 T
1101
2
s
2
ClF CNCO
v (CF )
s 2
2
1001.7/995.7 (39)
ClF CNCO
v (CF )
965
2
as
2
7
07.1 (1)
67.5 (1)
ClF CNCO
δ(CF2)
720
2
6
ClF CNCO
δ(NCO)
δ(NCO)
δ(CO)
670
2
588.0 (1)
595.1 (1)
91.3 (1)
ClF CNCO
613
2
5
ClF CC(O)N
615 T/599 S
2
a
b
−1
Relative intensities based on the integration of band areas are given in parentheses. Calculated vibrational frequencies (cm ) at the B3LYP/6-
c
−1
3
11+(3df) level reported in ref 6 for ClF CC(O)N are given for the singlet (S) and triplet (T) states. Reference 32, 2139 cm
2
a
Table 4. Experimental and Theoretical Structural Parameters of ClF CC(O)NCO
2
gauche−syn
gauche−anti
GED
calculations
GED
calculations
B3LYP/6-
31G(d)
MP2(full)/aug-cc-
B3LYP/6-
MP2(full)/aug-cc-
b
parameter
O1−C2
C2−N3
C2−C6
N3−C4
C4−O5
C6−Cl7
C6−F8
C6−F9
O1−C2−N3
O1−C2−C6
N3−C2−C6
C2−N3−C4
rg
re, ∠e
pVTZ
rg
re, ∠e
31G(d)
pVTZ
1
2
3
1
1
4
5
5
1.192(1)1
1.374(9)2
1.548(7)3
1.216(1)1
1.158(1)1
1.758(4)4
1.327(3)5
1.349(3)5
1.200(1)
1.388(9)
1.553(7)
1.223(1)
1.162(1)
1.764(4)
1.340(3)
1.351(3)
1.195(1)
1.378(9)
1.541(7)
1.218(1)
1.157(1)
1.756(4)
1.331(3)
1.343(3)
1.203
1.396
1.546
1.227
1.165
1.800
1.334
1.344
126.6
122.0
111.4
130.4
109.4
109.6
110.5
173.0
109.3
109.1
108.9
102.9
1.199
1.385
1.529
1.222
1.161
1.755
1.327
1.339
127.2
122.4
110.5
130.1
109.1
109.9
110.1
173.1
109.9
109.6
108.2
108.0
1.197(1)
1.384(9)
1.561(7)
1.221(1)
1.164(1)
1.767(4)
1.336(3)
1.356(3)
1.200
1.391
1.556
1.224
1.166
1.798
1.331
1.353
123.9
120.6
115.4
135.1
109.7
109.8
110.3
172.1
109.7
108.6
108.7
97.0
1.196
1.381
1.536
1.220
1.162
1.757
1.323
1.345
124.2
121.6
114.3
133.4
109.3
110.3
109.7
172.5
110.2
109.1
108.2
109.1
124.8(8)6
122.9(14)7
112.3(16)b
121.8(8)6
122.1(14)7
116.1(16)b
131.9(19)8
109.5(8)9
8
128.6(19)
9
C2−C6−Cl7
C2−C6−F8
C2−C6−F9
N3−C4−O5
Cl7−C6−F8
Cl7−C6−F9
F8−C6−F9
109.3(8)
1
1
0
0
10
109.8(5)
110.0(5)
110.2(5)
10
109.6(5)
e
e
173.1
172.5
1
1
1
1
11
110.0(3)
109.7(3)
110.2(3)
11
109.1(3)
c
c
108.1(15)
100.6(42)
108.1(15)
1
2
13
O1−C2−C6−
127.2(91)
Cl7
f
d
d
d
d
x/%
72(7)
81
61
28(7)
19
39
a
b
Distances are given in Å, valence and torsion angles are in degrees. Vibrational corrections to the equilibrium structure have been calculated using
B3LYP/6-31G(d) harmonic and cubic force fields. Three times standard deviations are given in parentheses. Superscript numbers 1, 2, ..., 13
c
represent groups, in which parameters were tied together in least-squares method by fixing differences between their values. Dependent parameter.
d
e
f
Calculated from the ΔG° value on the assumption that only gauche−syn and gauche−anti conformers exist. Fixed value. Total structural factor
Rstr = 5.4% was finally chosen for the two conformer model.
photoelectron spectrum should reflect the two weighted forms
arising from the energetically most favorable gauche−syn and
gauche−anti rotamers. In addition, theoretical calculations
sake of comparison calculated values of the most stable form
are used in Table 6.
The vertical ionization energies observed in the photo-
(OVGF/6-311+G(d)) for the two isomers do not predict
electron spectrum of ClF CC(O)NCO agree with the
2
appreciable differences in the ionization energies with respect
to the experimental resolution of 30 meV (∼240 cm ). For the
calculated values with the OVGF method. The first band in
the photoelectron spectrum is found at 11.54 eV and can be
−1
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The Journal of Physical Chemistry A
Article
Figure 7. He(I) photoelectron spectrum (PES) of ClF CC(O)NCO.
2
Table 6. Experimental and Calculated Ionization Energies
and MO Characters for ClF CC(O)NCO
2
a
a,b
band
exp. IP
calcd. Ev
MO
assignment
1
2
3
4
5
6
7
11.54
12.10
12.50
12.86
13.20
14.77
12.08
12.18
12.56
12.82
13.39
15.13
15.87
38
37
36
35
34
33
32
nO
πnb(NCO)
nCl
Figure 6. Experimental (open circles) and model (line) radial
distribution functions. The difference curves for different models are
shown below.
nCl
nN
π
b(CO)
15.53
nF
a
b
attributed to the ionization process from the highest occupied
molecular orbital (HOMO), corresponding to the nonbonding
Energies [eV]. OVGF from geometries at the B3LYP/6-311+G(d)
level of approximation for the gauche−syn form.
orbital at the carbonyl oxygen atom (n ). These ionization
O
energies were reported to be 11.21, 12.00, and 13.20 eV for
following three ionization bands observed at 13.20, 14.77,
and 15.53 eV are assigned as listed in Table 6.
4
0
30
41
CH C(O)CN, ClF CC(O)CN, and FC(O)CN, respec-
3
2
tively, showing the intermediate inductive effect of the ClCF2
group (with respect to CH and F) and the influence of the
Table 7. Details of the GED Experiment
3
electronegativity of the groups linked to CO on the IPs
parameter
short camera distance long camera distance
(
photoionization energies).
nozzle-to-plate distance, mm
accelerating voltage, kV
fast electrons current, μA
250.0
60
500.0
60
The second ionization band observed at 12.10 eV can be
attributed to the π (NCO) molecular orbital, which is in
nb
0.9
1.5
agreement with both calculations and experimental assignment.
An adiabatic ionization potential value of 11.76 eV has been
reported for the NCO radical using photoionization mass
a
electron wavelength , Å
0.048733
293
0.048597
293
nozzle temperature, K
b
−5
−5
4
2
residual gas pressure , mbar
1.6 × 10
2.1 × 10
spectrometry. For similar covalent molecules as CH C(O)-
3
4
3
exposure time, s
used s range, Å−
30
41
NCO this second potential was reported at 11.33 eV. The
1
8.2 − 34.0
2.2 − 16.0
third and fourth ionization bands observed at 12.50 and 12.86
c
number of inflection points
6
5
eV are again in trend with ClF CC(O)-containing compounds.
2
a
Thus, they are attributed to the ejection of electrons from the
Determined from C H diffraction patterns measured in the same
6 6
b c
experiment. During the measurement. Number of inflection points
two nonbonding orbitals of the chlorine atom (n ). These IPs
Cl
on the background line.
were reported at 13.19 and 13.71 eV for the corresponding
3
0
orbitals of the related molecule ClF CC(O)CN. The
2
Table 5. Selected Structural Parameters for ClF CC(O)NCO and the Related Compounds HNCO, H CC(O)NCO,
2
3
FC(O)NCO, and ClC(O)NCO
(
N)CO
NC(O)
C−N
CO
<NCO
<(C/H)NC
<OCN(CO)
124.8(8)
ref
a
ClF CC(O)NCO syn
re
re
rα
ra
ra
1.157(1)
1.218(1)
1.378(9)
1.195(1)
173.1
128.6(19)
123.11(15)
128.2(13)
125.9(11)
127.1(16)
this work
2
HNCO
1.16991(83)
1.159(6)
1.21220(76)
1.199(7)
173.33(20)
34
35
36
7
a
H CC(O)NCO syn
3
1.413(7)
1.388(4)
1.384(6)
1.199(6)
1.192(8)
1.201(16)
173.0
124.5(23)
128.7(6)
124.8(15)
FC(O)NCO syn
1.154(8)
1.215(9)
174.6(25)
173.4(23)
ClC(O)NCO anti
1.139(16)
1.218(23)
a
Assumed parameter kept fixed during refinement.
1
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Article
Photoionization Mass Spectrum. The ultraviolet photo-
Notes
ionization mass spectrum (PIMS) of ClF CC(O)NCO was
The authors declare no competing financial interest.
2
recorded together with the photoelectron spectra and is shown
in Figure 8. The PIMS confirms the identity of the sample. The
ACKNOWLEDGMENTS
■
spectrum of ClF CC(O)NCO mainly shows three peaks:
The authors thank Deutsche Forschungsgemeinschaft (DFG),
Alexander von Humboldt Stiftung (stipend for Y.V.V.),
Deutscher Akademischer Austauschdienst (DAAD, Regional
Program of Chemistry for Argentina supporting the PhD of
Latin-American students in La Plata), Agencia Nacional de
2
+
+
35/37
+
C(O)NCO , ClF C (
Cl isotopomers), F CC(O)N , and
2
2
+
F CC(O)NCO .
2
́
́ ́
Cientifica y Tecnica (ANPCYT), Consejo Nacional
Promocion
de Investigaciones Cientificas y Tec
Comision de Investigaciones de la Provincia de Buenos Aires
CIC), Facultad de Ciencias Exactas, Universidad Nacional de
La Plata (UNLP), and Universitat Bielefeld for financial
́
́
nicas (CONICET),
́
(
̈
support. C.O.D.V. and R.M.R. acknowledge CONICET and
ICCAS (Institute of Chemistry of the Chinese Academy of
Sciences) for a grant to travel and stay in Beijing. C.O.D.V.
thanks the Chinese Academy of Sciences for a Visiting
Professorship Award for the Senior International Scientists
2
011 and for the grant to travel and stay in Beijing.
REFERENCES
■
(
1) Ulrich, H. Chemistry and Technology of Isocyanates, 1st ed.; John
Wiley & Sons: London, 1997; p 514.
Figure 8. He(I) photoionization mass spectrum (PIMS) of ClF CC-
2
(
O)NCO.
(2) Liu, Q.; De Wijn, J. R.; Van Blitterswijk, C. A. J. Biomed. Mater.
Res. 1998, 40, 358−364.
(3) Alaee, M.; Livingstone, E. G.; Westwood, P. C. J. Am. Chem. Soc.
CONCLUSION
1993, 115, 2871−2876.
4) Torrico Vallejos, S.; Erben, M. F.; Willner, H.; Boese, R.; Della
Vedova, C. O. J. Org. Chem. 2007, 72, 9074−9080.
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6) Ramos, L. A.; Zeng, X.; Ulic, S. E.; Beckers, H.; Willner, H.; Della
■
(
ClF CC(O)NCO is a new nine-atomic molecule with
2
́
interesting properties. This compound has been fully
characterized in terms of physical, spectroscopic and structural
data. It adopts gauche−syn and gauche−anti conformations in
(
(
Ved
́
ova, C. O. J. Org. Chem. 2012, 77, 6456−6462.
the gaseous and liquid phases both of C symmetry according
(7) Mack, H.-G.; Oberhammer, H.; Della Ved
1989, 200, 277−288.
(8) Gobbato, K. I.; Della Ved
́
ova, C. O. J. Mol. Struct.
1
to vibrational spectroscopy, gas electron diffraction and
quantum chemical calculations. The structural parameters are
similar to those of related molecules, with some variations
mainly depending on the electronic nature of the binding group
R at the RC(O)NCO skeleton. The photolysis in matrix lead to
both, ClF CC(O)N and ClF CNCO, as photoproducts. The
́
ova, C. O.; Mack, H.-G. Spectrochim.
Acta 1994, 50A, 897−902.
(9) Curtius, T. Ber. Dtsch. Chem. Ges. 1850, 23, 3023−3033.
(10) Wang, W.; Ge, M. F.; Yao, L.; Zeng, X.; Sun, Z.; Wang, D.
Chem. Phys. Chem. 2006, 7 (6), 1382−1387.
11) Gombler, W.; Willner, H. J. Phys. E: Sci. Instrum. 1987, 20,
286−1288.
12) Schno
2
2
(
1
PE spectrum of ClF CC(O)NCO is characterized by the first
2
vertical ionization energy at 11.54 eV mainly corresponding to
the lone-pair orbital at the carbonyl oxygen atom. Some
remarkable geometrical parameters for the most stable gauche−
syn conformation are the CO double bond length of
(
̈
ckel, H. G.; Willner, H. Infrared and Raman Spectroscopy,
Methods and Applications Plenum Press: New York, 1994; p 297.
(13) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; 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.;
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J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
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1
.195(1) Å, the NCO angle with a value close to 180° and
the O−C−C−Cl torsion angle of 100.6(42)°.
ASSOCIATED CONTENT
■
*
S
Supporting Information
1
9
13
F and C NMR spectra of ClF CC(O)NCS, ClF CC(O)-
2
2
NCO, ClF CC(O)N (Figure S1 and S2); UV−vis spectra of
2
3
gaseous ClF CC(O)NCS, ClF CC(O)NCO, ClF CC(O)N
2
2
2
3
(
Figure S3), total and molecular electron scattering intensity
curves (Figure S4 and S5); interatomic distances, mean square
amplitudes and vibrational corrections (Tables S1 and S2);
experimental Cartesian coordinates of gauche−syn and
gauche−anti conformers (Tables S3 and S4). This material is
available free of charge via the Internet at http://pubs.acs.org.
(
14) Møller, C.; Plesset, M. S. Phys. Rev. 1934, 46, 618−622.
AUTHOR INFORMATION
Present Address
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