Chlorodifluoroacetyl isothiocyanate, ClF2CC(O)NCS: Preparation and structural and spectroscopic studies

Article abstract of DOI:10.1021/jp403549f

Chlorodifluoroacetyl isothiocyanate, ClF₂CC(O)NCS, was synthesized by the reaction of ClF₂CC(O)Cl with an excess of AgNCS. The colorless product melts at -85 C, and its vapor pressure follows the equation ln p = -4471.1 (1/T) + 11.35 (p [atm], T [K]) in the range -38 to 22 C. The compound has been characterized by IR (gas phase, Ar matrix, and matrix photochemistry), by liquid Raman, by ¹⁹F and ¹³C NMR, gas UV-vis, and photoelectron spectroscopy (PES), by photoionization mass spectrometry (PIMS), and by gas electron diffraction (GED). The conformational properties of ClF₂CC(O)NCS have been analyzed by joint application of vibrational spectroscopy, GED and quantum chemical calculations. The existence of two conformers has been detected in the gas and liquid phases, in which the C-Cl bond adopts a gauche orientation with respect to the C=O group; the C=O group is in syn- or anti-position with respect to the N=C double bond of the NCS group. The computed ΔG difference between these two gauche-syn and gauche-anti forms is ΔG = 0.63 kcal mol^-1 in the B3LYP/6-31G(d) approximation. The most significant gas-phase structural parameters for gauche-syn ClF₂CC(O)NCS are r_e(NC=S) 1.559(2) A, r_e(N=CS) 1.213(2) A, r_e(N-C) 1.399(7) A, r_e(C=O) 1.199(2) A, and ∠_e(CNC) 134.7(13). Photolysis of ClF₂CC(O)NCS using an ArF excimer laser (193 nm) mainly yields ClF₂CNCS, CO, and ClC(O)CF₂NCS. The valence electronic properties of the title compound were studied using PES and PIMS. The experimental first vertical ionization energy of 10.43 eV corresponds to the ejection primarily of the sulfur lone-pair electrons of the in-plane nonbonding orbital on the NCS group.

Full text of DOI:10.1021/jp403549f

Subscriber access provided by MCGILL UNIV
Article
Chlorodifluoroacetyl Isothiocyanate, ClF2CC(O)NCS:
Preparation, Structural and Spectroscopic Studies
Luis Alejandro Ramos, Sonia Elizabeth Ulic, Rosana Mariel Romano, Yury Viktorovich Vishnevskiy, Norbert
Werner Mitzel, Helmut Beckers, Helge Willner, Shengrui Tong, Maofa Ge, and Carlos Omar Della Védova
J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/jp403549f • Publication Date (Web): 07 Jun 2013
Downloaded from http://pubs.acs.org on June 9, 2013
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Physical Chemistry A is published by the American Chemical Society.
1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
Chlorodifluoroacetyl Isothiocyanate, ClF CC(O)NCS:
2
Preparation, Structural and Spectroscopic Studies
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
†
†
†
⊥
⊥
Luis A. Ramos, Sonia E. Ulic, Rosana M. Romano, Yury V. Vishnevskiy, Norbert W. Mitzel,
#
#
§
§
†,*
Helmut Beckers, Helge Willner, Shengrui Tong, Maofa Ge, and Carlos O. Della Védova
†
CEQUINOR (UNLPꢀCONICET), Departamento de Química, Facultad de Ciencias Exactas,
#
Universidad Nacional de La Plata, 47 esq. 115, 1900 La Plata, República Argentina. Fachbereich C
§
ꢀ
Anorganische Chemie, Bergische Universität Wuppertal, 42097 Wuppertal, Germany. State Key
http://www.youtube.com/watch?v=DJVtIcB4n8oLaboratory for Structural Chemistry of Unstable
and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
⊥Universität Bielefeld, Lehrstuhl für Anorganische Chemie und Strukturchemie, Universitätsstraße
25, 33615 Bielefeld, Germany.
1
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 2 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
ABSTRACT
2
Chlorodifluoroacetyl isothiocyanate, ClF CC(O)NCS, was synthesized by the reaction of
ClF
2
CC(O)Cl with excess of AgNCS. The colorless product melts at –85 ºC, and its vapor pressure
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
follows the equation ln p = ꢀ4471.1 (1/T) + 11.35 (p [Atm], T [K]) in the range –38 to 22 ºC. The
compound has been characterized by IR (gas phase, Ar matrix and matrix photochemistry), by
19
13
liquid Raman, by F and C NMR, gas UVꢀVis and photoelectron spectroscopy (PES), by
photoionization mass spectrometry (PIMS) and by gas electron diffraction (GED). The
2
conformational properties of ClF CC(O)NCS have been analyzed by joint application of vibrational
spectroscopy, GED and quantum chemical calculations. The existence of two conformers has been
detected in the gas and liquid phases, in which the C–Cl bond adopts a gauche orientation with
respect to the C=O group; the C=O group is in synꢀ or antiꢀposition with respect to the N=C double
bond of the NCS group. The computed ꢁG° difference between these two gaucheꢀsyn and gaucheꢀ
–1
anti forms is ꢁG° = 0.63 kcal mol in the B3LYP/6ꢀ31G(d) approximation. The most significant
gas phase structural parameters for gaucheꢀsyn ClF CC(O)NCS are r (NC=S) 1.559(2) Å, r (N=CS)
.213(2) Å, r (N–C) 1.399(7) Å, r (C=O) 1.199(2) Å, (CNC) 134.7(13)°. Photolysis of
2
e
e
1
e
e
∠
e
ClF CC(O)NCS using an ArF excimer laser (193 nm) mainly yields ClF CNCS, CO and
2
2
ClC(O)CF
2
NCS. The valence electronic properties of the title compound were studied using PES
and PIMS. The experimental first vertical ionization energy of 10.43 eV corresponds to the ejection
primarily of the sulfur loneꢀpair electrons of the inꢀplane nonbonding orbital on the NCS group.
KEYWORDS: Vibrational spectroscopy • matrix isolation • isothiocyanates • quantum chemical
calculations • photoelectron and photoionization spectroscopy • gas electron diffraction
2
ACS Paragon Plus Environment

Page 3 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
INTRODUCTION
Several studies on thioꢀ and isothiocyanates have been carried out recently related to their wide
variety of medicinal, pharmaceutical and industrial applications along their valuable spectroscopic
1,2
and electronic properties in ground and excited states. Due to their stability isothiocyanates are
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
important intermediate and final products in chemical industry. They are also present in a number
of phytochemicals found in cruciferous vegetables such as broccoli, cauliflower, cabbage and
Brussels sprouts. Consumption of cruciferous vegetables appears to be associated with a reduced
4
risk of degenerative diseases such as cancer and cardiovascular illnesses. In particular,
isothiocyanates inhibit the medicinal proliferation of tumor cells both in vitro and in vivo and are
used as chemopreventive agents. The initiating event for these effects seems to be acute cellular
stress caused by this class of compounds, although the elucidation of the mechanism is still at an
5
early stage. Due to their volatility and stability, the isothiocyanates can reach the troposphere and
react with radicals to give certain conversion products, thereby presenting a potential ecological
3
risk. These outcomes must be related with their chemical nature and based on their electronic
structures. Therefore, in this work we will combine several spectroscopic techniques and diffraction
methods to gain a detailed understanding of the title species.
1
Derivatives studied previously include fluorocarbonyl isothiocyanates, and other wellꢀknown
6
,7,8,9
carbonyl isothiocyanates.
2
For ClF CC(O)NCS, a hitherto unknown species, we will report the
results from an interdisciplinary study including its preparation, determination of physical
19
13
properties, its IR (gas phase, Ar matrix), liquid Raman, F and C NMR, gas UVꢀVis, and
photoelectron spectra (PES), photoionization mass spectra (PIMS) and its gas phase structure
determined by electron diffraction (GED). These data will be complemented and compared with
results from computations to analyze the conformational and photochemical behavior and the
2
molecular energy levels of ClF CC(O)NCS in its valence region.
EXPERIMENTAL SECTION
Synthesis
ClF
with an excess of silver thiocyanate, AgSCN. For this purpose 1.0 g ClCF
onto 1.4 g of dry AgSCN in a 250 ml glass vessel provided with a Young valve with PTFE stems
Young, London, U.K.). The reaction was carried out in vacuum for 1 hour at 15 ºC. Purification of
2
CC(O)NCS was synthesized by treatment of difluorochloroacetyl chloride, ClCF
2
C(O)Cl,
2
C(O)Cl were distilled
(
the product was performed by trapꢀtoꢀtrap distillations with traps held at –47, –95 and –196 ºC.
ClF CC(O)NCS was mainly isolated in the trap at −47 ºC. The trap held at – 95 ºC also contained
2
some of the product, which was further separated by slow distillation. The final yield was 95 %.
3
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 4 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Silver thiocyanate was prepared from AgNO and KSCN, and ClCF C(O)Cl by chlorination of the
3
2
corresponding acid, ClCF
2
5
C(O)OH, (Merck & Co.), with PCl .
Instrumentation and Procedure
a) General Procedure. Volatile materials were manipulated in a glass vacuum line equipped
(
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
with a capacitance pressure gauge (221 AHSꢀ1000, MKS Baratron, Burlington, MA), three Uꢀtraps
and valves. 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 FTIR spectrometer (see below). This
arrangement allows following the course of the reactions and the purification processes. The pure
compound was stored in flameꢀsealed glass ampoules under liquid nitrogen in a Dewar vessel. The
ampoules were opened with an ampoule key at the vacuum line, an appropriate amount was taken
1
0
out for the experiments, and then they were flameꢀsealed again. The vapor pressures of the sample
were measured in a small vacuum line equipped with a calibrated capacitance pressure gauge (MKS
Baratron, AHSꢀ100) and a small sample reservoir.
The melting point of ClF CC(O)NCS was determined by condensing 100 mg of the sample in
2
vacuum near the bottom of a small Lꢀshaped tube connected to a vacuum line. Then, the
–1
temperature was increased at a rate of about 1 ºC min starting at –100 ºC (cold ethanol bath). The
solid melts at –85 ºC to a colorless liquid. The vapor pressure of the liquid was measured with a
precision thermometer, in a similar way, in the temperature range between –38 and 22 ºC.
(b) Vibrational Spectroscopy. Infrared gas spectra were recorded on a Bruker Vector 25
–
1
–1
spectrometer, with a resolution of 2 cm in the range from 4000 to 400 cm .
Raman spectra of neat liquids were measured at room temperature in flameꢀsealed capillaries (3
mm o.d.) on a FT Bruker RFS 106/S spectrometer, equipped with a 1064 nm Nd:YAG laser, in the
–1
–1
region from 4000 to 100 cm using a resolution of 2 cm .
c) Matrix isolation experiments. For matrix isolation experiments carried out in Wuppertal
ClF CC(O)NCS was diluted with argon in a ratio of 1:1000 in a 1 L stainlessꢀsteel storage
container, and then small amounts of the mixture were deposited within 10 min onto the cold matrix
(
2
ꢀ5
support (16 K, Rhꢀplated Cuꢀblock) in a high vacuum (10 Pa). Temperatureꢀdependent
conformational studies 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 or 583 K.
IR spectra of matrixꢀisolated samples were recorded in a reflectance mode on a Bruker IFS 66v/S
2
spectrometer using a transfer optic. A liquid N cooled HgCdTe detector (MCT) and a KBr/Ge
–
1
beam splitter were used in the wavenumber range 5000 to 530 cm . For each spectrum with an
4
ACS Paragon Plus Environment

Page 5 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
–
1
apodized resolution of 0.25 cm 200 scans were added. More details of the matrix apparatus are
11
given elsewhere.
(
2
d) UV Spectroscopy. The UVꢀvisible spectrum of gaseous ClF CC(O)NCS was recorded using
a glass cell equipped with quartz windows (10 cm optical path length) on a Lambda EZ210 UV/Vis
spectrometer (PerkinꢀElmer). Measurements were carried out in the spectral region from 190 to 700
–
1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
nm with a sampling interval of 1.0 nm, a scan speed of 200 nm min , and a slit of 2 nm.
1
3
19
(
e) NMR Spectroscopy. For C and F NMR spectra, pure samples were flameꢀsealed in thinꢀ
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
2
5 ºC and C
6 6
D was used as an external lock and reference.
(
f) Quantum Chemical Calculations. DFT calculations were performed using the program
1
2
13
14
package GAUSSIAN 03. (MP2) calculations were carried out with the Firefly program. In the
first step, the potential surface of internal rotations along the C2ꢀC6 and C2ꢀN3 bonds was
calculated at the B3LYP/ccꢀpVTZ 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 degrees (see Figure 1).
Figure 1. Potential surface for rotation along bonds C2–C6 and C2–N3 calculated on B3LYP/ccꢀ
pVTZ level of theory. Only symmetryꢀunique minima were assigned.
In this way four low energy conformations were found: gaucheꢀsyn, gaucheꢀanti, synꢀsyn and
synꢀanti (see Figure 2). Using the B3LYP/6ꢀ31G(d) and MP2(full)/augꢀccꢀpVTZ approximations
full optimizations of geometries of these conformers were performed. Subsequent calculations of
5
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 6 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
vibrational frequencies proved that they correspond to true minima on the potential energy surface.
Thus, the reliability of the calculations is tested using different methods of approximation. For the
selection of the method reported antecedents from the literature for similar compounds within
1,5,9
selected applications are used.
(g) Photoelectron and Photoionization Mass Spectroscopy. The Beijing equipment used in this
15
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
work has been described previously. The photoelectron and photoionization massꢀspectrometer
consists of two parts: the doubleꢀchamber UPSꢀII machine and a timeꢀofꢀflight mass spectrometer.
The PES was recorded in the double chamber UPSꢀII equipment with a resolution of about 30 meV
+
2
as indicated by the Ar ( P3/2) photoelectron band. Experimental vertical ionization energies (PI)
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 timeꢀofꢀflight mass analyzer mounted
directly to the photoionization region. The relatively soft ionization is provided by singleꢀ
wavelength He I radiation. The PE and PIM spectra can be recorded successively within seconds
under identical conditions.
(h) Gas Electron Diffraction The electron diffraction patterns were recorded on the heavily
1
6
improved Balzers Eldigraph KDꢀG2 gasꢀphase electron diffractometer at the University of
Bielefeld. The experimental details are presented in Table 1. Two images for long and four images
for short nozzleꢀtoꢀplate camera distances were recorded on Fuji BASꢀIP MP 2025 imaging plates.
The plates with the diffraction patterns were scanned using a calibrated Fuji BASꢀ1800II scanner.
The intensity curves (Figure S1, supporting information) were obtained by applying the method
1
7
described earlier. Sector function and electron wavelengths were estimated using the method
1
8
described in lit. and the benzene diffraction patterns, recorded along with that of the substance
under investigation.
Table 1. Details of the GED experiment
Parameter
Short camera
250.0
Long camera
500.0
Nozzleꢀtoꢀplate distance, mm
Accelerating voltage, kV
Fast electrons current, ꢂA
60
60
0.1
0.1
a
Electron wavelength, Å
0.048733
293
0.048597
293
Nozzle temperature, K
b
ꢀ5
ꢀ5
Residual gas pressure, mbar
2×10
2×10
Exposure time, sec
40
30
ꢀ1
s range used, Å
6.2 – 34.0
6
2.2 – 15.0
4
c
Number of inflection points
a
Determined from C
6
H
6
diffraction patterns measured in the same experimental conditions.
6
ACS Paragon Plus Environment

Page 7 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
b
c
During the measurement.
Number of inflection points on the background line.
In order to obtain amplitudes of vibrations and curvilinear corrections used in the gasꢀphase electron
diffraction refinements, analytical quadratic and numerical cubic force fields were calculated for all
conformers employing the B3LYP/6ꢀ31G(d) approximation. The mean square amplitudes and
vibrational corrections to obtain the equilibrium structure were computed with the SHRINK
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
9,20,21,22
program.
RESULTS AND DISCUSSION
General Properties
Solid ClF CC(O)NCS melts at –85 ºC to a colorless liquid. The vapor pressure of the liquid was
2
measured over a temperature range between –38 and 22 ºC. Its temperature dependence can be
described by the equation (1) from which a boiling point of 121 ºC was extrapolated.
2
ClF CC(O)NCS is stable in the vapor and liquid phases at room temperature.
ln p = –4471.1 (1/T) + 11.35 (p [Atm], T [K])
(1)
1
9
The ambient temperature F NMR spectrum shows a singlet at
fluorine atoms of the ClCF
exhibits two triplets at = 155.3 ppm ( J(C–F) = 36.9 Hz) and
δ
= –64.6 ppm attributed to both
13
2
group (Figure S2, supporting information). The C NMR spectrum
2
1
δ
δ
= 117.9 ppm ( J(C–F) = 302.9 Hz) and
a singlet at 152.2 ppm, corresponding to the carbon atoms of the C=O, ClCF and NCS groups,
2
respectively (Figure S3, supporting information). These values are in good agreement with those
1
19
13
reported for similar compounds. The simplicity of both F NMR and C NMR spectra is the
resultant of the rapid inter conversion between the rotamers being the signal positions originated by
the weighted forms arising from the energetically most favorable gaucheꢀsyn and gaucheꢀanti
rotamers. The UVꢀvisible spectrum of gaseous ClF
shows an absorption band at λmax = 274 nm attributed to the n
chromophore and a stronger absorption at λmax = 199 nm, which could be due to the π
2
CC(O)NCS (Figure S4, supporting information)
π* transition located on the NCS (?)
π*
→
→
1
transition in the C=O chromophore, according to reported values for similar molecules. In Figure
2
3
24
S4 spectra of CClF
2
C(O)NCO and CClF
2
C(O)N
3
are included for comparison.
Computational chemistry
The presence of both a chlorine atom and an NCS group in ClF
2
CC(O)NCS raises the possibility
of more than one orientation around the C2–C6 and C2–N3 bonds (Figures 1 and 2). To evaluate
the expected conformational equilibrium, the potential energy surface for the internal rotation
7
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 8 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
around both bonds was calculated at the B3LYP/ccꢀpVTZ level of theory (Figure 1). In addition,
2
full optimizations of all possible conformers on the potential energy surface of ClF CC(O)NCS
were carried out using ab initio (MP2) and DFT (B3LYP) levels of theory. Four conformers,
denoted as gaucheꢀsyn, gaucheꢀanti, synꢀsyn and synꢀanti, were found to have energy minima
(Figure 1). The calculated energy differences of these rotamers and their estimated abundances at
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
room temperature are given in Table 2. The energy differences were computed with respect to the
lowest energy form for each theoretical method. For both methods the lowest energy rotamers
present also the lowest free energy differences at 298 K. At the B3LYP/6ꢀ31G(d) level of theory the
gaucheꢀsyn conformer was predicted to have less energy than the gaucheꢀanti form, while the
MP2(full)/augꢀccꢀpVTZ approximation gave the opposite results. All approximations result in
dominance of gaucheꢀsyn and gaucheꢀanti over synꢀsyn and synꢀanti conformers.
2
Figure 2. Conformations of ClF CC(O)NCS.
a
2
Table 2: Theoretical relative energy differences and abundances of the ClF CC(O)NCS conformers
B3LYP/6ꢀ31G(d) MP2(full)/augꢀccꢀpVTZ
gꢀs
gꢀa
0.67
0.63
23
sꢀs
sꢀa
1.47
1.26
4
gꢀs
gꢀa
0.00
0.00
57
sꢀs
sꢀa
1.24
1.04
5
–1
ꢁE, kcal mol
0.00
0.00
68
1.41
1.08
5
0.53
0.27
35
1.80
1.36
3
–1
ꢁGº, kcal mol
b
x , %
a
gꢀs, gꢀa, sꢀs and sꢀa denotations correspond to the gaucheꢀsyn, gaucheꢀanti, synꢀsyn and synꢀanti conformations,
8
ACS Paragon Plus Environment

Page 9 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
b
respectively. Calculated from ꢁGº according to the Boltzmann law for the temperature 298.15 K.
Vibrational Spectra
2
Gasꢀphase IR, argon matrix IR and Raman spectra of liquid ClF CC(O)NCS are shown in
Figure 3. The observed vibrational frequencies are compared in Table 3 with unscaled calculated
harmonic frequencies for two possible conformers at the B3LYP/6ꢀ31G(d) level of theory.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
ClF CC(O)NCS has 21 fundamental vibrational modes which are expected to be active in both IR
and Raman spectra.
2
Figure 3. Upper trace: IR spectrum of ClF CC(O)NCS isolated in an argon matrix (1:1000) at 15 K
–1
(
resolution: 0.25 cm ). Middle trace: IR spectrum of gaseous ClF
2
CC(O)NCS at 298 K (resolution:
–1
–1
2
cm ). Lower trace: Raman spectrum of liquid ClF CC(O)NCS at 298 K (resolution: 2 cm ). A
2
band due to HNCS is marked by an asterisk.
9
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 10 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
–1
Table 3. Experimental and calculated frequencies (cm ) and assignments of the fundamental vibrational
2
modes of ClF CC(O)NCS
[d]
Experimental
IR
Calculated
[
e]
Mode
Assignments
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
IR
Raman
gaucheꢀsyn
gaucheꢀanti
2058 (1460)
[
a]
[b]
[c]
(
liquid)
(
Gas)
(Ar Matrix)
1982 vs
1951 vs
1961.9
1939.1
1768.2
1755.4
1300.7
1263.7
1187.2
1181.0
1132.1
1126.1
992.8
ν
ν
ν
ν
ν
ν
ν
δ
ν
δ
as(NCS)
(C=O)
ν
ν
ν
ν
ν
ν
ν
ν
ν
1
2
3
4
5
6
7
8
9
1955
(6)
2025 (1806)
1814 (875)
1774 vs
1747
(100)
1799 (399)
1300 (182)
1291 m
ꢀ
(CꢀC), ν(CꢀN)
1260 w, sh
1188 s
1260
(6)
1255 (38)
1190 (292)
1136 (153)
as(CF
2
2
)
)
1176
1127
988
(11)
1183 (235)
as(CF
1130 s
995 m
(20)
(28)
1130 (100)
977 (146)
s
2
(CF )
984.0
964 (168)
870 w, sh
842 m
873.4
870
839
(4)
874 (199)
723 (40)
s
s 2
(NCS), ν (CF ), ν(CꢀN)
839.5
(14)
851 (267)
740 (13)
689 (138)
722.6
(CC(O)N)
721 vw
730
(20)
710.4
688 w
680.2
675
564
628
617
503
ꢀ
(16)
(56)
(36)
(45)
(11)
ꢀ
s
(CꢀN), δ(NCS), ν(CCl)
562 vw
568.0
669 (27)
620 (31)
628.2
(CF
2
),
ν
(CꢀCl)
ν
10
620 w
616.1
613 (40)
508 (5)
ν
ν
11
12
ꢀ
ꢀ
540 (9)
δ
δ
δ
(NCS)
(NCS)
498 (<1)
456 (10)
486 (<1)
450
441
430
361
(25)
(27)
(57)
(30)
(9)
(CF
2
),
δ
(CC(O)N),
(CꢀCl)
δ(NCS)
ν
13
450 vw
419 vw
448 (6)
421 (<1)
361 (1)
329 (1)
ν
ν
14
15
419 (<1)
δ
δ
(CF
2
),
ν
356 (2)
(CC(O)N)
3
3
2
2
34
17
53
27
ρ
(CClF
2
)
ν
ν
16
17
(17)
(17)
(24)
(39)
312 (2)
251 (6)
ρ
(CClF
2
)
224 (1)
178 (1)
70 (1)
ν
ν
ν
ν
18
19
20
21
189
185 (2)
62 (<1)
85 (1)
δ
δ
(ClCC),
(CNC)
δ(CCN)
67 (1)
τ((O)C–NCS)
τ(CClF –C(O))
33 (<1)
25 (<1)
2
a
b
Relative band intensities: s, strong; m, medium strong; w, weak; v, very; sh, shoulder Only the most intense Arꢀmatrix
c
d
bands are given. Relative intensities based on integrated band areas are given in parentheses. B3LYP/6ꢀ311+G(3df)
–
1
–1
e
calculated IR frequencies (cm ) and intensities in parentheses (km mol ).
ν, δ, ρ and τ represent stretching,
deformation, rocking and torsion modes, respectively.
For the present study the most interesting vibrational information appears in the carbonylic region.
1
0
ACS Paragon Plus Environment

Page 11 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
–
1
This mode can be related in a straightforward way to the strong signals at 1774 and 1747 cm in
the IR (gas) and Raman (liquid) spectra. As mentioned earlier in the computational chemistry
section, the two more abundant rotamers with gaucheꢀsyn and gaucheꢀanti orientations can be
expected to contribute to these spectra. In such a case, the matrixꢀisolation technique is especially
suitable to study the conformational equilibrium, because of the sharpness of the IR absorption
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
bands of species isolated in inert solid matrices. ClF CC(O)NCS was diluted in argon (1:1000) and
deposited onto the cold matrix support at 15 K. The matrix IR spectrum is shown in Figure 3 (upper
trace). Relevant conformational splitting was 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 matrix IR absorptions for equilibrium mixtures at 25 and 310 °C
were recorded. However, these matrix IR spectra revealed that the relative intensity of the bands
attributed to the gaucheꢀsyn conformation increases with temperature at the expense of the relative
intensity of the corresponding bands of the gaucheꢀanti form, which is contrary to the results
obtained from calculations (Table 2). This fact suggests that the gasꢀphase conformational
equilibrium composition might be perturbed during the cooling process. This perturbation can be
rationalized in terms of a low energy barrier for the gaucheꢀsyn→gaucheꢀanti interconversion, for
–1
25
which the reported value of 3 kcal mol can be regarded as an upper limit. Thus, due to a small
–1
barrier (probably < 3 kcal mol ), which allows for a rapid gaucheꢀanti → gaucheꢀsyn
interconversion during the deposition process, the lower energy gaucheꢀsyn rotamer on the gas is
formed at low temperatures from the gaucheꢀsyn rotamer. Thus, the gaucheꢀanti form generated at
higher temperatures at expenses of the gaucheꢀsyn form is again converted back to the lower energy
gaucheꢀsyn rotamer in the liquid He cooled matrix window. However, the presence of a gaucheꢀsyn
/gaucheꢀanti conformational equilibrium is strongly supported by (i) calculated relative energies of
two rotamers, (ii) the presence of several vibrational modes attributable to a higherꢀenergy
conformer, and (iii) the gas electron diffraction results (see below).
2
Photolysis of ClF CC(O)NCS
The UV spectrum of gaseous ClF
2
CC(O)NCS is depicted in Figure S4 (supporting
information). It shows intense and weak absorptions at 199 and 274 nm, respectively, that are
suitable to initiate UV photolysis processes.
When the matrix is irradiated 20 minutes using light with wavelength longer than 225 nm
only a small photoꢀconversion was observed. However, after exposing the matrix to UV radiation
with
2
λ = 193 nm (ArF laser, 3 mmJ) for 4 minutes the IR bands of ClF CC(O)NCS were completely
depleted.
11
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 12 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 4. IR difference spectrum recorded before and after 4 min of UV irradiation (λ = 193 nm) of
2
argon matrix isolated ClF CC(O)NCS. IR bands of newly formed species point upwards while those
of depleted ClF CC(O)NCS point downwards.
2
The IR difference spectrum showing the spectral changes of the former Arꢀmatrix isolated
2
ClCF C(O)NCS is shown in Figure 4. The photolysis mainly yields the isothiocyanate, ClF CNCS,
2
and CO. The photoproducts have been postulated taken into account the computational predictions
as listed in Table 4. Another photoevolution channel becomes apparent after a more detailed
ꢀ1
analysis of the spectrum. A band in the C=O stretching region at 1806 cm can be associated with a
ClC=O stretching band due to its position and the electronegativity of the chlorine substituent at the
carbonyl group. Thus, several bands of the photoproducts can also be attributed to the
2
rearrangement product ClC(O)CF NCS. A full list of the IR bands of the photoproducts is collected
in Table 4 together with computed frequencies.
–
1
Table 4. Observed band positions (cm ), relative intensities, and assignments for the IR bands of the Arꢀmatrix
2
isolated photolysis products of ClF CC(O)NCS(λ = 193 nm, 4 min) at 15 K.
IR (Matrix Ar)
Assignment
Molecule
Reference
ꢀ1
v (cm )
Mode
v(C≡O)
[a]
2
2
1
138.7
088.6
983.0
CO
ClC(O)CF
CClF NCS
2139
[
b]
2
NCS
v
as(NCS)
2062 (1619)
2058 (1535)
[b]
vas(NCS)
2
1
2
ACS Paragon Plus Environment

Page 13 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
[
b]
1
1
1
806.0
ClC(O)CF NCS v(C=O)
1870 (150)
2
[b]
268.2
ClC(O)CF
CClF NCS
ClC(O)CF
CClF NCS
ClC(O)CF
CClF NCS
ClC(O)CF
CClF NCS
ClC(O)CF
2
NCS v(C–N), v
v(C–N), v
s
s
(NCS) 1256(232)
(NCS) 1242 (510)
[b]
221.2/1216.4
2
[
b]
2
NCS
v
v
v
v
as(CF
2
)
1158(290)
1117 (281)
1088(212)
1142.2
[b]
2
as(CClF
2
)
[
b]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1095.7
1047.1
919.5
2
NCS
s
s
(CF
2
)
[b]
2
(CClF
2
)
1021 (345)
[b]
2
NCS v(CC)
987(50)
[
b]
2
v
as(CClF
2
)
884 (382)
833 (436)
885.4
[
b]
2
NCS vCCl
a
b
Ref. 26, This work. Frequencies computed at the B3LYP/6ꢀ311+(3df) levels of approximation.
ꢀ1
Calculated intensities in km mol are given in parentheses.
Gas electron diffraction analysis
Gas electron diffraction was used to determine the gasꢀphase structure and conformational
2
7
2
composition of ClF CC(O)NCS. The structural analysis was performed with the UNEX program.
All refinements were done using two intensity curves simultaneously (provided in Figure S5,
supporting information), one from short and another from long camera distance, which resulted
from averaging independent intensity curves obtained in experiments. For the definition of
independent geometrical parameters and their groups in leastꢀsquares refinements see Table 5. The
differences between values of parameters in one group were kept fixed on the values taken from
MP2(full)/augꢀccꢀpVTZ calculations. In order to describe the conformational behavior of
ClF CC(O)NCS by means of the GED data following models have been evaluated. The oneꢀ
2
conformer model for the gaucheꢀsyn, the gaucheꢀanti, the synꢀsyn and the synꢀanti conformers gave
total structural Rstr factors of 8.3, 8.6, 13.4 and 11.7 %, respectively. The refinement of the twoꢀ
conformer model consisting of the mixture of the gaucheꢀsyn and gaucheꢀanti conformations gave
R
str factor of 6.2 % and 58(10) % of the gaucheꢀanti form. The next consideration was the fourꢀ
conformer model. The refinement of ratios of all conformations leads to unstable results with very
high correlations between parameters. A stable solution was obtained after fixing both synꢀsyn and
synꢀanti forms to be 5 % leaving the gaucheꢀsyn and gaucheꢀanti conformations free to refine. This
model gave larger Rstr (6.7 %) and slightly worse agreement on the radial distribution functions (see
Figure 5). Thus, on the basis of electron diffraction data it is impossible to prove the presence of
synꢀsyn and synꢀanti conformers in the gas phase at the temperature of the experiment, since their
inclusion in the model
1
3
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 14 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Table 5. Experimental and theoretical parameters of ClF
2
CC(O)NCS obtained using GED method.
gaucheꢀanti
a
Parameters
gaucheꢀsyn
Calculations
GED
GED
Calculations
B3LYP/ MP2(full)/
ꢀ31G(d) augꢀccꢀpVTZ
B3LYP/ MP2(full)/
rg
re, ∠e
rg
re, ∠e
6
6ꢀ31G(d) augꢀccꢀpVTZ
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
1
3
4
5
5
6
1
2
3
1
3
4
5
5
6
O1ꢀC2
1.203(2) 1.199(2)
1.407(7) 1.399(7)
1.547(7) 1.535(2)
1.217(2) 1.213(2)
1.566(2) 1.559(2)
1.774(4) 1.767(4)
1.338(2) 1.330(2)
1.350(2) 1.343(2)
125.9(7)
1.203
1.393
1.544
1.218
1.563
1.800
1.334
1.344
125.9
1.200
1.378
1.528
1.214
1.552
1.755
1.327
1.340
126.4
122.6
111.0
138.9
109.0
110.0
110.0
175.0
110.0
109.6
108.2
109.0
1.200(2) 1.196(2)
1.404(7) 1.396(7)
1.556(2) 1.545(2)
1.217(2) 1.213(2)
1.566(2) 1.559(2)
1.775(4) 1.768(4)
1.336(2) 1.328(2)
1.352(2) 1.346(2)
124.4(7)
1.201
1.386
1.556
1.214
1.566
1.799
1.332
1.349
124.4
1.198
1.376
1.538
1.215
1.552
1.756
1.325
1.343
124.9
122.0
113.1
139.5
109.4
110.1
109.7
174.7
110.1
109.3
108.2
111.5
C2ꢀN3
C2ꢀC6
N3ꢀC4
C4ꢀS5
C6ꢀCl7
C6ꢀF8
C6ꢀF9
O1ꢀC2ꢀN3
O1ꢀC2ꢀC6
N3ꢀC2ꢀC6
C2ꢀN3ꢀC4
C2ꢀC6ꢀCl7
C2ꢀC6ꢀF8
C2ꢀC6ꢀF9
N3ꢀC4ꢀS5
Cl7ꢀC6ꢀF8
Cl7ꢀC6ꢀF9
F8ꢀC6ꢀF9
7
7
121.3(10) 122.2
120.7(10) 121.0
b
b
112.7(13) 111.9
114.9(13) 114.6
8
8
134.7(13) 136.8
135.3(13) 142.2
9
9
109.1(2)
109.5
109.7
110.4
174.9
109.3
109.1
109.0
109.5(2)
109.6
109.6
110.4
174.5
109.5
108.9
108.8
9
9
110.1(2)
110.1(2)
110.2(2)
9
9
109.8(2)
d
d
175.0
174.7
1
1
0
0
10
10
b
109.4(2)
109.5(2)
108.8(2)
109.0(8)
109.0(2)
109.0(8)
b
11
12
O1ꢀC2ꢀC6ꢀCl7
x, %
100.0(88) 103.2
115.2(48) 99.8
c
c
c
c
42(10)
75
39
58(10)
25
61
a
Vibrational corrections to get the equilibrium structure have been calculated using B3LYP/6ꢀ31G(d) harmonic and
cubic force fields. Three times standard deviations are given in parentheses. Superscript numbers 1,2,...,12 designate
groups, in which parameters were tied together between these groups in leastꢀsquares method by fixing differences
between their values.
b
c
Dependent parameter. Calculated from the ꢁGº value based on the assumption that only gaucheꢀsyn and gaucheꢀanti
d
conformers were present. Assumed value.
1
4
ACS Paragon Plus Environment

Page 15 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
did not significantly improve the agreement between experimental and model radial distribution
function. Therefore, the twoꢀconformer model with Rstr = 6.2% was considered as final. Its
refinement gives the results shown in Table 5.
The refinement of the angle N3–C4–S5 gave values nearly identical to theoretical ones but with
large standard deviations. Therefore, in the final model it was decided to fix this parameter at the
theoretical value. The largest correlations were (i) –0.69 between parameters in groups 9 and 10; (ii)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
0
.64 between parameters in groups 7 and 12; (iii) –0.63 between parameters in groups 4 and 10 (see
Table 5 for the definition of the groups). Interatomic distances, mean square amplitudes and
vibrational corrections are listed in Tables S1 and S2. Experimental Cartesian coordinates of
gaucheꢀsyn and gaucheꢀanti conformers are presented in Tables S3 and S4.
Figure 5. Experimental (open circles) and final model (line) radial distribution functions. The
difference curves for different models are shown below. The interatomic distances of the gaucheꢀanti
conformer are shown as vertical bars unless indicated gꢀs (distances in the gaucheꢀsyn conformer).
Two different theoretical approximations were used for the prediction of the stabilities of the
different conformers and the calculation of their geometrical parameters: B3LYP/6ꢀ31G(d) and
MP2(full)/augꢀccꢀpVTZ. As can be observed in Table 5, the former method is the one that better
reproduces the experimental geometrical parameters, while the later agrees with gas electron
1
5
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 16 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
diffraction experiments in the prediction of the relative stabilities of both forms.
2
The structural parameters obtained for gaucheꢀsyn ClF CC(O)NCS can be compared to a number
2
8
29
1
of related compounds, HNCS, FNCS, and FC(O)NCS, and a detailed listing of selected
parameters is provided in Table 6. The length of the isocyanate C=S bond in gaucheꢀsyn
2
ClF CC(O)NCS is similar to those of HNCS, FNCS and FC(O)NCS. The isothiocyanate N=C bond
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
is of similar length for these compounds and much closer to the different substituents with the
exception of that in FNCS. The C–N bonds between carbonyl group and NCS unit are much shorter
than a typical single N–C bond (1.46 Å), and in apparent contradiction with its energy barrier
2
behaviour discussed above, the longest being for gaucheꢀsyn ClF CC(O)NCS, while the
electronegative F substituent shorten this bond.
Some variation is observed for the almost linear NꢀCꢀS group angles and the angle CꢀNꢀC (or H–
N–C and F–N–C in the cases of HNCS or FNCS, respectively). For the latter the smallest value of
113.5° is found for FNCS. The carbonyl isothiocyanates have values of ≥130°, the maximum being
1
2
34.7(13)° for gaucheꢀsyn ClF CC(O)NCS.
Table 6. Selected structural parameters for gaucheꢀsyn ClF CC(O)NCS and the related compounds
2
HNCS, FNCS and FC(O)NCS
(N)C=S
N=C(S)
1.213(2)
C–N
C=O
<NCS
<(C/H/F)
NC
<OCN(CO)
125.9(7)
Ref.
as
ClF
2
CC(O)NCS
1.559(2)
1.399(7)
1.199(2)
175.0
134.7(13)
This
work
gaucheꢀsyn
HNCS
1.567(1)
1.557
1.207(3)
1.245
173.8(23)
170.2
131.7(19)
113.5
28
29
1
FNCS
a
FC(O)NCS syn
1.541(2)/
1.538(2)
1.215(2)/
1.220(2)
1.373(2)/
1.175(2)/
1.183(2)
173.9(2)/
173.8(1)
130.8(2)/
130.9(2)
129.4(2)/
128.2(2)
1.366(2)
as
a
Assumed parameter kept fixed during refinement. Values from the I and II nonequivalent molecules in crystal,
respectively.
Photoelectron Spectra
Photoelectron spectroscopy (PES) using a He(I) radiation (21.21 eV = 58.46 nm) is an useful
technique to study the valence electronic structure of molecules in combination with theoretical
.30, 31, 32
calculations.
2
The He(I) photoelectron spectrum of ClF CC(O)NCS is shown in Figure 6.
Outer Valence Green Function (OVGF) calculations were performed to obtain the ionization
energies in order to assign the PE spectrum. The experimental vertical ionization potentials (EI),
theoretical vertical ionization energies (E
v
; OVGF/6ꢀ311+G(d)), molecular orbitals (MO), and the
2
corresponding characters of outer valence shells for ClF CC(O)NCS are listed in Table 7.
1
6
ACS Paragon Plus Environment

Page 17 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
Additionally, the representation of the first eight HOMOs are given in Figure S6 (supporting
2
information). In agreement with the above discussion on the structure of ClF CC(O)NCS its He(I)
photoelectron spectrum is the resultant of the two weighted forms arising from the energetically
most favorable gaucheꢀsyn and gaucheꢀanti rotamers. In addition, theoretical calculations
(OVGF/6ꢀ311+G(d)) for the two isomers do not predict appreciable differences in the ionization
–1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
energies with respect to the experimental resolution of 30 meV (∼ 240 cm ). For the sake of
comparison calculated values of the lowest energy form are used for comparison in Table 7.
2
The vertical ionization energies observed in the photoelectron spectrum of ClF CC(O)NCS agree
with the calculated values of the OVGF method. The first band in the photoelectron spectrum,
centered at 10.43 eV, can be attributed to the ionization process from the highest occupied
molecular orbital (HOMO), which corresponds primarily to sulfur loneꢀpair electrons of the inꢀ
plane nonbonding orbital on the NCS group (πnb (NCS)). This ionization energy was also reported at
5
33
9.89 eV for CH
2
CHC(O)NCS and is consistent with the result of analogous molecules HNCS
9
(
9.94 eV) CH NCS (9.37 eV), GeH NCS (9.14 eV) and CH C(O)NCS, (9.75 eV), respectively,
3
3
3
showing the inductive effect of the ClCF
2
group (with respect to less electronegative groups) and
the influence of the electronegativity of the groups linked to C=O on the PI (photo ionization
energies).
The second ionization band observed at 10.54 eV can be attributed to the process involving the
outꢀofꢀplane πnb NCS molecular orbital. This assignment is supported by the computational results.
For a similar covalent molecules as CH =CHC(O)NCS this second potential was reported at 10.05
2
5
eV. The third ionization band at 11.50 eV is related with both the O lone pair and a bonded πb (NCS)
orbital (Figure S6, supporting information). The fourth and fifth ionization bands observed at 12.54
and 12.84 eV are attributed to the ejection of electrons from the two nonꢀbonding orbitals of the
chlorine atom (nCl). These PI were reported at 12.50 eV and 12.86 eV for the analogous orbitals of
23
the related molecule ClF
2
CC(O)NCO. The following two ionization bands observed at 13.54 and
1
4.48 eV are assigned as listed in the Table 7.
1
7
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 18 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 6. He(I) photoelectron spectrum (PES) of ClF CC(O)NCS.
2
Table 7. Experimental and Calculated Ionization Energies and MO Characters for
CClF
2
C(O)NCS.
a
EI exp.
eV)
Ev calc.
(eV)
Band
MO
Character
(
1
2
3
4
5
6
7
10.43
10.54
11.50
12.54
12.84
13.54
14.48
10.38
10.62
12.13
12.53
12.94
14.02
14.34
42
41
40
39
38
37
36
πnb (NCS)
πnb (NCS)
n
O
, πb (NCS)
n
Cl
nCl
π
π
b (NCS), πb (C=O)
b (NCS), πb (C=O)
a
OVGF from geometries at the B3LYP/6ꢀ 311+G(d) level of approximation for the gaucheꢀsyn form.
Photoionization Mass Spectrum
The ultraviolet photoionization mass spectrum (PIMS) of ClF CC(O)NCS was determined
2
together with the photoelectron spectra and is shown in Figure 7. The PIMS confirms the identity of
+
+
2
the sample. The spectrum of ClF CC(O)NCS mainly shows three peaks: NCS , C(O)NCS and
+
F CNCS .
2
1
8
ACS Paragon Plus Environment

Page 19 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
Figure 7. He(I) photoionization mass spectrum (PIMS) of ClF CC(O)NCS.
CONCLUSION
According to our GED results and in accord with the vibrational data and quantum chemical
calculations, ClF CC(O)NCS is present in an equilibrium of a lower energy gaucheꢀsyn and a
gaucheꢀanti conformer in the gas and liquid phases at ambient temperature. The most significant
structural parameters for the lowest energy form, gaucheꢀsyn ClF CC(O)NCS, are r (NC=S)
1.559(2) Å, r (N=CS) 1.213(2) Å, r (N–C) 1.399(7) Å, r (C=O) 1.199(2) Å, (CNC) 134.7(13)°.
2
2
e
e
e
e
∠
e
The PE spectrum of ClF CC(O)NCS is characterized by a first vertical ionization energy at 10.43
2
eV, mainly corresponding to the ejection of the primarily sulfur loneꢀpair electrons of the inꢀplane
nonbonding orbital on the NCS group. A rapid gaucheꢀanti → gaucheꢀsyn interconversion during
the matrix deposition process becomes apparent, which suggests a small CꢀN barrier of < 3 kcal
–1
mol . The presence of a second conformer is strongly supported by computational chemistry,
vibrational spectra and gas electron diffraction.
Matrix photolysis experiments with UV irradiation of
depleted the IR bands of ClF CC(O)NCS. Two main processes have been found: (i)
photodecomposition to ClF CNCS and CO, and (ii) rearrangement to ClC(O)CF NCS.
λ = 193 nm (laser Ar/F, 3 mmJ) completely
2
2
2
1
9
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 20 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
ACKNOWLEDGEMENT
The authors thank Deutsche Forschungsgemeinschaft (DFG), Alexander von Humboldt Stiftung
(
stipend for Yu.V.V.), Deutscher Akademischer Austauschdienst (DAAD, Regional Program of
Chemistry for Argentina supporting the PhD of LatinꢀAmerican students in La Plata), Agencia
Nacional de Promoción Científica y Técnica (ANPCYT), Consejo Nacional de Investigaciones
Científicas y Técnicas (CONICET), Comisión de Investigaciones de la Provincia de Buenos Aires
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
CIC), Facultad de Ciencias Exactas, Universidad Nacional de La Plata (UNLP) and Universität
Bielefeld for financial support. CODV and RMR acknowledge CONICET and ICCAS (Institute of
Chemistry of the Chinese Academy of Sciences) for a grant to travel and stay in Beijing. CODV
thanks the Chinese Academy of Sciences for a Visiting Professorship Award for the Senior
International Scientists 2011 and for the grant to travel and stay in Beijing.
Supporting information available: It contains the ClF
2
CC(O)NCS molecular electron scattering
19
13
intensity curve (Figure S1). The F and C NMR spectra of ClF CC(O)NCS, (Figure S2 and S3);
2
UVꢀVis spectrum of gaseous ClF
2
CC(O)NCS, ClF
2
CC(O)NCO, ClF
2 3
CC(O)N (Figure S4) and
characters of the highest occupied molecular orbitals of ClF
2
CC(O)NCS (Figure S6). Total
molecular electron scattering intensity curve (Figure S5); interatomic distances, mean square
amplitudes and vibrational corrections (Tables S1 and S2); experimental Cartesian coordinates of
gaucheꢀsyn and gaucheꢀanti conformers (Tables S3 and S4). This information is available free of
charge via the Internet at http://pubs.acs.org
2
0
ACS Paragon Plus Environment

Page 21 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
References
(
1) Ramos, L. A.; Ulic S. E.; Romano, R. M.; Tong, S.; Ge M. F.; Vishnevskiy, Yu. V.; Berger, R. J.
F.; Mitzel, N. W.; Beckers, H. et al. Chlorodifluoroacetyl Cyanide, ClF
Structure, and Spectroscopic Characterization, Inorg. Chem. 2011, 50, 9650–9659.
2) Koch, R.; Wentrup C. Rearrangements of Acyl, Thioacyl, and Imidoyl (Thio)cyanates to
2
CC(O)CN: Synthesis,
(
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Iso(thio)cyanates, Acyl Iso(thio)cyanates to (Thio)acyl Isocyanates, and Imidoyl Iso(thio)cyanates
to (Thio)acyl Carbodiimides, RCXꢀYCN RCXꢀNCY RCYꢀNCX RCYꢀXCN (X and Y = O, S,
NR′). J. Org. Chem. 2013, 78(5), 1802ꢀ1810.
(
3) Sommerlade, R.; Ekici, P.; Parlar H. Gas Phase Reaction of Selected Isothiocyanates With OH
Radicals Using a Smog Chamberꢀmass Analyzer System, Atmos. Environ. 2006, 40, 3306–3315.
4) Vermeulen, M.; Zwaneburg, B.; Chittenden, G. J. F.; Verhagen, H. Synthesis of Isothiocyanateꢀ
(
derived Mercapturic Acids, Eur. J. Med. Chem. 2003, 38, 729–737.
(5) Ge, M. F.; Ma, Ch.; Tong, S.; Xue W.; Pu, Z.; Wang D. Molecular and Electronic Structures of
Acryloyl Isothiocyanate, CH2=CHC(O)NCS: A Joint Experimental and Theoretical Study,
New J. Chem. 2009, 33, 2155–2161.
(6) Campbell, N. L.; Gillis, C. J.; Klapstein, D.; Nau, W. M.; Balfour, W. J.; Fougere, S. G.
Vibrational Spectra and Conformational Behaviour of Carbonyl Isothiocyanates XꢀCOꢀNCS, X = F,
Cl, Br, MeO, EtO, and Acetyl Isothiocyanate CH ꢀCOꢀNCS Spectrochim. Acta 1994, 51A, 787–
3
798.
(7) Xiao, H. Y.; Xue, Y.; Xu, X. J.; Xie, D. Q.; Yan, G. S. Theoretical Studies on Vibrational
Spectra of FC(O)NCS, Acta Chim. Sin. 2000, 58, 414 – 417.
(8) Durig, J. R.; Giurgis, G. A.; Krutules, K. A. Raman and Infrared Spectra, Conformational
Stability, Barriers to Internal Rotation, and Ab Initio Calculations of Trifluoroacetyl Isocyanate, J.
Mol. Struct. 1994, 328, 55–75.
(
9
) Zeng, X. Q.; Yao, L.; Ge, M. F.; Wang, D. X. Experimental and Theoretical Studies on the
Electronic Properties of Acetyl Pseudohalides CH C(O)X (X=NCO NCS and N ) J. Mol. Struct.
006, 789, 92–99.
3
3
2
(10) Gombler, W.; Willner H. A Method for Opening and Resealing Glass Ampoules Several Times
Under Sustained Vacuum, J. Phys. E: Sci. Instrum. 1987, 20, 1286–1288.
(
11) Schnöckel, H. G.; Willner, H.; Infrared and Raman Spectroscopy, Methods and Applications;
1994, pp 297.
12) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;
(
Montgomery Jr., J. A.; Vreven, T.; Kudin, K. N.; Burant et al. Gaussian 03; Revision B.04 ed.;
Gaussian, Inc.: Pittsburgh PA, 2003.
2
1
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 22 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(13 ) Møller, C.; Plesset, M. S. Note on an Approximation Treatment for ManyꢀElectron Systems,
Phys. Rev. 1934, 46, 618ꢀ622.
(
14) Granovsky, A.A.; Firefly version 7.1.G, www http://classic.chem.msu.su/gran/firefly/index.html.
(15) Willet, G. D. 1977, Ph. D. Thesis, La Trobe University (Australia).
16) Berger, R. J. F.; Hoffmann, M.; Hayes, S. A.; Mitzel, N. W. An Improved Gas Electron
(
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Diffractometer—The Instrument, Data Collection. Reduction and Structure Refinement Procedures,
Z. Naturforsch. B 2009, 64b, 1259–1268.
(17) Vishnevskiy, Yu. V. The Initial Processing of the Gas Electron Diffraction Data: An Improved
Method for Obtaining Intensity Curves From Diffraction Patterns, J. Mol. Struct.. 2007, 833, 30–41
(18) Vishnevskiy, Yu. V. The Initial Processing of the Gas Electron Diffraction Data: New Method
For Simultaneous Determination of the Sector Function and Electron Wavelength From Gas
Standard Data, J. Mol. Struct. 2007, 871, 24–32.
.
(19) Sipachev, V. A. The Use of QuantumꢀMechanical ThirdꢀOrder Force Constants in Structural
Studies, J. Mol. Struct. 2004, 235ꢀ240.
(
20) Sipachev, V. A. Local Centrifugal Distortions Caused by Internal Motions of Molecules
Mol. Struct. 2001, 567–568, 67–72.
21) Sipachev, V. A. Anharmonic Corrections to Structural Experiment Data, Struct. Chem. 2000,
1, 167 – 172.
, J.
(
1
(22) Sipachev, V. A. Calculation of Shrinkage Corrections in Harmonic Approximation, J. Mol.
Struct.: THEOCHEM 1985, 121, 143 – 151.
(
23) Ramos, L. A.; Ulic, S. E.; Romano, R. M.; Tong, S.; Ge, M. F.; Beckers, H.; Willner H., Della
Védova C. O. Chlorodifluoroacetyl Isocyanate, ClF CC(O)NCO: Preparation, Structural and
Spectroscopic Studies J. Phys. Chem. A. 2012, 116(47), 11586ꢀ11595.
24) Ramos L. A.; Zeng X.; Ulic S. E.; Beckers H.; Willner H., Della Védova C. O.
Clorodifluoroacetyl Azide, ClF CC(O)N : Preparation and Properties, J. Org. Chem. 2012, 77(15),
456ꢀ6462.
25) Bodenbinder, M.; Ulic, S. E.; Willner, H. A GasꢀPhase and Matrix Isolation Study of the
Equilibrium CH ONO (cis) ↔ CH ONO (trans) by FTIR Spectroscopy, J. Phys. Chem. 1994, 98,
441–6444.
26) Dubost, H. Infrared Absorption Spectra of Carbon Monoxide in Rare Gas Matrices,
Chem. Phys. 1976, 12, 139–151.
2
,
(
2
3
6
(
3
3
6
(
(27) Vishnevskiy, Y. V., UNEX version 1.5, http://molstruct.chemport.ru.
(28) Yamada, K.; Winnewisser, M.; Winnewisser, G.; Szalanski, L.B.; Gerry, M.C.L. Ground State
15
13
34
Spectroscopic Constants of H NCS, HN CS, and HNC S, and the Molecular Structure of
2
2
ACS Paragon Plus Environment

Page 23 of 24
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
Isothiocyanic Acid, J. Mol. Spectrosc. 1980, 79, 295–313.
29) Durig, J.R.; Zheng, Ch.; Deeb, H. On the Structural Parameters and Vibrational Spectra of
(
Some XNCS and XSCN (X=H, F, Cl, Br) Molecules, J.Mol. Struct. 2006, 784, 78–92.
(30 ) Yao, L.; Ge, M. F.; Wang, W.; Zeng, X.; Sun, Z.; Wang, D. Gas Phase Generation and
Electronic Structure Investigation of Chlorosulfanyl Thiocyanate ClSSCN
Inorg. Chem. 2006, 45, 5971–5975.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(31 ) Zeng, X.; Ge, M.F.; Sun, Z.; Wang, D. Nitrosyl Isocyanate (ONNCO): Gas Phase Generation
and a HeI Photoelectron Spectroscopy Study, Inorg. Chem. 2005, 44, 9283–9287.
(
32) Zeng, X.; Liu F.; Sun Q.; Ge M.F.; Zhang, J.; Ai, X.; Meng L.; Zheng, S.; Wang, D. Reaction of
AgN With SOCl : Evidence for the Formation of Thionyl Azide SO(N Inorg. Chem. 2004, 43,
799–4801.
33) Cradock, S.; Ebsworth, E.A.V.; Murdoch, J.D. Photoelectron Spectra of Some Group 4
3
2
3 2
)
4
(
Pseudohalides and Related Compounds, J. Chem. Soc. 1972, 68, 86–100.
2
3
ACS Paragon Plus Environment

The Journal of Physical Chemistry
Page 24 of 24
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
TOC
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
4
ACS Paragon Plus Environment