FT-IR and FT-Raman investigations of the chemosensing material para-hexafluoroisopropanol aniline

Article abstract of DOI:10.1002/jrs.2536

As an important chemosensingmaterial involving hexafluoroisopropanol (HFIP) for detecting nerve agents, para-HFIP aniline (p-HFIPA) has been firstly synthesized through a new reaction approach and then characterized by nuclear magnetic resonance and mass

Full text of DOI:10.1002/jrs.2536

Research Article
Received: 17 August 2009
Accepted: 17 September 2009
Published online in Wiley Online Library: 13 November 2009
(wileyonlinelibrary.com) DOI 10.1002/jrs.2536
FT-IR and FT-Raman investigations
of the chemosensing material
para-hexafluoroisopropanol aniline
Lingtao Kong,a,b Jin Wang,a∗ Yong Jia,a,b Zheng Guoa and Jinhuai Liua∗
As an important chemosensing material involving hexafluoroisopropanol (HFIP) for detecting nerve agents, para-HFIP aniline
(p-HFIPA) has been firstly synthesized through a new reaction approach and then characterized by nuclear magnetic resonance
and mass spectrometry experiments. Fourier transform infrared absorption spectroscopy (FT-IR) and FT-Raman spectra of
p-HFIPA have been obtained in the regions of 4000–500 and 4000–200 cm−1, respectively. Detailed identifications of its
fundamental vibrational bands have been given for the first time. Moreover, p-HFIPA has been optimized and vibrational
wavenumber analysis can be subsequently performed via density functional theory (DFT) approach in order to assist these
identifications in the experimental FT-IR and FT-Raman spectra. The present experimental FT-IR and FT-Raman spectra of
c
p-HFIPA are in good agreement with theoretical FT-IR and FT-Raman spectra. Copyright ꢀ 2009 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: p-HFIPA; FT-IR spectroscopy; FT-Raman spectroscopy; vibrational properties; DFT approach
Introduction
Here, we describe a facile synthesis of one powerful hydrogen-
bonding compound, i.e. para-HFIP aniline (p-HFIPA). If it is
functionalized on single-wall carbon nanotubes (SWNTs), the hy-
brids can be applied as powerful intermediate sensing material
possessing excellent sensitivity and selectivity for detection of
explosives and chemical warfare agents, e.g. 2,4-dinitrotoluene,
2,4,6-trinitrotoluene, sarin or its simulant dimethyl methylphos-
phonate (DMMP), etc. It can be expected that the sensors based
on SWNTs functionalized with p-HFIPA can efficiently improve
their sensitivities and selectivities due to efficient accumulation
of chemical vapors through the strong hydrogen-bond acidity of
HFIP groups in p-HFIPA. At present, many kinds of organic poly-
mers containing HFIP groups have been synthesized and applied
in some fields;[6,14–22] however, the nanomaterials functionalized
with p-HFIPA have never been reported.
Hexafluoroisopropanol (HFIP) substituents have drawn consid-
erable attention due to their high sensitivities and selectivities
for explosives and chemical warfare agents.[1–6] HFIP maxi-
mizes hydrogen-bond acidity of hydroxyl groups by electron-
withdrawing effect of fluorine atoms and minimizes hydrogen-
bond basicity of hydroxylic oxygen atoms simultaneously, which
contributes to efficiently inhibiting self-association.[7] Moreover,
the HFIP group with a strong hydrogen-bonding effect can bring
about some remarkable changes in the physical, chemical and
biological properties of new compounds or materials, which are
suitable for diverse applications in the areas of materials science,
medical science and industry.[8–11] The obvious absorption of
organophosphorus vapors on the compound involving HFIP sub-
stituents was firstly recognized by Barlow et al.[12,13] Subsequently,
organic compounds containing HFIP groups can act as sensi-
tive sensors for explosives, chemical agents or simulants,and/or
volatile organic compounds; moreover, these compounds can be
applied in acoustic wave devices, chemiresistors, chemicapacitors,
microcantileversandfluorescencesensingmethods.[1,2,8,14–21] Ad-
ditionally,HFIPsubstituents,whichcanserveastheabsorbentlayer
on these sensors and interact with the strongly hydrogen-bond
basic compounds via hydrogen bonding, contribute to absorbing
the vapors into the polymer film on the device surface so as to
increase sensing response.
Comparison between vibrational region of fluoroalcohol hy-
droxyl in the HFIP groups before and after organophosphorus
and explosive vapors’ absorption via Fourier transform infrared
absorption spectroscopy (FT-IR) have been reported recently. It is
suggested that the absorption wavenumber of hydroxyls could be
∗
Correspondence to: Jin Wang, Key Laboratory of Biomimetic Sensing and
Advanced Robot Technology, Institute of Intelligent Machines, Chinese
Academy of Sciences, Hefei, AnHui 230031, PR China. E-mail: jwang@iim.ac.cn
Jinhuai Liu, Key Laboratory of Biomimetic Sensing and Advanced Robot
Technology, Institute of Intelligent Machines, Chinese Academy of Sciences,
Hefei, AnHui 230031, PR China. E-mail: jhliu@iim.ac.cn
More recently, investigations on sensors based on fluoroalco-
hol hydrogen-bond acidic groups functionalized nanomaterials
have been extensive. Carbon nanotubes modified with HFIP
groups can greatly improve sensitivities and selectivities of the
sensors.[1,2] Undoubtedly, more analogous materials with fluo-
rinated hydrogen-bond acidic groups will be developed in the
future.
a
Key Laboratory of Biomimetic Sensing and Advanced Robot Technology,
Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei, AnHui
230031, PR China
b
School of Chemistry and Chemical Engineering, AnHui University, Hefei, AnHui
230039, PR China
c
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Copyright ꢀ 2009 John Wiley & Sons, Ltd.

L. Kong et al.
shifted in the presence of DMMP or nitrobenzene due to forma-
tion of hydrogen bond.[5,12,23] Hence, it is important to investigate
infrared spectra of HFIP-containing compounds. To our knowl-
edge, no detailed vibrational IR and Raman analyses have been
performed on the p-HFIPA. Hence, the experimental FT-IR and
FT-Raman spectra of as-prepared p-HFIPA have been obtained in
the present work. On the other hand, its vibrational spectra can
be independently calculated in order to support identifications of
vibrational modes and to be compared with its experimental FT-IR
and FT-Raman spectra and also to provide spectroscopic data
which are useful in comparison with some other HFIP-substituted
compounds.
derivatives with respect to the Cartesian coordinates. As far as the
theoretical Raman spectrum is concerned, the intensity of a Stokes
Raman band is proportional to its differential scattering cross
section; moreover, the theoretical differential Raman scattering
cross section of a Stokes band can be associated with the normal
mode. In order to obtain information on the form of the normal
modes, the potential energy distribution (PED) in terms of the
internal coordinates has been calculated.
Results and Discussion
Stretching vibrational bands of p-HFIPA
According to optimization of geometry of p-HFIPA, it has a
non-planar structure with C1 point group symmetry. All the 66
fundamentalvibrationsareactiveinbothIRabsorptionandRaman
scattering. Two observed absorption bands with positions at ca
3397and3328 cm−1 canbeassignedasasymmetricandsymmetric
stretches of NH2, respectively (Fig. 2 and Table 1). Compared
to previously observed asymmetric and symmetric stretching
vibrational bands of aniline, which are positioned at 3508 and
Experimental
Hexafluoroacetone trihydrate (98%) was obtained from Sigma.
Aniline (97%) and all other chemicals (extra purity grade) were
obtained from Shanghai Chemical Co. Ltd (Shanghai, China). FT-IR
spectrawererecordedonaNexus-870spectrophotometer(4 cm−1
resolution, KBrpellets). Nuclearmagneticresonance(NMR)spectra
were acquired at 25 ◦C using a Bruker Avance spectrometer. Mass
spectra were recorded on a Micromass GCT-MS. FT-Raman spectra
were measured with a Renishaw 2000 model confocal microscopy
Raman spectrometer (2 cm−1 resolution), with a CCD detector
and a holographic notch filter (Renishaw Ltd, Gloucestershire, UK).
Radiation of 514.5 nm from an air-cooled argon ion laser was used
for the FT-Raman excitation.
3422 cm−1 [25]
respectively, the two stretching vibrational bands
,
are shifted toward lower wavenumbers when HFIPA-substituted
molecule is formed. It can be expected that obvious hydrogen
bondingcanbeformedbetweenOHandNHofp-HFIPA;moreover,
the force constant of amino group in p-HFIPA is decreased and
its stretching vibrational bands are redshifted in comparison with
aniline (Table S1, Supporting Information). As illustrated in Table 1,
the calculated vibrational wavenumbers of NH2 stretches are in
agreementwiththeexperimentalobservationsifthescaling factor
0.9613[26–31] for B3LYP/6-311++G(d,p) is employed. In order to
checkthereliabilityforthepredictionofthestretchingvibrations,a
vibrationalwavenumberanalysisofanilinebasedontheoptimized
structure is also performed at the B3LYP/6-311++G(d,p) level.
Furthermore, the corrected asymmetric and symmetric stretches
of NH2 in aniline are located at 3533 and 3438 cm−1, respectively,
which are well consistent with the previous observations and
theoretical results using B3LYP/6-311++G(df,pd).[32] On the other
hand, it is suggested that intensity of the symmetric stretches of
NH2 is much stronger than those of the asymmetric stretches of
NH2 and stretching vibration of hydroxyl group, according to the
theoretical analysis of Raman activation of NH stretching vibration.
As shown from experimental observations of FT-Raman spectrum
in Fig. 3, the intensity of NH2 symmetric stretching vibration at
3333 cm−1 is obviously stronger than that of the NH2 asymmetric
stretching vibration at 3406 cm−1, which is in agreement with the
theoretical prediction. However, as shown from FT-IR spectrum
(Fig. 2), the stretching vibrational band of hydroxyl could not be
observed due to overlapping with the broad absorption from NH
stretches in the present experiment.
Aniline (0.0931 g, 1.0 mmol) and p-toluenesulfonic acid (0.01 g)
were dissolved in toluene (10 ml) in the presence of small amount
of molecular sieves under an atmosphere of Ar. After heating to
100 ◦C, the toluene solution (5 ml) of hexafluoroacetone trihydrate
(0.220 g, 1.0 mmol) was then added dropwise over 0.5 h. The
temperaturewasincreasedto110 ◦Candmaintainedbetween110
and 120 ◦C via heating for 2 days under magnetic stirring. Then,
the mixture was cooled and filtered to yield 0.16 g crude product.
Recrystallization gave pure compound (0.11 g, 69%) with rose pink
◦
1
color. H NMR [400 MHz, (CD3)2SO, 25 C, transcranial magnetic
stimulation (TMS), δ] (refer to Fig. S1, Supporting Information):
7.291 ppm (d, benzene-2H, J = 8.44 Hz), 6.619 ppm (d, benzene-
2H, J = 8.74 Hz), 5.421 ppm (s, NH2), 8.158 ppm (s, OH); 19F
NMR (376 MHz, 25 ◦C, TMS, δ): −74.308 ppm. Experimental 1H
NMR spectrum is in good agreement with the theoretical NMR
spectrum (shown in Fig. 1) (7.796, 7.717, 6.770, 6.712 ppm). High
resolution mass specra (HRMS): calculated for C9H7NOF6, 259.0432
(M+), found 259.0441.
Computational Methods
DFT has been used to calculate the equilibrium structures of
C9H7NOF6 in the form of Becke’s three-parameter exchange
functional in combination with the Lee, Yang and Parr (LYP)
correlation functional (B3LYP) combined with split valence basis
sets 6-311++G(d,p). Equilibrium molecular geometry was fully
optimized and harmonic vibrational wavenumber analysis was
then performed to confirm the minima on the potential energy
surface (no imaginary vibrational wavenumbers). All calculations
were performed using the GAUSSIAN03 program package.[24] In
order to assist assignments of vibrational modes, the theoretical
infrared and Raman spectra were calculated. The infrared
intensities were calculated on the basis of the dipole moment
The C–H stretching bands of the phenyl ring in p-HFIPA can be
observedat3083, 3069, 3052and3030 cm−1. Thewavenumbersof
the C–H stretching vibrations calculated at B3LYP/6-311++G(d,p)
level can be in good agreement with the present observations if
thescalingfactor0.9613forvibrationalwavenumbersisemployed.
As far as the C–H stretching bands in p-HFIPA are concerned, the
C–H stretches can be divided into three types, i.e. two stretches
assigned to be C–H groups which are close to the HFIP group
and one degenerate stretch at lower wavenumbers attributed
to be C–H groups nearing amino substituent. The observations
and assignments of C–H stretches in aniline were also located
between 3000 and 3100 cm−1 in previous experimental (Table
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FT-IR and FT-Raman investigations of p-HFIPA
10000
50000
0
7.40
7.30
7.20
7.10
7.00
6.90
6.80
6.70
6.60
6.50
ppm (t1)
Figure 1. Experimental and theoretical NMR spectra of p-HFIPA. (a) Observed and (b) calculated with B3LYP/6-311+G(2d,p) with reference TMS.
S1, Supporting Information) and theoretical works,[33,34] which
implies that the present assignment of C–H stretching vibrations
in p-HFIPA should be reliable. In the Raman spectrum, four bands
at 3088, 3069, 3051 and 3031 cm−1 can be assigned to be these
vibrations. Moreover, PED calculations suggest that all the C–H
vibrations in the phenol rings are pure modes. Unlike the C–N
stretch in aniline at 1282 cm−1 (Table S1, Supporting Information),
the observed vibrational band at 1308 cm−1 can be assigned
to be the C–N stretch in p-HFIPA. As illustrated in Table 1,
the stretching vibration C–N has predominant contribution to
mode Q51 (1310 cm−1) in calculations, which is perfectly in
agreement with the observations. In the case of the p-HFIPA,
the symmetric C–C stretching vibration in HFIP group is located
at 1260 cm−1 using B3LYP/6-311++G(d,p), which is obviously
higher than its corresponding antisymmetric stretching vibration
at 1199 cm−1. In the experimental IR spectrum, a very strong B/A
hybridized band at 1264 and 1221 cm−1 could be observed and
assigned as symmetric and asymmetric C–C stretching vibrations
in HFIP group, respectively. In contrast, the Raman activity of the
vibrational band at 1254 cm−1, which is assigned as symmetric
C–C stretching vibrations in the HFIP group, is proven to be
weak. Compared to the vibrational mode Q45 with position at
1187 cm−1 in the the p-HFIPA, PED calculations suggest that
mode Q46 with position at 1190 cm−1 is shown as the coupling of
the in-phase C–F stretch and the C–C (between C3F6 and Ph ring)
stretching vibration; on the contrary, the in-phase C–F stretch
plays a dominant role in contributing to the mode Q45 (Table 1).
Compared to the C–F in-phase asymmetric stretch in HFIP
corresponding to bands at 1146 cm−1[35] (Table S1, Supporting
Information), the very strong bands at 1188 cm−1 are associated
with the C–F in-phase asymmetric stretch in the experimental
IR spectrum of p-HFIPA and the band structure appears as an
A-typeband. IncomparisonwiththeC–Fin-phasestretch, theC–F
out-of-phase asymmetric stretch is redshifted toward 1151 cm−1
and its band structure can be observed as C/B hybridized band.
It should be noted that the vibrational wavenumber of the
C–F in-phase asymmetric stretch in p-HFIPA is obviously higher
than that of the C–F out-of-phase asymmetric stretch according
to the present calculations and observations. For comparison
with p-HFIPA, parental HFIP is also calculated at the B3LYP/6-
c
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L. Kong et al.
much stronger than those of the C–F out-of-phase asymmetric
stretches, which are in good agreement with the conclusions on
p-HFIPA. Additionally, the observations and calculations of the
C–F stretches in hexafluorothioacetone also suggest that the C–F
in-phase stretches were higher in wavenumbers than that of out-
of-phaseC–Fstretches,[36,37] whichsupportsthepresenttendency
in p-HFIPA.
The C–O stretching vibration in the experimental observations
can be observed at 1121 cm−1 and appears as C/B hybridized
band. As seen from the vibration of the p-HFIPA, the calculated
wavenumber of the C–O stretch is located at 1109 cm−1 and the
dipole moment is changed between the c-axis and the b-axis,
which is in good agreement with the experimental observations.
The breathing vibrational mode of the phenyl ring can be
observed at 880 cm−1 and band structure appears as C-type band.
According to a vibrational wavenumber analysis of p-HFIPA, the
ring breathing vibration at 845 cm−1 using B3LYP/6-311++G(d,p)
is obviously redshifted in contrast with the trigonal ring breathing
vibration (1029 cm−1), viz, the C–C–C in phenyl ring out-of-phase
stretches. Moreover, as illustrated in Table 1, the infrared activity of
theformerisstrongerthanthatofthelatter.Incomparisonwiththe
C-type band of the former, the band structure of the latter could
be shown as A/B hybridized band, which is also reflected from its
corresponding dipole moment mainly changing along a-axis.
Deformation vibrational bands of p-HFIPA
Although the Q58 mode at 1650 cm−1 can be ascribed
to be the coupled vibrations involving in-phase stretches
C(2)–C(3)/C(5)–C(6) of the p-HFIPA and in-plane bending (inp)
vibration of NH2, the inp vibration of NH2 in p-HFIPA mainly con-
tributestothemodeQ59at1668 cm−1. Thismodecanbeassigned
to the bands at 1617 cm−1 in the FT-IR spectrum of p-HFIPA. As
illustrated in Table 1, PED calculations indicate that the vibrational
mode at the 1667 cm−1 is almost a pure mode; in contrast, the
modeatthe1650 cm−1 isobviouslyahybridizedvibrationalmode.
As shown in the experimental IR spectrum of p-HFIPA, the
NH2 rocking vibration can be observed at 1086 cm−1 as A/B hybrid
band. AsillustratedinTable 1, thepredominantcontributionofthe
mode Q40 of the p-HFIPA at 1076 cm−1 originated from the NH2
Figure 2. Experimental and theoretical FT-IR spectra of p-HFIPA at the
range of 4000–500 cm−1. (a) Observed and (b) calculated with B3LYP/6-
311++G(d,p) without using scaling factor.
311++G(d,p) level. The in-phase asymmetric stretches of C–F
can be located at 1188 and 1177 cm−1, whereas the out-of-
phase asymmetric stretches of C–F are shifted to the lower
wavenumbers, viz, 1138 and 1081 cm−1. Moreover, the infrared
activities of the C–F in-phase asymmetric stretches of HFIP are also
Table 1. Comparison of the experimental fundamental vibrational wavenumbers (cm−1) and theoretical harmonic wavenumbers (cm−1) and
infrared intensities (km mol−1) and Raman scattering activities (SR, Å4 amu−1) of p-HFIPA
Calculated wavenumbers using
Observed wavenumbers
(cm−1
B3LYP/6-311++G(d,p)
)
(cm−1
)
FT-IR
Raman
Unscaled
Scaleda
IR intensity Raman activity
Characterization of normal modes with PED (%)
ν(O–H) (100)
–
3537
3406
3333
3088
3069
3051
3031
1616
–
3808
3681
3580
3225
3197
3164
3163
1668
1650
1613
1549
1468
3660
3539
3441
3100
3073
3041
3041
1658
1640
1603
1540
1459
51
22
39
54
61
3397 m
3328 m
3083 w
3069 w
3052 w
3030 w
1617 ms
–
νas(N–H) (100)
244
71
νs(N–H) (100)
0.7
2.6
15
ν(C–H) (100)
87
ν(C–H) (100)
104
86
ν(C–H) (100)
11
218
20
ν(C–H) (100)
61
ρinp(N–H) (92)
32
ρinp(N–H) (64), in-phase ν(C–C) of phenyl ring (36)
νas(C–C) (83)
–
–
14
1.4
1520 m
–
1512
–
81
3.9
0.1
Out-of-phase νs(C–C) (32), in-phase γ (C–H) (45)
Out-of-phase ν(C–C) (38), out-of-phase ρinp(C–H) (43)
0.7
c
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FT-IR and FT-Raman investigations of p-HFIPA
Table 1. (Continued)
Calculated wavenumbers using
B3LYP/6-311++G(d,p)
(cm−1
Observed wavenumbers
(cm−1
)
)
FT-IR
Raman
Unscaled
Scaleda
IR intensity Raman activity
Characterization of normal modes with PED (%)
ρinp(COH) (91)
1373 w
–
1373
–
1373
1366
1334
1318
1260
1236
1217
1199
1190
1187
1168
1147
1123
1109
1076
1029
976
1365
1358
1326
1310
1252
1229
1210
1192
1183
1180
1161
1140
1116
1102
1070
1023
970
40
4
5.6
0.1
3.3
7.6
1.6
Out-of-phase γ (C–H) (72), γ (N–H) (14)
Out-of-phase νas(C–C) (57), γ (C–H)(26), ρinp(COH) (11)
ν(C–N) (73), γ (C–H)(16)
1342 w
1308 m
1339
1308
1254
1231
–
18
60
1264 PR vs
–
292
28
νs(C–C) in C2F6 (87)
21
16
4.3
23
5.2
ν(C–C) in C2F6 and Ph (65), νas(C–C) in C2F6 (14)
In-phase ρinp(C–H) (81)
–
68
1221 vs
–
–
233
313
390
4
νas(C–C) in C2F6 (69) and ρinp(C–H) (20)
In-phase νas(C–F) (58), ν(C–C) in C3F6 and Ph (27)
In-phase νas(C–F) (89)
1187
–
1188 vs
1170 w
–
–
0.7
0.8
1.4
2.7
1.3
0.6
0.1
0.6
2
Out-of-phase ρinp(C–H) (75), out-of-phase νas(C–F) (12)
Out-of-phase νas(C–F) (78), ν(C–O) (12)
Out-of-phase νas(C–F) (74), ν(C–O) (15)
ν(C–O) (88)
1142
–
0.9
1151 m
1121 m
1086 w
1020 vw
–
61
119
15
–
1083
–
γ (N–H) (91)
3
Out-of-phase ν(C–C) in phenyl ring (84)
tw(C–H) (99)
–
0.6
968 m
943 ms
–
961
937
–
967
961
35
88
70
23
45
1
Out-of-phase ω(C–H) (93)
948
942
νas(C–C) in C3F6 (48), ω(C–H) (52)
γ (COH) (59), ω(C–H) (30)
918
912
2.1
880 w
829 mw
–
887
825
–
845
840
28
10
0.4
Ring breath (86)
833
828
In-phase ρoop(C–C) in phenyl ring (46), ω(C–H) (47)
Out-of-phase ρoop(C–C) in phenyl ring (44), ω(C–H) (51)
824
819
736 w
747
744
740
12
6.8
In-phase ρinp(C–F) (57), out-of-phase ρoop(C–C) in phenyl
ring (38)
–
722
–
742
702
658
631
606
560
543
535
531
498
487
423
408
375
355
346
332
330
311
297
286
259
251
738
698
654
627
602
557
540
532
528
495
484
420
406
373
353
344
330
328
309
295
284
257
249
9
1.4
0.1
5.5
2
ρinp(C–F) (41), out-of-phase ρoop(C–C) in phenyl ring (49)
Out-of-phase ρinp(C–F) (84)
Ring torsion (85)
707 m
43
–
645
–
0.7
638 PR vw
7
4
ρinp(C–C–O) in C2F6 (67), ring torsion (21)
Ring torsion (68), in-phase ρinp(C–F) (13)
Out-of-phase ρ(C–F) (72), ring ω(18)
In-phase ρ(C–F) (39), ω(N–H) (30) and ring ω(25)
ω(N–H) (46), ring ω(51)
–
603
553
528
–
0.1
0.6
1.5
0.8
0.7
5.7
0.4
0.1
1.2
0.7
0.9
1.0
0.8
1.4
0.2
1.8
5.7
0.4
0.8
566 vw
2
–
2
539 PR w
35
5
–
–
Out-of-phase ρ(C–F) (93)
503 m
498
–
171
152
ω(N–H) (86)
–
–
–
–
–
–
–
–
–
–
–
–
–
ω(N–H) (92)
–
4.4
0.8
12
tw(ring) (81)
406
–
ρinp(C–C–N) (94)
Ring ω(58), ω(N–H) (33)
352
–
26
11
21
53
69
9
ω(C–O–H) (65), tw(N–H) (22), ring ω(11)
γ (C–O–H) (55), ω(C–F) (21), tw(N–H) (13)
tw(N–H) (78), ω(O–H) (12)
tw(N–H) (46), ω(O–H) (53)
ω(O–H) (91), tw(N–H) (8)
–
328
304
293
274
255
–
ω(O–H) (64), ω(C2F6) (25)
0.7
1.3
10
ρoop(FC–C–CF) (90)
ρoop(OH–C–C2F6) (84)
ρoop(OH–ring–NH2) (41), ω(O–H) (45)
ν, Stretching; νs, symmetrical stretching; νas, asymmetrical stretching; ρ, bending; ρinp, in-plane bending; ρoop, out-of-plane bending; γ , rocking; tw,
twisting; ω, wagging.
a High and low wavenumbers are scaled by the factors of 0.9613[26–31] and 0.9940.[36]
c
J. Raman Spectrosc. 2010, 41, 989–995
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
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L. Kong et al.
vibrational wavenumber analysis of the two vibrational modes
supportstheexperimentalidentifications.Inconclusion,thescaled
vibrational wavenumbers of p-HFIPA using the DFT approach
are in good agreement with the experimental observations,
suggesting that the present vibrational assignments are reliable.
Considering the fact that the HFIP derivatives are being widely
used in chemosensing materials for detecting some nerve agents,
the present detailed infrared spectrum analysis of p-HFIPA
could provide valuable information for identifying more novel
chemosensing materials involving HFIP.
Acknowledgements
This work is supported by the National High Technology Research
and Development Program of China (grant No. 2007AA022005),
the National Basic Research Program of China (grant No.
2007CB936603) and the National Natural Science Foundation of
China (Grant Nos. 60604022 and 10635070).
Supporting information
Supporting information may be found in the online version of this
article.
Figure 3. Comparison of FT-Raman spectra of p-HFIPA. (a) Observed and
(b) calculated with B3LYP/6-311++G(d,p).
References
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is blueshifted compared to that (1054 cm−1) in aniline (Table S1,
Supporting Information). In addition, the NH2 wagging band can
also be observed at 503 cm−1 in p-HFIPA. As shown from Fig. 2, the
degenerate CF3 deformation can be observed at 707 cm−1 and the
band contour appears as C-type band. According to vibrational
wavenumber analysis of p-HFIPA (Table 1), the vibrational band at
702 cm−1 can be assigned as out-of-phase CF3 bending vibration,
which is similar to the previous observations on CF3 deformations
in CF3I molecule.[38,39] Although the infrared activity of ring torsion
is quite weak, the Raman activity of ring torsion is relatively strong,
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Conclusions
p-HFIPA has been synthesized through a new facile route, i.e.
hexafluoroacetone trihydrate reacting with aniline in toluene with
the aid of p-toluenesulfonic acid. Its FT-IR and FT-Raman spectra
have been obtained for the first time. In order to assist the new
identifications of its fundamental vibrational bands, vibrational
wavenumber analysis of p-HFIPA based on optimized geometry
has been given. Some new important findings are given below.
p-HFIPA has been optimized through DFT approach, i.e.
B3LYP combined with 6-311++G(d,p) basis sets. The stretching
vibrational wavenumbers of NH2 in p-HFIPA are redshifted
compared to those in aniline; however, the scissoring vibrational
wavenumber of NH2 is not shifted when p-HFIPA substituents
are formed. The two strongest vibrational bands at 1264
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asymmetric stretches of HFIP groups in p-HFIPA, respectively.
Additionally, the other very strong vibrational bands at 1188
and 1151 cm−1 are associated with C–F in-phase and out-of-
phase asymmetric stretches in p-HFIPA. Moreover, the calculated
c
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J. Raman Spectrosc. 2010, 41, 989–995

FT-IR and FT-Raman investigations of p-HFIPA
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