A comprehensive study on infrared spectra of 2-hydroxyxanthone

Article abstract of DOI:10.1080/00387010.2011.607206

A study on the IR spectra of 2-hydroxyxanthone that was both experimental and theoretical was carried out in this work. The optimized structure and related spectral parameters were obtained by using the Becke-3-Lee-Yang-Parr (B3LYP) method with the 6-31G* and 6-311G** basis sets. The corresponding geometrical parameters were compared with each other. Detailed assignments of the vibration frequencies were performed. The agreement between the scaled theoretical frequencies and the observed frequencies was found to be quite good. Also, the calculation accuracies of the two basis sets are close. Copyright Taylor & Francis Group, LLC.

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A Comprehensive Study on Infrared Spectra of 2-
Hydroxyxanthone
Ruijuan Qu a , Qi Zhang a , Xuesheng Zhang a & Zunyao Wang a
a State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment,
Nanjing University , Nanjing , China
Published online: 16 Apr 2012.
To cite this article: Ruijuan Qu , Qi Zhang , Xuesheng Zhang & Zunyao Wang (2012) A Comprehensive Study on Infrared
Spectra of 2-Hydroxyxanthone, Spectroscopy Letters: An International Journal for Rapid Communication, 45:4, 240-245, DOI:
10.1080/00387010.2011.607206
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Spectroscopy Letters, 45:240–245, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0038-7010 print=1532-2289 online
DOI: 10.1080/00387010.2011.607206
A Comprehensive Study on Infrared
Spectra of 2-Hydroxyxanthone
Ruijuan Qu,
Qi Zhang,
ABSTRACT A study on the IR spectra of 2-hydroxyxanthone that was both
experimental and theoretical was carried out in this work. The optimized
structure and related spectral parameters were obtained by using the
Becke-3-Lee-Yang-Parr (B3LYP) method with the 6-31Gꢀ and 6-311Gꢀꢀ basis
sets. The corresponding geometrical parameters were compared with each
other. Detailed assignments of the vibration frequencies were performed.
The agreement between the scaled theoretical frequencies and the observed
frequencies was found to be quite good. Also, the calculation accuracies of
the two basis sets are close.
Xuesheng Zhang,
and Zunyao Wang
State Key Laboratory of Pollution
Control and Resources Reuse,
School of the Environment,
Nanjing University, Nanjing,
China
KEYWORDS 2-hydroxyxanthone, B3LYP, IR
INTRODUCTION
Xanthones, 9H-xanthen-9-ones, are heterocyclic compounds with the
dibenzo-c-pyrone framework. The parent compound itself does not exist
in the natural world, but its derivatives are widely distributed in nature. Nat-
urally occurring xanthones are often separated from various parts of plants,
such as Rheedia acuminata bark,[1] Cratoxylum cochinchinense,[2] Gentianu-
ceae, Guttiferae, Anacardiaceae, and metabolic products of some lower
fungi, for example, marine-derived fungi[3] and Penicillium raistrickii.[4] Early
pharmacological studies have shown that xanthones have a very wide range
of pharmacological activities and considerable bioactivity, including anti-
bacterial, analgesic,[5] cytotoxic,[6] febrifuge,[7] antimalaria,[8] and antituber-
culosis[9] bioactivity. Due to their pronounced toxicity, they are classified
as mycotoxins.[10]
Research on xanthone derivatives began in the 1960s. Synthesis and
modification of natural xanthones not only form an important supplement
to natural xanthones but also are very helpful to the development of new
chemical entities. Also, studies on their vibration spectra might be useful
for the design of novel drugs. However, to the best of our knowledge,
the number of articles about the theoretical spectra of xanthones has been
limited over the past few years. Therefore, an attempt was made in this work
to comprehensively study the theoretical and experimental IR vibrational
spectra of a xanthone derivative named ‘‘2-hydroxyxanthone.’’ Vibrational
spectroscopy has proven to be effective in the refinement of chemical struc-
tures as well as in researches on reaction kinetics of organic compounds.
Received 4 May 2011;
accepted 19 July 2011.
Address correspondence to
Zunyao Wang, State Key Laboratory
of Pollution Control and Resources
Reuse, School of the Environment,
Nanjing University, Jiangsu Nanjing
210046, P. R. China. E-mail:
wangzun315cn@163.com
240

Also, this work can be of great help to understand
spectral properties of its analogues.
RESULTS AND DISCUSSION
Molecular Geometry
In the current article, optimized geometrical para-
meters and IR vibrational frequencies are computed
by DFT=B3LYP method with 6-31Gꢀ and 6-311Gꢀꢀ
basis sets. We choose the density functional theory
(DFT) method rather than the Hartree-Fock (HF)
method for the following two points. First, the DFT
method requires relatively few computational
resources.[11] Second, comparisons between the fre-
quencies calculated with the two methods and the
experimental values reveal that the DFT method pre-
dicts more accurately for the molecular structure and
vibrational spectra. Furthermore, the observed
vibrational spectrum is assigned and compared with
the theoretical ones.
The optimized structure and atomic numbering of
the title compound is illustrated in Fig. 1. Note that
rings of C1C2C3C4C5C6, C4C5C10C9C8O7, and
C9C8C11C12C13C14 are defined as R1, R2, and R3,
respectively. The absence of negative frequencies
indicates that the molecule is at stationary point on
the potential energy surface. The global minimum
energy at B3LYP=6-31Gꢀ and B3LYP=6-311Gꢀꢀ level
is ꢁ725.880220 a.u. and ꢁ726.064465 a.u., respect-
ively. In this study, geometry optimization parameters
were obtained without symmetry constraints. The
selected structural parameters, including bond
lengths, bond angles, and dihedral angles, are
reported in Table 1. Clearly, bond lengths calculated
at the 6-31Gꢀ level are slightly larger than those
obtained at the 6-311Gꢀꢀ level. The largest deviation
is in the O16-H24 bond, the value of which is only
MATERIALS AND METHODS
General
˚
0.008 A. For bond angles, the situation is different.
Treatment of acetylsalicylic acid with thionyl
chloride gave the acid chloride, which readily
reacted with p-dimethoxy-benzene under the
Friedel-Crafts conditions to form the benzophenone
derivative. The precursor 2-methoxy-xanthone was
synthesized via the reaction of the benzophenone
derivative with potassium hydroxide and ethanol
under reflux for 72 hr. Further treatment of
2-methoxy-xanthone with hydrobromic acid under
reflux over nitrogen gave the crude product 2-hydro-
xyxanthone.
The values of C1C2C3 angle, C4C5C6 angle, and
C4O7C8 angle computed at the two levels are equal.
The bond angle values of C5C10O15 and H24O16C13
calculated with the small basis set are slightly smaller.
However, a contrary trend was observed in cases of
angles C5C10C9, C9C8C11, and C12C13C14. With
regard to dihedral angles, the corresponding values
are almost identical to each other. These values
confirm the planar conformation of the molecule.
Vibrational Analysis
The infrared absorption spectra of 2-hydroxyx-
anthone diluted in the KBr pellets was recorded
using a Nexus 470 FT-IR spectrophotometer (Thermo
Nicolet Co., USA) at room temperature.
It is of interest to study the spectral features in IR
spectra, which strongly correlate to those of
vibrational structures. This enables us to identify
chemical structures and to carry out researches on
Method of Calculation
The structural geometry was optimized using
B3LYP method at 6-31Gꢀ and 6-311Gꢀꢀ levels of the-
ories with the Gaussian 03 program.[12] Based on the
Gaussian output files, IR vibration frequencies were
obtained. Aided by the Gaussview program,[13] we
made the vibrational assignments with a high degree
of accuracy. In order to offset the errors resulting
from electron correlation effects and basis-set defi-
ciencies, the scaling factors were introduced to scale
down the theoretical wave numbers.
FIGURE 1 The optimized geometric structure and atom num-
bering of 2-hydroxyxanthone. (color figure available online.)
241
A Comprehensive Study on Infrared Spectra

TABLE 1 Comparison of Selected Bond Lengths, Bond Angles, Dihedral Angles of 2-Hydroxyxanthone Computed Using DFT/B3LYP
Method with Two Different Basis Sets
Parameters
B3LYP=6-31Gꢀ
B3LYP=6-311Gꢀꢀ
O16-H24
0.970
0.962
˚
Bond length (A)
C1-C2
1.406
1.388
1.400
1.404
1.406
1.366
1.371
1.404
1.477
1.480
1.397
1.402
1.388
1.407
1.389
1.367
1.403
1.385
1.398
1.402
1.405
1.364
1.370
1.401
1.477
1.480
1.395
1.400
1.385
1.405
1.386
1.366
C14-H23
C10 ¼ O15
1.084
1.228
1.082
1.222
C2-C3
C3-C4
Bond angle (ꢂ)
C1-C2-C3
C4-C5
120.8
118.6
119.5
114.3
120.6
122.9
119.7
109.2
120.8
118.6
119.5
114.2
120.5
123.0
119.6
109.5
C5-C6
C4-C5-C6
C4-O7
C4-O7-C8
O7-C8
C5-C10-C9
C8-C9
C9-C8-C11
C5-C10
C9-C10
C8-C11
C9-C14
C11-C12
C12-C13
C13-C14
C13-O16
C5-C10-O15
C12-C13-C14
H24-O16-C13
Dihedral angle (ꢂ)
H19-C3-C4-O7
C6-C5-C10-O15
O15-C10-C9-C14
H24-O16-C13-C14
0.0
0.0
0.0
0.0
0.0
0.0
180.0
180.0
reaction kinetics. For instance, IR spectroscopy has
been used in the structural elucidation of 1-phenyla-
cridones.[14] The experimental frequencies with gen-
eral mode assignments are summarized in Table 2.
The observed IR spectrum is shown in Fig. 2. The
detailed vibrational assignments of 2-hydroxyx-
anthone are briefly discussed in the following
paragraphs.
TABLE 2 Experimental and Calculated Frequencies (cmꢁ1) and General Mode Assignments for 2-Hydroxyxanthone
B3LYP=6-31Gꢀ
Freq.
Unscaled
B3LYP=6-311Gꢀꢀ
Experimental
Freq.a
Vibrational
Assignmentsd
No.
Scaledb
IR intensity
Reduced mass
Unscaled
Scaledc
1
2
–
326
569
313
547
119.7
11.8
17.9
50.8
31.4
2.5
1.1
3.3
7.2
7.1
1.7
7.0
1.4
1.5
2.6
5.2
3.0
3.0
3.1
6.7
12.4
1.1
1.1
311
569
301
551
c O-H
c C-H R3
d-R1, d-R3
b C-O R2, d-R3
c C-H R3
562 w
3
622 m
753 ms
826 m
872 w
641
616
642
622
4
793
762
792
767
5
822
790
830
804
6
900
865
895
867
trigonal ring breathing
b C-H
b O-H
vas C-C
=
vas C-O R2, v C C R3
7
1108 m
1147 ms
1230 s
1305 m
1342 ms
1465 vs
1582 ms
1620 s
1655 s
3196 s
3314 s
1170
1215
1355
1396
1500
1519
1540
1686
1748
3223
3756
1125
1168
1303
1342
1442
1460
1480
1621
1680
3088
3598
50.2
123.8
391.1
83.7
100.1
187.9
185.5
45.7
223.7
4.6
1158
1204
1342
1378
1484
1502
1522
1670
1730
3201
3836
1121
1166
1299
1334
1437
1454
1474
1617
1675
3067
3675
8
9
10
11
12
13
14
15
16
17
=
=
v C C R1, v C C R3
=
v C C R1, b O-H
=
v C C R3
=
v C C R3
=
v C O
v C-H
v O-H
59.0
avs: very strong; s: strong; ms: medium strong; m: medium; w: weak.
bWith the scale factor of 0.958 for calculated wave numbers greater than 3000 cmꢁ1 and the scale factor of 0.9613 for lower wave numbers.
cWith the scale factor of 0.958 for calculated wave numbers greater than 3000 cmꢁ1 and the scale factor of 0.9682 for lower wave numbers.
dv: stretching; vas: asym. Stretching; b: in-plane bending; c: out-of-plane bending; d: deformation.
R. Qu et al.
242

to the O–H out-of-plane bending. However, this
band is not observed in the IR spectrum.
C–H Vibrations
The band of C–H stretching vibration in the title
compound was observed at 3196 cmꢁ1 in the IR
spectrum. For aromatic structures, the C–H in-plane
bending modes usually arise in the region
1000–1300 cmꢁ1[16] In the present study, the C–H
in-plane bending vibration showed as a medium
band at 1108 cmꢁ1, which corresponds to the theor-
etical frequencies at 1125 cmꢁ1 on 6-31Gꢀ level and
1121 cmꢁ1 on 6-311Gꢀꢀ level. A medium IR band
observed at 826 cmꢁ1, in reasonable agreement wiꢁth1
the computed data 790 cmꢁ1 (6-31Gꢀ) and 804 cm
(6-311Gꢀꢀ), is assigned to C–H out-of-plane bending
vibration in R3. Another weak IR band at 562 cmꢁ1 is
assigned to this mode, too. Theꢁc1alculated bands at
547 cmꢁ1 for 6-31Gꢀ and 551 cm for 6-311Gꢀꢀ well
match the experimental result.
C¼O and C–O Vibrations in Ring R2
The stretching frequency of the carbonyl group
has been most extensively studied by infrared spec-
troscopy. Since the electronegativity of carbon and
oxygen is different, the bonding electrons are not
equally distributed along the two atoms. The lone
pairs of electrons on oxygen also have influence
on the nature of the carbonyl group. This highly
polar group usually gives rise to an intense infrared
absorption band. For the title molecule, the strong
C¼O stretching vibration is observed at 1655 cmꢁ1
in IR spectra, which agrees well with the scaled
values at 1680 cmꢁ1 (6-31Gꢀ) and 1675 cmꢁ1
(6-311Gꢀꢀ).
The theoretical frequencies at 1342 cmꢁ1 on
6-31Gꢀ level and 1334 cmꢁ1 on 6-311Gꢀꢀ level with
medium intensity are both in reasonable agreement
with the experimental data (1305 cmꢁ1 in IR spec-
trum). The observation from the Gaussview program
reveals that the vibration mainly results from the
combination of the C-O asymmetric stretching and
the R3 C¼C aromatic semicircle stretching vibration.
The band appeared at 753 cmꢁ1, which corresponds
to 762 cmꢁ1 on 6-31Gꢀ level and 767 cmꢁ1 on
6-311Gꢀꢀ level, and is assigned to C-O in-plane bend-
ing vibration interacting with deformation of R3.
FIGURE 2 The theoretical and experimental IR spectra of
2-hydroxyxanthone. (color figure available online.)
O–H Vibrations
It is known that hydrogen bonding easily affects
the O–H stretching vibrations. A free or non-hydro-
gen–bonded hydroxyl group absorbs strongly in
the range of 3550–3700 cmꢁ1. The O–H stretching
band would shift to the region 3200–3550 cmꢁ1 if
hydrogen bonding is present in a 5- or 6-membered
ring system.[15] The strong band observed at
3314 cmꢁ1 is assigned to O–H stretching vibration,
showing that 2-hydroxyxanthone is hydrogen
bonded. The O–H in-plane bending vibration
appears as a medium-strength band at 1147 cmꢁ1,
corresponding to the scaled frequencies at
1168 cmꢁ1 on 6-31Gꢀ level and 1166 cmꢁ1 on
6-311Gꢀꢀ level. The calculated bands at 313 cmꢁ1
for 6-31Gꢀ and 301 cmꢁ1 for 6-311Gꢀꢀ are ascribed
243
A Comprehensive Study on Infrared Spectra

Ring Vibrations
The peak observed at 622 cmꢁ1, which corre-
sponds to the theoretꢁic1al data at 616 cmꢁ1 on
6-31Gꢀ level and 622 cm on 6-311Gꢀꢀ level, results
from the coupling of the ring deformation vibrations
of R1 and R3. The trigonal ring breathing vibration is
observed at 872 cmꢁ1. And the ꢁc1alculated bands at
865 cmꢁ1 for 6-31Gꢀ and 867 cm for 6-311Gꢀꢀ well
match the observation. The medium strong IR band
at 1342 cmꢁ1, corresponding to the calculated values
at 1442 cmꢁ1 on 6-31Gꢀ level and 1437 cmꢁ1 on
6-311Gꢀꢀ level, is mainly due to the C¼C stretching
vibrations of the two phenyl rings. The R1 ring
stretching vibration appears at 1465 cmꢁ1 in the IR
spectrum, which shows excellent agreement with
the scaled frequencies at 1460 cmꢁ1 for 6-31Gꢀ and
1454 cmꢁ1 for 6-311Gꢀꢀ. This band is coupled with
in-plane bending of OH. The R3 C¼C stretching
vibrations showed as two absorptions, the medium
strong band at 1582 cmꢁ1 and the strong band at
1620 cmꢁ1. Both of the experimental frequencies
are consistent with the corresponding theoretical
values.
FIGURE 3 Correlation graph between the scaled and the
observed frequencies at different level of theories. (color figure
available online.)
Comparisons of the Experimental and
Theoretical Frequencies
Due to the combination of vibrational anharmoni-
city and basis-set incompleteness, the DFT=B3LYP
method tends to overestimate the fundamental fre-
quencies. It is necessary to scale down the calculated
vibrational frequencies so that they can fit with the
experimental ones. The work done by Palafox et al.
describes the interest and necessity of scaling to cor-
rect the deficiencies in the calculation of the har-
monic vibrational wave numbers.[17] The vibrational
frequencies greater than 3000 cmꢁ1 are uniformly
scaled by 0.958, and the lower wave numbers are
scaled by 0.9613 at the 6-31Gꢀ level and 0.9682 for
the 6-311Gꢀꢀ basis set.[18] The unscaled and scaled
wave numbers are also reported in Table 2. It can
be seen from Table 2 that after application of the
scaling factors, the theoretical calculations agree well
with the experimental data. Comparison between the
calculated and observed vibrational spectra helps us
to further understand the vibrational modes. The cal-
culated IR spectrum is also shown in Fig. 2 for visual
comparisons. In addition, a correlation graph
between the scaled and observed frequencies is
adopted to judge the prediction agreement with
experiment (Fig. 3).
Using the least squares method, the correlation
equation between the theoretical values calculated
at the B3LYP=6-31Gꢀ level and the experimental fre-
quencies is obtained as follows:
y ¼ 1:0353 x ꢁ 31:853
ð1Þ
r2 ¼ 0:9898
Also, the correlation equation between the calcu-
lated frequencies at the B3LYP=6-311Gꢀꢀ level and
the experimental data is as follows:
y ¼ 1:0446 x ꢁ 42:244
ð2Þ
r2 ¼ 0:9859
Obviously, for the two correlation equations, the
slopes are almost equal to 1.00, the intercepts are
relatively small, and the squared correlation coeffi-
cients r2 are larger than 0.98, indicating that good
R. Qu et al.
244

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CONCLUSION
A relatively comprehensive study on the vibrational
spectrum of 2-hydroxyxanthone was carried out. The
molecular geometry was optimized by B3LYP method
with 6-31Gꢀ and 6-311Gꢀꢀ basis sets. The vibrational
frequencies were then calculated using the same
method and compared with the experimental values.
In general, the scaled theoretical vibration frequen-
cies are consistent with the observations. The small
basis set 6-31Gꢀ gives the best match to the observed
spectra, and also this method provides the best
linearity between calculated and experimental wave
numbers (with a correlation coefficient of 0.9898).
The larger squared correlation coefficients
(r2 > 0.98) indicate that the computed values may
reproduce the observed frequencies. Furthermore,
vibrational modes were assigned with a high degree
of accuracy by employing the Gaussview program.
ACKNOWLEDGMENTS
This work was financially supported by the
National Natural Science Foundation of China
(41071319, 20977046, 20737001).
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