Synthesis and characterization of an anticoagulant 4-hydroxy-1-thiocoumarin by FTIR, FT-Raman, NMR, DFT, NBO and HOMO-LUMO analysis

Article abstract of DOI:10.1016/j.molstruc.2013.01.014

Experimental and theoretical investigations on the molecular structural, electronic and the vibrational characteristics of 4-hydroxy-1-thiocoumarin are presented. Conformational analysis was carried out to obtain the more stable configuration of the compo

Full text of DOI:10.1016/j.molstruc.2013.01.014

Journal of Molecular Structure 1037 (2013) 305–316
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and characterization of an anticoagulant 4-hydroxy-1-thiocoumarin
by FTIR, FT-Raman, NMR, DFT, NBO and HOMO–LUMO analysis
b
b
c
d
V. Arjunan a, , R. Santhanam , S. Sakiladevi , M.K. Marchewka , S. Mohan
⇑
a Department of Chemistry, Kanchi Mamunivar Centre for Post-Graduate Studies, Puducherry 605 008, India
b Research and Development Centre, Bharathiar University, Coimbatore 641 046, India
c Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw 2, Poland
d Department of Physics, Hawassa University, Main Campus, Hawassa, Ethiopia
h i g h l i g h t s
"
"
"
"
"
FTIR, FT-Raman and NMR investigations of 4-hydroxy-1-thiocoumarin were carried out.
A reduction in the bond angle S1–C2–O16 (117.3°) is due to the high electronegativities of sulfur and oxygen atoms.
1H and 13C NMR chemical shifts and the electronic transitions of the molecule were discussed.
The intramolecular charge transfer from
B3LYP method with 6-311++G(d,p) and cc-pVTZ basis sets are more reliable.
p .
(C3–C4) to pꢀ(C2–O16) has stabilization energy of 22.37 kcal molꢁ1
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 October 2012
Received in revised form 5 January 2013
Accepted 7 January 2013
Available online 16 January 2013
Experimental and theoretical investigations on the molecular structural, electronic and the vibrational
characteristics of 4-hydroxy-1-thiocoumarin are presented. Conformational analysis was carried out to
obtain the more stable configuration of the compound. The vibrational frequencies were obtained by
DFT/B3LYP calculations employing 6-311++G(d,p), 6-31G(d,p), cc-pVTZ basic sets and B3PW91 method
with 6-311++G(d,p) basis set and are compared with FTIR and FT-Raman spectral data recorded in the
region of 4000–400 and 4000–100 cmꢁ1, respectively. The total electron density and molecular electro-
static potential surfaces of the molecule were constructed to display electrostatic potential (elec-
tron + nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. 1H and
13C NMR spectra were recorded and 1H and 13C nuclear magnetic resonance chemical shifts of the mole-
cule were calculated by using the Gauge-Independent Atomic Orbital (GIAO) method and analyzed. The
picture of localized bonds and lone pairs, stabilization energy of the delocalization of electrons, the charge
and hybridisation of the atoms of 4-hydroxy-1-thiocoumarin were clearly explained by NBO analysis.
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
FTIR
FT-Raman
NMR
4-Hydroxy-1-thiocoumarin
DFT
NBO
1. Introduction
crystallizes in a non-centro symmetric space group, Pc, an excellent
candidate for second harmonic generation (SHG) effects, showing
Coumarin derivatives possessing diverse biological activities
play important role as versatile building blocks for the synthesis
of natural products and biologically active compounds [1]. Many
coumarin derivatives were reported as anti-diabetic, bactericides,
anti-allergy compound, therapeutic agents for fibrosis, cardiovascu-
lar agents, diagnostic probes for amyloid accumulation disease,
antibacterial agent, control of anti-ageing and their prospects as
skin-lightening compounds, fluorescent brighteners and to investi-
gate neuronal circuits in tissues [2]. The molecule 1-thiocoumarin
high non-linear optical (NLO) activity [3]. Especially, 4-hydroxy-1-
thiocoumarin has been used as useful intermediates for the synthe-
sis of anti-coagulants, herbicides, and anticancer agents and its
derivatives are used as rodenticides. For rodent’s control, second-
generation single-dose anticoagulant rodenticides such as brodifa-
coum, bromadiolone, difenacoum, flocoumafen have been intro-
duced. Of these flocoumafen, a derivative of 4-hydroxycoumarin
has been found to be the most effective against many species of
rodents. Moreover, its sulfur analog, thioflocoumafen, a derivative
of 4-hydroxy-1-thiocoumarin showed more potent anticoagulant
activity than flocoumafen with lower toxicity [4]. Benzothiopyran
skeleton is an important structural moiety in the preparation of
⇑
Corresponding author. Tel.: +91 413 2211111, mobile: +91 9442992223; fax:
+91 413 2251613.
pharmaceuticals [5–8], showing
a higher biological activity
E-mail address: varjunftir@yahoo.com (V. Arjunan).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.01.014

306
V. Arjunan et al. / Journal of Molecular Structure 1037 (2013) 305–316
Scheme 1.
compared to the corresponding benzopyran [9]. Benzothiopyranon-
es serve as key intermediates for the synthesis of bio-logically active
compounds [10–12]. Reterosynthetic approach of derivatives of
4-hydroxy-1-thiocoumarin such as Thioflocoumafen [13] and
reaction of 4-hydroxy-1-thiocoumarin with catechols for the syn-
thesis of 8,9-dihydroxy-5-thiocoumestans [14] was reported.
Substituted benzothiopyranones are widely used against hyperten-
sion [15] and have been tested for antimicrobial and antitumour
activity [16]. Some thiocoumarins have exhibited anti-vitamin K
activity, plant and animal growth arrest activity [17]. Synthesis of
4-hydroxy-1-thiocoumarin derivatives having potent anticoagulant
properties were also reported in the literature [18,19].
Various 3-substituted derivatives of 4-hydroxy-1-thiocoumarin
have been synthesized[20]. Reactions of 4-hydroxy-1-thiocoumarin
towards amines and phenyl hydrazine were studied [21]. Prepara-
tion of 3-substituted 4-hydroxy-1-thiocoumarin from carboxylic
ester with methyl thiosalicylate [22] was reported. Munshi and
Row have reported X-ray diffraction and theoretical based charge
reaction mixture with vigorous stirring and stirred at room tem-
perature for 30 min. The reaction mixture was cooled to 0–5 °C.
Then 20 ml of 1 N HCl was added. The organic layer was washed
with saturated brine solution, dried and concentrated at reduced
pressure to give diethyl-2-(2-acetylmercapto)benzoylmalonate
(b) (9.3 g). The mixture of 2.7 g of crude diethyl-2-(2-acetylmerca-
pto)benzoylmalonate (8.0 mmol), 100 ml of 3 N HCl and 120 ml of
ethanol was refluxed for about 3 h, cooled to 10 °C and filtered un-
der suction. The product was washed with water, dried in air to af-
ford pale yellowish crystal. The yield is 1.6 g (80%). The mixture of
1.0 g of crude 3-carbethoxy-4-hydroxy-1-thiocoumarin (c)
(4.0 mmol), 5 ml of concentrated HCl, 5 ml of H2O and 10 ml of eth-
anol was refluxed for 2 h, cooled to 10 °C and filtered by suction.
The product 4-hydroxy-1-thiocoumarin (d) was washed with
water, dried in the air to afford pale yellowish crystal. The yield
of the product is 91%. The melting point (209–210 °C) of 4-hydro-
xy-1-thiocoumarin has been determined.
density analysis for understanding weak C–Hꢂ ꢂ ꢂO and C–Hꢂ ꢂ ꢂ
pinter-
2.2. Measurement of FTIR, FT-Raman and NMR spectra
actions in some coumarin including 1-thiocoumarin [23]. Even
though many compounds synthesized by using 4-hydroxy-1-
thiocoumarin the structure and vibrational fundamental analysis
of 4-hydroxy-1-thiocoumarin and its derivatives by both experi-
mental and theoretical methods have not reported.
The FTIR spectrum of the sample in KBr was recorded at room
temperature in the region 4000–400 cmꢁ1 using Bruker IFS 66 V
spectrometer with a Globar source, Ge/KBr beam splitter, and a
MCT detector. The frequencies for all sharp bands are accurate to
2 cmꢁ1. The FT-Raman spectrum was also recorded in the range
4000–100 cmꢁ1 by the same instrument with FRA 106 Raman
module equipped with Nd:YAG laser source with 200 mW powers
The structure and analysis of the vibrational fundamentals of
4-hydroxy-1-thiocoumarin (4HTC) by both experimental and
theoretical methods have not reported. In the present work, the
infrared and Raman spectral analysis and the structural parameters
of 4-hydroxy-1-thiocoumarin have been investigated. The assign-
ments are aided by DFT/B3LYP method using 6-311++G(d,p),
6-31G(d,p), cc-pVTZ basis sets and B3PW91/6-31++G(d,p) method.
operating at 1.064
l
m. A liquid nitrogen cooled-Ge detector was
used. The spectral resolution is 2 cmꢁ1
.
1H (400 MHz; CDCl3) and
13C (100 MHz; CDCl3) nuclear magnetic resonance (NMR) spectra
were recorded on a Bruker HC400 instrument. The chemical shifts
for protons are reported in parts per million scales (d scale) down-
field from tetramethylsilane.
2. Experimental section
2.1. Preparation of 4-hydroxy-1-thiocoumarin
3. Computational details
4-Hydroxy-1-thiocoumarin was prepared based on the reported
procedure [24]. The various steps involved in the synthesis has
been depicted in the reaction Scheme 1. 4.0 g of thionylchloride
(33.6 mmol) was added to a well stirred solution of 5.5 g of 2-acet-
ylmercaptobenzoic acid (a) (28 mmol) and 30 mg of urea in 4.5 ml
anhydrous toluene at 10–15 °C. The reaction mixture was heated in
an oil bath at 100–110 °C for 3 h, then cooled to room temperature
to give 2-acetylmercaptobenzoyl chloride. The mixture containing
4.8 g diethylmalonate (28 mmol), 0.71 g magnesium (29.2 mmol),
3.9 g ethanol (85.3 mmol), 0.25 ml CCl4 and 40 ml anhydrous ether
was refluxed for about 3.5 h and then cooled to 0–5 °C. Then 6.0 g
of 2-acetylmercaptobenzoyl chloride (28 mmol) was added to the
The stable molecular structure of 4-hydroxy-1-thiocoumarin in
the ground state is optimized and the structural parameters have
been computed by utilizing Becke’s three parameter hybrid func-
tional (B3) [25,26] combined with gradient corrected correlation
functional of Lee–Yang–Parr (LYP) [27] with high level triple zeta
6-311++G(d,p), cc-pVTZ and standard split-valence polarized 6-
31G(d,p) [28] basis sets along with B3PW91/6-311++(d,p) method
on a Intel core-i5 processor using Gaussian 09 W program [29] to
characterize all stationary points as minima. The optimized struc-
tural parameters of 4-hydroxy-1-thiocoumarin were used for har-
monic vibrational frequency calculations resulting in IR and Raman
frequencies together with intensities and Raman depolarization ra-

V. Arjunan et al. / Journal of Molecular Structure 1037 (2013) 305–316
307
where
v
0 is the exciting frequency (cmꢁ1),
v
i is the vibrational wave-
number of the ith normal mode, h, c and k are universal constants,
and f is the suitably chosen common scaling factor for all the peak
intensities.
4. Results and discussion
4.1. Conformational analysis
Molecular geometry is a sensitive indicator of intra and inter-
molecular interactions. The accurate determination of geometrical
distortions in the rings is an important tool for investigating the
nature of the interactions between the ring and the substituents.
Conformational analysis of the compound was carried out using
G09 program. All the possible geometry of the conformers was
optimized to find out the energetically and thermodynamically
most stable configuration of the compound. The potential energy
barrier obtained by the rotation of the hydroxyl group with the
dihedral angle C10–C4–O17–H18 of 4HTC using by B3LYP/
6-31G(d,p) method is depicted in Fig. 1. It is possible to determine
the barrier energies of the internal rotation of the hydroxyl group
in 4HTC from the potential energy surface. All Possible conforma-
tions of the compound under investigation are shown in the
Fig. 2. The compound has four different conformations. The
stability of the conformer is in the order I > II > III > IV. The energy
difference between the most stable (I) and the second stable (II)
Fig. 1. Potential energy surface of 4-hydroxythiocoumarine determined by B3LYP/
6-31G(d,p) method.
tios. The potential energy distribution of the vibrational modes of
the compounds are also calculated through normal coordinate
analysis using the force constants obtained from the B3LYP/6-
311++G(d,p) method utilizing the program of Fuhrer et al. [30].
The GIAO method with PCM model is one of the most common
approaches for calculating nuclear magnetic shielding tensors. The
1H and 13C NMR isotropic shielding were calculated with CDCl3
solvent effect by B3LYP/6-311++G(d,p) method. The isotropic
shielding values were used to calculate the isotropic chemical
shifts (d) with respect to tetramethylsilane using the relation
conformations is 3.42 kcal molꢁ1 while between
I and III is
3.59 kcal molꢁ1. In 4HTC it was found that the hydroxyl group is
coplanar with the ring because there are strong conjugated,
resonance, and hydrogen-bonding effects between the group and
the benzene ring. The conformer II is slightly out of planar. The
conformer IV is the unstable transition structure. The conforma-
tional analysis of 4HTC obviously reveals that the planar conformer
I needs 3.42 kcal molꢁ1 to enable the non-planar conformer II
which has the –OH group perpendicular to the ring.
diso(X) =
r
TMS(X) ꢁ
riso(X), where diso – isotropic chemical shift
and riso – isotropic shielding constant.
Isoelectronic molecular electrostatic potential surfaces (MEP)
and electron density surfaces [31] were calculated using
6-311++G(d,p) basis set. The molecular electrostatic potential
(MEP) at a point r in the space around a molecule (in atomic units)
can be expressed as:
Z
0
0
X
~
ZA
q
ðr Þdr
VðrÞ ¼
ꢁ
4.2. Structural properties
0
~
~
~
~
jr ꢁ rj
jRA ꢁ rj
A
q
(r0) is the
A complete geometrical optimization was performed within the
CS point group symmetry and the most stable optimized molecular
structure of 4-hydroxy-1-thiocoumarin is shown in Fig. 3. The opti-
mized structural parameters bond lengths and the bond angles for
the geometry of 4-hydroxy-1-thiocoumarin at B3PW91 levels with
6-311++G(d,p) and B3LYP levels with 6-311++G(d,p), cc-pVTZ, 6-
31G(d,p) basis sets are presented in Table 1. DFT calculations
shows shortening of bond length in C3–C4 (1.357 Å) which con-
firms the presence of double bond character. The energies and
thermodynamic parameters of the compounds have also been
computed at B3PW91 levels with 6-311++G(d,p) basic sets and
B3LYP methods with 6-311++G(d,p), cc-pVTZ, 6-31G(d,p) basis sets
and are presented in Supplementary Table S1. The compound 4-
hydroxy-1-thiocoumarin is cyclic, planar and aromatic in nature
due to the continuous delocalization of electrons in the coumarin
ring system. The oxygen atom of the –OH group and the ketonic
(C@O) oxygen atoms of the compound are exactly in the plane of
the ring. This is confirmed by the corresponding dihedral angles
C2–C3–C4–O17 (180°) and C4–C3–C4–O16 (180°). The bonds S1–
C2 (1.814 Å) and S1–C9 (1.757 Å) have variation in their distances
similar to a feature quite common in coumarins. The double bonds
C3@C4 and C2@O16 are confirmed by their respective distances of
1.357 Å and 1.211 Å. More distortion in bond parameters is ob-
served in the hetero ring than in the benzene ring. The bond angle
varies with respect to the electro negativity, number of lone pair of
electrons and conjugation of the double bond present in an atom.
where ZA is the charge on nucleus A, located at RA and
electronic density function for the molecule. The first and second
terms represent the contributions to the potential due to nuclei
and electrons, respectively. V(r) is the resultant at each point r,
which is the net electrostatic effect produced at the point r by both
the electrons and nuclei of the molecule. The molecular electro-
static potential (MEP) serves as a useful quantity to explain hydro-
gen bonding, reactivity and structure–activity relationship of
molecules including biomolecules and drugs [32]. Structures result-
ing from the plot of electron density surface mapped with electro-
static potential surface depict the shape, size, charge density
distribution and the site of chemical reactivity of a molecule. Gauss-
View 5.0.8 visualization program [33] has been utilized to construct
the MEP surface, the shape of highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) orbitals.
The electronic properties such as HOMO and LUMO energies were
determined by DFT/6-311++G(d,p) method [34–37]. The energy dis-
tribution of the molecular orbitals [38] and LUMO–HOMO energy
gap have also been estimated.
The Raman scattering activities (Si) calculated by Gaussian 09
program were suitably converted to relative Raman intensities
(Ii) using the following relationship derived from the basic theory
of Raman scattering [39].
4
fðm0
ꢁ
miÞ Si
Ii ¼
mi½1 ꢁ expðꢁhc i=kTÞꢃ
m

308
V. Arjunan et al. / Journal of Molecular Structure 1037 (2013) 305–316
Fig. 2. The possible conformers of 4-hydroxythiocoumarine determined by B3LYP/6-31G(d,p) method.
The structure has weak intramolecular attractive force (C5–
B3LYP and B3PW91 methods. The RMSD of the bond angles deter-
mined by various methods does not show any significant
difference.
H12ꢂ ꢂ ꢂO17) between the oxygen atom of the hydroxyl group and
the proton of the benzene moiety than normal hydrogen bond. This
induces a very small tilt by 3.5° of the hydroxyl group towards the
hydrogen atom (H12). The lesser bond angle C10–C4–O17 (113.6°)
than the angle of O17–C4–C3 (120.6°) confirm the presence of
intramolecular attractive force between the hydrogen (H12) and
the hydroxyl oxygen atom (O17). The bond angle decreases when
the electronegativities of the ligand atoms are more than that of
central atom. There is increase in the distance between bond pair
since they are now closer to ligand atoms. Due to this, they tend
to move closer resulting in the decrease in bond angle. In virtue
of this, a remarkable reduction is seen in the bond angle of S1–
C2–O16 (117.3°). Due to the electronic repulsion of O16 atom at-
tached to the C2 with that of sulfur, a significant deviation from
trigonality in bond angle C3–C2–O16 (125.1°) is observed. This is
0.4°less than that of many 4-hydroxycoumarin derivatives [40].
The presence of electron donating hydroxyl group in the title com-
pound increases the bond angle of the central atom (C3–C4–
C10 = 125.8°) at the point of substitution. Bond lengths and bond
angles in the thiocoumarin moiety of 4-hydroxy-1-thiocoumarin
are in good agreement with structurally related thiocoumarin
derivatives such as 4-hydroxy-3-methoxycarbonyl-1-thiocouma-
rin [41] and 2-thiocoumarin [42]. All the methods used to
determine the structural parameters of the compound are well
agreed with the experimental data. The root mean square devia-
tions (RMSD) between the experimental and theoretical bond
lengths were calculated. For B3LYP method the RMSD are 0.016,
0.015 and 0.017 corresponds to 6-311++G(d,p), cc-pVTZ and 6-
31G(d,p) basis sets, respectively. In comparison, B3LYP method
with 6-311++G(d,p) and cc-pVTZ basis sets and B3PW91 method
are more reliable. This is due to the effect of diffuse functions in
4.3. Analysis of molecular electrostatic potential
The mapping of electrostatic potential onto the iso-electron
density surface simultaneously displays electrostatic potential
(electron + nuclei) distribution, molecular shape, size and dipole
moments of the molecule and it provides a visual method to
understand the relative polarity [38]. The total electron density
Fig. 3. The optimized geometry of 4-hydroxy-1-thiocoumarin by B3LYP/6-
311++G(d,p) method with atom labels.

V. Arjunan et al. / Journal of Molecular Structure 1037 (2013) 305–316
309
Fig. 4. The total electron density surface mapped with electrostatic potential of 4-hydroxy-1-thiocoumarin determined by B3LYP/6-311++G(d,p) method.
and MEP surfaces of the molecules under investigation are con-
structed by using B3LYP/6-311++G(d,p) method. The total electron
density mapped with electrostatic potential surface of 4-hydroxy-
1-thiocoumarin is shown in Fig. 4. The charges derived from an
electrostatic potential computation give useful information about
chemical reactivity. The electrostatic potential is computed by cre-
ating an electrostatic potential grid. These atomic point charges
give a better indication of likely sites of attack.
The color scheme for the MEP surface is red, electron rich, par-
tially negative charge; blue, electron deficient, partially positive
charge; light blue, slightly electron deficient region; yellow,
slightly electron rich region; green, neutral; respectively. The re-
gion around the carbonyl group represents the most negative po-
tential region (red) and more positive charge around hydrogen
atom of hydroxyl group. The predominance of light green region
in the MEP surfaces corresponds to a potential halfway between
the two extremes red and dark blue color.
of 4-hydroxy-1-thiocoumarin have positive charge and the positive
charge on C4, C10 and C5 is due to the presence of highly electro-
negative oxygen atom in hydroxyl group and the magnitude of po-
sitive charge on carbon decreases in the order of C4 > C10 > C5
which confirms (–I) effect of oxygen atom of hydroxyl group at-
tached at C4 position of 4-hydroxy-1-thiocoumarin. The expected
positive charge on C2 carbon atom was diminished and acquired
negative charge due to the presence of least electronegative sulfur
atom bonded to the carbonyl group of carbon atom (C2@O16) and
also lone pair of electrons on sulfur atom are involved in delocal-
ization of heterocyclic ring. The Supplementary Fig. S1 depicts
the correlation of natural charges of the different atoms present
in 4-hydroxy-1-thiocoumarin.
4.6. Donor acceptor interactions: perturbation theory energy analysis
Natural bond orbital analysis provide an efficient method for
studying intra- and inter molecular bonding and interaction among
bonds, and provides a convenient basis for investigating charge
transfer or conjugative interaction in molecular systems [44]. The
bonding–anti bonding interaction can be quantitatively described
in terms of the NBO approach that is expressed by means of sec-
ond-order perturbation interaction energy E(2) [45–48]. This en-
ergy represents the estimate of the off-diagonal NBO Fock matrix
element. The stabilization energy E(2) associated with i (donor) ? j
(acceptor) delocalisation is estimated from the second-order per-
turbation approach as given below
4.4. Analysis of frontier molecular orbital
The frontier molecular orbital plays an important role in the
electric and optical properties, as well as in the UV–Visible spectra
and chemical reaction [38]. The energies of HOMO, LUMO, LUMO+1
and HOMOꢁ1 orbitals of the compound in gas phase are ꢁ6.6345,
ꢁ2.2229, ꢁ1.0634 and ꢁ7.1088 eV, respectively. The LUMO and
HOMO orbital energy gap is calculated using B3LYP/6-
311++G(d,p) method is equal to +4.4115 eV. The positive and neg-
ative phase is represented in red and green color, respectively are
shown in Fig. 5 for 4-hydroxy-1-thiocoumarin.
F2ði; jÞ
Eð2Þ ¼ q
i ej
ꢁ
ei
4.5. Topological charge distribution
where qi is the donor orbital occupancy, ei and ej are diagonal ele-
ments (orbital energies) and F(i, j) is the off-diagonal Fock matrix
element. The larger the E(2) Value, the interaction between the elec-
tron donors and electron acceptors is more, i.e., greater the extent of
conjugation.
The calculation of effective atomic charges plays an important
role in the application of quantum mechanical calculation to
molecular systems [43]. The atomic charges of 4-hydroxy-1-thio-
coumarin calculated by NBO analysis using the B3LYP/6-
311++G(d,p) method are presented in Table 2. Six hydrogen atoms
NBO analysis shows that intramolecular charge transfer in
4-hydroxy-1-thiocoumarin from
p
(C3–C4) to pꢀ(C2–O16) with

310
V. Arjunan et al. / Journal of Molecular Structure 1037 (2013) 305–316
Table 1
Structural parameters of 4-hydroxy-1-thiocoumarin calculated by B3PW91 method with 6-311++G(d,p), B3LYP method with 6-311++G(d,p), cc-PVTZ, 6-31G(d,p) basis sets.
Structural parameters
4-Hydroxy-1-thiocoumarin
B3PW91/6-311++G(d,p)
B3LYP/6-311++G(d,p)
B3LYP/cc-PVTZ
B3LYP/6-31G(d,p)
Experimentala
Internuclear distance (Å)
S1–C2
S1–C9
C2–C3
C2@O16
C3@C4
C3–H11
C4–C10
C4–O17
C5–C6
C5–C10
C5–H12
C6–C7
C6–H13
C7–C8
C7–H14
C8–C9
1.805
1.754
1.442
1.219
1.363
1.088
1.453
1.353
1.385
1.409
1.084
1.400
1.086
1.400
1.086
1.404
1.086
1.411
0.966
0.014
1.819
1.763
1.443
1.213
1.360
1.087
1.454
1.358
1.383
1.409
1.081
1.399
1.083
1.386
1.084
1.403
1.084
1.410
0.964
0.016
1.814
1.757
1.439
1.211
1.357
1.085
1.452
1.355
1.380
1.406
1.079
1.395
1.081
1.382
1.082
1.399
1.082
1.407
0.964
0.015
1.824
1.765
1.444
1.216
1.363
1.088
1.457
1.357
1.385
1.411
1.083
1.401
1.085
1.388
1.086
1.405
1.086
1.413
0.967
0.017
1.781
1.739
1.464
1.213
1.393
1.456
1.324
1.376
1.403
1.396
1.380
1.398
1.403
C8–H15
C9–C10
O17–H18
RMSD
Bond angle (°)
C2–S1–C9
S1–C2–C3
S1–C2–O16
C3–C2–O16
C2–C3–C4
105.1
118.1
117.1
124.7
126.5
113.7
119.8
125.5
120.9
113.5
121.0
120.4
118.5
119.7
120.0
120.3
120.3
120.2
119.5
120.5
120.2
119.3
116.6
123.9
119.5
120.1
120.9
119.0
109.9
1.04
104.9
117.8
117.1
125.0
126.7
113.7
119.6
125.8
120.7
113.5
121.0
120.4
118.6
119.7
120.0
120.3
120.3
120.2
119.5
120.5
120.1
119.3
116.6
123.8
119.6
120.2
121.0
118.8
109.9
1.06
105.1
117.6
117.3
125.1
126.8
113.7
119.5
125.7
120.6
113.6
121.1
120.3
118.6
119.7
120.0
120.3
120.2
120.2
119.5
120.6
120.2
119.3
116.7
123.7
119.6
120.2
121.0
118.8
109.6
1.09
105.0
117.7
117.1
125.1
126.7
113.6
119.7
125.7
120.8
113.4
121.0
120.5
118.5
119.7
120.0
120.3
120.3
120.2
119.5
120.6
120.2
119.3
116.7
123.7
119.5
120.0
121.0
118.9
109.4
1.06
106.0
119.7
114.1
126.2
122.8
C2–C3–H11
C4–C3–H11
C3–C4–C10
C3–C4–O17
C10–C4–O17
C6–C5–H10
C6–C5–H12
C10–C5–H12
C5–C6–C7
C5–C6–H13
C7–C6–H13
C6–C7–C8
C6–C7–H14
C8–C7–H14
C7–C8–C9
C7–C8–H15
C9–C8–H15
S1–C9–C8
S1–C9–C10
C8–C9–C10
C4–C10–C5
C4–C10–C9
C5–C10–H9
C4–O17–H18
RMSD
125.9
120.6
113.4
121.2
120.0
120.0
120.2
116.8
122.9
120.2
119.6
118.3
RMSD – Root mean square deviation.
a
Values taken from Refs. [41,42].
stabilization energy of 22.37 kcal molꢁ1 and from
p
(C5–C6) to
5. Vibrational analysis
pꢀ(C7–C8) and pꢀ(C7–C8) antibonding orbitals with stabilization
energies of 21.16 and 19.21 kcal molꢁ1, respectively and from
The observed FTIR and FT-Raman spectra of 4-hydroxy-1-thio-
coumarin are shown in Figs. 6 and 7. The observed and calculated
frequencies using B3LYP levels with 6-311++G(d,p) and cc-pVTZ
basis sets along with their relative intensities, probable assign-
ments and potential energy distribution (PED) are summarized in
Table 4. The observed and calculated frequencies of B3PW91/6-
311++G(d,p) and B3LYP/6-31G(d,p) methods were given in Supple-
mentary Table S2. The different methods used to analyse the fun-
damental vibrational modes of the compound reveal the effect of
diffuse functions and the reliability of the methods. The normal
mode animations were made possible with GaussView 5.0.8 [33]
and Chemcraft programs [49] to support the vibrational assign-
ments exactly.
p
(C7–C8) to pꢀ(C5–C6), pꢀ(C9–C10) has stabilization energies of
17.61 and 20.78 kcal molꢁ1 and from
p
(C9–C10) to pꢀ(C5–C6),
pꢀ(C7–C8) with stabilization energies of 18.25 and 16.25 kcal molꢁ1
,
respectively are listed in Table 3.
The energy contribution of LP(2) S1 ? pꢀ(C2–
pO16), LP(2)
S1 ? pꢀ(C9–C10), LP(2) O16 ? rꢀ(S1–C2), LP(2) O16 ? rꢀ
(C2–C3) are 28.16, 23.12, 35.88, 17.80 kcal molꢁ1 respectively,
and hence there is a possibility for delocalization of lone pair
(LP) of electrons between S1 and C2–O16. The energy contribution
of LP(2) O17 ? pꢀ(C3–C4) is 34.85 which shows that possibility of
delocalization of lone pair electrons between O17 and C3–C4 are
listed in Table 3.

V. Arjunan et al. / Journal of Molecular Structure 1037 (2013) 305–316
311
Table 2
Calculated atomic charges of 4-hydroxy-1-thiocoumarin
by natural bond orbital (NBO) analysis by B3LYP/6-
311++G(d,p) method.
Atom
Natural charge
S1
C2
C3
C4
C5
C6
C7
C8
ꢁ0.636268
ꢁ0.123170
ꢁ0.619678
1.797534
0.186380
ꢁ0.625499
ꢁ0.267561
ꢁ0.606819
ꢁ0.706375
0.906795
0.169742
0.195415
0.165604
0.168701
0.177596
ꢁ0.274825
ꢁ0.178830
0.271259
C9
C10
H11
H12
H13
H14
H15
O16
O17
H18
Fig. 5. The Frontier molecular orbitals of 4-hydroxy-1-thiocoumarin determined by
B3LYP/6-311++G(d,p) method.
1333, 1302, 1277, 1272 and 1242 cmꢁ1 in both Raman and infrared
spectra has assigned to the ring stretching vibrations. Of these
bands 1611, 1555, 1302 cmꢁ1 appears very strong in IR spectra,
whereas in Raman spectrum the band 1607 cmꢁ1 is very strong
and 1512, 1333 cmꢁ1 bands are strong. The assignments of all
the ring in-plane and out-of-plane modes are presented in Tables
4 and S2.
Table 3
Second order perturbation theory analysis of Fock matrix of 4-hydroxy-1 thiocoum-
arin by NBO method using B3LYP/6-311++G(d,p) level.
Donor (i) ? acceptor (j)
(C2–C3) ? rꢀ(C4–O17)
(C2@O16) ? pꢀ(C3@C4)
E(2)a (kJ molꢁ1
)
E(j) ꢁ E(i)b (a.u.) F(I, j)c (a.u.)
r
4.56
4.85
4.52
22.37
9.32
5.17
6.11
4.06
21.16
19.21
4.82
1.06
0.41
1.23
0.31
0.31
0.71
0.99
1.31
0.29
0.27
0.91
1.27
1.09
1.08
0.93
1.28
0.29
0.28
1.29
1.10
1.29
0.30
0.31
0.30
1.25
1.19
0.26
0.26
0.44
0.73
1.25
0.38
0.062
0.042
0.067
0.077
0.051
0.055
0.070
0.065
0.070
0.067
0.059
0.077
0.063
0.059
0.055
0.064
0.065
0.070
0.069
0.063
0.071
0.064
0.068
0.065
0.065
0.067
0.077
0.072
0.113
0.105
0.075
0.104
p
r
(C3–C4) ? rꢀ(C4–C10)
p
p
(C3@C4) ? pꢀ(C2@O16)
5.2. C–H vibrations
(C3@C4) ? pꢀ(C9@C10)
r
r
r
p
p
(C3–H11) ? rꢀ(S1–C2)
(C3–H11) ? rꢀ(C4–C10)
(C4–C10) ? rꢀ(C3–C4)
The aromatic structure shows the presence of the C–H stretch-
ing vibrations in the region 3100–3000 cmꢁ1 which is the charac-
teristic region for the identification of the C–H stretching
vibrations [53–55]. The observed bands in IR at 3084, 3040,
2984 cmꢁ1 attributed to C–H stretching vibrations of 4-hydroxy-
1-thiocoumarin. DFT computations predict these modes at 3091,
3046, 2992 cmꢁ1 for B3LYP/cc-pVTZ level of theory. The results
showed that the experimental and theoretical data were in good
agreement. DFT computations calculated modes at 3067 and
3058 cmꢁ1 at B3LYP/cc-pVTZ level for C–H vibrations are not ob-
served in both experimental infrared and Raman spectra.
The bands corresponding to the C–H in-plane bending vibra-
tions of aromatic compounds appears in the region 1400–
1050 cmꢁ1 [54,55]. The C–H in plane bending vibrations in 4-hy-
droxy-1-thiocoumarin identified at 1146, 1101 and 1076 cmꢁ1 in
the infrared spectrum and 1155 cmꢁ1 in Raman spectrum. The
respective predicted bands are 1156, 1103 and 1075 cmꢁ1 at
B3LYP/cc-pVTZ level and the bands not observed in experimental
are 1181, 1213 cmꢁ1 at B3LYP/cc-pVTZ level for C–H in-plane
bending vibrations.
(C5@C6) ? pꢀ(C7@C8)
(C5@C6) ? pꢀ(C9@C10)
r
r
r
r
r
r
(C5–C10) ? rꢀ(S1–C9)
(C5–H12) ? rꢀ(C9–C10)
(C5–H12) ? rꢀ(C9–C10)
(C6–H13) ? rꢀ(C5–C10)
(C7–C8) ? rꢀ(S1–C9)
(C7–C8) ? rꢀ(C8–C9)
5.86
4.51
4.02
4.04
4.04
p
p
(C7@C8) ? pꢀ(C5@C6)
(C7@C8) ? pꢀ(C9@C10)
17.61
20.78
4.60
4.47
4.95
15.93
18.25
16.85
4.12
r
r
r
p
p
p
(C8–C9) ? rꢀ(C9–C10)
(C8–H15) ? rꢀ(C9–C10)
(C9–C10) ? rꢀ(C5–C10)
(C9–C10) ? pꢀ(C3–C4)
(C9@C10) ? pꢀ(C5@C6)
(C9@C10) ? pꢀ(C7@C8)
r
(O17–H18) ? rꢀ(C4–C10)
LP(1) S1 ? rꢀ(C9–C10)
LP(2) S1 ? pꢀ(C2–O16)
LP(2) S1 ? pꢀ(C9–C10)
LP(2) O16 ? rꢀ(S1–C2)
LP(2) O16 ? rꢀ(C2–C3)
LP(1) O17 ? rꢀ(C3–C4)
LP(2) O17 ? pꢀ(C3–C4)
4.72
28.16
23.12
35.88
17.80
5.71
The absorption bands arising from C–H out-of-plane bending
vibrations are usually observed in the region 1000–675 cmꢁ1
[54,55]. The ring out-of-plane modes for 4-hydroxy-1-thiocouma-
rin have appeared in the range 1040–810 cmꢁ1. The IR spectrum
shows weak band at 1032 cmꢁ1, medium band at 874 cmꢁ1 and
strong bands at 833 and 816 cmꢁ1; in the Raman spectrum there
34.85
a
b
c
Stabilization (delocalisation) energy.
Energy difference between i (donor) and j (acceptor) NBO orbitals.
Fock matrix element i and j NBO orbitals.
is a strong band at 1032 cmꢁ1 and a weak band at 876 cmꢁ1
.
5.1. C–C vibrations
5.3. O–H vibration
The C–C stretching (ring) vibrations have given rise to charac-
teristic bands in both the observed IR and Raman spectra, covering
the spectral range from 1610 to 1300 cmꢁ1 [50–52]. For 4-hydro-
xy-1-thiocoumarin there are nine C–C vibrations. The observed
bands at 1629, 1611, 1607, 1555, 1551, 1512, 1508, 1462, 1446,
The O–H group gives rise to three vibrations namely (stretching,
in-plane and out-of plane bending vibrations). The O–H group
vibrations are likely to be the most sensitive to the environment,
so they show pronounced shifts in the spectra of the hydrogen
bonded species. The hydroxyl stretching vibrations are generally

312
V. Arjunan et al. / Journal of Molecular Structure 1037 (2013) 305–316
Fig. 6. FTIR spectrum of 4-hydroxy-1-thiocoumarin.
Fig. 7. FT-Raman spectrum of 4-hydroxy-1-thiocoumarin.
[56] observed at around 3500 cmꢁ1. In experimental spectrum
band observed at 3370 cmꢁ1 has been assigned for O–H stretching
vibration and the corresponding band determined at B3PW91/6-
311++G(d,p), B3LYP method with 6-311++G(d,p), cc-pVTZ and 6-
31G(d,p) basic sets are 3383, 3360, 3383 and 3391 cmꢁ1, respec-
tively. Experimentally observed very strong band in Raman at
1196 cmꢁ1 and strong band at 1196 cmꢁ1 in observed IR spectrum
has been assigned to O–H in-plane bending vibration which shows
good agreement with the calculated one.
5.5. C–S vibrations
In general C–S stretching vibrations occur in the region of 700–
600 cmꢁ1 [58] and in general C–S stretching vibrations result in
strong band in Raman spectra which are normally easy to identify.
In the present study, the band identified at 676 cmꢁ1 in Raman and
650 cmꢁ1 in IR spectra are assigned to C–S stretching vibrations.
The theoretically computed wavenumbers by B3LYP/cc-pVTZ
method at 661 and 658 cmꢁ1 are assigned to C–S stretching vibra-
tions. The in plane and out-of-plane bending of CSC bending vibra-
tions are theoretically predicted at 434 and 129 cmꢁ1 by B3LYP/cc-
pVTZ method.
5.4. C@O vibrations
The C@O stretching frequency appears strongly in the IR spec-
trum in the range 1600–1850 cmꢁ1 because of its large change in
dipole moment. The carbonyl group vibrations give rise to charac-
teristics bands in vibration spectra and its characteristic frequency
used to study a wide range of compounds. The intensity of these
bands can increase owing to conjugation or formation of hydrogen
bonds [57]. A very strong IR absorption band at 1701 cmꢁ1 is read-
ily assigned to the carbonyl vibration in the 4-hydroxy-1-thio-
coumarin; the corresponding DFT computed mode at 1712 cmꢁ1
at B3LYP/cc-pVTZ, level is good agreement with the observed
one. Strong in plane bending and a medium out of plane bending
of C@O observed at 949 and 629 cmꢁ1, respectively in the experi-
ment IR spectrum and a weak Raman band at 628 cmꢁ1 which is
good with the calculated frequencies which is shown in Tables 4
and S2.
6. Scale factor
The vibrational frequencies obtained by quantum chemical cal-
culation are typically larger than their experimental counterparts,
and thus, empirical scaling factors are usually used to match the
experimental vibrational frequencies [59]. These scaling factors de-
pend on both the method and basis sets used in calculations, and
they are determined from the mean deviation between the calcu-
lated and experimental frequencies [60,61]. The optimum scale
factors for vibrational frequencies were determined by minimizing
the residual
N
ꢀ
ꢁ
X
2
D
¼
k
xTi heor
ꢁ
mEi xpt
i

Table 4
The observed FTIR, FT-Raman and calculated frequencies using B3LYP method with cc-pVTZ and 6-311++G(d,p) basis set along with their relative intensities, symmetry species, probable assignments and potential energy distribution
(PED) of 4-hydroxy-1-thiocoumarin.a
Species Observed wavenumber B3LYP/cc-pVTZ calculated wavenumber
B3LYP/6-311++G(d,p) calculated wavenumber
Assignment % PED
(cmꢁ1
FT IR
)
FT-Raman
3077 s
Unscaled (cmꢁ1) Scaled (cmꢁ1) IR intensity Raman activity Depolarization ratio Unscaled (cmꢁ1) Scaled (cmꢁ1) IR intensity Raman activity Depolarization ratio
A0
A0
A0
A0
A0
A0
3370 w
3084 m
3802
3220
3195
3185
3173
3149
3368
3081
3064
3055
3037
2981
76.92
3.03
12.45
5.66
1.08
0.474
0.509
1.000
0.375
0.218
0.623
0.28
0.20
0.18
0.71
0.75
0.29
3818
3218
3193
3183
3171
3150
3374
3088
3070
3060
3044
2987
83.93
2.56
11.08
5.34
1.03
0.486
0.517
1.000
0.378
0.220
0.634
0.30
0.19
0.17
0.70
0.75
0.27
m
m
m
m
m
m
OH
CH
CH
CH
CH
CH
92mOH
85mCH
87mCH
82mCH
80mCH
81mCH
3040 m
2984 m
2756 m
2579 m
1701 vs
6.51
6.07
1555 + 1196
1611 + 949
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A00
A00
A0
A00
A00
A00
A0
A0
A0
A0
A0
A00
A0
A0
A0
A00
A0
A0
A00
A00
A00
A00
A00
A00
A00
A00
1730
1651
1634
1586
1514
1468
1451
1341
1294
1258
1225
1199
1193
1168
1114
1086
1061
1009
983
1697
1625
1607
1551
1504
1458
1442
1319
1273
1238
1209
1192
1177
1151
1097
1072
1028
995
604.43
163.99
26.83
42.72
14.63
7.37
0.280
0.299
0.150
0.411
0.128
0.009
0.121
0.235
0.008
0.007
0.115
0.013
0.021
0.013
0.105
0.019
0.232
0.001
0.001
0.002
0.008
0.012
0.002
0.004
0.012
0.025
0.002
0.041
0.004
0.001
0.082
0.004
0.003
0.029
0.008
0.026
0.022
0.004
0.002
0.005
0.004
0.002
0.31
0.17
0.69
0.30
0.35
0.46
0.28
0.29
0.60
0.63
0.33
0.42
0.72
0.53
0.14
0.25
0.12
0.75
0.75
0.75
0.75
0.41
0.75
0.75
0.73
0.20
0.75
0.11
0.75
0.75
0.09
0.29
0.75
0.60
0.75
0.47
0.25
0.37
0.75
0.75
0.75
0.75
1724
1649
1631
1582
1507
1461
1442
1341
1289
1254
1222
1195
1190
1164
1110
1079
1057
1002
973
876
820
809
779
734
709
665
651
636
610
501
493
480
437
436
379
356
346
273
218
181
125
66
1702
1630
1612
1556
1508
1462
1446
1323
1277
1242
1209
1196
1178
1155
1101
1076
1032
991
948
875
832
815
765
745
724
675
649
628
621
519
507
461
447
430
373
350
301
287
214
194
122
67
714.55
179.98
30.07
45.97
19.02
8.09
0.412
0.399
0.184
0.526
0.136
0.013
0.142
0.266
0.007
0.012
0.122
0.014
0.021
0.012
0.121
0.013
0.289
0.001
0.001
0.001
0.005
0.013
0.005
0.001
0.017
0.034
0.002
0.048
0.001
0.092
0.001
0.004
0.032
0.000
0.011
0.028
0.026
0.005
0.002
0.003
0.004
0.001
0.35
0.14
0.71
0.30
0.42
0.38
0.27
0.29
0.65
0.69
0.31
0.48
0.70
0.56
0.13
0.31
0.09
0.75
0.75
0.75
0.75
0.45
0.75
0.75
0.72
0.14
0.75
0.11
0.75
0.06
0.75
0.22
0.58
0.75
0.75
0.46
0.23
0.33
0.75
0.75
0.75
0.75
m
m
m
m
m
m
m
m
m
m
C@O
CC
CC
CC
CC
CC
CC
CC
CC
CC
92mC=O
81mCC
84mCC
83mCC
81mCC
87mCC
79mCC
75mCC
1629 m
1607 vs
1551 s
1611 vs
1555 vs
1508 s
1512 w
1462 m
1446 w
1333 s
1272 w
29.79
2.36
35.91
1.80
1323 vs
1277 vs
1242 s
22.01
143.21
44.89
80.19
1.07
43.13
65.13
26.83
8.26
23.96
174.49
32.28
77.43
1.13
44.70
68.58
29.74
10.65
0.01
76mCC
78mCC
bCH
bOH
bCH
bCH
bCH
bCH
52bCH + 16bCCC
54bOH + 12bCO
50bCH + 18bCCC
52bCH + 22bCCC
55bCH + 18bCCC
50bCH + 16bCCC
1196 s
1196 vs
1155 w
1146 w
1101 m
1076 vw
1032 w
1032 s
876 w
766 w
c
c
CH
CH
51
47
c
c
CH + 24cCCC
CH + 18cCCC
0.00
1.45
949 s
874 m
833 s
816 s
766 s
746 vs
725 w
945
1.47
0.56
bC@O
69bC=O + 12bCCS
893
871
0.05
c
c
c
CH
CH
CH
45c
42c
43c
CH + 21cCCC
CH + 18cCCC
CH + 14cCCC
842
812
828
811
38.39
2.10
45.93
2.20
42.25
23.10
6.56
14.18
1.52
4.10
0.32
22.16
1.21
0.96
3.22
792
757
712
761
741
720
36.46
25.46
6.14
bCCC
bCCC
bCCC
47bCCC + 19bCH
45bCCC + 19bCH
41bCCC + 21bCH
78mCS
75mCS
69cC=O + 14cCCS
676 vs
628 w
511 m
668
664
671
645
13.40
1.33
m
m
c
CS
CS
C@O
650 w
629 m
638
624
4.01
628
617
0.12
bCCC
bCCC
bCCC
42bCCC + 21bCH
45bCCC + 19bCH
46bCCC + 14bCO
521 w
509 w
463 m
449 w
504
516
1.25
502
480
504
458
19.81
0.82
c
OH
59cOH + 18cCO
440 s
456
438
444
429
34.58
2.81
bCCS
bCSC
52bCCS + 16bC=O
58bCSC + 18bC=O
6.39
412
355
345
402
347
298
57.94
10.13
8.57
93.58
11.59
8.49
1.46
6.95
0.87
0.69
0.63
c
c
c
c
c
c
c
CCC
CCC
CCC
CCC
CCC
CCS
CSC
45c
46c
47c
42c
44c
46c
42c
CCC + 22cCH
CCC + 18cCH
CCC + 12cCH
CCC + 20cCH
CCC + 18cCH
CCS + 21cC=O
CSC + 22cC=O
303 m
289 m
273
284
1.08
223
216
6.33
196 s
188
191
0.60
130
124
0.87
70
64
0.76
Lattice mode
a
m
– stretching; b – in-plane bending; and c – out of plane bending.

314
V. Arjunan et al. / Journal of Molecular Structure 1037 (2013) 305–316
Fig. 8. 1H NMR spectrum of 4-hydroxy-1-thiocoumarin.
Fig. 9. 13C NMR spectrum of 4-hydroxy-1-thiocoumarin.
where xiTheor and miExpt are the ith theoretical harmonic frequency
and ith experimental fundamental frequency (in cmꢁ1), respectively
and N is the number of frequencies included in the optimization
which leads to
skeleton. To furnish a definite assignment and analysis 1H and
13C NMR spectra, theoretical calculations on chemical shift of 4-hy-
droxy-1-thiocoumarin were done by Gauge Independent Atomic
Orbital (GIAO) method at B3LYP/6-311++G(d,p) level with CDCl3
solvent.
rffiffiffiffi
D
RMS ¼
N
The 1H and 13C theoretical and experimental chemical shifts,
isotropic shielding constants and the assignments of 4-hydroxy-
1-thiocoumarin are also given in the Table 5. Aromatic carbons
give signals with chemical shift values from 100 to 200 ppm
[62,63]. The experimental chemical shifts of the compound occur
in the range of 126.38–182.45 ppm. The chemical shift of carbonyl
carbon (C2) is observed in the downfield at 182.45 ppm due to the
partial ionic nature of the carbonyl group. Due to the more electro-
negative oxygen and sulfur atoms in ring, the chemical shift of the
carbon atoms in heterocyclic ring are set to downfield. Therefore,
the chemical shift of C4 is also observed at the downfield at
166.93 ppm. The C3 carbon atom is highly shielded than C4 due
to the delocalization of the lone pair electrons from O17 to the
adjacent C4@C3. The chemical shifts of the benzene ring carbon
atoms C5, C6, C7, C8, C9 and C10 are assigned to 131.48, 123.79,
126.84, 126.09, 136.88 and 126.38 ppm, respectively. The peak ob-
served at 77 ppm is due to solvent CDCl3.
The linear fit equations y = 1.002x ꢁ 2.5437 and y = 1.0009x
ꢁ 5.3231 were used in this study for 6-311++G(d,p) and cc-pVTZ
basis sets, respectively. The root mean square (RMS) deviations
for these methods are 1.4 and 3.8, respectively. The correlation of
the calculated and experimental wavenumbers of 4-hydroxy-1-
thiocoumarin determined by B3LYP and B3PW91 methods are illus-
trated in Supplementary Fig. S2. The scaled frequencies of B3PW91/
6-311++G(d,p) and B3LYP/6-31G(d,p) methods were determined by
the linear equations y = 1.0031x ꢁ 5.2039 and y = 0.9998x
ꢁ 1.7435. The RMS deviations between the observed and the theo-
retical wavenumbers are 2.5 and 1.8, respectively. It is concluded
that, among the B3LYP methods the presence of diffuse functions
minimizes the deviations drastically.
1H chemical shifts of 4-hydroxy-1-thiocoumarin were acquired
from the NMR spectrum and interpreted to define the possible dif-
ferent effects which act on the shielding constants of protons. The
characteristic down field signal at d 11.71 ppm is attributed to the
aromatic proton (H12) of benzene ring moiety. The electronegative
oxygen atom (O17) present in the carbon atom (C4) deshields the
7. NMR spectral studies
The observed 1H and 13C NMR spectra of the compound 4-hy-
droxy-1-thiocoumarin are given in Figs. 8 and 9, respectively.
The NMR serves as a great resources in determining the structure
of an organic compound by revealing the hydrogen and carbon

V. Arjunan et al. / Journal of Molecular Structure 1037 (2013) 305–316
315
Table 5
The experimental and calculated 1H and 13C isotropic chemical shifts (diso, ppm) with respect to TMS and isotropic magnetic shielding tensors (
riso) of 4-hydroxy-1-thiocoumarin
by B3LYP/6-311++G(d,p) method.
Assignment
riso (1H)
Cal. (diso
)
Expt. (d)
Assignment
riso
(
13C)
Cal. (diso
)
Expt. (d)
H11
H12
H13
H14
H15
H18
26.35
23.77
24.56
24.44
24.50
27.51
5.62
8.20
7.41
7.53
7.47
4.46
5.68
11.71
7.18
7.78
7.46
3.41
C2
C3
C4
C5
C6
C7
C8
C9
C10
0.74
79.13
15.81
53.58
54.30
48.84
53.96
35.88
57.73
183.79
105.40
168.72
130.95
130.23
135.69
130.57
148.65
126.80
182.45
103.26
166.93
131.48
123.79
126.84
126.09
136.88
126.38
proton (H12) by means of a weak intramolecular hydrogen bonding
of the type C5–H12ꢂ ꢂ ꢂO17 which reduces the electron density on
H12 resulted in downfield chemical shift. The aromatic protons ap-
peared downfield signals at d values 7.18, 7.78 and 7.46 for protons
H13, H14 and H15, respectively. The protons H13 and H14 gives
multiplet signals while H15 gives a singlet. The upfield signal at d
5.68 ppm corresponds to olefinic proton of heterocyclic ring. In gen-
eral due to deshielding effect of oxygen atom, the signal for hydro-
xyl proton may be in downfield [64] but in 4-hydroxy-1-
thiocoumarin due to intramolecular hydrogen bonding of oxygen
atom of hydroxyl group, d value of hydroxyl proton (H18) is ob-
served in upfield at 3.41 ppm. The calculated chemical shifts are
in good agreement with the experimental values. The correlation
of the calculated and experimental 1H and 13C chemical shifts of
4-hydroxy-1-thiocoumarin are presented in Supplementary Fig. S3.
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