Structural characteristics and harmonic vibrational analysis of the stable conformer of 2,3-epoxypropanol by quantum chemical methods

Article abstract of DOI:10.1016/j.saa.2012.05.012

The FT-IR and FT-Raman spectra of H bond inner conformer of 2,3-epoxypropanol have been recorded in the regions 3700-400 and 3700-100 cm^-1, respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The normal coordinate analysis was carried out to confirm the precision of the assignments. The structure of the conformers H bond inner and H bond outer1 were optimised and the structural characteristics were determined by density functional theory (DFT) using B3LYP and MP2 methods with 6-31G and 6-311++G basis sets. The vibrational frequencies were calculated in all these methods and were compared with the experimental frequencies which yield good agreement between observed and calculated frequencies. The electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach.

Full text of DOI:10.1016/j.saa.2012.05.012

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 96 (2012) 24–34
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Structural characteristics and harmonic vibrational analysis of the stable
conformer of 2,3-epoxypropanol by quantum chemical methods
b
a
c
V. Arjunan a, , T. Rani , R. Santhanam , S. Mohan
⇑
a Department of Chemistry, Kanchi Mamunivar Centre for Post-Graduate Studies, Puducherry 605 008, India
b Centre for Research and Development, PRIST University, Thanjavur 613 403, India
c Department of Physics, Hawasa University Main Campus, Hawasa, Ethiopia
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
The conformational analysis of 2,3-epoxypropanol were performed. The structure of the conformers H
bond inner and H bond outer1 were optimised and the structural characteristics were determined by
DFT and MP2 methods with 6-31G⁄⁄ and 6-311++G⁄⁄ basis sets. The complete vibrational assignment
and analysis of the fundamental modes of the most stable conformer H bond inner was carried out using
the experimental FTIR and FT-Raman data, and quantum mechanical studies.
"
"
"
FTIR and FT-Raman investigations of
2,3-epoxypropanol were carried out.
The conformational analysis of this
compound was performed.
Energy, structural, thermodynamical
characteristics H bond inner and H
bond outer1 conformers were
determined.
"
"
The electronic properties and NBO
analysis were carried out.
Steric effect of hydroxymethyl group
on the epoxy ring parameters has
been analysed.
a r t i c l e i n f o
a b s t r a c t
Article history:
The FT-IR and FT-Raman spectra of H bond inner conformer of 2,3-epoxypropanol have been recorded in
the regions 3700–400 and 3700–100 cmꢀ1, respectively. The spectra were interpreted in terms of funda-
mentals modes, combination and overtone bands. The normal coordinate analysis was carried out to con-
firm the precision of the assignments. The structure of the conformers H bond inner and H bond outer1
were optimised and the structural characteristics were determined by density functional theory (DFT)
using B3LYP and MP2 methods with 6-31G⁄⁄ and 6-311++G⁄⁄ basis sets. The vibrational frequencies
were calculated in all these methods and were compared with the experimental frequencies which yield
good agreement between observed and calculated frequencies. The electronic properties HOMO and
LUMO energies were measured by time-dependent TD-DFT approach.
Received 2 February 2012
Received in revised form 19 April 2012
Accepted 3 May 2012
Available online 12 May 2012
Keywords:
FTIR
FT-Raman
2,3-Epoxypropanol
DFT
Ó 2012 Elsevier B.V. All rights reserved.
MP2
Introduction
The epoxide namely ethylene oxide is an important industrial
chemical used as an intermediate in the production of ethylene
glycol and other chemicals, and as a sterilant for foods and medical
⇑
Corresponding author. Tel.: +91 413 2211111; mobile: +91 9442992223; fax:
+91 413 2251613.
E-mail address: varjunftir@yahoo.com (V. Arjunan).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.05.012

V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 96 (2012) 24–34
25
supplies. Ethylene oxide gas kills bacteria (and their endospores),
mould and fungi, and can therefore be used to sterilize substances
that would be damaged by sterilizing techniques such as pasteur-
ization that rely on heat. Additionally, ethylene oxide is widely
used to sterilize medical supplies such as bandages, sutures and
surgical implements. Ethylene glycol is more commonly known
for its use as an automotive coolant and antifreeze. Chiral epoxides
are versatile building blocks for modern enantioselective synthesis
due to their regio- and stereochemically controlled reactivity with
a broad range of nucleophiles [1–3]. Among these, aryl glycidyl
ethers have been widely used for the production of non-racemic
drugs with b-adrenergic activities [1,4]. 2,3-Epoxypropanol is
widely used to a considerable extent in the textile, plastics, phar-
maceutical, cosmetics, detergent and photochemical industries
[5]. Currently, 2,3-epoxypropanol is used as a stabilizer in the man-
ufacture of vinyl polymers and natural oils and as an intermediate
in the synthesis of glycerol, glycidyl ethers, and amines. It also is
used as an alkylating agent, demulsifier, dye leveling agent and
for sterilizing milk of magnesia. The immunotoxic potential of
2,3-epoxypropanol was evaluated in female mice and found that
glycidol is an immunosuppressive agent in female mice [6]. 1-Bro-
mo-2,3-epoxypropane used to make rubber, to synthesis polymers
[7], an effective cross linking agents of the biological materials and
have pronounced antigen-depressive properties [8], to synthesis
many organic compounds [9–13] and used attractive chiral build-
ing blocks for asymmetric synthesis [14]. The importance of epox-
ides in organic synthesis arises partly from the occurrence of the
strained three-membered ring unit in a number of interesting nat-
ural products [15–19].
The DFT calculations with the hybrid exchange–correlation
functional B3LYP (Becke’s three parameter (B3) exchange in con-
junction with the Lee–Yang–Parr’s (LYP) correlation functional)
have been proved to be very effective [20–23] for vibrational stud-
ies on various epoxy compounds [24–34], and show better agree-
ment with the experimental values of structural characteristics.
Investigations on the conformational analysis of 2,3-epoxypropa-
nol are still being carried out [35–38], but the detailed structure
of the most stable H bond inner and H bond outer1 conformer and
the vibrational investigations of the most stable H bond inner are
inconclusive on 2,3-epoxypropanol. Thus, in the present investiga-
tion, owing to the industrial and biological importance of 2,3-
epoxypropanol, the structural parameters of the H bond inner and
H bond outer1 conformers were determined from MP2 and B3LYP
methods with 6-311++G(d,p) and 6-31G(d,p) basis sets and are dis-
cussed in detailed manner. The vibrational frequencies of most sta-
ble H bond inner conformer are determined experimentally and
theoretically and a detailed vibrational analysis was carried out.
The middle fraction of the distillate was used for spectroscopic
analysis. The FTIR and FT-Raman spectra were recorded with neat
liquid in CsBr windows. The FTIR spectrum of the compound was
recorded on a Bruker IFS 66 V spectrometer equipped with a Glo-
bar source, Ge/KBr beam splitter, and a TGS detector in the range
3700–400 cmꢀ1. The spectral resolution is 2 cmꢀ1. The FT-Raman
spectrum of the compound was also recorded in the range 3700–
100 cmꢀ1 using the same instrument with FRA 106 Raman module
equipped with Nd:YAG laser source operating at 1.064 lm line
with 200 mW powers. A liquid N2 cooled-Ge detector was used.
The frequencies of all sharp bands are accurate to 2 cmꢀ1
.
Computational methods
The restricted Hartree–Fock, Moller–Plesset (MP2) and DFT-
B3LYP [21–23,39] correlation functional calculations to second or-
der with full electron correlation have been performed with Gauss-
ian-03 [40] program, invoking gradient geometry optimisation [41]
on an Intel core-i5/3.30 GHz processor. The standard 6-31G(d,p)
and higher level 6-311++G(d,p) basis sets were employed for opti-
misation. The optimised structural characteristics of H bond inner
and H bond outer1 conformers are determined using the same
methods. For the most stable H bond inner conformer obtained,
the vibrational wavenumbers were calculated in order to provide
data for making a complete vibrational assignments and additional
information with regard to the structural characteristics of 2,3-
epoxypropanol. The optimised structural parameters were used
in the vibrational frequency calculations resulting in IR and Raman
frequencies together with intensities and Raman depolarisation ra-
tios, thermodynamic properties and energies of optimised
structures.
The Raman scattering activities (Si) calculated by Gaussian 03W
program were suitably converted to relative Raman intensities (Ii)
using the following relationship derived from the basic theory of
Raman scattering [42].
4
fðm0
ꢀ
miÞ Si
Ii ¼
mi½1 ꢀ expðꢀhc i=kTÞꢁ
m
where, m0 is the exciting frequency (cmꢀ1), vi is the vibrational
wavenumber of the ith normal mode, h, c and k are universal con-
stants, and f is the suitably chosen common scaling factor for all
the peak intensities. The force constants obtained from B3LYP/6-
311++G(d,p) method has been utilised in the normal coordinate
analysis by Wilson’s FG matrix method [43–45] utilising the pertur-
bation program of Fuhrer et al. [46].
To check whether the chosen set of assignments contribute the
most to the potential energy associated with normal coordinates of
the molecules, the potential energy distribution (PED) has been
calculated using the relation
Experimental details
FiiL2
kk
ik
PED ¼
2,3-Epoxypropanol was prepared using the reported procedure
[34]. To a solution of allyl alcohol (2.16 g, 30 mmol) in dichloro-
methane (30 cm3) was added a solution of 70% m-chloroperbenzoic
acid (8.12 g, 33 mmol) in dichloromethane (75 cm3) in portions at
a temperature below 25 °C. After stirring the solution overnight at
20 °C, the reaction mixture was cooled inside a freezer and m-chlo-
robenzoic acid was quickly filtered off and the solid was washed
with cold (0 °C) dichloromethane (25 cm3). The combined cold
(0 °C) filtrates were then shaken with a saturated K2CO3 solution
(15 cm3) and the salted out benzoate salts were quickly filtered
off and the solid was washed with dichloromethane (25 cm3).
The combined organic layers were dried (Na2SO4), concentrated
and distilled to give 2,3-epoxypropanol (47% yield). The purity of
the sample was determined from the boiling point; 68–69 °C
(20 mm Hg) and elemental analysis.
where PED is the contribution of the ith symmetry coordinate to the
potential energy of the vibrations whose frequency is mk, Fii is the
force constant evaluated by the damped least square technique,
Lik is the normalised amplitude of the associated element (i,k) and
kk the eigenvalue corresponding to the vibrational frequency k
(kk = 4p2 2mk2). The potential energy distribution corresponding to
c
each of the observed frequencies shows the reliability and accuracy
of the spectral analysis.
Based on the optimised geometry obtained from B3LYP/6-
311++G(d,p) level of theory, the absorption wavelength (kmax),
oscillator strength (f) and the energies of frontier orbitals were cal-
culated for H bond inner conformer using TD-B3LYP/6-311++G(d,p)
method. The molecular electrostatic potential surfaces (MEPS) and

26
V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 96 (2012) 24–34
electron density surfaces of H bond inner conformer of 2,3-epoxy-
propanol were constructed by using 6-311++G(d,p) basis set. The
molecular electrostatic potential serves as a useful quantity to ex-
plain hydrogen bonding, reactivity and structure–activity relation-
ship of molecules including biomolecules and drugs [47,48].
Structures resulting from the plot of electron density surface
mapped with electrostatic potential surface depict the shape, size,
charge density distribution and the site of chemical reactivity of a
molecule. The molecular electrostatic potential (MESP) at a point ‘r’
in the space around a molecule (in atomic units) can be expressed
as:
H bond outer2 conformer [50]. The H bond inner was found to be
0.5802 kcal molꢀ1 more stable than the
H bond outer1 and
2.5806 kcal molꢀ1 more stable than the H bond outer2 conformers.
The Newman projections corresponding to the H bond inner, H bond
outer1 and H bond outer2 conformers are depicted in Fig. 2.
Molecular geometry
The general molecular structure and atom numbering of the
most stable conformers H bondinner, H bond outer1 and H bond out-
er2 of 2,3-epoxypropanol are represented in Fig. 3. Structural
parameters bond length, bond angle and the dihedral angle calcu-
lated for H bond inner and H bond outer1 conformers of 2,3-epoxy-
propanol employing B3LYP and MP2 methods using 6-31G(d,p)
and 6-311++G(d,p) basis sets are presented in Table 1. From the
structural data given in Table 1 it is observed that the various bond
distances and bond angles of the conformers calculated under
study are found to be nearly the same at B3LYP and MP2 levels
of theory, yields in excellent agreement with the experimental data
of similar type conformer of epibromohydrin [34]. The C1–C2 bond
distance of the epoxide ring is 0.05Å shorter than the C2–C7 bond.
The dihedral angles C1–C2–C7–O10, O3–C2–C7–O10 and C2–C7–
O10–H11 predicted for H bond inner conformer from this investiga-
tion by B3LYP/6-311++G(d,p) method is 28°, 40.7° and –52.8°,
respectively. These are quite agreed with the experimentally pre-
dicted dihedral angles by microwave spectroscopy as 27°, 41.5°
and 47.5°, respectively for H bond inner conformer [37,50]. Simi-
larly, for the H bond outer1 form of the 2,3-epoxypropanol these
dihedral angle predicted from B3LYP/6-311++G(d,p) method is
ꢀ143.1°, ꢀ75.3° and 59.9° while the corresponding values deter-
mined from microwave study is 141, ꢀ72.5° and ꢀ55.5°, respec-
tively [37,50].
The influence of the substituent (–CH2OH) on the molecular
parameters, particularly in the angle of ring carbon atoms of 2,3-
epoxypropanol seems to be negligible. In 2,3-epoxypropanol the
O–H bond distance is the shortest and the corresponding stretch-
ing wavenumber is expected to be in the higher range of the spec-
trum. The calculated thermodynamic parameters for H bond inner
conformer of 2,3-epoxypropanol employing B3LYP and MP2 meth-
ods using 6-311++G(d,p) basis sets are given in Table 2. There is not
much deviation in the thermodynamical properties calculated
from these methods. The dipole moment and its principal inertial
axes are strongly depending upon the conformation of the mole-
cule. The dipole moment of H bond inner conformer has been deter-
mined by microwave study is 1.64 Debye [50] and is well agreed
with the calculated value. All other thermodynamic properties of
the compounds under investigation have also been summarised
in Table 2.
!
Z
X
ZA
q
ðr0 Þdr0
VðrÞ ¼
ꢀ
ꢀ!
!
!
!
jr0 ꢀ r j
j RA ꢀ r j
A
where, ZA is the charge on nucleus A, located at RA and
q
(r0) is the
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. Gauss View 5.0.8 visualisa-
tion program [49] has been used to construct the MESP surface, the
shape of highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) orbitals.
Results and discussion
Conformational analysis
Conformational analysis of 2,3-epoxypropanol was carried out
using G03 program. All the possible geometry of the conformers
was optimised to find out the energetically and thermodynami-
cally most stable configuration of the compound. The potential en-
ergy barrier obtained by the rotation of the CCOH group from 0 to
360° with the dihedral angle C2–C4–O5–H11 of 2,3-epoxypropanol
by B3LYP/6-311++G(d,p) method is depicted in Fig. 1. According to
conformational analysis [50,51] and the infrared work on 2,3-
epoxypropanol, the H bond inner and H bond outer1 conformers
were expected to be the dominating conformers [52]. In the H bond
inner conformer, an intra molecular hydrogen bond is formed be-
tween the hydroxyl H atom and the oxygen atom of the oxirane
ring. In H bond outer1, pseudo-
the proton acceptors rather than the oxirane O atom, whereas
the pseudo-
-electrons of the CꢀC bond are the acceptors in the
p-electrons of the CꢀO bond are
p
Analysis of molecular electrostatic potential (MESP)
The molecular electrostatic potential surface (MESP) which is a
method of mapping electrostatic potential onto the iso-electron
Fig. 1. Potential energy surface scan of 2,3-epoxypropanol with dihedral angle C2–
C4–O5–H11.
Fig. 2. Newman projections of the stable conformers of 2,3-epoxypropanol.

V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 96 (2012) 24–34
27
obviously from the Figs. 4 and 5 that the region around the oxygen
atoms represents the most negative potential region (red)1. The
most positive potential lie around the hydrogen of the –O–H group.
The predominance of light green region in the MESP surfaces cor-
responds to a potential halfway between the two extremes red
and dark blue colour.1
Vibrational analysis of H bond inner conformer
The geometry of 2,3-epoxypropanol under investigation are
considered by possessing C1 point group symmetry. All vibrations
are active in both IR and Raman. The symmetry coordinates of
the compound is given in Table 3. The experimental FTIR and FT-
Raman spectra of 2,3-epoxypropanol along with the theoretical
infrared and Raman spectra are shown in Figs. 7 and 8. The ob-
served and calculated frequencies using MP2 and B3LYP methods
with 6-31G(d,p) and 6-311++G(d,p) basis sets along with their rel-
ative intensities, probable assignments and potential energy distri-
bution (PED) are summarised in Table 4.
Carbon vibrations
The characteristic response of epoxides in the infrared is associ-
ated with the stretching vibration of the COC system. Since the
vibrational characteristics of this system would not be expected
to differ greatly from the CCC system, it is not surprising to find
the response to COC stretching in the same general region. How-
ever, since vibrations involving oxygen atoms result in greater di-
pole moment changes than those involving carbon atoms, more
intense infrared bands are observed for epoxides. As the ring be-
comes smaller, the asymmetrical COC stretching vibration moves
progressively to lowest wavenumbers (longer wave length),
whereas the symmetrical stretching vibration (ring breathing
mode) moves to higher wavenumbers. The symmetrical stretching
or ring breathing mode of the epoxy ring, all ring bonds stretching
and contracting in-phase, occurs near 1250 cmꢀ1. Under C1 sym-
metry, the strong line observed in the infrared spectrum of 2,3-
epoxypropanol at 1254 cmꢀ1 and in Raman the very strong line ob-
served at 1252 cmꢀ1 are ascribed to the COC symmetric stretching
modes. The bands observed in the infrared spectrum at 3062 and
2927 cmꢀ1 are attributed to the asymmetric and symmetric
stretching vibrations of the methylene group of the ring, respec-
tively. The in-plane –CH2– deformation vibration falls from 1650
to 1400 cmꢀ1. The deformational bands of 2,3-epoxypropanol is
obtained at 1485 and 1492 cmꢀ1 in IR and Raman spectra, respec-
tively, as medium bands.
Another band appears in the region 950–810 cmꢀ1 attributed to
asymmetrical ring stretching in which the C–C bond is stretching
during contraction of C–O bond. The very strong vibrational band
appeared at 906 and 900 cmꢀ1 is due to the COC asymmetric
stretching of 2,3-epoxypropanol. The C–C stretching modes of
2,3-epoxypropanol are assigned to the bands at 1333 cmꢀ1 in the
Fig. 3. Structure and atom numbering of (a) H bond inner, (b) H bond outer1 and (c)
H bond outer2 conformers of 2,3-epoxypropanol.
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 [48]. The total electron density
and MESP surfaces of the conformers of 2,3-epoxypropanol under
investigation are constructed by using B3LYP/6-311++G(d,p) meth-
od. The total electron density surface mapped with the electro-
static potential, the electrostatic potential contour maps for
positive and negative potentials, and the electrostatic potential
surface of 2,3-epoxypropanol are shown in Figs. 4–6, respectively.
The colour scheme for the MESP surface is red, electron rich,
partially negative charge; blue, electron deficient, partially positive
charge; light blue, slightly electron deficient region; yellow,
slightly electron rich region; green, neutral; respectively. It is
IR while the respective Raman band is observed at 1332 cmꢀ1
.
These frequencies appear in the respective range [28,53] and the
PED confirms the results and further shows that these modes are
pure.
The modes observed at 941 and 951 cmꢀ1 are assigned to the
CCO in-plane bending vibrations of 2,3-epoxypropanol. The COC
in-plane bending mode of 2,3-epoxypropanol has been observed
at 849 and 852 cmꢀ1 in IR and Raman spectra, respectively. The
other C–C in-plane bending of 2,3-epoxypropanol has been found
at 820 cmꢀ1 as strong and medium lines in IR and in Raman spectra.
1
For interpretation of color in Figs. 4 and 5, the reader is referred to the web
version of this article.

Table 1
Structural parameters calculated for H bond inner and H bond outer1 conformers of 2,3-epoxypropanol employing B3LYP and MP2 methods using 6-31G(d,p) and 6-311++G(d,p) basis sets.
Structural parameters
H bond inner
H bond outer1
Epibromohydrina
(microwave)
MP2/6-
311++G(d,p)
B3LYP/6-
311++G(d,p)
B3LYP/6-
31G(d,p)
MP2/6-
311++G(d,p)
B3LYP/6-
311++G(d,p)
B3LYP/6-
31G(d,p)
Internuclear distance (Å)
C1–C2
C1–O3
C1–H4
C1–H5
C2–O3
C2–H6
C2–C7
C7–H8
1.465
1.449
1.086
1.085
1.438
1.09
1.511
1.094
1.099
1.414
0.964
1.465
1.443
1.086
1.085
1.436
1.09
1.514
1.093
1.1
1.468
1.433
1.087
1.088
1.44
1.088
1.506
1.097
1.094
1.424
0.963
1.468
1.438
1.086
1.087
1.443
1.089
1.502
1.098
1.093
1.421
0.963
1.468
1.433
1.087
1.087
1.441
1.089
1.505
1.098
1.093
1.424
0.964
1.469
1.433
1.090
1.090
1.442
1.091
1.508
1.101
1.096
1.419
0.968
1.474
1.447
1.087
1.087
1.444
1.089
1.502
1.091
1.091
C7–H9
C7–O10
O10–H11
1.416
0.965
Bond angle (degree)
C2–C1–O3
C2–C1–H4
C2–C1–H5
C1–C2–O3
C1–C2–H6
C1–C2–C7
O3–C1–H4
O3–C1–H5
C1–O3–C2
H4–C1–H5
O3–C2–H6
O3–C2–C7
H6–C2–C7
C2–C7–H8
C2–C7–H9
C2–C7–O10
H8–C7–H9
H8–C7–O10
H9–C7–O10
C7–O10–H11
59.1
119.3
118.9
59.9
118.3
121.9
114.3
114.5
61.0
117.0
114.1
114.6
115.4
109.7
108.5
112.1
108.2
107.1
111.1
105.7
59.2
119.6
119.3
59.7
118.3
122.6
114.7
114.8
61.2
59.5
119.5
119.7
59.0
118.6
121.9
115.2
115.1
61.4
115.4
113.6
115.6
115.2
109.7
109.6
111.8
108.3
111.4
105.9
108.2
59.5
119.4
119.2
59.2
118.7
121.4
114.8
114.7
61.3
116.3
113.4
114.1
116.1
109.1
110.3
111.0
108.8
111.2
106.4
106.1
59.6
119.5
119.7
59.0
118.5
122.0
115.2
115.1
61.4
115.5
113.5
115.1
115.4
109.5
110.0
111.8
108.3
111.1
106.0
107.9
59.6
119.5
119.7
59.0
118.5
122.0
115.2
115.1
61.4
115.5
113.8
114.4
115.4
109.1
110.2
111.4
107.9
111.7
106.4
106.5
119.1
119.3
120.0
116.0
116.2
116.3
114.1
115
111.6
111.0
114.7
109.7
108.6
112.8
107.7
106.9
110.9
107.2
Dihedral angle (degree)
H4–C1–C2–H6
H4–C1–C2–C7
H5–C1–C2–H6
H5–C1–C2–C7
C1–C2–C7–H8
C1–C2–C7–H9
C1–C2–C7–O10
O3–C2–C7–H8
O3–C2–C7–H9
O3–C2–C7–O10
H6–C2–C7–H8
H6–C2–C7–H9
H6–C2–C7–O10
C2–C7–O10–H11
H8–C7–O10–H11
H9–C7–O10–H11
ꢀ0.5
ꢀ155.7
154.3
ꢀ0.9
ꢀ0.1
ꢀ155.2
154.1
ꢀ1.0
ꢀ0.2
ꢀ155.9
153.5
ꢀ2.2
1.5
ꢀ155.8
155.2
ꢀ2.1
1.9
ꢀ154.4
154.9
ꢀ1.3
1.9
ꢀ155.0
154.3
ꢀ2.6
90.9
91.1
89.5
ꢀ16.9
102.6
ꢀ139.8
50.5
ꢀ19.6
ꢀ17.0
101.3
ꢀ140.8
50.5
ꢀ151.0
ꢀ27.9
159.5
ꢀ82.4
40.7
ꢀ151.4
ꢀ28.0
159.8
ꢀ82.7
40.7
ꢀ153.3
ꢀ29.8
157.2
ꢀ85.5
37.9
99.4
ꢀ143.1
48.3
167.2
ꢀ75.3
ꢀ176.5
ꢀ57.5
60.0
170.0
ꢀ72.4
ꢀ174.7
ꢀ55.2
62.4
168.8
ꢀ73.4
ꢀ174.5
ꢀ56.2
61.6
ꢀ64.9
ꢀ64.8
ꢀ66.9
53.2
52.7
50.4
176.2
ꢀ51.9
ꢀ172.3
69.7
176.1
ꢀ52.8
ꢀ173.5
69.3
173.8
ꢀ46.6
ꢀ167.4
75.1
57.4
59.9
57.6
ꢀ64.2
ꢀ62.8
ꢀ64.7
177.5
179.7
177.8
a
Values are taken from Ref. [30,50].

V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 96 (2012) 24–34
29
Table 2
The calculated thermodynamic parameters for H bond inner conformer of 2,3-epoxypropanol employing B3LYP and MP2 methods using 6-311++G(d,p) basis sets.
Thermodynamic parameters (298 K)
H bond inner
MP2/6-311++G(d,p)
B3LYP/6-311++G(d,p)
B3LYP/6-31G(d,p)
Experimentala (microwave)
SCF energy (a.u.)
ꢀ267.6840
61.22
17.25
70.85
59.44
ꢀ268.4075
60.16
17.59
75.13
58.34
ꢀ268.3281
61.82
17.05
70.73
60.04
Total energy (thermal), Etotal (kcal molꢀ1
)
Heat capacity at const. volume, Cv (cal molꢀ1 Kꢀ1
)
Entropy, S (cal molꢀ1 Kꢀ1
)
Vibrational energy, Evib (kcal molꢀ1
)
Zero point vibrational energy, Eo (kcal molꢀ1
)
58.11
57.0
58.73
Rotational constants (GHz)
A
B
C
10.31
4.15
3.81
10.31
4.15
3.81
10.31
4.15
3.81
10.35
4.10
3.78
Dipolemoment (Debye)
lx
ly
lz
ltotal
–0.80
1.60
1.14
2.12
–0.73
1.37
0.87
1.78
–80
1.28
0.82
1.72
1.64
a
Values are taken from Ref. [50].
Fig. 4. The total electron density iso surface mapped with electrostatic potential of
H bond inner conformer of 2,3-epoxypropanol.
Fig. 5. The contour map of electrostatic potential of H bond inner conformer of 2,3-
epoxypropanol.
The C–C out of plane bending modes are observed at 617 and
612 cmꢀ1. All these assignments are agreed well with the reported
literatures [31,35]. The C–C in-plane bending and out of plane
bending vibrations are described as mixed modes and have about
18–22% PED contributions mainly from C–H in-plane bending and
out of plane bending vibrations, respectively.
of CH present in the epoxy ring of 2,3-epoxypropanol is determined
by DFT method at 2983 cmꢀ1. The PED contribution of this stretch-
ing mode indicated as highly pure modes like the carbon–carbon
stretching fundamentals.
The C–H in-plane bending modes are observed in the region
1400–1000 cmꢀ1. These modes are observed in 2,3-epoxypropanol
is obtained in the IR at 1425 and in Raman at 1415 cmꢀ1. The C–H
out of plane bending mode of epoxy derivatives are observed in the
region 1100 to 600 cmꢀ1. The C–H out of plane bending vibrations
of 2,3-epoxypropanol are assigned to the bands observed at
1124 cmꢀ1 in the infrared spectrum. The C–H in-plane and out of
plane bending vibrations have substantial overlapping with the
ring CCO in-plane and out of plane bending modes, respectively.
In 2,3-epoxypropanol the O–H stretching mode is observed at
3400 cmꢀ1 in the IR as shoulder and 3410 cmꢀ1 in Raman while
the C–O stretching is seen at 1080 and 1076 cmꢀ1 in the IR and Ra-
man spectra, respectively. The bands observed at 1398 and
1396 cmꢀ1 is attributed to the O–H in-plane bending mode of
2,3-epoxypropanol. The out of plane bending mode of 2,3-epoxy-
propanol is found at 747 in IR and 740 cmꢀ1 in Raman spectra.
The NCA predicts that the O–H modes are mixed with C–O mode.
C–H vibrations
Methylene (–CH2–) group vibrations
The C–H stretching vibrations of epoxy rings are normally found
between 3050 and 2900 cmꢀ1. In this region the bands are not
affected appreciably by the nature of substituents. The wavenumber
It is stated that the –CH2– stretching vibrations occur in the re-
gion 3100–2850 cmꢀ1. The asymmetric –CH2– stretching vibration

30
V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 96 (2012) 24–34
Fig. 6. The electrostatic potential surface of
H
bond inner conformer of 2,3-
epoxypropanol.
Fig. 7. (a) Experimental FTIR (b) Infrared (B3LYP/6-311++G⁄⁄) and (c) Infrared
(MP2/6-311++G⁄⁄) spectra of 2,3-epoxypropanol.
Table 3
Symmetry coordinates for 2,3-epoxypropanol.a
Symmetry coordinates
Description
*
S1 = r1,6 ꢀ r1,7
ma CH2
ms CH2
*
S2 = r1,6 + r1,7
S3 = r2,8
m C2H8
S4 = r4,9 ꢀ r4,10
ma CH2
ms CH2
d CH2
S5 = r4,9 + r4,10
*
S6 = 4b6,1,7 ꢀ b3,1,6 ꢀ b2,1,6 ꢀ b3,1,7 ꢀ b2,1,7
S7 = b9,4,10
d CH2
S8 = 2b4,2,8 ꢀ b1,2,8 ꢀ b3,2,8
S9 = r1,3 ꢀ r2,3
b C2H8
ma C1O3C2*
S10 = r1,3 + r2,3
ms C1O3C2*
S11 = b2,4,9 + b2,4,10 ꢀ b5,4,9 + b5,4,10
q
x
s
CH2
CH2
CH2
S12
S13
S14
S15
S16
=
=
=
=
=
c2,4,9
c5,4,9
c3,2,8
c3,1,6
c3,1,6
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
c2,4,10
c5,4,10
c1,2,8
c
C2H8
*
c2,1,6
c2,1,6
+
ꢀ
c3,1,7
c3,1,7
ꢀ
c2,1,7
c2,1,7
x
s
CH2
*
+
CH2
S17 = 2b1,3,2 ꢀ b3,1,2 ꢀ b3,2,1
b C1O3C2*
S18 = b1,2,3
b C1C2O3*
S19 = r2,4
S20 = r4,5
S21 = r5,11
m
m
m
C2C4
C4O5
O5H11
S22 = b1,2,4 + b3,2,4
b C2C4
C2C4
b C4O5
C4O5
b O5H11
O5H11
S23
S24 = b2,4,5
S25
S26 = b4,5,11
S27
=
c1,2,4
ꢀ
c3,2,4
c
=
c2,4,5
c
=
c4,5,11
c
Definitions are made in terms of the standard valance coordinates; ri,j is the bond
distance between the atoms i and j; bi,j,k is the valance angle between the atoms i, j
and k, with j the central atom; ci,j,k is the out of plane angle between the atoms i, j
and k, with j the central atom;
s
i,j is the torsion vibration between the atoms i and j.
a
m
– stretching; b – in-plane bending; d – deformation; – rocking; – out of
q
c
Fig. 8. (a) Experimental FT-Raman (b) Raman (B3LYP/6-311++G⁄⁄) and (c) Raman
(MP2/6-311++G⁄⁄) spectra of 2,3-epoxypropanol.
plane bending;
Ring modes.
x – wagging; s– twisting/torsion.
*
at 3005 and 2867 cmꢀ1 are attributed to the asymmetric and sym-
metric stretching vibrations of the methylene group, respectively.
The in-plane –CH2– deformation vibration falls from 1650 to
1400 cmꢀ1. The deformational bands of 2,3-epoxypropanol is
appears from 3100 to 3000 cmꢀ1 and the symmetric –CH2–
stretching is observed in the range 3000–2850 cmꢀ1. In the case
of 2,3-epoxypropanol the bands observed in the infrared spectrum

Table 4
The observed FTIR, FT-Raman and calculated frequencies using B3LYP/6-31G(d,p) and HF/6-311++G(d,p) methods along with their relative intensities, probable assignments and potential energy distribution (PED) of 2,3-
epoxypropanol.a
Species Observed
wavenumber
(cmꢀ1
MP2/6-311++G⁄⁄ calculated wavenumber
B3LYP/6-31G⁄⁄ calculated
B3LYP/6-311++G⁄⁄ calculated wavenumber
Depolariszation
ratio
Assignment %PED
wavenumber
)
FTIR
FTR
Unscaled
Scaled
IR
Raman
Unscaled
Scaled
IR
Unscaled
Scaled
IR
Raman
(cmꢀ1
3761
)
(cmꢀ1
3423
)
intensity intensity
(cmꢀ1
3810
)
(cmꢀ1
3429
)
intensity (cmꢀ1
)
(cmꢀ1
3422
)
intensity intensity
A
3400
sh
3410
sh
48.68
0.256
38.30
3720
43.99
0.232
0.11
mO–H
92mOH
*
A
A
3062 m 3068 s
3240
3152
3078
2994
9.32
22.67
0.339
1.000
3259
3166
3096
3008
12.42
24.51
3168
3087
3073
2994
12.93
29.25
0.327
1.000
0.73
0.15
m
m
aCH2
aCH2
95mCH
93mCH
3005
vs
3012
vs
A
A
3138
3117
2981
2961
15.71
20.52
0.499
0.554
3154
3132
2996
2975
17.72
26.90
3076
3046
2983
2955
23.42
24.50
0.430
0.549
0.21
0.39
m
C–H
91mCH
94mCH
*
2927
vs
2932
vs
msCH2
A
A
A
A
A
A
A
2867 s
1485 m 1492 m 1553
1447 m 1457 m 1532
1425 s
1398 s
1333 s
1254 s
2876 m 3021
2870
1491
1471
1405
1391
1332
1250
54.66
3.21
1.90
24.96
21.89
6.14
0.930
0.022
0.053
0.035
0.048
0.026
0.116
3031
1583
1574
1482
1470
1402
1321
2879
1504
1495
1408
1397
1332
1255
58.77
1.98
0.38
11.75
44.27
12.93
2.27
2954
1521
1509
1442
1427
1364
1283
2865
1490
1479
1413
1399
1336
1257
63.73
4.06
2.05
37.22
13.34
7.21
0.865
0.018
0.050
0.032
0.043
0.023
0.110
0.20
0.45
0.70
0.75
0.18
0.64
0.16
m
sCH2
94mCH
*
dCH2
dCH2
bC–H
bO–H
77dCH2 + 19bCCO
79dCH2 + 17bCC
81bCH + 12bCCO
69bOH + 16bCO
93mCC
1415 m 1464
1396 m 1449
1332 w 1387
m
m
C–C
1252
vs
1302
2.42
3.86
sCOC*
90mCOC
A
A
1225 s
1156
vw
1139 m 1140 s
1124 m
1095 s
1080 m 1076
vw
1244
1159 m 1192
1194
1144
17.94
3.10
0.030
0.011
1257
1210
1194
1150
19.89
0.39
1228
1169
1203
1146
21.56
6.76
0.028
0.030
0.40
0.72
x
CH2
61
65
x
CH2 + 24sCH2
sCH2
sCH2 + 22xCH2
*
A
A
A
A
1188
1146
1127
1060
1140
1100
1082
1060
3.43
37.70
11.77
27.90
0.044
0.009
0.004
0.018
1202
1163
1141
1078
1142
1105
1084
1078
6.36
22.36
23.48
34.31
1161
1119
1107
1040
1137
1097
1084
1040
0.22
29.70
17.97
36.28
0.017
0.007
0.003
0.016
0.46
0.55
0.32
0.72
xCH2
64
75
67
82
xCH2 + 26sCH2
c
s
m
C–H
CH2
C–O
cCH + 18cCCO
sCH2 + 24xCH2
mCO + 14mCC
*
A
1037
1036 m
993
993
18.85
0.045
1011
1011
12.70
976
976
18.95
0.036
0.39
bCCO*
69bCCO + 16bCH
vs
A
A
A
A
A
A
A
A
941 s
906 vs
849 vs
820 vs
747 s
617 m
501 m
951 m
900 vs
852 s
820 m
740 s
612 w
500 m
388 m
941
862
779
639
546
367
268
183
941
862
779
639
546
367
268
183
14.84
38.78
11.49
34.37
125.72
16.41
1.14
0.041
0.048
0.044
0.009
0.006
0.004
0.004
0.001
960
882
799
644
520
374
269
189
960
882
799
644
520
374
269
189
16.18
32.61
11.53
24.67
139.50
21.00
0.98
921
837
765
631
526
365
263
174
921
837
765
631
526
365
263
174
19.90
42.12
13.19
32.53
123.68
20.41
1.25
0.031
0.042
0.040
0.009
0.006
0.004
0.003
0.001
0.35
0.68
0.52
0.67
0.71
0.68
0.16
0.53
q
m
CH2
69 CH2 + 22bCH
90m COC
68bCOC + 20bCH
67bCC + 22bCH
q
aCOC*
bCOC*
bC–C
c
c
O–H
C–C
75
75
c
c
OH + 18cCO
CC + 18cCH
bC–O
C–O
69bCO + 16bOH
75cCO + 18cOH
14.51
20.37
16.78
c
a
m
– stretching; b – in-plane bending; d – deformation;
q – rocking; c – out of plane bending; x – wagging and s – twisting.
*
Ring vibration modes.

32
V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 96 (2012) 24–34
obtained at 1447 and 1457 cmꢀ1 in IR and Raman spectra, respec-
tively, as medium bands. Likewise, the out of plane bending –CH2
wagging and twisting vibrations are also assigned in the expected
range. The wagging band appears between 1300 and 1150 cmꢀ1
.
Therefore, the band at 1225 cmꢀ1 in the infrared are attributed to
the –CH2– wagging mode of 2,3-epoxypropanol. The vibrations ob-
served at 1159 cmꢀ1 is assigned to the –CH2– twisting mode of 2,3-
epoxypropanol, respectively. These –CH2– vibrations are also in
good agreement with literature values [28,32,36].
Ring –CH2– group vibrations
The ring –CH2– group frequencies make a significant contribu-
tion to 2,3-epoxypropanol spectra. Some of the fundamentals can
be associated to each –CH2– group, namely the symmetrical,
ms(CH2), and asymmetrical, ma(CH2), stretching modes; the sym-
metrical, d(CH2) hydrogen deformation mode; the in-plane –CH2–
rocking and out of plane –CH2– wagging and twisting hydrogen
bending modes. The methylene symmetric stretching mode,
m
s(CH2) of 2,3-epoxypropanol is observed at 2927 cmꢀ1 in IR spec-
trum. Similarly the asymmetric stretching vibrations of 2,3-epoxy-
propanol is found at 3062 and 3068 cmꢀ1 in the infrared and in
Raman spectra, respectively. The methylene hydrogen deformation
mode is also well established and the methylene deformation
mode, d(CH2) of 2,3-epoxypropanol is obtained at 1485 cmꢀ1 in
IR and at 1492 cmꢀ1 in Raman. The methylene deformational mode
is mainly coupled with the CCO in-plane bending vibrations. In 2,3-
epoxypropanol, the bands observed at 1139 and 1095 cmꢀ1 in the
IR spectrum are assigned to the –CH2– wagging and twisting
modes, respectively. These assignments are substantiated by the
reported literature [34–38,53]. The methylene wagging and twist-
ing modes are significantly overlapping to each other.
Electronic properties
Molecular orbitals, when viewed in a qualitative graphical rep-
resentation, can provide insight into the nature of reactivity, and
some of the structural and physical properties of molecules. Well
known concepts such as conjugation, aromaticity and lone pairs
are well illustrated by molecular orbitals. The energies of HOMO,
LUMO, LUMO+1 and HOMOꢀ1 and their orbital energy gaps are
calculated using B3LYP/6-311++G(d,p) method and the pictorial
illustration of the frontier molecular orbitals and their respective
positive and negative regions are shown in Fig. 9 for H bond inner
conformer of 2,3-epoxypropanol.
The positive and negative phase is represented in red and green
colour, respectively. The calculated energy gap of HOMO–LUMO’s
explains the ultimate charge transfer interface within the mole-
cule. The HOMO characterizes the electron donating ability, the
LUMO characterizes the electron accepting ability, and the gap be-
tween HOMO and LUMO characterizes the molecular chemical sta-
bility [54]. The energy gap between HOMO and LUMO is a critical
parameter in determining molecular electrical transport proper-
ties. The energies of four important molecular orbitals of 2,3-
epoxypropanol: the second highest and highest occupied MO’s
(HOMO and HOMOꢀ1), the lowest and the second lowest unoccu-
pied MO’s (LUMO and LUMO+1) were calculated and are presented
in Table 5. The frontier orbital energy gap in case of H bond inner is
found to be 7.4903 eV. The very high band gap energy signifies the
stability of H bond inner conformer of 2,3-epoxypropanol. The low-
est singlet ? singlet spin-allowed excited states of 2,3-epoxypro-
panol was taken into account for the TD-DFT calculation in order
to investigate the properties of electronic absorption. The experi-
mental kmax values are obtained from the UV–Visible spectra re-
corded in Shimadzu UV–Visible spectrophotometer. The
Fig. 9. The frontier molecular orbitals of
epoxypropanol.
H bond inner conformer of 2,3-
theoretical electronic absorption spectrum of 2,3-epoxypropanol
gives two absorption bands with a maximum at 179.05 and
176.35 nm. The absorption bands are caused by the n ?
r
⁄ transi-
tions. The more intense band at 179.05 nm is due to the n ?
r
⁄
transitions of an alcoholic group. The calculated absorption wave-
lengths (kmax) are in good agreement with the experimental
wavelengths.

V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 96 (2012) 24–34
33
Table 5
Experimental and calculated absorption wavelength (k), excitation energies (E), oscillator strength (f) and frontier orbital energies of 2,3-epoxypropanol by TD-DFT method.
k (Expt.; nm)
k (cal.; nm)
E (eV)
f
Assignment
EHOMO
ELUMO
EHOMOꢀ1
ELUMO+1
ELUMOꢀ EHOMO
185.15
174.35
179.05
176.35
6.9247
7.0307
0.024
0.015
n ?
n ?
r
r
⁄
⁄
ꢀ7.7096 eV
ꢀ0.2193 eV
ꢀ8.1349 eV
0.0465 eV
7.4903 eV
wavenumbers. A better agreement between the computed and
experimental frequencies can be obtained for 2,3-epoxypropanol
by using the scale factor of 1.0 in the very low frequency region.
B3LYP and MP2 methods with 6-31G(d,p) and 6-311++G(d,p) basis
sets minimised the deviations very much between the computed
and experimental frequencies and the correction factors are all
much closer to unity. The linear regression between the calculated
and experimental frequencies of 2,3-epoxypropanol by MP2 and
B3LYP methods using 6-311++G(d,p) basis set has been presented
in Fig. 10.
Conclusions
The complete optimised geometrical parameters of H bond inner
and H bond outer1 conformations of 2,3-epoxypropanol with DFT-
B3LYP and MP2 methods using 6-31G(d,p) and 6-311++G(d,p) ba-
sis sets were discussed in detailed manner and compared with the
experimental data. The thermodynamic properties of the opti-
mised geometry of the H bond inner have also been determined
by ab initio and DFT calculations. The vibrational frequencies of
the fundamental modes of the most stable H bond inner conforma-
tions of the 2,3-epoxypropanol molecule have been precisely as-
signed and analysed and the theoretical results were compared
with the experimental vibrations. The energies of important MOs
and the kmax of the compound were also evaluated from TD-DFT
method.
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