Synthesis, structural elucidation and DFT studies of ortho-hydroxy acetophenones

Article abstract of DOI:10.1016/j.molstruc.2009.08.013

Two ortho-hydroxy acetophenones, namely 2,6-dihydroxy-4-methyl acetophenone [C₉H₁₀O₃] (1) and 2,4-dihydroxy-3-acetyl-6-methyl acetophenone [C₁₁H₁₂O₄] (2) have been synthesized and character

Full text of DOI:10.1016/j.molstruc.2009.08.013

Journal of Molecular Structure 936 (2009) 277–282
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structural elucidation and DFT studies of ortho-hydroxy acetophenones
Saikat K. Seth a,b, Dipak K. Hazra c, Monika Mukherjee c, Tanusree Kar a,
*
a Department of Materials Science, Indian Association for the Cultivation of Science, Kolkata 700032, India
b Department of Physics, M.G. Mahavidyalaya, Bhupatinagar, Midnapore (E), West-Bengal, India
c Department of Solid State Physics, Indian Association for the Cultivation of Science, Kolkata 700032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 July 2009
Received in revised form 10 August 2009
Accepted 15 August 2009
Available online 20 August 2009
Two ortho-hydroxy acetophenones, namely 2,6-dihydroxy-4-methyl acetophenone [C9H10O3] (1) and
2,4-dihydroxy-3-acetyl-6-methyl acetophenone [C11H12O4] (2) have been synthesized and characterized
by spectroscopic and X-ray structural studies. Compound (1) crystallizes in monoclinic system, space
group P21/c, with a = 3.888(3) Å, b = 26.974(17) Å, c = 14.940(9) Å, b = 91.919(8)°, Z = 8, whereas com-
pound (2) crystallizes in orthorhombic system, space group Pbca, with a = 7.255(2) Å, b = 14.410(4) Å,
c = 18.332(1) Å, Z = 8. The crystal packing of (1) exhibits intermolecular O–HÁÁÁO hydrogen bonds forming
a parallel chain propagating along (0 1 0) direction, whereas in (2), the combination of intermolecular
Keywords:
Acetophenone
Crystal structure
DFT studies
C–HÁÁÁO hydrogen bonds and
p–p interactions generate a two-dimensional network. The molecular
geometries and electronic structure of (1) and (2) were calculated at the DFT level using the hybrid
exchange correlation functional, BLYP, PW91, PBE and BP.
HOMO–LUMO energies
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
on the hydrogen bridge length is with substitution at the phenyl
ring of the ortho-hydroxy acetophenones. As part of our ongoing
Self assembly is the fundamental molecular recognition process
adopted by nature to generate the elegant and intricate molecular
machinery from which life is built. Appropriate complementarities
between the substrate and the substituting group are the neces-
sary prerequisite for molecular recognition. The properties of
crystalline material strongly depend on how the constituent com-
ponents are organized with respect to one another and a control
over this organization directly provides a handle over the func-
tional properties of the material. Crystals are assembled in sponta-
neous process called self-assembly that proceeds through a series
of molecular recognition events. Identification of robust recogni-
tion motif or a pattern of recognition is at the heart of gaining a
control over the self-assembly process. A recognition event be-
tween a set of molecular components is the outcome of the mutual
interaction through various forces that is in operation. Hydrogen
bonding still remains the most reliable and widely used means of
enforcing molecular recognition [1–3] of crystalline materials,
studies to elucidate the relationships between the characteristics
of the functional dyes containing acetophenone skeletons and their
molecular structures and to investigate the possibilities for inter-
and intramolecular hydrogen bonding in the solid state, the X-
ray structure analyses were undertaken. In this paper we report
synthesis, spectroscopic characterization, crystal structures deter-
mination and hydrogen bonding of 2,4-dihydroxy-4-methyl aceto-
phenone (1) and 2,4-dihydroxy-3-acetyl-6-methyl acetophenone
(2) along with the DFT calculations to investigate the molecular
geometry and electronic structure.
2. Experimental
2.1. Synthesis
A mixture of orcinol (1.00 gm, 0.0074 mol) and glacial acetic
acid (15 ml) was stirred at 0 °C with subsequent addition of boron
trifluoride etherate (7.54 ml, 0.0592 mol) following by stirring at
room temperature for 48 h. The reaction mixture was cooled and
most of acetic acid was distilled out under reduced pressure. The
mixture was then quenched with sodium-bicarbonate solution
and extracted with (3 Â 20) ml of chloroform. The organic layer
was separated and dried under anhydrous sodium sulphate. Then
the organic layer was concentrated. The product was purified with
silica gel chromatography. Elution with petroleum-ether:ethyl ace-
tate (5:1) furnished the required compound (1) and further elution
with the same in the ratio (11:50) furnished compound (2).
other weaker forces such as
p–p [4–7] forces associated with aro-
matic- systems have also been successfully utilized in this regard.
p
Over the years much effort has been concentrated on characteriza-
tion of hydrogen bonded systems in order to provide parameters to
describe hydrogen bond strength and geometry [8–13]. The inves-
tigations in hydrogen bonding of ortho-hydroxy acetophenones
[14–19] proved that the greatest steric impact of a substituent
* Corresponding author. Fax: +91 33 2473 2805.
E-mail address: mstk@iacs.res.in (T. Kar).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.08.013

278
S.K. Seth et al. / Journal of Molecular Structure 936 (2009) 277–282
Table 2
Compound (1): NMR data exists in the literature [20].
Compound (2): 1H NMR (300 MHZ, CDCl3): d 2.58 (S, 3H), 2.66(S,
3H), 2.75 (S, 3H), 6.30 (S, 1H), 14.2 (S, 1H) (for intra molecular
H-bonding), 15.74 (for intermolecular hydrogen bonding); 13C
NMR (75 MHZ, CDCl3): d 25.9, 33.0, 33.6, 109.1, 113.4, 113.4,
149.15, 169.2, 170.5, 204.3, 205.6.
Selected bond lengths (Å), bond angles (°) determined by X-ray diffraction and DFT
calculations for the title compounds.
Compound (1)
X-ray
Compound (2)
DFT(BLYP) X-ray DFT(BLYP)
Bond lengths
C2–C3
C3–C4
C4–C5
C5–C6
C5–C8
C8–C9
O1–C4
O2–C6
(Moiety A) (Moiety B)
1.383(5)
1.374(5)
1.426(5)
1.431(5)
1.452(5)
1.479(5)
1.356(4)
1.342(4)
1.258(4)
–
1.386(5)
1.378(5)
1.415(5)
1.417(5)
1.465(5)
1.491(5)
1.361(4)
1.357(4)
1.255(4)
–
1.408
1.395
1.427
1.443
1.474
1.516
1.384
1.349
1.260
–
1.432(2) 1.444
1.431(2) 1.453
1.420(2) 1.430
1.414(2) 1.430
1.470(2) 1.476
1.492(2) 1.511
1.328(2) 1.335
1.340(2) 1.338
1.247(2) 1.263
1.466(2) 1.467
1.500(2) 1.520
1.254(2) 1.271
2.2. Crystallographic analysis
Single crystal X-ray diffraction intensity data of the title com-
pounds were collected at 150(2) K using a Bruker APEX-II CCD dif-
fractometer equipped with graphite monochromated Mo
Ka
radiation (k = 0.71073 Å). Data reductions were carried out using
the program Bruker SAINT [21]. Because of very small values of
the absorption coefficients, no absorption corrections were ap-
plied. The structures of both the compounds were solved by direct
methods and refined by the full-matrix least-square technique on
F2 with anisotropic thermal parameters to describe the thermal
motions of all non hydrogen atoms using the programs SHELXS97
and SHELXL97 [22], respectively. All hydrogen atoms were located
from difference Fourier map and treated as riding. A summary of
crystal data and relevant refinement parameters are given in
Table 1. Selected bond lengths and angles of compounds (1) and
(2) are given in Table 2.
O3–C8
C3–C10
C10–C11
O4–C10
–
–
–
–
–
–
Bond angles
C5–C8–C9
C6–C5–C8
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C7
O1–C4–C3
O1–C4–C5
O2–C6–C7
O3–C8–C5
O4–C10–C3
O4–C10–C11
124.3(4)
120.2(4)
121.3(4)
121.4(4)
115.9(3)
121.3(4)
120.7(4)
117.9(3)
117.7(4)
119.1(3)
–
123.8(4)
119.7(3)
121.2(4)
121.3(3)
116.0(3)
122.3(4)
120.8(3)
117.9(3)
117.6(3)
119.3(3)
–
123.02
118.70
120.97
121.82
115.97
121.39
119.55
118.63
117.27
119.94
–
123.3(1) 123.77
119.2(1) 118.36
117.8(1) 117.46
122.4(1) 122.49
116.6(1) 116.95
121.5(1) 120.84
120.4(1) 119.75
117.3(1) 117.77
117.1(1) 117.27
119.1(1) 119.24
120.0(1) 120.62
115.1(1) 114.37
–
–
–
2.3. Computational
The isolated molecule DFT calculations were carried out using
DMol3 code [23] of the Materials studio of system of programs in
the framework of a generalized-gradient approximation (GGA)
[24]. The starting atomic coordinates were taken from the final
X-ray refinement cycle. The geometry of the molecules was fully
optimized using the hybrid exchange–correlation functional BLYP
[25,26], PW91 [27], PBE [24] and BP [28,29] with a double numeric
plus polarization (DNP) basis set. The electronic structures were
calculated at the same level. No constraints to bonds, angles or
dihedral angles were applied in the calculations, and all atoms
were free to optimize. Convergence in the calculations was as-
sumed to be reached when the total energy change between two
consecutive self-consistent field (SCF) cycles was less than
1 Â 10À5 a.u.
3. Results and discussion
3.1. Structural description
The molecular views [30] of (1) and (2) with atom numbering
scheme are shown in Figs. 1 and 2, respectively. There are two
Table 1
Crystal data and structure refinement parameters for C9H10O3 (1) and C11H12O4 (2).
(1)
(2)
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system, space group
a, b, c (Å)
C9H10O3
166.17
150(2)
0.71073
Monoclinic, P21/c
3.888(3), 26.974(17), 14.940(9)
C11H12O4
208.21
150(2)
0.71073
Orthorhombic, Pbca
7.255(2), 14.410(4), 18.332(1)
a
, b,
c
(°)
90.0, 91.919(8), 90.0
1566.0(17)
90.0, 90.0, 90.0
1916.5(8)
Volume (Å3)
Z
8
8
Density (calc.) (Mg/m3)
Absorption coefficient (mmÀ1
F(000)
1.410
0.106
704
1.443
0.110
880
)
Crystal size (mm3)
Limiting indices
0.18 Â 0.10 Â 0.08
À3<=h<=3, À25<=k<=25, À14<=l<=14
8537/1383 [R(int) = 0.0683]
100.0
0.28 Â 0.24 Â 0.18
À8<=h<=8,À17<=k<=17,À21<=l<=21
16710/1689 [R(int) = 0.0298]
100.0
Reflections collected/unique
Completeness to h (%)
Refinement method
Data/restraints/parameters
Goodness-of À fit on F2
Full-matrix least-squares on F2
1383/0/227
Full-matrix least-squares on F2
1689/0/141
1.038
1.067
Final R indices [I > 2
R indices (all data)
r(I)]
R1 = 0.0463, wR2 = 0.1145
R1 = 0.0621, wR2 = 0.1255
0.245 and À0.223
R1 = 0.0344, wR2 = 0.0969
R1 = 0.0397, wR2 = 0.1030
0.218 and À0.232
Largest diff. peak and hole (eÅÀ3
)
P
P
P
P
||Fo| À |Fc||/ |Fo|, wR2 = [ {(Fo À Fc2)2}/ {w(Fo2)2}]1/2, w = 1/{
r
2(Fo2) + (aP)2 + bP}, where a = 0.0838P and b = 0.0000 for (1) and a = 0.0552P and b = 0.7062 for (2).
2
R1
=
P = (Fo2 + 2Fc2)/3 for both the structures.

S.K. Seth et al. / Journal of Molecular Structure 936 (2009) 277–282
279
Fig. 1. An ORTEP view and atom numbering scheme of molecule (1) with displacement ellipsoids at the 30% probability level.
molecules in the independent part of the unit cell in (1) but com-
pound (2), consists one independent molecule in the unit cell.
There are only minor differences in geometrical parameters of
the two independent moieties A and B in (1) (Table 2). These mol-
ecules in the asymmetric unit are almost flat. The angle between
the best planes of both (acyl and aromatic) fragment in (1) are
2.71(12)° and 1.79(13)° for moiety A and B, respectively. In (2),
the acyl group which is ortho to both the hydroxyl goup and ortho
to methyl group forms angles 4.76(5)° and 2.51(4)° with the aro-
matic ring. The intramolecular geometry of the title compounds
are dominated by hydrogen bond involving the hydroxyl groups
and the oxygen atom of the carbonyl groups. Experimental obser-
vation gives the shortest distances between the oxygen molecules
are 2.475(4) Å in (1) and 2.417(1) Å in (2), which are relatively
strong and almost coplanar with the aromatic rings. In (1), the pla-
narity of the hydrogen bonded molecular fragment passing
through the hydrogen bond O2B–H2BÁÁÁO3B is largely deviated
from the least square mean planes of the aromatic ring by
1.79(1)° and that for (2) is 2.40(3)° for O1–H1ÁÁÁO4 hydrogen bond.
Intramolecular hydrogen bonding has little effect on the C–O
bond lengths [C6A–O2A, C6B–O2B, C6–O2, C4–O1] of the partici-
Fig. 2. An ORTEP view and atom numbering scheme of molecule (2) with
displacement ellipsoids at the 30% probability level.
Fig. 3. Generationof1-D infinite parallel chainpropagatingalong [0 1 0]direction incompound(1). The hydrogen atoms not involve inhydrogenbonding shownasbrokenoff bonds.

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S.K. Seth et al. / Journal of Molecular Structure 936 (2009) 277–282
Table 3
consider the substructures generated by each type hydrogen bonds
acting individually, and then the combination of the substructures
to build a framework. In (1), the hydroxyl O1A atom in the mole-
cule at (x, y, z) acts as a donor to O2B atom in the molecule at
(1 À x, À½ + y, ½ À z) and another carboxyl atom O1B atom in
the molecule acts as a donor to the carbonyl O3A atom of acetyl
group in the molecule at (x À 1, y, z), so generating an infinite par-
allel one-dimensional chain propagating along [0 1 0] direction.
Similar molecular recognition have been noticed before
[31,34,35] where the organization of molecules displays parallel
chain. Since O1A, O3A atoms are in molecule ‘A’ and O1B, O2B
atoms in molecule ‘B’, the molecular packing contain almost paral-
lel molecules with alternating ABABABÁÁÁ chains which stacks par-
allel to b-axis (Fig. 3).
Hydrogen bonding geometry of C9H10O3 (1) and C11H12O4 (2) (Å, °).
D–HÁÁÁA
Compound 1
O2B–H2BÁÁÁO3B
O2A–H2AÁÁÁO3A
O1B–H1BÁÁÁO3A(i)
O1A–H1AÁÁÁO2B(ii)
d(D–H)
d(HÁÁÁA)
d(DÁÁÁA)
D–HÁÁÁA
0.82
0.82
0.82
0.82
1.74
1.78
1.93
1.96
2.475(4)
2.508(4)
2.734(4)
2.765(4)
148.0
147.0
166.0
166.0
Compound 2
O1–H1ÁÁÁO4
0.82
0.82
0.96
1.67
1.75
2.58
2.417(1)
2.488(1)
3.530(2)
3.632(7)
150.0
147.0
170.0
O2–H2ÁÁÁO3
C11–H11AÁÁÁO4(iii)
Cg(1)ÁÁÁCg(1)(iv)
Cg(1) is the centroid of (C2–C7) ring.
Symmetry codes: (i) x À 1, y, z; (ii) 1 À x, À½ + y, ½ À z; (iii) 1 À x, Ày, 2 À z; (iv)
The molecules of compound (2) are linked by C–HÁÁÁO and
p–p
½ + x, y, 3/2 À z.
stacking interactions (Table 3). The formation of molecular frame-
work can be readily analyzed in terms of one-dimensional sub-
structures. In the first substructure the methyl C11 atom of
acetyl group in the molecule at (x, y, z) acts as hydrogen bond do-
nor to carbonyl O4 atom in the molecule at (1 À x, Ày, 2 À z), gen-
erating a centrosymmetric R22(8) ring. In another substructure, the
pating phenol group of (1) and (2). The C–O bond distances lying in
the range 1.342(4)–1.361(4) Å in (1) and 1.328(2)–1.340(2) Å in (2)
(Table 2) are similar to those found in analogous structures. These
bond distances do not vary significantly despite the differing inter-
molecular interaction patterns observed in various compounds
[19,31–35]. Due to involvement in hydrogen bonding also the car-
bonyl C@O bonds lengths [1.255(4)–1.258(4) Å in (1) and
1.247(2)–1.254(2) Å in (2)] are somewhat longer than those re-
ported earlier [32,36] but agree well with [31,33,37]. The bond
lengths of the benzene ring of both compounds are distorted: those
flanking the carbonyl group, C5A–C4A, C5A–C6A, C5B–C4B, C5B–
C6B in (1) and C5–C4, C5–C6, C3–C2, C3–C4 in (2) are in the range
1.414(2)–1.432(2) Å, whereas the others lie between 1.374(2)–
1.390(2) Å (Table 2).
molecules are interacting through
p–p stacking interactions. The
phenyl rings C2–C7 of the molecules at (x, y, z) are in contact with
the partner molecule at (½ + x, y, 3/2 À z) with a ring centroid sep-
aration of 3.6322(7) Å, The combination of two type of substruc-
tures generated through C–HÁÁÁO hydrogen bonds and
p–p
interactions results in a two-dimensional supramolecular frame-
work in (2) (Fig. 4). This dual recognition induced self-assembly
of the monomeric units has been observed in the literature
[16,31,33,37], where it has been found that the
actions with other weak dipolar interactions are responsible for the
formation of molecular self-assembly. However this stacking
p–p stacking inter-
The crystal structures adopted by (1) and (2) are quite different.
The structure of (1) includes a combination of intra and intermo-
lecular O–HÁÁÁO hydrogen bonding interactions. It is convenient to
p–p
interaction has not been thoroughly explored so far as a routine
tool in the design and construction of self-assembled structures.
Fig. 4. Monomeric units of (2) link one another by self-complementary C11–H11AÁÁÁO4 hydrogen bonds and
p–p stacking interactions leading to the formation of 2-D
assembly.

S.K. Seth et al. / Journal of Molecular Structure 936 (2009) 277–282
281
Fig. 5. (a) Superposition of molecular conformations obtained from X-ray analysis (blue and green), and DFT calculation (red) of compound (1). (b) Total electronic charge
density isosurface of compound (1) set at 0.15 eÅÀ3 using DFT method. (c) Charge density of HOMO orbital of the compound (1) calculated by DFT method. (d) Charge density
of LUMO orbital of the compound (1) calculated by DFT method. (For interpretation of colour mentioned in this figure, the reader is referred to the web version of this article.)
Fig. 6. (a) Superposition of molecular conformations obtained from X-ray analysis (blue), and DFT calculation (red) of compound (2). (b) Total electronic charge density
isosurface of compound (2) set at 0.15 eÅÀ3 using DFT method. (c) Charge density of HOMO orbital of the compound (2) calculated by DFT method. (d) Charge density of
LUMO orbital of the compound (2) calculated by DFT method. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of
this paper.)

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S.K. Seth et al. / Journal of Molecular Structure 936 (2009) 277–282
3.2. Geometry and electronic structure
Appendix A. Supplementary data
A superposition of the molecular conformations of (1) and (2) as
established by the quantum mechanical calculations and X-ray
studies show an excellent agreement (Figs. 5a and 6a). Since the
resulting molecular geometry depends on the choice of functionals,
theoretical calculations were carried out with the BLYP [25,26],
PW91 [27], PBE [24], and BP [28,29] levels of theory using the nu-
meric DNP basis set. Different functionals describe different classes
of molecules with varying degrees of accuracy. Between the four
functionals used for the DFT calculation, the results with the BLYP
functional agree more closely with the X-ray analysis of the title
compounds. The largest deviation of the geometrically optimized
bond lengths/angles from the corresponding experimental values
is 0.037 Å for C–C and 1.5° for C–C–C for both the compounds (Ta-
ble 2). The small differences between the calculated and observed
geometrical parameters can be attributed to the fact that the the-
oretical calculations were carried out with isolated molecules in
the gaseous phase, whereas the experimental values were based
on molecules in the crystalline state. All oxygen atoms in both
compounds bear negative charges. The carbon atoms of the phenyl
ring (C2, C4, and C6), and C8 of acyl group in (1) and in (2), phenyl
ring (C2, C4, and C6), and C8, C10 of acyl group bear positive
charges; the remaining carbon atoms of the phenyl rings bear neg-
ative charges. The large electron densities at the carbonyl O atom
(O3) in (1) and (O3, O4) in (2) suggests possible protonation. The
net charges of atoms and the molecular orbital energy of com-
pound (1) and (2) calculated at the BLYP level are listed in Table
S1 (Supplementary). The total electronic charge density isosurface,
set at 0.15 eÅÀ3 for an isolated molecule for both compounds (Figs.
5b and 6b), indicates that charge density are equally distributed in
over the entire molecules.
Crystallographic data (excluding structure factors) for the struc-
tures reported in this article have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary
publication number CCDC 732688 and 732689 of compounds (1)
and (2), respectively. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, CambridgeCB2
1EZ, UK. Fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2009.08.013.
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S.K. Seth is grateful to the DST-funded National Single Crystal
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