Three isomeric forms of hydroxyphenyl-2-oxazoline: 2-(2-hydroxyphenyl)-2- oxazoline, 2-(3-hydroxyphenyl)-2-oxazoline and 2-(4-hydroxyphenyl)-2-oxazoline

Article abstract of DOI:10.1107/S0108270105027812

Crystal structures are reported for three isomeric compounds, namely 2-(2-hydroxyphenyl)-2-oxazoline, (I), 2-(3-hydroxyphenyl)-2-oxazoline, (II), and 2-(4-hydroxyphenyl)-2-oxazoline, (III), all C₉H₉NO ₂ [systematic names: 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (I), 3-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (II), and 4-(4,5-dihydro-1,3-oxazol-2-yl) phenol, (III)]. In these compounds, the deviation from coplanarity of the oxazoline and benzene rings is dependent on the position of the hydroxy group on the benzene ring. The coplanar arrangement in (I) is stabilized by a strong intramolecular O-H...N hydrogen bond. Surprisingly, the 2-oxazoline ring in molecule B of (II) adopts a ³T₄ (^C2T _C3) conformation, while the 2-oxazoline ring in molecule A, as well as that in (I) and (III), is nearly planar, as expected. Tetramers of molecules of (II) are formed and they are bound together via weak C-H...N hydrogen bonds. In (III), strong intermolecular O-H...N hydrogen bonds and weak intramolecular C-H...O hydrogen bonds lead to the formation of an infinite chain of molecules perpendicular to the b direction. This paper also reports a theoretical investigation of hydrogen bonds, based on density functional theory (DFT) employing periodic boundary conditions.

Full text of DOI:10.1107/S0108270105027812

organic compounds
Acta Crystallographica Section C
Crystal Structure
monomer (W oÈ rner et al., 1995). Although the syntheses of
these compounds have already been reported [(I): Cwik et al.
Communications
(2002), Black & Wade (1972) and Peterson et al. (1980); (II):
ISSN 0108-2701
Three isomeric forms of hydroxy-
phenyl-2-oxazoline: 2-(2-hydroxy-
phenyl)-2-oxazoline, 2-(3-hydroxy-
phenyl)-2-oxazoline and 2-(4-hydroxy-
phenyl)-2-oxazoline
a
b
c
Vratislav Langer, * Miroslav Ko o sÏ , Dalma Gyepesov a ,
Kalle (1969); (III): Nonnenmacher & Plieninger (1982)], their
crystal structures have not been published until now. Among
c
d
d
Mariana Sl a dkovi cÏ ov a , Jozef Lusto nÏ and Juraj Kronek
8
7 matches from the Cambridge Structural Database (CSD,
a
Department of Chemical and Biological Engineering, Division of Materials and
February 2005 update, Version 5.26; Allen, 2002) for (I), only
15 structures were relevant (i.e. having a 4,5-unsubstituted
2-oxazoline ring and a 3,4,5,6-unsubstituted 2-hydroxyphenyl
moiety), but in all these compounds the 2-(2-hydroxyphenyl)-
Surface Chemistry, Subdivision of Inorganic Environmental Chemistry, Chalmers
b
University of Technology, SE-412 96 G oÈ teborg, Sweden, Institute of Chemistry,
Slovak Academy of Sciences, D u bravsk a cesta 9, SK-845 38 Bratislava, Slovak
c
Republic, Institute of Inorganic Chemistry, Slovak Academy of Sciences, D u bravsk aÂ
d
cesta 9, SK-845 36 Bratislava, Slovak Republic, and Polymer Institute, Slovak
2
-oxazoline has been reported only as a ligand in several
complexes with metals such as Fe, Mn, Ni, V, Zn, Al, In and Re
e.g. Qian et al., 2004; Kooijman et al., 2002; Miller et al., 1999;
Academy of Sciences, D u bravsk a cesta 9, SK-845 36 Bratislava, Slovak Republic
Correspondence e-mail: langer@chalmers.se
(
Received 5 August 2005
Accepted 5 September 2005
Online 17 September 2005
Melchior et al., 1999). For compounds (II) and (III), a CSD
search revealed only one and 13 similar structures, respec-
tively, but none of them had a relevant hydroxy group in the
meta or para position of the benzene ring.
Crystal structures are reported for three isomeric compounds,
namely 2-(2-hydroxyphenyl)-2-oxazoline, (I), 2-(3-hydroxy-
phenyl)-2-oxazoline, (II), and 2-(4-hydroxyphenyl)-2-oxazo-
line, (III), all C H NO [systematic names: 2-(4,5-dihydro-1,3-
9
9
2
oxazol-2-yl)phenol, (I), 3-(4,5-dihydro-1,3-oxazol-2-yl)phenol,
II), and 4-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (III)]. In these
(
compounds, the deviation from coplanarity of the oxazoline
and benzene rings is dependent on the position of the hydroxy
group on the benzene ring. The coplanar arrangement in (I) is
stabilized by a strong intramolecular OÐHÁ Á ÁN hydrogen
bond. Surprisingly, the 2-oxazoline ring in molecule B of (II)
3
C2
Figure 1
The atom-numbering scheme for (I), with atomic displacement ellipsoids
drawn at the 50% probability level.
adopts a T ( T ) conformation, while the 2-oxazoline ring
C3
4
in molecule A, as well as that in (I) and (III), is nearly planar,
as expected. Tetramers of molecules of (II) are formed and
they are bound together via weak CÐHÁ Á ÁN hydrogen bonds.
In (III), strong intermolecular OÐHÁ Á ÁN hydrogen bonds and
weak intramolecular CÐHÁ Á ÁO hydrogen bonds lead to the
formation of an in®nite chain of molecules perpendicular to
the b direction. This paper also reports a theoretical
investigation of hydrogen bonds, based on density functional
theory (DFT) employing periodic boundary conditions.
Comment
Cyclic imino ethers, among them 2-oxazolines, are important
intermediates in organic synthesis. The title compounds, (I)±
(
III), were prepared in the course of our research focused on
cyclic imino ethers and their utilization in polymer chemistry
Kronek et al., 1998), as hydroxyphenyl-2-oxazolines are
Figure 2
The atom-numbering scheme for (II), with atomic displacement ellipsoids
drawn at the 50% probability level.
(
known to produce poly(ether-amides) on heating of the
o602 # 2005 International Union of Crystallography
DOI: 10.1107/S0108270105027812
Acta Cryst. (2005). C61, o602±o606

organic compounds
Selected geometric parameters for (I), (II) and (III) are
compared in Table 1. The numbering schemes, together with
the corresponding atomic displacement ellipsoid plots, are
shown in Figs. 1±3, respectively. The crystal packings of (I) and
the arrangement of molecule B in the tetramer, as well as
hydrogen bonding.
As seen from the values of the acute angles between the
ꢀ
planes of the oxazoline and benzene rings [0.74 (4) for (I),
ꢀ
(
II) are depicted in Figs. 4 and 5, respectively. The hydrogen-
4.75 (16) and 3.49 (17) for molecules A and B of (II),
ꢀ
bonding schemes for (II) and (III) are shown in Figs. 6 and 7,
respectively. The hydrogen-bonding geometries for (I), (II)
and (III) are compared in Table 2. The theoretical investiga-
tion of hydrogen bonds was performed using the Vienna ab
initio simulation package VASP (Kresse & Furthm uÈ ller, 1996;
Kresse & Hafner, 1993). The calculations were based on
density functional theory (DFT) with periodic boundary
conditions (Jones & Gunnarsson, 1989).
respectively, and 11.22 (6) for (III)], the mutual position of
these rings re¯ects the location (ortho, meta or para, respec-
tively) of the hydroxy group on the benzene ring. In this
respect, the coplanarity of both rings in the o-hydroxy deri-
vative, (I) (Fig. 1), and the most evident deviation from
coplanarity in the p-hydroxy derivative, (III), is observed. We
assume that the coplanar arrangement of the rings and the
synperiplanar orientation of atom O2 (ortho-hydroxy group)
with respect to the C1ÐN1 bond in (I) is stabilized by the
strong intramolecular O2ÐH2Á Á ÁN1 hydrogen bond (Table 2).
The 2-oxazoline ring in (I) and (III) is nearly planar.
Surprisingly, in the case of compound (II), with two molecules,
A and B, in the asymmetric unit, the values of the relevant
dihedral angles (Table 1) and puckering parameters (Cremer
2
2
In this regard, free rotation about the sp ±sp C1ÐC4 bond
could be suf®ciently restricted, leading to possible atropi-
somerism, and this is probably responsible for the chirality
because, although there is no chiral atom in (I), optical activity
Ê
ꢀ
&
Pople, 1975), Q = 0.108 (3) A and ' = 310.3 (17) , indicate
that this ring in molecule B deviates signi®cantly from
planarity (twisting about the C3BÐC2B bond) and adopts a
2
D
0
of [ꢀ] = 3.0 (c = 1, CHCl ) was observed for this compound.
3
3
C2
T ( T ) conformation, while the 2-oxazoline ring in mol-
The synperiplanar arrangement of atom N1 relative to the
C4ÐC5 bond, with atom N1 directed slightly below the
benzene ring plane, is observed for both molecules A and B of
the m-hydroxy derivative, (II) (Fig. 2). In the case of molecule
A, similar to the C5ÐO2 and C1ÐN1 bonds in (I), the C6Ð
O2 and C1ÐN1 bonds are oriented cis with respect to the
plane perpendicular to the plane of the benzene and oxazoline
rings across the C1ÐC4 bond. In contrast, the orientation of
the C6ÐO2 and C1ÐN1 bonds is trans in the case of molecule
B. For the p-hydroxy derivative, (III), shown in Fig. 3, the
C1ÐN1 and C4ÐC5 bonds are oriented antiperiplanar, with
atom N1 directed slightly above the plane of the benzene ring.
4
C3
ecule A is again nearly planar. This difference may be due to
Figure 3
The atom-numbering scheme for (III), with atomic displacement
ellipsoids drawn at the 50% probability level.
Figure 5
Figure 4
The unit-cell contents of (I) in projection along the a axis. H atoms not
involved in hydrogen bonding have been omitted for clarity.
A projection of the structure of (II) along the a axis. The tetramers are
bound together via weak hydrogen bonds (dashed lines). H atoms not
involved in hydrogen bonding have been omitted for clarity.
ꢁ
Acta Cryst. (2005). C61, o602±o606
Langer et al.
Three isomers of C
H
9 9
NO
2
o603

organic compounds
The C1ÐC4 bonds (Table 1) in compounds (I)±(III) indi-
cate a weak conjugation between the 2-oxazoline ring substi-
tuted at the C-2 position (C1) and the benzene ring.
The hydrogen-bonding patterns can be described using
graph-set theory (Bernstein et al., 1995; Grell et al., 1999). For
an S(6) string. For (II), there are two strong hydrogen bonds of
the OÐHÁ Á ÁN type, two weak intramolecular bonds of the
CÐHÁ Á ÁO type and one weak intermolecular interaction of
the CÐHÁ Á ÁN type. On the ®rst-level graph-set, the hydrogen-
bonding pattern can be classi®ed as D(2) for hydrogen bonds
(IIa) and (IIb), as S(5) for (IIc) and (IIe), and as a C(7) chain
(
I), there is just one intramolecular hydrogen bond of the OÐ
HÁ Á ÁN type, which is, on the ®rst-level graph-set, described as
for hydrogen bond (IId) (Table 2). On the second-level graph-
4
set, the above-mentioned tetramer is described as an R (28)
4
ring formed by hydrogen bonds (IIa) and (IIb), apart from
3
3
2
D (14) and D (10) for bonds (IIa) and (IId), and (IIb) and
3
(
(
IId), respectively. The ®rst-level graph-set descriptors for
III) are C(8) for the strong hydrogen bond (IIIa) and S(5) for
the weak intramolecular hydrogen bond (IIIb). The molecules
thus form an in®nite chain along [101]. The assignment of
graph-set descriptors was performed using PLUTO, as
described by Motherwell et al. (1999), and the notation of the
hydrogen bonds here is as de®ned in Table 2.
Experimental
Compound (I) was prepared according to the procedure of
Kobayashi et al. (1984). In the ®rst step, methyl 2-hydroxybenzoate
was reacted with an excess of ethanolamine at 413 K to give the
corresponding hydroxyamide. This, in the next step, upon treatment
with thionyl chloride, afforded the required compound, (I).
Compounds (II) and (III) were prepared analogously starting from
the methyl 3-hydroxybenzoate and methyl 4-hydroxybenzoate,
respectively. The analytical data of all three title compounds were in
accordance with those published previously. Colourless single crystals
of adequate quality for diffraction analysis [with the exception of (II)]
were obtained by slow crystallization from nearly saturated solutions
in ethanol under moderate cooling in a refrigerator.
Figure 6
A tetramer of molecules of (II) formed via hydrogen bonds (dashed
lines). H atoms not involved in hydrogen bonding have been omitted for
clarity.
Compound (I)
Crystal data
�
3
C
H
9 9
NO
2
D
x
= 1.394 Mg m
M
r
= 163.17
Mo Kꢀ radiation
Monoclinic, P2 =n
Cell parameters from 8192
re¯ections
1
Ê
a = 5.7562 (1) A
b = 11.2464 (1) A
Ê
ꢀ
ꢂ = 2.5±33.0
ꢃ = 0.10 mm
T = 173 (2) K
Ê
c = 12.1365 (1) A
� 1
ꢀ
ꢁ
= 98.162 (1)
Ê
3
V = 777.72 (2) A
Z = 4
Block, colourless
0.80 Â 0.42 Â 0.40 mm
Data collection
Siemens SMART CCD area-
detector diffractometer
2785 independent re¯ections
2451 re¯ections with I > 2ꢄ(I)
!
scans
Absorption correction: multi-scan
SADABS; Sheldrick, 2002)
min = 0.724, Tmax = 0.961
3125 measured re¯ections
Rint = 0.026
ꢀ
ꢂ
max = 33.0
(
T
h = � 8 ! 8
k = � 16 ! 17
l = � 18 ! 17
1
Re®nement
2
2
2
2
Re®nement on F
2
o
w = 1/[ꢄ (F ) + (0.0707P)
2
R[F > 2ꢄ(F )] = 0.040
wR(F ) = 0.119
S = 1.03
+ 0.1146P]
where P = (F
(Á/ꢄ)max = 0.001
2
2
o
2
c
+ 2F
)/3
Ê
� 3
2
1
785 re¯ections
20 parameters
Áꢅmax = 0.36 e A
Ê
� 3
Áꢅmin = � 0.20 e A
Figure 7
The hydrogen-bonding pattern in the crystal lattice of (III). H atoms not
involved in hydrogen bonding have been omitted for clarity.
H-atom parameters constrained
Extinction correction: SHELXTL
(Bruker, 2001)
Extinction coef®cient: 0.051 (7)
ꢁ
o604 Langer et al. Three isomers of C
9
H NO
9 2
Acta Cryst. (2005). C61, o602±o606

organic compounds
Table 1
Comparison of selected interatomic parameters (A, ) for compounds
I)±(III).
Compound (II)
Ê
ꢀ
(
Crystal data
�
3
C
M
9
H
9
NO
2
D
x
= 1.360 Mg m
(
I)
(IIA)
(IIB)
(III)
r
= 163.17
Mo Kꢀ radiation
Monoclinic, P2 =c
Cell parameters from 8192
re¯ections
1
C1ÐC4
C1ÐO1
C1ÐN1
1.4619 (10)
1.3481 (9)
1.2832 (10)
1.466 (4)
1.356 (3)
1.281 (4)
1.467 (4)
1.359 (3)
1.276 (4)
1.4654 (16)
1.3575 (13)
1.2775 (14)
Ê
a = 11.3650 (2) A
Ê
ꢀ
b = 12.5867 (1) A
ꢂ = 2.4±25.0
ꢃ = 0.10 mm
T = 173 (2) K
Ê
c = 11.2966 (2) A
� 1
ꢀ
ꢁ
= 99.534 (1)
C2ÐN1ÐC1ÐO1
C3ÐO1ÐC1ÐN1
C1ÐN1ÐC2ÐC3
C1ÐO1ÐC3ÐC2
N1ÐC2ÐC3ÐO1
N1ÐC1ÐC4ÐC9
O1ÐC1ÐC4ÐC9
N1ÐC1ÐC4ÐC5
O1ÐC1ÐC4ÐC5
0.07 (10)
� 1.64 (10)
1.43 (8)
� 2.1 (4)
� 2.4 (4)
5.5 (3)
� 2.8 (4)
� 4.7 (4)
8.7 (3)
2.11 (14)
1.25 (14)
� 4.32 (13)
� 3.83 (13)
4.86 (13)
� 9.22 (18)
172.50 (11)
168.38 (12)
� 9.90 (16)
Ê
3
V = 1593.63 (4) A
Z = 8
Needle, colourless
0.58 Â 0.18 Â 0.16 mm
2.32 (8)
5.6 (3)
9.5 (3)
Data collection
� 2.27 (8)
� 179.65 (7)
0.06 (10)
0.40 (11)
� 179.89 (6)
� 6.6 (3)
173.1 (3)
� 5.2 (4)
� 6.9 (4)
174.8 (2)
� 10.9 (3)
� 6.2 (5)
174.9 (3)
173.9 (3)
� 5.0 (4)
Siemens SMART CCD area-
detector diffractometer
2663 independent re¯ections
2167 re¯ections with I > 2ꢄ(I)
!
scans
Absorption correction: multi-scan
SADABS; Sheldrick, 2002)
min = 0.816, Tmax = 0.985
4444 measured re¯ections
Rint = 0.056
ꢀ
ꢂ
max = 25.0
(
T
h = � 13 ! 13
k = � 14 ! 14
l = � 13 ! 13
Table 2
Comparison of hydrogen-bonding geometry (A, ) for compounds (I)±
(III) and results of density functional theory (DFT) calculations.
1
Ê
ꢀ
Re®nement
2
2
2
2
Re®nement on F
2
o
w = 1/[ꢄ (F ) + (0.079P)
2
Notation
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
R[F > 2ꢄ(F )] = 0.068
wR(F ) = 0.175
S = 1.00
+ 2.9545P]
where P = (F
(Á/ꢄ)max < 0.001
Áꢅmax = 0.39 e A
Áꢅmin = � 0.22 e AÊ
2
2
2
c
o
+ 2F
)/3
(
I)
O2ÐH2Á Á ÁN1
0.84
1.052
1.88
1.513
2.6238 (9)
2.481
148
150.22
� 3
DFT
Ê
2
2
663 re¯ections
37 parameters
� 3
i
(
(
(
(
IIa)
IIb)
IIc)
IId)
DO F2 AT ÐH2AÁ Á ÁN1B
0.84
1.92
1.619
1.88
1.582
2.43
2.384
2.60
2.375
2.45
2.388
2.732 (3)
2.637
2.709 (3)
2.615
2.764 (4)
2.767
3.540 (4)
3.467
164
169.2
167
166.97
100
98.9
H-atom parameters constrained
1.028
0.84
1.05
0.95
1.083
0.95
1.097
0.95
1.083
O2BÐH2BÁ Á ÁN1A
Compound (III)
DFT
C5BÐH5BÁ Á ÁO1B
DFT
Crystal data
ii
C7AÐH7AÁ Á ÁN1A
171
�
3
C
9
H NO
9
2
D
x
= 1.394 Mg m
DFT
CD 9F AT ÐH9AÁ Á ÁO1A
175.94
100
98.84
M
r
= 163.17
Mo Kꢀ radiation
(IIe)
2.767 (4)
2.769
Monoclinic, P2 =n
Cell parameters from 6730
re¯ections
1
Ê
a = 4.7778 (1) A
Ê
ꢀ
iii
b = 14.9883 (2) A
ꢂ = 2.3±33.1
ꢃ = 0.10 mm
T = 173 (2) K
(IIIa)
(IIIb)
O2ÐH2Á Á ÁN1
0.84
1.86
2.6997 (13)
2.522
2.7874 (15)
2.830
178
Ê
c = 10.9194 (1) A
� 1
DFT
C5ÐH5Á Á ÁO1
DFT
1.043
0.95
1.032
1.480
2.46
2.474
177.43
100
99.31
ꢀ
ꢁ
= 95.945 (1)
Ê
3
V = 777.74 (2) A
Z = 4
Plate, colourless
0.60 Â 0.32 Â 0.06 mm
1
2
1
2
1
3
1
Symmetry codes: (i) 2 � x; 1 � y; � z; (ii) 1 � x; ‡ y; � � z; (iii) x � 2
;
2
� y; z � 2
.
Data collection
ꢀ
CÐOÐH angles (109.5 ) were kept ®xed, while the torsion angles
were allowed to re®ne, with the starting positions based on the
circular Fourier synthesis.
Siemens SMART CCD area-
detector diffractometer
2784 independent re¯ections
2064 re¯ections with I > 2ꢄ(I)
!
scans
Absorption correction: multi-scan
SADABS; Sheldrick, 2002)
min = 0.710, Tmax = 0.994
3219 measured re¯ections
Rint = 0.038
ꢀ
ꢂ
max = 33.1
For all compounds, data collection: SMART (Siemens, 1995); cell
re®nement: SAINT (Siemens, 1995); data reduction: SAINT and
SADABS (Sheldrick, 2002); program(s) used to solve structure:
SHELXTL (Bruker, 2001); program(s) used to re®ne structure:
SHELXTL; molecular graphics: DIAMOND (Brandenburg, 2005);
software used to prepare material for publication: SHELXTL.
(
T
h = � 7 ! 7
k = � 22 ! 22
l = � 16 ! 16
1
Re®nement
2
2
2
2
Re®nement on F
2
o
w = 1/[ꢄ (F ) + (0.0613P)
2
R[F > 2ꢄ(F )] = 0.047
wR(F ) = 0.133
S = 1.02
+ 0.2076P]
where P = (F
2
2
2
c
o
+ 2F
)/3
(Á/ꢄ)max < 0.001
The ®nancial support of this work by the Scienti®c Grant
Agency (VEGA, Slovak Academy of Sciences, grant Nos.
/3104/23 and 2/3033/23) is gratefully acknowledged.
Ê
� 3
� 3
2
1
784 re¯ections
19 parameters
Áꢅmax = 0.32 e A
Áꢅmin = � 0.21 e AÊ
2
H-atom parameters constrained
The sample of (II) used for data collection was not a single crystal.
Nevertheless, it was possible to resolve one set of diffractions from
one domain. As a result, there were overlapping re¯ections; 118
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: DN1097). Services for accessing these data are
described at the back of the journal.
re¯ections were omitted from the data set due to severe F
o c
/F
discrepancies (F >> F ). H atoms for all three compounds were
o
c
re®ned isotropically and constrained to ideal geometry using an
appropriate riding model. For aromatic H atoms, the CÐH distance
Ê
was kept ®xed at 0.95 A, and for secondary H atoms, CÐH was ®xed
References
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Ê
at 0.99 A. For the hydroxy groups, the OÐH distances (0.84 A) and
Ê
ꢁ
Acta Cryst. (2005). C61, o602±o606
Langer et al.
Three isomers of C
H
9 9
NO
2
o605

organic compounds
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