(±)-cis-2-Methyl-4-oxocyclohexane-carboxylic acid: Catemeric hydrogen bonding in a δ-keto acid derived from Hagemann's ester

Article abstract of DOI:10.1107/S0108270103024545

The crystallization of (±)-cis-2-methyl-4-oxocyclohexanecarboxylic acid as acid-to-ketone hydrogen-bonding catemers was investigated. It was stated that in either chair conformation for the compound, one of the two cis-related susbstituents must be axial. The hydrogen bonds progress from the carboxyl group of each molecule to the ketone group of a translationaly related neighbor. It was found that three intermolecular C-H···O close contacts exist involving both carboxyl O atoms. The peak separation conforms to the shifts observed in catemers, due to removal of hydrogen bonding from the acid C=O group and addition of hydrogen bonding to the ketone group.

Full text of DOI:10.1107/S0108270103024545

organic compounds
3
tuents must be axial. The steric requirements of the sp methyl
Acta Crystallographica Section C
Crystal Structure
2
group are normally signi®cantly greater than for the sp
Communications
carboxyl group (Hirsch, 1967). However, in the present case,
an axial methyl group encounters only a single 1,3-diaxial
interaction (at C6) because of the presence of the C4 ketone,
while an axial carboxyl has interactions at both C3 and C5.
The result is that, in (I), the methyl group is the less sterically
demanding, and therefore the preferred, axial substituent.
Once these demands (and the need to stagger the methyl H
atoms) have been met, the resulting conformer is quite rigid,
in contrast to the dynamic situation in solution. The only
remaining conformational option is rotation of the carboxyl
unit about C1ÐC7. In (I), this group is turned so that the C1Ð
C6 bond coincides with the carboxyl plane [torsion angle O2Ð
ISSN 0108-2701
(
Æ)-cis-2-Methyl-4-oxocyclohexane-
carboxylic acid: catemeric hydrogen
bonding in a d-keto acid derived from
Hagemann's ester
Roger A. Lalancette* and Hugh W. Thompson
ꢀ
Carl A. Olson Memorial Laboratories, Department of Chemistry, Rutgers University,
Newark, NJ 07102, USA
C7ÐC1ÐC6 = � 0.5 (4) ]. The dihedral angle for the ketone
(O1/C3/C4/C5) versus the carboxyl (O2/O3/C7/C1) groups is
ꢀ
Correspondence e-mail: rogerlal@andromeda.rutgers.edu
4
6.7 (2) .
Received 10 July 2003
Accepted 24 October 2003
Online 8 November 2003
The title compound, C H O , crystallizes as acid-to-ketone
8
The partial averaging of CÐO bond lengths and CÐCÐO
12
3
hydrogen-bonding catemers, in which hydrogen bonds
progress from the carboxyl group of each molecule to the
ketone group of a translationally related neighbor [OÁ Á ÁO =
angles by disorder often seen in acids is unique to the
carboxyl-pairing hydrogen-bonding mode, whose geometry
permits transposition of the two carboxyl O atoms. With
catemers and other non-dimeric acid modes, no signi®cant
averaging is observed. For (I), the CÐO bond lengths are
Ê
ꢀ
2
.738 (3) A and OÐHÁ Á ÁO = 153 (4) ]. Four separate hy-
drogen-bonding chains proceed through the cell in centro-
symmetrically related pairs along axes lying in the ab plane.
Three intermolecular CÐHÁ Á ÁO close contacts exist involving
both carboxyl O atoms. Factors contributing to the choice of
hydrogen-bonding mode are discussed.
Ê
1.194 (3) and 1.332 (4) A, with CÐCÐO angles of 126.1 (3)
ꢀ
and 111.9 (3) . Our own survey of 56 keto acid structures
which are not acid dimers gives average values of 1.200 (10)
Ê
and 1.32 (2) A, and 124.5 (14) and 112.7 (17) for these lengths
ꢀ
Ê
and angles, in accord with typical values of 1.21 and 1.31 A,
ꢀ
and 123 and 112 cited for highly ordered dimeric carboxyls
(Borthwick, 1980).
Fig. 2 illustrates the packing of the cell and the hydrogen-
Comment
bonding arrangement. There are no hydrogen-bonding
connections among any of the four molecules within the
chosen cell. Rather, each is part of one of four separate
translational hydrogen-bonding chains proceeding through
Our study of the crystallography of keto-carboxylic acids
explores the molecular characteristics that control their ®ve
known hydrogen-bonding modes. Beyond the dimeric and
catemeric (chain) modes seen in simple acids, the presence of
an additional receptor in the system leads to another three
observed hydrogen-bonding modes involving the ketone
group. The title compound, (I), crystallizes with acid-to-
ketone catemeric hydrogen bonding. We have previously
shown that this pattern, overall the second most commonly
encountered, becomes predominant wherever centrosym-
metry is precluded (Thompson & Lalancette, 2003) or
rendered dif®cult. Among the latter cases are those like (I)
where molecular ¯exibility is severely restricted (Barcon et al.,
Ê
the cell along axes lying in the ab plane [OÁ Á ÁO = 2.738 (3) A
ꢀ
and OÐHÁ Á ÁO = 153 (4) ]. Because of the centrosymmetry of
the cell, the chains are counterdirectionally paired. Those at
the ends of the chosen cell advance by one cell each, either
positively or negatively, in both a and b. The remaining mol-
2
002). When this occurs, the acid is often unable to ®nd a
dimeric crystallization mode of suitably low potential energy
vis- aÁ -vis alternative packing modes, and catemeric hydrogen-
bonding results. We have studied several examples of simple
cyclohexane and cyclopentane keto acids in which such low
degrees of conformational ¯exibility are found to lead to acid-
to-ketone catemers.
Figure 1
The asymmetric unit for (I). Displacement ellipsoids are set at the 20%
probability level.
Fig. 1 shows the asymmetric unit for compound (I). In either
chair conformation for (I), one of the two cis-related substi-
Acta Cryst. (2003). C59, o679±o681
DOI: 10.1107/S0108270103024545
# 2003 International Union of Crystallography o679

organic compounds
dimerically hydrogen-bonded carboxyl and a normal ketone
group.
Experimental
A commercially available technical (90% pure) grade of Hage-
mann's ester (4-carbethoxy-3-methyl-2-cyclohexen-1-one) was
hydrogenated in 95% ethanol with a 5% Pd/C catalyst, and the
concentrated liquid product was directly saponi®ed without puri®-
2 3
cation. After passage through a short column of Al O and distil-
lation in a short-path cold-®nger apparatus, the product crystallized
upon refrigeration. Crystals suitable for X-ray analysis (m.p. 333 K)
were obtained from hexane/diethyl ether. An attempt to produce
the trans-epimer by base-catalyzed equilibration of the ketal ester led
to an approximately 4:1 epimer mixture, which showed no inclination
to crystallize.
Crystal data
�
3
C
8
H O
12 3
D
x
= 1.284 Mg m
M
r
= 156.18
Monoclinic, P2
Mo Kꢁ radiation
1
/n
Cell parameters from 37
re¯ections
Figure 2
Ê
a = 6.7540 (10) A
A packing diagram, with extracellular molecules included to illustrate the
four hydrogen-bonding catemers. For clarity, all carbon-bound H atoms,
except for the methyl H atoms, have been removed. Displacement
ellipsoids are set at the 20% probability level.
Ê
b = 5.7250 (10) A
ꢀ
ꢂ = 3.3±11.4
Ê
c = 21.078 (4) A
� 1
ꢃ = 0.10 mm
T = 296 (2) K
ꢀ
ꢀ
= 97.46 (2)
Ê
3
V = 808.1 (2) A
Z = 4
Parallelepiped, colourless
0.50 Â 0.20 Â 0.04 mm
ecules are glide-related to those at the cell ends, and their
chains proceed either by one cell positively in a and one
negatively in b or vice versa.
Data collection
Siemens P4 diffractometer
Rint = 0.051
ꢂmax = 25.0
ꢀ
2
ꢂ/ꢂ scans
Absorption correction: numerical
SHELXTL; Sheldrick, 1997)
min = 0.976, Tmax = 0.996
174 measured re¯ections
We characterize the geometry of hydrogen bonding to
carbonyls using a combination of the HÁ Á ÁO C angle and the
HÁ Á ÁO CÐC torsion angle. These describe the approach of
the H atom to the O atom in terms of its deviation from,
h = � 1 ! 8
(
T
k = � 1 ! 6
l = � 25 ! 25
2
3 standard re¯ections
every 97 re¯ections
intensity variation: <1.5%
1415 independent re¯ections
910 re¯ections with I > 2ꢄ(I)
ꢀ
respectively, C O axiality (ideal = 120 ) and planarity with
ꢀ
the carbonyl group (ideal = 0 ). In (I), these angles are
ꢀ
ꢀ
Re®nement
HÁ Á ÁO C = 138.0 (11) and HÁ Á ÁO CÐC = � 52.2 (2) . The
latter angle represents hydrogen bonding markedly out of the
plane of the ketone carbonyl and would appear to be far from
2
2
2
2
Re®nement on F
2
o
w = 1/[ꢄ (F ) + (0.076P)
2
R[F > 2ꢄ(F )] = 0.064
wR(F ) = 0.172
S = 1.05
+ 0.2612P]
where P = (F
(Á/ꢄ)max < 0.001
Áꢅmax = 0.24 e A
Áꢅmin = � 0.17 e AÊ
2
2
2
c
o
+ 2F
)/3
`
ideal'.
Ê
� 3
1
1
415 re¯ections
04 parameters
Three intermolecular CÐHÁ Á ÁO close contacts were found
� 3
Ê
for the carboxylic acid O atoms [O2Á Á ÁH5A (2.58 A) to a
H atoms treated by a mixture of
independent and constrained
re®nement
Ê
molecule translationally related in a, and O3Á Á ÁH6B (2.65 A)
Ê
and O3Á Á ÁH8B (2.6 A), both to the same neighbor transla-
Ê
tionally related in b]. These distances all lie within the 2.7 A
range we employ for non-bonded CÐHÁ Á ÁO packing inter-
actions (Steiner, 1997). Using compiled data for a large
number of such contacts, Steiner & Desiraju (1998) ®nd
Table 1
Selected geometric parameters ( AÊ , ).
ꢀ
O2ÐC7
1.194 (3)
126.1 (3)
O3ÐC7
1.332 (4)
111.9 (3)
Ê
signi®cant statistical directionality even as far out as 3.0 A and
conclude that these are legitimately viewed as `weak hydrogen
bonds', with a greater contribution to packing forces than
simple van der Waals attractions.
O2ÐC7ÐC1
O3ÐC7ÐC1
The solid-state (KBr) IR spectrum of (I) has C
O
�
1
absorptions at 1732 (COOH) and 1693 cm (ketone). This
peak separation conforms to the shifts seen typically in cate-
mers, due, respectively, to removal of hydrogen bonding from
the acid C O group and addition of hydrogen bonding to the
Table 2
Hydrogen-bonding geometry (A, ).
Ê
ꢀ
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
1.96 (4)
DÁ Á ÁA
DÐHÁ Á ÁA
i
O3ÐH3Á Á ÁO1
0.84 (4)
2.738 (3)
153 (4)
ketone group. In CHCl solution, these absorptions are seen,
3
�
1
probably reversed, at 1710 and 1705 cm , consistent with a
Symmetry code: (i) 1 ‡ x; 1 ‡ y; z.
ꢁ
o680 Lalancette and Thompson
8
C H
O
12 3
Acta Cryst. (2003). C59, o679±o681

organic compounds
All H atoms were found in electron-density difference maps.
The carbon-bound H atoms were placed in calculated positions
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: FR1436). Services for accessing these data are
described at the back of the journal.
Ê Ê Ê
0.97 A for methylene, 0.98 A for methine, and 0.96 A for methyl
(
H atoms) and allowed to re®ne as riding models on their parent
atoms; their isotropic displacement parameters were ®xed at
References
1
20% of the anisotropic displacement parameters of their parent
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Borthwick, P. W. (1980). Acta Cryst. B36, 628±632.
atoms for methine and methylene H atoms, and 150% for methyl
H atoms. The hydroxyl H atom was allowed to vary positionally,
2
and its displacement parameter was ®xed at 0.08 A .
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&
Ê
E. L. Eliel, pp. 204±208. New York: Wiley Interscience.
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XSCANS; data reduction: XSCANS; program(s) used to solve
structure: SHELXS97 in SHELXTL (Sheldrick, 1997); program(s)
used to re®ne structure: SHELXL97 in SHELXTL; molecular
graphics: SHELXP97 in SHELXTL; software used to prepare
material for publication: SHELXL97 in SHELXTL.
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Inc., Madison, Wisconsin, USA.
Steiner, T. (1997). Chem. Commun. pp. 727±734.
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ꢁ
Acta Cryst. (2003). C59, o679±o681
Lalancette and Thompson
8
C H
O
12 3
o681