organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
dered between two positions, denoted by unprimed (major
site) and primed (minor site) labels, respectively. The disorder
originates from two conformations of the cyclohexane ring,
which are related by an inversion of the ring. A calculation of
the least-squares planes has shown that the ring is puckered in
such a manner that atoms C1, C2, C3 and C4 are coplanar
ISSN 0108-2701
Ê
2-(Phenylaminomethylidene)cyclo-
hexane-1,3-dione
within experimental error [r.m.s. deviation = 0.002 (2) A],
while atoms C5 and C6 are unequally displaced from this
plane on opposite sides, with out-of-plane displacements of
Ê
0.531 (7) and 0.227 (12) A, respectively. The corresponding
Viktor Kettmann,a* Jan Lokaj,b Viktor Milata,b Milan
c
Â
Âd
Æ
Marko and Magdalena Stvrtecka
aFaculty of Pharmacy, Comenius University, Odbojarov 10, Bratislava 83232, Slovak
Republic, bFaculty of Food and Chemical Technology, Slovak Technical University,
Radlinskeho 9, Bratislava 81237, Slovak Republic, cZentiva a.s., Nitrianska 100,
Hlohovec 92027, Slovak Republic, and dDepartment of Physics, University of
Constantine the Philosopher, Nitra 94101, Slovak Republic
displacements of atoms C50 and C60 in the inverted confor-
Ê
mation are 0.518 (9) and 0.264 (15) A, respectively. Thus, the
Correspondence e-mail: kettmann@fpharm.uniba.sk
conformation of the two puckered rings can be described,
according to Duax et al. (1976), as intermediate between half-
chair, with a local pseudo-twofold axis along the mid-points of
the C2ÐC3 and C5ÐC6 (or C50ÐC60) bonds, and sofa, with a
local pseudo-mirror along the C2Á Á ÁC5 (or C2Á Á ÁC50) direc-
tion. The Cremer & Pople (1975) puckering parameters are
Received 4 February 2004
Accepted 16 February 2004
Online 11 March 2004
In the title compound, C13H13NO2, there is polarization of
ꢀ-electron density from the amine N atom to the acceptor
carbonyl groups: as a result, the molecule exists predomi-
nantly in an azomethino-1,3-diketone tautomeric form. There
is crystallographic evidence that the phenyl ring, although
roughly coplanar with the rest of the molecule, is deconjugated
with the adjacent ꢀ system of the molecule. The cyclohexane
ring adopts an unsymmetrical half-chair conformation and
converts between two inversion-related conformers. The
molecule is stabilized by an intramolecular hydrogen bond,
while the intermolecular packing is dominated by a number of
short CÐHÁ Á ÁO contacts.
ꢀ
Q = 0.499 (6) A, ꢁ = 50.8 (3) and ' = 104.0 (7)ꢀ (calculated
Ê
for the sequence C1±C6); the corresponding parameters for
ꢀ
Ê
the inverted ring are Q = 0.525 (8) A, ꢁ = 128.7 (2) and
' = 79.3 (7)ꢀ (sequence C1±C4/C50/C60).
As noted above, the main purpose of this work was to
establish the (ꢀ) electron distribution within the ꢀ-electronic
portion of the molecule. Firstly, as shown in Table 1, the C7Ð
N1ÐC8 valence angle is larger than 120ꢀ, i.e. the amine N
atom is sp2-hybridized, with the lone-pair electrons available
for ꢀ-bonding. Secondly, as estimated from the bond-order±
bond-length curves proposed by Burke-Laing & Laing (1976),
the bond order of the N1ÐC7 single bond is higher (ꢁ1.7)
than that of the C2 C7 double bond (ꢁ1.5). Furthermore,
the C1ÐC2 and C2ÐC3 bond distances are signi®cantly
Comment
Recently, as part of our ongoing study on the structure±
activity relationships of biologically active compounds, we
focused our attention on the title compound, (I), following
reports that such derivatives exhibit photobleaching activity as
assayed in tobacco (Nicotiana tabacum) cultured cells (Wang
et al., 1997). It was shown that the chlorophyll and carotenoid
contents of cells treated with the cyclic dione disappeared
within 24 h under light, but not dark, conditions. However, the
rapid onset of photobleaching activity did not result from
inhibition of protoporphyrinogen oxidase, indicating that
some other mechanism of action might operate, for example,
electron transport between the drug molecule and the
photosynthetic pigments. Thus, to shed some light on the
molecular mechanism of action, we initiated a study of the
ꢀ-electronic structure of the dione in both ground and photo-
activated states by a combination of theoretical and experi-
mental techniques. In this communication, we report on the
crystal structure of (I).
2
Ê
shorter than the normal value of 1.487 A reported for a Csp Ð
Csp2 single bond (Shmueli et al., 1973). These ®ndings, coupled
with the lengthening of the two carbonyl bonds with respect to
the range normally accepted for a C O double bond (1.20±
Ê
1.22 A), imply that there is extensive ꢀ-electron delocalization
Figure 1
A displacement ellipsoid plot of (I), with the labelling scheme for the
non-H atoms, which are drawn as 35% probability ellipsoids. Primes
indicate the minor-site atoms.
The molecular structure, along with the atom-numbering
scheme, is shown in Fig. 1. Atoms C5, C6 and O1 are disor-
o252 # 2004 International Union of Crystallography
DOI: 10.1107/S0108270104003610
Acta Cryst. (2004). C60, o252±o254
Kettmann, Viktor
