As a consequence of the high activation barrier for oxime nitrogen inversion, the dioximes1,1'-bicyclohexylidene-4,4'-dione dioxime (
1) and 1,1'-bicyclohexyl-4,4'-dione dioxime (
2) aswell as their related monooximes 1,1'-bicyclohexylidene-4-one oxime (
3) and 1,1'-bicyclohexyl-4-one oxime (
4) consist of a mixture of stereoi
somers. For
1, the configurational stereoi
somers1-
E and
1-
Z were identified in solution in a ratio 1:1 (
13C NMR). Moreover, in the solidstate,
1-
Z as well as
3 also consist of conformational enantiomers, viz.
1-
Z(
RR)/
1-
Z(
SS) and
3-
R/
3-
S, respectively, which rapidly interconvert in solution due to ring inversions of thecyclohexyl moieties. Whereas dioxime
2 consists of an enantiomer pair (
2-
RR/
2-
SS) and a
meso form (
2-
RS/
2-
SR) in a ratio 1:1:2, for monooxime
4 an enantiomer pair (
4-
R/
4-
S) in aratio 1:1 is found (chiral HPLC). Upon recrystallization of crude
1-
4 no segregation ofstereoi
somers occurs [
1H and
13C NMR, FT-IR, (chiral) HPLC, and WAXD]. Both dioximes
1 and
2 crystallize in the achiral
P2
1/
c space group and possess nearly identical structuresbuild up from stacked layers consisting of parallel oriented noncovalent polymer-like chainsformed via intermolecular oxime dimer formation by (self) complementary hydrogen bonding[
![](/isubscribe/journals/cmatex/11/i06/eqn/cm9806329e10001.gif)
(6) motif in graph-set notation]. In the unit cell both molecules possess
Ci symmetry. Inaddition,
Ci symmetry is found in the six-membered rings resulting from hydrogen bondingof two oxime groups. Similar centrosymmetric oxime dimerization is also observed for
3and
4 in the solid state. The
Ci symmetry and the presence of multiple stereoi
somers can bereconciled if chiral recognition is operational in the solid state, i.e. intermolecular dimerichydrogen bonding occurs only between oxime groups of units possessing opposite configurations. This poses restrictions on the stereoisomer distribution within the noncovalent polymer-like chains, viz. it dictates their linear rodlike topology. The oxime disorder observed in allcrystal structures is attributed to random stacking of differently oriented noncovalentpolymer-like chains (
1 and
2) or dimers (
3 and
4).