Concomitant dimorphism and helical self-assembly in a C<SUB>2h</SUB>-symmetric 'locked' cyclitol

A conformationally locked C2h symmetric tetrol concomitantly crystallized in two polymorphic modifications, differing principally in the mode of molecular association by C-H&#183;&#183;&#183;O hydrogen bonds; the non-centrosymmetric tetragonal polymorph exhibits two complementary helical molecular arrangements mediated by O-H&#183;&#183;&#183;O and C-H&#183;&#183;&#183;O hydrogen bonds

Additive induced polymorphous behavior of a conformationally locked hexol

The influence of molecular additives on the crystal structure adopted by a C2h symmetric, conformationally locked hexol 2 forms the object of the present study. It has been observed that the polycyclitol 2 crystallizes in two polymorphic (&#945; and &#946; forms) and one pseudopolymorphic (monohydrate) modification, depending on the presence and nature of the additive employed. Thus, with the sole exception of trimesic acid, which induces 2 to crystallize in the denser &#946; form, the molecular additives screened in this study either failed to promote polymorphism in 2 or caused it to crystallize as a monohydrate. The putative role of trimesic acid in providing an alternate crystallization pathway to the polyol 2 has been discussed

Studies in crystal engineering: topochemical photodimerization of (±)-p-fluorobenzylidenepiperitone

The effect of fluoro substitution on the nature of crystal packing and the solid state photo-behaviour of the title non-planar molecule is examined. The steering capability of fluorine and the role of molecular topology in crystal packing are discussed. Crystallographic evidence for a C-H … F hydrogen bond is provided

Studies in Crystal Engineering: Topochemical Photodimerization of (\pm) -p -Flourobenzylidenepiperitone

The effect of fluoro substitution on the nature of crystal packing and the solid state photo-behaviour of the title non-planar molecule is examined. The steering capability of fluorine and the role of molecular topology in crystal packing are discussed. Crystallographic evidence for a $C-H^{...}F$ hydrogen bond is provided

Photobehavior of crystalline 4-styrylcoumarin dimorphs: structure-reactivity correlations

4-Styrylcoumarin crystallizes from chloroform and hexane mixture in two morphologically different modifications. The monoclinic form (needles, P2(1)/c) undergoes stereospecific photodimerization producing anti head-to-tail dimer across pyrone double bond, whereas the triclinic modification (prisms, P ($) over bar 1) dimerizes yielding photodimer of the same configuration, but across styrenic double bond. Single crystal X-ray analyses of the dimorphs reveal the packing differences permitting rationalization of the regio- and stereochemistry of the photoproducts. The significantly low dimer yield from the prismatic crystals is rationalized

Structure of tri-1-naphthylborane-benzene (1/1) complex, c30h21b.c6h6

M r= 470.46, rhombohedral, R3, a =8.710(4)A, a=91.10(3) o, V= 660.4 (9) A 3, Z= 1,D m= 1.170 (flotation in KI solution), D x=1.183 Mg m -a, Mo Kct, 2 = 0.7107/~,, /t =0.033 mm -1, F(000) - 248.0, T= 293 K, R -- 4.6%(481 unique reflections). The molecule has C a symmetry and is propeller shaped, the angle of twist about the B-C bond being 41.5 (7) °. The space group being chiral, this is yet another example of spontaneous resolution. The results of a thermal-motion analysis are discussed

Unusual photobehaviour of crystalline 7-methoxy-4-methylcoumarin

7-Methoxy-4-methylcoumarin undergoes a solid-state photo [2 + 2] cycloaddition upon UV irradiation to yield two photodimers. The formation of the minor product appears to be a direct consequence of the formation of the topochemically controlled dimer

Unusual photobehaviour of crystalline 7-methoxy-4-methylcoumarin

7-Methoxy-4-methylcoumarin undergoes a solid-state photo [2 + 2] cycloaddition upon UV irradiation to yield two photodimers. The formation of the minor product appears to be a direct consequence of the formation of the topochemically controlled dimer

Photobehavior of crystalline 4-styrylcoumarin dimorphs: structure-reactivity correlations

4-Styrylcoumarin crystallizes from chloroform and hexane mixture in two morphologically different modifications. The monoclinic form (needles, P2<SUB>1</SUB>/c) undergoes stereospecific photodimerization producing anti head-to-tail dimer across pyrone double bond, whereas the triclinic modification (prisms,) dimerizes yielding photodimer of the same configuration, but across styrenic double bond. Single crystal X-ray analyses of the dimorphs reveal the packing differences permitting rationalization of the regio- and stereochemistry of the photoproducts. The significantly low dimer yield from the prismatic crystals is rationalized