O. Ya. Borbulevych

Substituent steric effects and molecular structure of anionic σ-complexes of 5,7-dinitroquinoline

Abstract Molecular structure and conformational flexibility of Meisenheimer complexes of 5,7-dinitroquinoline derivatives are studied experimentally using X-ray diffraction and theoretically by semi-empirical AM1 calculations. The dihydrocycle is found to possess high conformational flexibility in all anionic σ-complexes considered. Substituent steric effects at the saturated carbon atom of the anion significantly influence the equilibrium conformation and deformability of the partially hydrogenated ring. An increase of the bending strain does not cause considerable changes of the conformational characteristics of ring. In the crystal phase, the geometry of the anion depends essentially on the crystal structure and on the cation coordination.

Electron density distribution in the crystal of the Meisenheimer complex of potassium 3-methyl-5′, 7′-dinitro-5′, 8′-dihydrospiro(1,3-oxazolidine-2,8′-quinolinide) based on X-ray diffraction data at 153 K

The electron density distribution in the crystal of the Meisenheimer complex of potassium 3-methyl-5′, 7′-dinitro-5′, 8′-dihydrospiro(1,3-oxazolidine-2,8′- quinolinide) (1) was studied based on the data of precision X-ray diffraction study. The experimental data were compared with the results of quantum-mechanical calculations. The electron density distributions in the regions of the nitro groups are substantially different in spite of the similarity in the geometric parameters of these groups. In addition, there is a discrepancy between the exprimental and theoretical data on this distribution. The effect of the cation on the electronic strucure of the anion in the crystalline phase is the most probable cause of the differences observed. To reveal this effect.ab initio calculations of different anion1-K+ systems were performed and a topological analysis of the electron density distributions was carried out. Depending on the mode of coordination of the cation to the anion, the former determines the contribution of alternative resonance forms to the structure of the anion.

Structures of condensation products of ortho-aminophenols with ninhydrin

Condensation of ortho-aminophenols and N-benzylsulfonyl-o-phenylenediamine with ninhydrin afforded tetracyclic products, the amino group entering into condensation with the carbonyl group at position 1 of ninhydrin. The structures of the reaction products were established by 1H NMR spectroscopy and X-ray diffraction analysis.

Molecular and crystal structure of 2-cyano-(2E)-pentadien-2,4-oic acid and ethyl-2-cyano-(2E)-pentadien-2,4-oate

X-ray study of 2-cyano-(2E)-pentadien-2,4-oic acid (1) and its ethyl ester (2) showed that the molecules of1 and2 in the crystalline phase form stacks by translating along the shortest crystallographic axis. The nature of the intermolecular interactions favoring the formation of such β-structures was analyzed within the framework of the Bader topological theory. Possible routes of topochemical reactions of compounds1 and2 are considered.

Regioselectivity in the reactions of the acetonate ion with electron-deficient arenes

The reactions of the acetonate ion with 1,3-dinitro-5-X-, 1,3-X2-5-nitro- (X = NO2, CN, COOCH3, CONH2, COO–, and H), and 1,3,5-tricyanobenzenes were studied by 1H NMR and electronic absorption spectroscopy and by quantum-chemical methods. The kinetic factor is decisive for the initial attack of the carbanion on the C(2) atom of unsymmetrical arenes. However, σ-adducts in which a nucleophile is added to the C(4) atom are more stable thermodynamically. In the case of 1,3-X2-5-nitrobenzenes (X = CN, COOCH3, or CONH2), the σ-adducts with the acetonate group in para-position to the X group unexpectedly proved to be very stable. The structures of the σ-adducts based on trinitro- and 1,3-dinitro-5-cyanobenzenes were determined by X-ray diffraction analysis. Quantum-chemical calculations (the AM1 and PM3 semiempirical methods and the density functional method) were used to interpret the reaction regioselectivity and the molecular and electronic structures of the σ-adducts.

Molecular and electronic structures and conformational analysis of derivatives of 9-nitroanthracene, anionic σ-complexes

Potassium 10-methoxy-9-nitroanthracenide was studied by X-ray diffraction analysis. The central ring of the anthracene fragment adopts an asymmetrically flattened boat conformation. The bond lengths in the C(Ar)−C(NO2)−C(Ar) fragment are indicative of the presence of conjugation between the π-systems of the benzene rings and the nitro group owing to a substantial contribution of theaci form to the structure of the nitro group. Quantum-chemical calculations of anionic σ-complexes of 9-nitroanthracene derivatives were performed. In all cases, the central ring adopts two conformations with the pseudoaxial and pseudoequatorial orientations of the substituents at the saturated C(10) atom, respectively. The relative stability of the conformers and the factors determining the stability were considered. The minima on the potential energy surface have a flattened shape in spite of relatively high barriers to the conformational transition (2–4 kcal mol−1). The deviation of the C(Ar)−C(Ar)−C(sp3)−C(Ar) torsion angle from the equilibrium value by ±20° causes an increase in the energy of the anion by less than 1 kcal mol−1. The effect of the substituents on the charge distribution was considered.

Structures of oxidation products of 4,6-di-tert-butylpyrogallol

Oxidation of 4,6-di-tert-butylpyrogallol gave two dimeric products instead of the expected 4,6-di-tert-butyl-3-hydroxy-1,2-benzoquinone (2). It was established by X-ray diffraction analysis that the first product has the structure of tetra-tert-butyl-6, 10a-dihydroxy-1,2-dioxo-3,4a,7,9-1,2,4a, 10a-tetrahydrodibenzo-1,4-dioxine. From this it follows that compound 2 undergoes regio- and stereospecific dimerization according to the [2π+4π]-cycloaddition mechanism,viz, the hetero Diels—Alder reaction. The double intensities of the signals in the1H NMR spectrum are indicative of a symmetrical structure of the second product, 2,6,4′, 6′-tetra-tert-butyl-4,4′-dihyroxy-3,5,3′,5′-tetraoxo-4,4′-bi(cyclohexene), which is a racemate of enantiomers formed upon recombination (r+r orl+l) of the intermediate of oxidation of pyrogallol, namely, of ther,l-stereogenic 3,5-di-tert-butyl-1-hydroxy-2,6-dioxocyclohex-3-enyl radical.

N-substituted amides of 2-cyanopenta-2E,4-dienoic acid

N-Substituted amides of 2-cyanopenta-2E,4-dienoic acid were synthesized by condensation ofN-substituted cyanoacetamides with acrolein in a dioxane-DMSO solution in the presence of Zn(OAc)2·2H2O as a condensing agent. X-ray diffraction study of 3-methylanilide of 2-cyanopenta-2E,4-dienoic acid (2d) demonstrated that the crystal structure of this compound is similar to that of 2-cyanopenta-2E,4-dienoic acid studied previously. However, the presence of themeta-tolyl substituent in molecule2d apparently results in the fact that the β-structure, which is typical of 2-cyanopenta-2E,4-dienoic acid, does not exist in the crystalline phase of2d.

Synthesis and conformation of 6,8,10-trinitro-1,4-dioxaspiro[4.5]decane

Abstractcis, trans-6,8,10-Trinitro-1,4-dioxaspiro[4.5]decane was synthesized by reduction of the corresponding spirocyclic anionic δ-complex with potassium tetrahydroborate. The molecular structure and the conformation of the title compound were established by X-ray diffraction analysis and1H NMR spectroscopy.

The N-phenylamide of 2-cyano-5-phenylpent-2-en-4-ynoic acid

The central 2-cyanocarboxyaminoprop-2-enylic fragrent of the title compound, 2-cyano-5,N-diphenylpent 2-en-4-ynamide, C 18 H 12 N 2 O, is planar. The phenyl rings are rotated with respect to this plane. Molecules are linked by N-H…O hydrogen bonds and form stacks by translation along the crystallographic c axis.