Romana Anulewicz

The effect of the methoxy group on the geometry of the benzene ring supported by crystal structure studies and Ab Initio Calculations. Crystal and Molecular Structure of 4-(4-Methoxyphenyl)-2,6-diphenylpyridine and 1-Methyl-4-(4-methoxy-phenyl)-2,6-diphenylpyridinium perchlorate.

Abstract Crystal and molecular structures of 4-(4-methoxyphenyl)-2,6-diphenylpyridine (I) and 1-methyl-4-(4-methoxyphenyl)-2,6-diphenyl pyridinium perchlorate (II) are repoded, with R=0.052 and 0.070, respectively. The lower precision of II is due to disorder of the perchlorate anion. A geometrical analysis of 8 p-substituted derivatives of anisole shows that the methoxy group interacts strongly with the ring via the resonance effect. Significant deformations of the exo-cyclic bond angles at MeO- substituted carbon atom are due to steric hinderance between ortho CH and Me group. Ab initio calculations for anisole are in line with the observed planar conformation of these systems. The difference in energy between the planar and perpendicular conformers is 1.4 kcal/mole at the 6-31G* level. The intramolocular interactions between the -OMe group and Cipso-CorthoH are explored through additional ab initio calculations. They induce more double character of Cipso-Cortho bond, thereby causing one Kekule structure to be preferred.

Angular group-induced bond alternation. III. The case of ortho-dimethoxybenzene derivatives. Crystal and molecular structure of 3,4-dimethoxybenzaldehyde (4-methylphenyl)sulfonylhydrazone

Abstract The crystal and molecular structure of the 3,4-dimethoxybenzaldehyde (4-methylphenyl)-sulfonylhydrazone is reported, with R = 0.0647. Application of the HOSE model to the molecular geometry of the title compound, together with the most precise molecular geometries for 36 ortho -dimethoxy derivatives of benzene retrieved from Cambridge Structural Database (CSD) and supplemented by ab initio RHF/6-311G ∗∗ calculations, led to the conclusion that the o -dimethoxy groups cause significant changes in ring geometry, fully in line with the concept of Angular Group Induced Bond Alternation (AGIBA).

Separation of the energetic and geometric contribution to the aromaticity. Part IX. Aromaticity of pyrazoles in dependence on the kind of substitution

Abstract Crystal and molecular structures of the 4-(4′-N,N-dimethylaminophenyl)-3,5-dimethyl-1,7-diphenyl-bis-pyrazolo[3,4-b;4′,3′-e]pyridine (I) and 3,5-dimethyl-1,4,7-triphenyl-bis-pyrazolo[3,4-b;4′,3′-e]pyridine (II) are reported, with R = 0.0505 and 0.0538, respectively. Application of the HOMA model1 to molecular geometry of the title compounds enriched by the data for pyrazoles retrieved from CSD and from RHF/6-311G∗∗ ab-initio calculations led to the conclusion formulated as a rule that decrease of aromaticity of pyrazole is caused by an increase of the double bond character of the exo-cyclic bonds with substituents attached to C3 and C4 atoms in the ring.

Crystal structures of 5-fluoro-dUrd and its 2 and/or 4-thio analogues: Models of substituted dUMP pyrimidine ring interacting with thymidylate synthase

In order to understand the influence on thymidylate synthase interactions with dUMP analogues of the pyrimidine ring 2- and/or 4-thio, and 5-fluoro substitutions, X-ray diffractions by crystals of 5-fluoro-dUrd and its 2- and 4-thio, and 2,4-dithio analogues were measured, the four structures solved and refined. The following conclusions were suggested by results of comparative analyses of structural parameters (bond lengths, valence angles), followed by theoretical considerations based on calculated resonance structure distributions and aromaticity indices of the uracil, thiouracil, fluorouracil and fluorothiouracil rings. The effect of 4-thio substitution of FdUMP, altering specificity of inactivation of thymidylate synthases from various sources, is probably due to weaker proton acceptor power of the 4-thio substituent and increasing acidity (enhanced proton-donor power) of the N(3)-H moiety, resulting in an impaired fitness into the network of hydrogen bonds in the enzyme active center cleft. 2,4-Dithio substitution results in (i) impaired pyrimidine ring recognition by the enzyme active center, due to the 4-thio substituent (ii) increased pyrimidine ring aromaticity in dUMP, leading to resistance of C(6) to nucleophilic attack by the enzyme active center cysteine and (iii) altered planarity of the pyrimidine ring and deflections, with respect to the ring plane, of substituents at C(2), C(4) and C(5). 5-Fluoro substitution apparently activates the pyrimidine ring towards the interaction with thymidylate synthase by producing local strain, which results in an increased reactivity as predicted by the Walsh-Bent rule.

Hydrogen bonded Schiff bases; di-anil of 2-hydroxy-5-methyl-isophthaldehyde

Abstract Structural and spectroscopic properties of solid dianil of 2-hydroxy-5-methyl-isophthaldehyde have been investigated. This is a Schiff base containing intramolecular O–H…N hydrogen bonding. Single crystal X-ray diffraction shows that the possibly equivalent hard structural parameters (bond lengths and the valence angles) of the title molecule are hardly differentiated by an asymmetric hydrogen bonding and different conformations of the anil wings. 13 C MAS NMR results are more sensitive and they clearly show the influence of [O–H…N] hydrogen bonding on the chemical shifts of the central ring carbon atoms.

Crystal and molecular structure of the lithium p-nitrosophenolate dihydrate dimer: an example of a strong dependence of the π-electron cooperative substituent effect on the hydrogen-bonding network in the crystal lattice

Abstract The crystal and molecular structure of lithium p -nitrosophenolate dihydrate dimer (LNP) is solved by X-ray diffraction with relatively high precision (the mean esd for the bond lengths is 0.002–0.003 A; wR = 0.0433). NMR studies and ab initio (6-31G) calculations indicate that the free anions have primarily a quinoid structure, whose contribution to the crystal lattice strongly depends on hydrogen bonding. Comparison of the reported structure with sodium tri- and magnesium hexahydrate p -nitrosophenolate perchlorates indicates that LiO interactions somewhat resemble the hydrogen bond.

Complexes of Mercury(II) Cyanide with Crown Ethers in Dimethylsulfoxide

The complexation of mercury(II) cyanide with macrocyclic ligands 15-crown-5,18-crown-6 and dibenzo-24-crown-8 in dimethylsulfoxide was studied using199Hg NMR measurements. No significant complexation with 15-crown-5was observed. The stability constants Ks for 1 : 1 complexes with two other ligands were determined and found to be similar, in contrary to the results reported in nitrobenzene. Solvent effects on Ks values obtained are discussed in comparison with the literature data. X-ray crystal structure of Hg(CN)2.A18-crown-6 was also determined.

Diastereoisomers of a prednisolone derivative

The crystal and molecular structures of two synthetic corticosteroid diastereoisomers were determined by X-ray diffraction methods. (22R)-21-acetoxy-16α,17α-furfurylidenedioxy-11β-hydroxy-pregna-1,4-diene-3,20-dione, C28H32O8, crystallized in the orthorhombic system, space group P212121,a=6.346(1),b=14.106(2),c=27.901(3) Å, andZ=4. (22S)-21-acetoxy-16α, 17α-furfurylidenedioxy-11β-hydroxy-5 pregna-1,4-diene-3,20-dione ethanolate, C28H32O8 ·C2H5OH, crystallized in the monoclinic system, space group C2,a=20.382(5),b=8.331(1),c=17.346(4)Å, β=103.43(2)°, andZ=4. A change of configuration at the C(22) chirality center has influence on the remote parts of the molecules. The long-range effects appear in the ability to form intermolecular hydrogen bonds by different atoms and consequently in the solvation of the (S) diastereoisomer.

Crystal Structure and Solid State 13C Nmr Analysis of Methyl 3,4,6-Tri-O-Acetyl-2-Deoxy-2-(3-Phenylureido)-β-D-Glucopyranoside

ABSTRACT The X-ray diffraction analysis of methyl 3,4,6-tri-O-acetyl-2-deoxy-(3-phenylureido)-β-D-glucopyranoside was performed and showed that the molecules are associated by two NHz.O=C hydrogen bonds. One molecule with disorder of an acetyl group at C-4 was found in the asymmetric crystal unit. The signals in 13C CPMAS NMR spectrum are duplicated indicating that local symmetry is lower than those of the crystal.