Tuncer Hökelek

Intramolecular hydrogen bonding and tautomerism in Schiff bases. Part I. Structure of 1,8-di[N-2-oxyphenyl-salicylidene]-3,6-dioxaoctane

Abstract 1,8-Di[N-2-oxyphenyl-salicylidene]-3,6-dioxaoctane (1) and 1,8-di[N-2-oxyphenyl-2-oxo-1-naphthylidenemethylamino]-3,6-dioxaoctane (2) are obtained from the reaction of triethylene glycol bis(2-aminophenyl ether) with salicylaldehyde and 2-hydroxy-1-naphthaldehyde. Compounds (1) and (2) have been characterized by elemental analysis, IR, 1H-NMR and UV-visible techniques and the structure of compound (1) has been examined crystallographically. The UV-visible spectra of 2-hydroxy Schiff bases are studied in different solvents and acidic media. Compound (2) is in tautomeric equilibria (phenolimine, OH…N ⇌ keto-amine, O…HN forms) in polar and non-polar solvents. These tautomers are not observed in polar and non-polar solvents for (1) as supported by 1H-NMR and UV-visible data. The keto-amine form is observed in acidic solutions of chloroform and benzene, but it is not observed in solutions DMSO and EtOH for compounds (1) and (2). Compound (1) is in the form of phenol-imine in solid state and a crystallographically centrosymmetric multidentate Schiff base ligand, containing two imine nitrogen, two hydroxy and four etheric O atoms. There is a strong intramolecular [ OH ⋯ N = 1.488(3) A ] hydrogen bond. The C  N imine bond and CNC bond angle are 1.270(3)A and 123.5(2)°. It crystallizes in the monoclinic space group P2 1 n with a = 6.301(1), b = 13.624(1), c = 16.189(1) A , β = 100.28(1)°, V = 1367.4(3) A 3 , Z = 2 and Dx = 1.313 g cm−3.

Amino acid synthesis using (L)-pyroglutamic acid as a chiral starting material

Abstract Deprotonation of protected pyroglutamates 1(c), 1(d), 1(e) with lithium di-isopropylamide (LDA) or lithium hexamethyldisilazide (LiHMDS) in THF, followed by reaction with electrophiles, leads to the formation of 4-substituted pyroglutamates in good yield. This approach has been used for the synthesis of the novel amino acid (4).

Investigation of some parameters influencing electrocrystallisation of PbO2

Abstract Optimum electrocrystallisation conditions of PbO2 have been investigated in acetonitrile by controlling experimental parameters such as water content, current density, electrolyte concentration, and acidity. It was determined that the crystallinity, conductivity and β-content of PbO2 films are highly dependent on these factors and that electrodeposition solution, which has 6 M water, 0.1 M lead perchlorate and no acid, gave the best crystalline PbO2 with 99% of β form. The conductivity value of this film was 6028 S/cm. All analyses were confirmed by XRD method

pH-independent decomposition reactions of l-ascorbic acid in aqueous metal solutions—I. Formation and structures of CoII and GdIII oxalates

Abstract The reactions of l -ascorbic acid in aqueous CoII and GdIII solutions were investigated at pH values of 2,6 and 12. IR spectral studies reveal that the initially formed metal-ascorbates slowly decompose to the solid oxalate complexes in a pH-independent manner. The compositions of the cobalt oxalates were defined as CoC2O4·2H2O and those of GdIII showed variations due to the stereochemical changes in the precursor ascorbate complexes related to pH. X-ray crystal analyses were performed and the structure of Gd2(C2O4)3·6H2O is reported for the first time.

High temperature bromination VI: Bromination of benzobarrelene

Abstract The electrophilic addition of bromine to benzobarrelene in chloroform at 10° C followed by repeated chromatography combined with fractional crystallization allowed us to isolate ten products 12–21 Structural determination of these compounds revealed that the barrelene skeleton was rearranged completely. 18–21 are alcohol compounds which arise from hydrolysis of 12, 13, 14, and 15, respectively. High temperature bromination of benzobarrelene in decalin at 150 °C followed by repeated chromatography combined with fractional crystallization gave us 18 products. Nonrearranged products 24, 25, and 26 have been isolated in 50% yield. All compounds have been characterized properly, especially by 200 MHz 1H NMR and 50 MHz 13C NMR spectra. Furthermore, it has been concluded that high temperature bromination of bicyclic systems gives more non-rearranged products. If the molecule is more strained, the tendency to rearrange decreases as in the case of benzonorbornadiene.

Phosphorus–nitrogen compounds part 27. Syntheses, structural characterizations, antimicrobial and cytotoxic activities, and DNA interactions of new phosphazenes bearing secondary amino and pendant (4-fluorobenzyl)spiro groups

A number of partly (7-9) and fully (10a-12d, Scheme 1) substituted mono(4-fluorobenzyl)spiro cyclotriphosphazenes was prepared. The structures of the compounds were determined by MS, FTIR, 1D and 2D NMR techniques. The crystal structures of 9, 11b and 12b were verified by X-ray diffraction analysis. In vitro cytotoxic activity of the phosphazenes (10a-12d) against HeLa cervical cancer cell lines was evaluated. Compound 12c was found to be the most effective, as it is a cytotoxic reagent that might activate apoptosis by altering mitochondrial membrane potential. Compounds 10b, 11b and 12b showed very good activity against yeast strains Candida tropicalis and Candida albicans. BamHI and HindIII digestion results demonstrate that the compounds (10a-12a, 10b-12b, 10d-12d), and (9, 10c-12c) bind with G/G and A/A nucleotides, respectively.

Tetra­aqua­bis[4-(dimethyl­amino)benzoato-κO]manganese(II) dihydrate

# 2007 International Union of Crystallography All rights reserved The title Mn complex, [Mn(C9H10NO2)2(H2O)4] 2H2O, is monomeric and centrosymmetric. It contains two 4-dimethylaminobenzoate ligands, four coordinated and two uncoordinated water molecules, all ligands being monodentate. The four O atoms in the equatorial plane around the Mn atom form a slightly distorted square-planar arrangement, while the distorted octahedral coordination is completed by the two water O atoms in the axial positions. In the crystal structure, intraand intermolecular O—H O hydrogen bonds link the molecules into chains.

Synthesis of 2,3-, 2,5-, and 2,6-disubstituted-benzobarrelenes high temperature bromination II

Bromination of 2-bromo-1,4-dihydro-1,4-ethenonaphthalene (7) at -0 0C has been found to give five rearranged tribromides 8, 9, 10, 11, and 12 via Wagner-Meerwein rearrangement with accompanying aryl and alkyl migration. It has been shown that the endo tribromides 9and 11 are secondary products formed by bromine-catalyzed reaction of the corresponding exo tribromides. The bromination of 7 at 78 °C resulted in the formation of the non-rearranged products 21, 22, 23, and 24 with bicyclo-[2.2.2]skeleton. The structure of 8, 10, 11 and 21 have been determined by X-ray structural analysis. The dehydrobromination of the tribromides 21, 22, 23, and 24 with potassium tert-butoxide provided the corresponding benzobarrelenes 2a, 3a, and 4a in high yield. Reaction of dibromobenzobarrelenes with CuCN resulted in the formation of dicyano derivatives 2b, 3b, and 3b. Reaction of 3a with BuLi and subsequent quenching with MeI afforded dimethyl derivative 3c.

Bis(isonicotinamide-κN1)bis­[4-(methyl­amino)benzoato]zinc(II) monohydrate

In the title ZnII complex, [Zn(C8H8NO2)2(C6H6N2O)2]·H2O, the Zn atom is coordinated by two 4-methylaminobenzoate (MAB) and two isonicotinamide (INA) ligands in a distorted trigonal-bipyramidal geometry; one of the MAB ions acts as a bidentate ligand while the other MAB and the two INA are monodentate ligands. The dihedral angles between the carboxyl groups and the adjacent benzene rings are 8.52 (22) and 5.10 (14)°. In the crystal, intermolecular O—H⋯O and N—H⋯O hydrogen bonding links the molecules into a supramolecular structure. Weak intermolecular C—H⋯O interactions are also present.

Schiff bases and their complexes with metal ions. Part II. Structures of N-n-butyl-2-hydroxy-1-naphthaldimine and bis[N-n-pentyl-2-hydroxy-1-naphthaldiminato]nickel(II)

AbstractThe Schiff base ligand (1), [C15H17NO] crystallizes in the monoclinic space group P21/c witha=10.054(3),b=10.313(3), c=13.173(4)Å, β=107.42(4)°,V=1303.2(7)Å3,Z=4,Dx=1.159 g cm−3, and μ(MoKα)=0.674 cm−1. The C2-O[1.23(1)Å] and C3−C4 [1.33(2)Å] bond lengths are short, due to its quinoidal structure. In the Schiff base nickel complex (2), [Ni(C16H18NO)2] the asymmetric unit is comprised of two half-complexes. It crystallizes in the triclinic space group