Synthesis of 2- and 4-chloropyrimidines with hydroxyphenyl substituents by the interaction of Vilsmeier-Haack reagents with (hydroxyphenyl)dihydropyrimidin-2- and -4-ones

The reaction of 2- and 4-hydroxypyrimidines containingortho- andpara-hydroxyphenyl substituents with Vilsmeier-Haack reagents generatedin situ from DMF and SOCl₂ or POCl₃ results in the chemoselective replacement of the heterocyclic hydroxyl group by chlorine and formylation of the phenolic hydroxyl group. Aryl formates are hydrolyzed under the conditions of their isolation to give the corresponding phenols, especially if the pyrimidyl fragment isortho to the formyloxy group.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1105–1108, June, 1993.     

The self-ordering properties of novel phthalocyanines with out-of-plane alkyl substituents

Two novel homologous series of phthalocyanines were prepared from 2,2-dialkylindane and 2,2-dialkyl-1,3-benzodioxole precursors. It was anticipated that attaching alkyl chains to five-membered rings, fused to the peripheral sites of the phthalocyanine ring, would result in the adoption of an out-of-plane configuration and thereby discourage cofacial aggregation, to provide an analogy with picket-fence porphyrins. This strategy proved partially successful. Some members of the series of phthalocyanines derived from 2,2-dialkyl-1,3-benzodioxoles, in which the alkyl chains are linked to the phthalocyanine via a cyclic ketal, form spin-coated thin films in which the phthalocyanine cores are perfectly isolated. This behaviour is associated with the formation of a disordered crystal that appears as a mesophase in the thermal profile of these materials. However, the phthalocyanines derived from 2,2-dialkylindanes display a columnar mesophase over a wide temperature range, with some liquid crystalline derivatives at ambient temperature. A single-crystal X-ray diffraction structure of the octahexyl derivative of this series shows how the columnar assembly accommodates the out-of-plane alkyl chains by tilting the macrocyclic plane of the phthalocyanine components with respect to the axis of the column. This study helps to emphasise the importance of both the steric and electronic effects of substituents on the packing behaviour of phthalocyanines in the condensed phase, and especially the role of electron-donating oxygen atoms directly attached to the ring.     

Aggregation in detergent-free ternary mixtures with microemulsion-like properties

Aggregation in liquid mixtures is a ubiquitous phenomenon when water and at the same time rather unpolar compounds are present. Of special interest in recent years have been systems, in which the tendency of phase separation of a binary mixture is overcome by the solubilization ability of a short-chain alcohol as a third component. In such systems, polar and nonpolar domains coexist in absence of traditional long-chain surfactants. Their microemulsion-like properties, which lead to the names “detergent-less microemulsions” and “surfactant-free microemulsions” (SFMEs), have been studied by a variety of experimental methods and by simulations. In this review we summarize work that has been pursued to characterize these systems and give a short account of their various applications.     

Synthesis and mesomorphic properties of benzoxazole derivatives with lateral multifluoro substituents

Fluorinated aromatics is generally chosen as mesogenic cores to design novel liquid crystal compounds. Here, a series of benzoxazole derivatives with laterally multifluorinated biphenyl units, 2-(3′,3-difluoro ?4′-alkoxy-1,1′-biphenyl-4-yl)-benzoxazole derivatives (coded as nPF(3)PF(3)Bx), are synthesized and characterized, where methyl and nitro moieties are selected as terminal groups to investigate the effects of different polar substituents on the liquid crystal properties. The compounds nPF(3)PF(3)Bx show enantiotropic mesophases with mesophase ranges of 0–40°C and 0–63°C on heating and cooling for hydrogen-terminated derivatives (nPF(3)PF(3)BH), 43–93°C and 54–123°C for methyl-terminated ones (nPF(3)PF(3)BM), 60–108°C and 74–152°C for nitro terminated ones (nPF(3)PF(3)BN), respectively. They exhibit photoluminescence emission peaks at 390–392 nm and UV–vis absorption bands with maxima at 327–330 nm, respectively. The results reveal that lateral multifluoro substituents lead to a decrease in melting/clearing points, while electron-withdrawing terminal nitro moiety results in increases in both melting point and mesophase range.     

Aggregation properties of copper dibenzo-barrelenophthalocyanine

Depending on the solvent in which they are placed or from which they have been obtained, sterically hindered copper octa-tert-butyltetra-4,5-dibenzobarrelenophthalocyanines in solution and as a powder can take a monomeric form or dimer or trimer aggregate forms. In the aggregates, the molecules are disposed opposite one another around a high-order axis at an angle of 45° from equatorial displacement.Institute for the Chemistry of Natural Organic Materials, Russian Academy of Sciences, Krasnoyarsk 660000. Scientific-Research Institute for Organic Itermediates and Dyes, Moscow 103787. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 171–175, February, 1995. Original article submitted December 22, 1994.     

A comparison of linear optical properties and redox properties in chalcogenopyrylium dyes bearing ortho-substituted aryl substituents and tert-butyl substituents

A series of thiapyrylium pentamethine dyes (4 and 12-15) bearing 2,2'-di-tert-butyl-6,6'-diphenyl, 2,2'-di-tert-butyl-6,6'-bis(2,6-dimethylphenyl), 2,2'-di-tert-butyl-6,6'-bis(2-methylphenyl), 2,2',6,6'-tetrakis(2,6-dimethylphenyl), and 2,2',6,6'-tetrakis(2-methylphenyl) substituents, respectively, were prepared and their linear optical properties and electrochemical redox properties were measured and compared to thiapyrylium pentamethine dyes 3 and 5. The tert-butyl and 2,6-dimethylphenyl substituents give nearly identical chromophores with respect to values of lambda(max), molar extinction coefficients (epsilon), bandwidths at half-height (nu(1/2)), and lack of absorption in the visible spectrum. The 2-methylphenyl substituent imparts linear optical properties that are intermediate between those of the tert-butyl and phenyl substituents. The 2,6-dimethylphenyl and 2-methylphenyl substituents impart greater oxidative stability based on anodic shifts in oxidation potential.     

The electro-optic properties of fluorinated polydialkoxyphosphazenes with different lengths of side substituents

Polydialkoxyphosphazenes with partially fluorinated side substituents of different lengths in dioxane and ethyl acetate are studied via the methods of the equilibrium electro-optic Kerr effect, isothermal translational diffusion, and viscosimetry. It is experimentally found that the magnitude and sign of the Kerr constant depend on the length of the side substituents. The observed dependence is explained by the changes in the optical polarizability tensor and the angle between the direction of the permanent dipole moment and the primary axis of optical polarizability of the monomer unit of these macromolecules with an increase in the number of carbon atoms in the chains of alkoxy substituents attached to phosphorus. It is shown that fluorinated polydialkoxyphosphazenes are comblike polymers with high equilibrium skeletal rigidity and non-coincident principal directions of the optical polarizability and dielectric polarizability of the monomer unit.     

Chiral recognition properties of chiral 18-crown-6 ethers with aromatic substituents

The chiral recognition properties of chiral 18-crown-6 ethers with phenyl, 1-naphthoxymethyl, 1-naphthylmethyl, or 2,3,5,6-tetramethylphenylmethyl substituents for -phenylglycine methyl ester and 1-phenylethylamine perchlorate were investigated by a standard extraction procedure. The chiral recognition factor of 1-naphthoxymethyl substituted crown ether is 2.0 for the former salt but near 1.0 for the latter, whereas that of the other crown ethers is not so dependent on the structure of salts, which indicates the importance of the mutual relation of the structure of host and quest molecules.     

Electron donor and acceptor properties of alkyl substituents

The polar effects of alkyl substituents in electrophilic and nucleophilic chemical and electronic transitions is discussed. The question of the importance of hyperconjugation in the electron donor properties of alkyl substituents is raised. In view of the cogent arguments of Dewar, it is doubtful whether quantum mechanical calculations embodying hyperconjugation constitute proof of this effect. That the art of quantum mechanics may not yet be sufficiently developed to be used as proof for or against secondary resonance effects also is evidenced by the calculations of Simpson, who found that an internal dispersion force model (in which conjugation was neglected) reproduced the properties of butadiene just as satisfactorily as the models embodying conjugation. The experimental facts do not unequivocally support the hyperconjugation hypothesis and indeed are, at least in part, contradictory to it. In particular, the demonstration that the Baker-Nathan Effect² may be due to the influence of alkyl substituents on the differential solvation of ground and transition states casts doubt on the interpretation that this experimental effect is due to a dominant role of C-H hyperconjugation.

In nucleophilic chemical reactions, rate or equilibrium constants for para (or meta) alkyl derivatives are somewhat smaller than those of the corresponding hydrogen compounds. A number of authors have interpreted this in terms of a permanent electron donor role of alkyl substituents (e.g. by hyperconjugation) relative to the hydrogen substituent. However, this static viewpoint of substituent effects fails to account for the finding that p-alkyl substituents function as apparent electron acceptors (relative to the p-hydrogen substituent) in appreciably lowering the energy of the nucleophilic principal electronic transition of phenol, anisole, aniline and N,N-dimethylaniline. These results are qualitatively rationalized in terms of ‘substituent-polarizability” and electronegativity.

The p-neopentyl substituent lowers the energy of both electrophilic and nucleophilic electronic transitions to an appreciably greater extent than either the p-methyl or p-t-butyl substituent. This extra stabilizing effect of the neopentyl substituent on both electron deficient and electron rich centers may be due to an internal dispersion force interaction, since the geometry of the neopentyl compounds is particularly favorable for such an interaction.     

Liquid crystalline epoxides with long lateral substituents: Mechanical and thermal properties

In this work, mechanical and thermal properties of liquid crystalline epoxides (LCEs) with long lateral substituents from 4 to 12 carbon atoms cured with diaminodiphenylmethane were evaluated and analyzed by dynamic mechanical analysis, tensile tests, scanning electron micrographs (SEM), and thermo‐gravimetrical analysis. The experimental results indicated that the Young's modulus and α, β transitions in crosslinked networks are associated with the length of lateral substituents. The plastic deformation in fracture surfaces was observed by SEM. Thermal stability, water and solvent absorption of cured networks was dependent on the length of lateral substituents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2835–2841, 2007     

Optical and redox properties of ruthenium phthalocyanine complexes tuned with axial ligand substituents

The optical and electrochemical properties of the ruthenium phthalocyanine complexes [[(t-Bu)4Pc]Ru(4-Rpy)2], where R = NO2, Me, NH2, and NMe2, are reported. The electron density at the macrocycle may be adjusted using the axial ligand substituents, which have varying electron-donating/withdrawing strengths. Electrochemical data show that the axial pyridine ligand substituents exert significant influence over the phthalocyanine ring-based redox processes. The axial ligands also influence the electronic absorption properties of the complexes with influence also being observed in the electrogenerated oxidized and reduced species.     

Synthesis and mesomorphic properties of chiral swallow-tailed thioester liquid crystals with lateral substituents

Two homologous series of chiral swallow-tailed thioester materials, 1-ethylpropyl (R)-2-[3-fluoro-4-(4'-alkyloxybiphenylcarbonylthio)phenoxy]propionates, I-6 (m = 8-12), and 1-ethylpropyl (R)-2-[3-methyl-4-(4'-alkyloxybiphenylcarbonylthio)phenoxy]propionates, II-6 (m = 8-12), have been synthesized and their mesomorphic phases studied. The results show that materials I-6 (m = 8-12) with a fluoro substituent, display the phase sequence I-BPII-N*-SmC*-Cr, whereas materials II-6 (m = 8-12) with a methyl substituent display the phase sequence I-N*-TGBA*-SmA*-Cr during cooling. The physical properties of the SmC* phase in materials I-6 were measured. The results show that the maximum P _s values are in the range 91-95 nC cm^-2 and the maximum tilt angles are about 34-37°.     

Metallophthalocyanines with rod-shaped substituents

4-(4′-Dioctylaminocarbonylbiphenyloxy) phthalonitrile was synthesized from 4-(4′-carboxybiphenyloxy)phthalonitrile and dioctylamine in the presence of Et₃N. Metallophthalocyanines (Zn, Co and Cu) substituted with four dioctylaminocarbonyl biphenyloxy groups on the peripheral positions were prepared from 4-(4′-dioctylaminocarbonylbiphenyloxy)phthalonitrile and the corresponding divalent metal salts (Zn(CH₃COO)₂, CoCl₂ and CuCl₂). The new phthalocyanines are soluble in common organic solvents. These compounds were characterised by ¹H-NMR, ¹³C-NMR, FT-IR, UV-Vis and mass spectroscopies.     

Aluminoxanes with acetylacetonate substituents

The reaction of tetraalkylaluminoxanes (R₄Al₂O; R  Me, Et and i-Bu) with acetylacetone (acacH) has been studied at various molar ratios. The acetylacetonate substituents were found to have a destabilizing effect on the stability of the aluminoxanes. The stability of these compounds decreases in the order: R₄Al₂O > R₃acacAl₂O > R₂(acac)₂Al₂O ? (acac)₄Al₂O.Aluminoxanes with acetylacetonate substituents undergo disproportionation, yielding aluminium trisacetylacetonate. The alkyl group also has an effect on the stability of alkylacetylacetonatoaluminoxanes, which decreases in the order i-Bu > Et > Me.     

Quadratic and cubic nonlinear optical properties of salts of diquat-based chromophores with diphenylamino substituents

A series of chromophoric salts has been prepared in which 4-(diphenylamino)phenyl (Dpap) electron donor groups are connected to electron-accepting diquaternized 2,2'-bipyridyl (diquat) units. The main aim is to combine large quadratic and cubic nonlinear optical (NLO) effects in potentially redox-switchable molecules with 2D structures. The chromophores have been characterized as their PF(6)(-) salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. The visible absorption spectra are dominated by intense π → π* intramolecular charge-transfer (ICT) bands, and all of the compounds show two reversible or quasireversible diquat-based reductions and partially reversible Dpap oxidations. Single crystal X-ray structures have been obtained for one salt and for the precursor compound (E)-4-(diphenylamino)cinnamaldehyde, both of which adopt centrosymmetric space groups. First hyperpolarizabilities β have been measured by using hyper-Rayleigh scattering (HRS) with a 800 nm laser, and Stark (electroabsorption) spectroscopy of the ICT bands affords estimated static first hyperpolarizabilities β(0). The directly and indirectly derived β values are large and generally increased substantially for the bis-Dpap derivatives when compared with their monosubstituted analogues. Polarized HRS studies show that the NLO responses of the disubstituted species are dominated by "off-diagonal" β(zyy) components. Lengthening the diquaternizing alkyl unit lowers the electron-acceptor strength and therefore increases the ICT energies and decreases the E(1/2) values for diquat reduction. However, compensating increases in the ICT intensity prevent significant decreases in the Stark-based β(0) responses. Cubic NLO properties have been measured by using the Z-scan technique over a wavelength range of 520-1600 nm, revealing relatively high two-photon absorption cross-sections of up to 730 GM at 620 nm for one of the disubstituted chromophores.     

Synthesis and mesomorphic properties of banana-shaped achiral molecules with central and lateral halogen substituents

Three banana-shaped achiral compounds, derivatives of 4-chloro-1,3-phenylene bis[4-(4-n-decanyloxyphenyliminomethyl)benzoate], were synthesized with variation of a substituent (X=H, F, or Cl); their antiferroelectric properties are described. The mesomorphic and switching properties were characterized by polarizing optical microscopy, differential scanning calorimetry, triangular wave method, and X-ray diffraction. The introduction of a lateral halogen substituent in the Schiff's base moiety prevents the regular stacking of the molecules, resulting in a decrease of melting temperature and leads to formation of the switchable SmC* phase in the melt. All of the compounds showed antiferroelectric switching, and their values of spontaneous polarization on reversal of an applied electric field were 260, 480, and 300 nC cm^-2, respectively, for X=H, F and Cl.