Benzene Fragments Research Articles

Synthesis and electronic absorption spectra of substituted tetrabenzoporphins

Zinc complexes of tetrabenzoporphins with substituents in the benzene fragments of the molecule were synthesized by the template tetramerization of substituted 3-carboxymethylphthalimidines or phthalimides with malonic or phenylacetic acid in the presence of zinc acetate, as well as by substitution reactions in the tetrabenzoporphin molecule. The metal-free compounds were obtained from the corresponding zinc complexes by the action of a stream of hydrogen chloride in chloroform. The electronic absorption spectra of the synthesized compounds were investigated.

Quasiclassical trajectory study of the n = 3 overtone state of benzene

A benzene fragment HC 3/DC 3 is used as a model for benzene in a quasiclassical trajectory study of the intramolecular decay of the n=3 overtone. The calculated linewidth (fwhm) for the CH overtone is ≈ 4 cm −1 and that for CD <1 cm −1. This trajectory result for the n=3 CH overtone is in excellent agreement with experimental results for the n=3 overtone of rotationally cold C 6H 6

ChemInform Abstract: Nitro‐ and Aminosubstituted 10,10‐Dimethyl‐10‐sila‐2‐azaanthrones.

AbstractDie Nitrierung des Dihydrosilaazaanthracens (I) mit Aluminiumnitrat in Acetanhydrid liefert unter gleichzeitiger Oxidation Gemische der Verbindungen (II)‐(V).

Ab initio calculations of phenylene ring motions in polyphenylene oxide

AbstractAn important class of polymers is comprised, in part, of 1,4‐disubstituted phenylene groups. It is widely believed that large amplitude phenylene torsional motions play a critical role in determining such physical properties as the toughness and degree of crystallinity of these polymers. We have studied what is perhaps the simplest polymer in this class, polyphenylene oxide (PPO), using ab initio quantum chemistry methods to determine the conformational properties, torsional potential energy functions, and vibrational frequencies. From our calculations on dimer (diphenyl ether) and trimer (para‐diphenoxy benzene) fragments emerges a qualitative description of the mechanism of phenylene rotation in the polymeric material.

Nitro- and amino-substituted 10,10-dimethyl-10-sila-2-azaanthrones

Under conditions of the Mencke reaction, 10,10-dimethyl-9,10-dihydro-10-sila-2-azaanthracene is nitrated on the benzene fragment of the molecule, but the corresponding ketone is nitrated on the pyridine fragment. Dihydrosilaazaanthrone is nitrated by nitrating mixture in positions 5, 7, and 8 of the benzene fragment of the molecule. The nitro-substituted dihydrosilazaanthrones have been reduced to the corresponding amino derivatives.

Probing argon–benzene van der Waals molecules and isotopically substituted benzene with laser-ionization mass spectrometry

Ultrasensitive wavelength-dependent laser-ionization mass spectrometry is applied to spectroscopic studies of argon–benzene van der Waals molecules and isotopically substituted benzene molecules. Argon–benzene fragments either in its 1B2u excited electronic state or subsequent to being ionized. Substitution of a single 13C atom in the benzene monomer ring leads to an observable spectroscopic splitting whose magnitude can be accurately predicted from the 1B2u excited-state force field recently developed by Krogh-Jesperson et al. [ J. Phys. Chem.88, 5503 ( 1984)].

Quinazoline cardiovascular agents (review)

The chemistry of quinazoline compounds has a more than centuries-old history; however, the intensive search for biologically active substances in this series began only in the last few decades. The establishment of the quinazoline structure of the antimalarial alkaloid febrifugine [i], which was isolated from the Chinese plant aseru (Dichroa febrifuga Lout.), and the synthesis and study of its analogs [2-4], as well as quinazoline derivatives of the antimalarial quinoline and pyrimidine medicinal preparations [5-7] and azo compounds with chemotherapeutic action [8, 9], have served as an impetus for the initiation of the indicated studies. Earlier research in the nineteen fifties and sixties revealed the effectiveness in experiments of synthetic quinazolines not only with respect to malaria inducers but also in diseases induced by other protozoa [8, I0], as well as bacteria [9, ii] and viruses [12]. An important stage in the development of research on the biological activity of quinazoline compounds was the discovery of the considerable soporific and sedative action of 2methyl-3-aryl-4-quinazolone derivatives [13-16]. Synthesized on the basis of general concepts of the structure of analgesics far which the presence of a tertiary nitrogen atom and a quaternary carbon atom in the B position relative to it is characteristic [17], these substances [18] stimulated an extensive search for pharmacologically active quinazoline compounds. In the last 10-15 yr the search for quinazoline medieinals has been characterized by significant advances. Whereas only two quinazoline preparations, viz., the soporific and anticonvulsive agent methaqualone [2-methyl-3-(o-methylphenyl)-4-quinazolone] and the diuretic quinethazone (6-sulfamido-7-chloro-l,2,3,4-tetrahydro-4-quinazolone) [19], were used in medical practice in 1968, 50 quinazoline derivatives were being used in medicine in 1980 [20]. The preparations of this chemical class include medicinals with the most diverse types of biological action, viz., soporific, sedative, tranquilizing, analgesic, anticonvulsant, antitussive, myorelaxant, antirheumatic, hypotensive, antiallergic, bronehodilating~ antidiabetic, oholagogue, diuretic, cytostatic, antimalarial, spermatoeidal, etc. [20, 21]. A broad spectrum of chemotherapeutic activity (antiprotozoal, antifungal, antibacterial, and antivirus) in conjunction with anti-inflammatory action has been observed for 2-styryl-4aminoquinazoline derivatives [22-27]. The advances in the search for biologically active quinazoline compounds and medicinal preparations created on the basis of them have been reflected in several hundred patents that have been published in this period (see a previous review [28]) and in a large number of original papers and series of published reviews [4, 19, 20, 28-31]. Unfortunately, because of the volume and diversity of the general material on biologically active quinazoline compounds~ the more specific problem of the investigation of quinazoline cardiovascular agents has not been sufficiently completely reflected in these reviews. This served as the basis for the selection and correlation of the data on this important problem. Medicinal preparations that lower the arterial pressure [32, 33] occupy an important position among cardiovascular agents. In series of quinazoline derivatives the search for substances of this type was begun after the detection in the course of pharmacological screening of the hypotensive activity of 4-quinazolones that have a glycine amide or 8-alanine amide residue in the 3 position [34]. Unsubstituted 4-quinazolone and its derivatives with various substituents in the I, 2, and 3 positions and in the benzene fragment of the molecules have also been studied to determine the relationship between the structure and the biological activity in the indicated direction [35]. Most of the tested substances in the case

Formation of H(n=4) and CH(A2Δ) by the Electron Impact Dissociation of Benzene, Pyridine, and Pyrazine

Abstract Benzene, pyridine, and pyrazine were excited by electron impact (0–70 eV) under low pressure conditions. In the wavelength region of 250–510 nm, emissions from H, CH, C2, and CN (except for benzene) fragments were observed. Formations of H(n=4) and CH(A2Δ) from benzene, pyridine, and pyrazine were investigated. The appearance potentials for the hydrogen Balmer β emission were determined to be 19.5±1.0 eV in benzene, 19.7±1.0 eV in pyridine, and 19.6±1.0 eV in pyrazine. The appearance potentials for the CH(A-X) emission were also determined to be 12.7±1.0 and 21.4±1.0 eV in benzene, 20.1±1.0 eV in pyridine, and 18.5±1.0 eV in pyrazine. No emissions from the excited parent species of pyridine and pyrazine were observed.

The structure sensitivity of cyclohexane dehydrogenation and hydrogenolysis catalyzed by platinum single crystals at atmospheric pressure

The dehydrogenation and hydrogenolysis of cyclohexane catalyzed by platinum single-crystal surfaces has been investigated at total reactant pressures of 115 to 760 Torr and temperatures of 533 to 573 K. The flat (111), stepped (557), and kinked (25, 10, 7) and (10, 8, 7) surfaces used in this study were characterized in ultrahigh vacuum by low-energy electron diffraction and Auger electron spectroscopy, before and after reaction experiments. Benzene, cyclohexene, n-hexane, and alkane fragments with carbon number less than 6 were observed as reaction products. The rate of dehydrogenation to benzene on the four surfaces increased in the order (111) < (557) < (10, 8, 7) < (25, 10, 7). On the other and, the hydrogenolysis rates and the rate of cyclohexene production were highest on the (111) surface. In general, the reaction rates decreased with increasing reaction time. The decrease of the dehydrogenation rates was due to reversible product inhibition by benzene, as well as the irreversible adsorption of tightly bound carbonaceous deposits. The hydrogenolysis rates did not exhibit product inhibition and decreased solely as the result of the irreversibly adsorbed carbonaceous species. The strength of inhibition by benzene increased in the order (25, 10, 7) < (10, 8, 7) < (557) < (111). These high-pressure results using single-crystal catalysts are compared to similar studies previously performed at pressures of less than 10 −5 Torr. A comparison is also made to studies by others using dispersed platinum catalysts.

ChemInform Abstract: PHOTOELECTRON SPECTROSCOPY OF BENZOPHENONE, ACETOPHENONE AND THEIR ORTHO‐ALKYL DERIVATIVES

Abstract The photoelectron spectra of benzophenone, acetophenone and their alkyl derivatives were measured. The photoelectron bands are discussed in the light of the influence of the molecular geometry. In benzophenone the π conjugation between the two benzene rings is the main factor determining the splitting of the original benzene orbitals. The deviation from the coplanarity between the two benzene rings accounts well for the observed effects. In the ortho -alkyl substituted compounds the strong steric inhibition of resonance due to the substituents allows their spectra to be discussed in terms of overlapping ionization of the two isolated benzene fragments. In the acetophenone derivatives the effects of alkyl substitution split the low energy overlapping band system of the acetophenone. Ionization energy values estimated through Heilbronner's relationship agree with the experimental findings for the n and π ( a 2 ) ionization.

Photoelectron spectroscopy of benzophenone, acetophenone and their ortho-alkyl derivatives

The photoelectron spectra of benzophenone, acetophenone and their alkyl derivatives were measured. The photoelectron bands are discussed in the light of the influence of the molecular geometry. In benzophenone the π conjugation between the two benzene rings is the main factor determining the splitting of the original benzene orbitals. The deviation from the coplanarity between the two benzene rings accounts well for the observed effects. In the ortho-alkyl substituted compounds the strong steric inhibition of resonance due to the substituents allows their spectra to be discussed in terms of overlapping ionization of the two isolated benzene fragments. In the acetophenone derivatives the effects of alkyl substitution split the low energy overlapping band system of the acetophenone. Ionization energy values estimated through Heilbronner's relationship agree with the experimental findings for the n and π ( a 2) ionization.

The diels-alder chemistry of 1-vinyl-2-pyridones

The Diels-Alder chemistry of a series of 1-vinyl-2-pyridones using a variety of dienophilic species including dimethyl acetylenedicarboxylate, benzyne, maleic anhydride and methyl vinyl ketone has been explored in order to determine the generality of this method for generation of N-vinylisoquinuclidines. In general, the cycloaddition reactions lead to modestly high yeilds of the azabicyclooctane products. In the course of these studies, we noted that retro-Diels-Alder reactions of N-vinylisoquinuclidienones lead to generation of N-vinylisocyanates and a benzene fragment while the corresponding mono-unsaturated isoquinuclidenones form the corresponding pyridones by elimination of an ethylene unit. Lastly, the regio- and stereochemical courses for the π2+ π4 addition reactions of methyl vinyl ketone and 1-vinyl-2-pyridones were investigated. The major products from these reactions appear to result from reaction pathways predicted to be of low energy using first-order molecular orbital methods.

ChemInform Abstract: UV‐SPECTRA OF N‐VINYLPYRROLES

The effect of the structure and the medium on the position and intensity of the absorption bands in the UV spectra that attest to the presence of a single conjugation system in N-vinylpyrroles is thoroughly analyzed. The tendency for a reduction in the intensity of the conjugation (disruption of the coplanarity) is appreciable as branching of the alkyl group in the 2 position increases. A pronounced interaction of the benzene and ethylene fragments through the pyrrole ring is observed.

UV spectra of N-vinylpyrroles

The effect of the structure and the medium on the position and intensity of the absorption bands in the UV spectra that attest to the presence of a single conjugation system in N-vinylpyrroles is thoroughly analyzed. The tendency for a reduction in the intensity of the conjugation (disruption of the coplanarity) is appreciable as branching of the alkyl group in the 2 position increases. A pronounced interaction of the benzene and ethylene fragments through the pyrrole ring is observed.

Electronic effects in cations of aza-aromatic compounds

The ionization constants of quaternary salts of hydroxy derivatives of quinolinium and benzo[h]quinolinium ions correlate satisfactorily (r=0.99, s=0.07) with the σj constants calculated by a modified F,M method. Correlation analysis makes it possible to assume that the electron distribution in the benzene fragments of the investigated cations is determined by the electrostatic effect of the quaternized nitrogen atom and direct polar conjugation of the hydroxyl group with it.

Reactions of [14]annulene and dehydro[14]annulene with organotricarbonylchromium complexes: crystal and molecular structures of hexacarbonyl-trans-6a,12a-dihydro-octalenedichromium(0̄), tricarbonyl-1,4-dihydrophenanthrenechromium(0), and tricarbonylphenanthrenechromium(0)

The crystal structures of the title compounds have been determined from X-ray diffractometer data by Patterson and Fourier methods. Hexacarbonyl-trans-6a,12a-dihydro-octalenedichromium(0), (I), triclinic, space group P, Z= 1, a= 11·33(1), b= 7·10(1), c= 9·67(1)A, α= 102·1(1), β= 135·1(1), γ= 100·1(1)°.Tricarbonyl-1,4-dihydrophenanthrenechromium(0), (II), monoclinic, space group P21/n, Z= 4, a= 8·649(3), b= 12·256(6), c= 10·915(4)A, β= 95·4(1)°. Tricarbonylphenanthrenechromium(0), (III), monoclinic, space group P21/c, Z= 4, a= 8·64(4), b= 11·69(4), c= 13·95(5)A, β= 101·8°. The structures were refined by least squares to R 0·103 [(I). 693 reflections], 0·084 [(II), 1456 reflections], and 0·050 [(III), 1898 reflections].(I) has Ci symmetry with two Cr(CO)3 moieties bound to the triene fragments of the dihydro-octalene ring. In (II) the Cr(CO3) is symmetrically bound to a benzene fragment of 1,4-dihydrophenanthrene. The results for (III) are compared with those obtained for an orthorhombic modification.