Isobenzopyryliumsalts: VII—13C n.m.r. shifts of 1-arylisobenzopyrylium salts and correlation with Hammett parameters

The signal identifications of isobenzopyrylium salts has been achieved on the basis of proton broad-band and off-resonance decoupled ¹³C n.m.r. spectra of twelve different 1-arylisobenzopyrylium salts and eight model compounds. From the ¹³C shifts valuable information about pK values, the aromatic character and the conjugative effects of isobenzopyrylium salts was obtained.     

Biosynthesis of cytochalasans. Part 4. The mode of incorporation of common naturally-occurring carboxylic acids into cytochalasin D1.

Utilization of sodium [1-¹⁴C]-, [2–¹⁴C]-, and [1,2-¹³C]-acetates, [1-¹⁴C]-, [1-¹³C]-, or [2-¹⁴C]-propionates, [1-¹⁴C]-or [2-¹⁴C]-malonates, of [1-¹⁴C]- or of [1-¹⁴C]-myristic acid, or of [1-¹⁴C]- and [1-¹⁴C]-palmitic acid in the biosynthesis of cytochalasin D ( 1 ) by Zygosporium masonii was determined by degradation studies or by carbon magnetic resonance spectroscopy. The precursors were incorporated primarily via the acetate-malonate pathway to generate 1 from nine intact acetate units, eight of which are coupled in a head to tail fashion to form the C₁₆-polyketide moiety.     

The ESR. Spectrum of the Radical Anion of 1,1,2,2,9,9,10,10-Octafluoro [2.2]paracyclophane

The radical anion of 1,1,2.2,9,9,10, 10-octafluoro[2.2]paracyclophane ( 1 ) has been generated by electrolytic reduction of 1 in 1,2-dimethoxyethane (tetrabutylammonium perchlorate as the supporting salt). The hyperfine coupling constants of the eight ¹⁹F-nuclei and the eight protons, a_f = 3.35 and a_H ≈ 0.10 mT, are qualitatively reproduced by INDO. calculations. According to these calculations, the singly occupied orbital of 1 ^? can be represented by an A_g-combination of two ‘symmetric’ benzene LUMO's, with a substantial transfer of spin population into the 2s-AO's of the F-atoms. Line-width alternation in the ESR. spectrum of 1 ^? indicates an ion pairing of the radical anion with its counter-ion Bu₄N^?. The energy barrier to the migration of the cation between two equivalent sites at the radical anion is determined as 14±2 kJ/mol.     

Carbon-13 NMR of polycyclic aromatic compounds. 1—Methoxybenz[a]anthracene-7, 12-diones

Benz[a]anthracene-7, 12-dione, eight monomethoxybenz[a]anthracene-7, 12-diones and two dimethoxybenz[a]anthracene-7, 12-diones were analyzed by ¹³C and ¹H NMR. All ¹³C and ¹H resonances have been assigned. Substituent effects on the ¹³C chemical shifts are discussed.     

Studies on the charge transfer complex and polymerization. XVI. Spontaneous copolymerization of cyclopentene and sulfur dioxide

The alternating copolymerization of cyclopentene and sulfur dioxide was studied. It takes place spontaneously at ?15°C. The rate of copolymerization in toluene was found to be proportional to [CPT]³ and [SO₂]² with the overall activation energy of 16.5 kcal/mole. Terpolymerizations with eight different third monomers were carried out to examine the character and behavior of the copolymerization system of CPT and SO₂. However, the polymerizations with styrene and methyl methacrylate as the third monomers were found to be extraordinary, in that all the three components are not incorporated into the polymer chain.     

Stereoselective synthesis of C-tetrasubstituted azabicyclo[X.3.0]alkane amino acids

By a stereoselective alkylation approach a synthesis of eight enantiopure, sterically constrained C^α-tetrasubstituted azabicycloalkane amino acids was carried out.     

Two New Indole Alkaloids from Tabernaemontana hystrix Steud. (Apocynaceae)

Two new monoterpene indole alkaloids named ibogamine‐7,8‐dione ( 1 ) and 12‐methoxyvoachalotine ( 2 ), and eight known ones, coronaridine ( 3 ), coronaridine hydroxyindolenine ( 4 ), 5‐oxocoronaridine ( 5 ), 3‐oxocoronaridine hydroxyindolenine ( 6 ), 3‐oxocoronaridine ( 7 ), vobasine ( 8 ), ibogamine ( 9 ), and olivacine ( 10 ), were isolated from a CH₂Cl₂ extract of the root bark from Tabernaemontana hystrix. The structures of the compounds were elucidated on the basis of spectroscopic data analyses, mainly ¹H‐ and ¹³C‐NMR, including 2D experiments (¹H,¹H‐COSY, HMBC, and HMQC).     

13C NMR spectra of natural products. 2—eudesmanolides

The ¹³C NMR spectra of eight eudesmanolides have been measured and the chemical shifts assigned. Among the compounds studied are the naturally occurring α-cyclocostunolide, santamarin, arbsculin A and reynosin.     

Thermodynamic properties of peptide solutions. Part 15. Partial molar isentropic compressibilities of some glycyl dipeptides in aqueous solution at 15 and 35°C

The partial molar isentropic compressibilities at infinite dilution,K _s,2 ^o , have been obtained for eight glycyl dipeptides of sequence gly-X (X is an amino acid) in aqueous solution at the temperatures 15 and 35°C. The results have been combined with those obtained at 25°C, that were reported earlier, to evaluate the temperature dependences ofK _s,2 ^o for the dipeptides in the temperature range 15 to 35°C. TheK _s,2 ^o values for all the dipeptides are negative and increase (become more positive) with an increase in temperature. The slopes of the temperature dependences ofK _s,2 ^o for the dipeptides with typically hydrophobic side-chains are significantly larger than those for dipeptides with hydrophilic side-chains.     

Holo‐ and Hemidirected Coordination Spheres in a Novel Three‐Dimensional Polymeric KIPbII Heteropolynuclear Complex: X‐Ray Crystal Structure of [KPb(AcO)2(SCN)]n

A novel three‐dimensional polymeric K^IPb^II heteropolynuclear complex, [KPb(AcO)₂(SCN)]_n, with mixed acetate and thiocyanate ligands, has been synthesized and characterized. Its single‐crystal X‐ray structure (Fig. 1) shows three types of K⁺ ions with coordination numbers of seven, and three types of Pb²⁺ ions with coordination numbers of eight, eight, and nine, respectively. The Pb centers (Pb(1) and Pb(3); Fig. 1) with coordination numbers of nine and eight, respectively, possess stereochemically ‘inactive’ electron lone pairs, and the coordination sphere is holodirected. However, the arrangement of O‐, N‐, and S‐atoms for the eight‐coordinated Pb(2) suggests a gap or hole in the coordination geometry around this atom. This ‘hole’ is possibly occupied by a stereochemically ‘active’ electron lone pair of Pb(2), and its coordination sphere is, thus, hemidirected.     

Electronic rearrangements during chemical reactions. II. Planar dissociation of ethylene

The direct dissociation of ethylene into two methylenes is studied along the least motion reaction path by means of an ab initio multiconfiguration self-consistent-field (MCSCF ) calculation. All eight configurations arising from those valence orbitals that form the CC bonds, seven of them singlet coupled and one triplet coupled, are taken into account. The HCH bond angle is optimized along the entire reaction path. Separate MCSCF optimizations are carried through for the lowest two states of ¹A_g symmetry. The (¹A_gσ²π²) ethylene ground state dissociates into two (³B₁σπ) ground-state methylenes. The (¹A_gσ²π*²) excited state of ethylene dissociates into two (¹A₁σ²) excited methylenes. It is established that both these dissociations proceed without any barrier in the energy curve. In the ground state, where orbital symmetry is conserved, the π-bond breaks before the σ-bond, and the calculated heat of reaction agrees within 6 kcal/mol with the experimental value. In the excited state, where orbital symmetry is not conserved, the nonbonded repulsion between methylene σ₂ lone pairs is found to blend into the antibonding character of the excited ethylene, yielding an energy curve that is everywhere repulsive. However, the variation of the HCH angle during the dissociation process is not simple, initially it expands and subsequently it contracts. Quantitative analytical approaches are developed which furnish conceptual interpretations of the orbital changes and configurational changes along the reaction path.     

The size distribution of210Po in the atmosphere around Mt. Sakurajima in Kagoshima prefecture, Japan

The concentration and size distribution of²¹⁰Po in particulate matters in the atmosphere were measured around the active volcano, Mt. Sakurajima in Kagoshima prefecture, Japan. The samples were collected eight times at four sampling points for the period from June 1994 to January 1996. The highest concentration of²¹⁰Po was 2940 μBq/m³ at Akamizu located 2 km away from the crater of Mt. Sakurajima. The²¹⁰Po concentrations decreased with the increase of distance from Mt. Sakurajima. The size distribution curves of²¹⁰Po in the particulate matters showed that²¹⁰Po is usually condensed to fine particles smaller than 2 μm in diameter. In addition, it was suggested that the²¹⁰Po concentration in particulate matters collected at Akamizu was affected by the wind direction over Mt. Sakurajima.     

Multiresidue Analysis of Pesticides in Environmental Waters by Capillary Electrophoresis Using Simultaneous UV and Electrochemical Detection

A rapid multiresidue method has been developed for the analysis of eight pesticides (triazines, triazinones and ureas) in environmental waters. A simple end‐column electrochemical detector was used in combination with an available commercial capillary electrophoresis instrument with UV detection. The determination of these pesticides using micellar electrokinetic capillary chromatography (MEKC) with dual electrochemical and UV detection is the first time reported. In both detection systems, a linear range was obtained for the eight pesticides, concentrations lower than 5.0×10^?5 mol L^?1, in 0.020 mol L^?1 boric acid at pH 8.3 and containing 0.025 mol L^?1 of sodium dodecylsulfate, to obtain selectivity in the additional separation by micellar distribution process. Under these conditions a lower detection limit than 2.0×10^?6 mol L^?1 (0.15 pmol of pesticide) was achieved for the most of them. The eight pesticides are resolved in less than 14 min.     

A Study on the Intramolecular Mitsunobu Reaction of N6‐(ω‐Hydroxyalkyl)adenines

The cyclization of N ⁶‐(ω‐hydroxyalkyl)adenines with a N⁶H‐group leads to N⁶,N1 ring closure regardless of the method of the cyclization that was used. Five‐membered to eight‐membered rings were obtained using NBS/PPh₃; however, under Mitsunobu conditions, the eight‐membered fused purine was not formed. Surprisingly, the cyclization of N ⁶‐methyl‐N ⁶‐(4‐hydroxybutyl)adenine only leads to N⁶,N7 ring closure using both methods.     

Solution <Superscript>1</Superscript>H n.m.r. of paramagnetic Co<Superscript>2+</Superscript>complexes with dioxobis(carboxymethyl)tetraazamacrocycles

Paramagnetic shifts in the ¹H n.m.r. spectra were observed for high-spin Co²⁺ complexes with 12--14-membered tetraazamacrocycles incorporating two amide groups and two pendant carboxymethyl groups. The pseudocontact term due to the dipolar interaction between the metal ion and the resonant protons was calculated on the basis of X-ray structures, and the Fermi contact term due to spin delocalization was determined. The ethylenediamine moiety of the ligand molecule is coordinated in an unsymmetric manner, even in solution, and internal motion (involving conformational change of the macrocyclic frame and exchange of coordinate bonds) is much slower than the n.m.r. observation frequency. In the 12-membered macrocyclic complex Co(L12), three of the eight CH₂ groups fix their orientation in the n.m.r. time scale; in Co(L13) only one CH₂ group fixes its orientation; in Co(L14) all CH₂ groups undergo a rapid reorientation. The facility in internal motion increases with the ring size, and shows a correlation with the chemical stabilities of these Co²⁺ complexes against oxidation; to atmospheric oxygen, Co²⁺(L12) is the most resistant and Co²⁺(L14) is the most susceptible.     

Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCF?MO?LC(LCGO) Methode. IX. Das System (Li2H)−

The system (Li₂H)^? has been investigated ab initio for several nuclear positions, taking all eight electrons into account, using the Allgemeines Programmsystem/SCF ? MO ? LC (LCGO ) Verfahren. A stable molecule was found for the linear symmetric configuration with a bond distance of R_LiH = 3.41 a.u., and a total energy of ?15.3874 a.u., which is about 0.0114 a.u. (0.311 eV, 7.61 kcal/mole) lower than the sum of the comparable SCF energies of the systems LiH and Li^?. The force constant of the symmetric vibration was estimated to be k = 1.64722 × 10⁶ dyn/cm and the frequency to be ω = 1998.9 cm^?1. The results are discussed.     

Synthesis and Configuration of the Eight Diastereoisomeric Racemates of Dactyloxene-B. The relative configuration of dactyloxene-B and -C

The eight possible diastereoisomeric racemates of dactyloxene-B have been synthesized by a non-stereoselective route and their configurations and predominant conformations determined by 360-MHz-¹H-NMR. and 90.5-MHz-¹³C-NMR. spectroscopy. Natural dactyloxene-B and -C are shown to have the relative configuration rel-(2R, 5R, 9S, 10R) and rel-(2R, 5S, 9S, 10R), respectively.     

Etude par Résonance Magnétique Nucléaire de dérivés phosphores. Etude de dithiaphospholanes-1,3,2

The proton NMR spectral analysis of eight different 1,3,2-dithiaphospholanes with various groups attached to the phosphorus atom has been performed. The AA′BB′X (X phosphorus atom) system shows that the two ³J(P? S? C? H) coupling constants have a small magnitude and opposite signs. Using the ³J(HH) values, the torsion about the C₄—C₅ bond has been evaluated. The conformational requirements in the two isomers of the 2 phenyl-4-methyl-1,3,2-dithiaphospholane are also discussed.     

Photoactive Cryptands. Crystal Structure of the Sodium Cryptate of the Tris(phenanthroline) Macrobicyclic Ligand

The crystal structure of the complex [phen · phen · phen] · NaBr · 2 CHCl₃ of the macrobicyclic ligand 1 has been determined. The complex is of cryptate type, the Na⁺ cation being contained in the molecular cavity of 1 and coordinated to all eight N-atoms. The ligand has a propeller shape and interconverts in solution between the two enantiomeric helical forms.     

Synthesis and structures of cobalt(II) complexes of meso-tetraphenyloctaphyrin(1.0.1.0.1.0.1.0)s

Some meso-tetraphenyloctaphyrin(1.0.1.0.1.0.1.0)s and their Co(II) complexes were prepared and characterized on the basis of the ¹H NMR spectra and X-ray crystallography. These octaphyrins have a figure eight structure. The methyl and methylene protons directly bound to the bipyrrole β-position at the crossing point of the figure eight loop were very close to Co(II) and showed their ¹H NMR resonances in the range of 30–300 ppm. The insertion of Co(II) into the octaphyrin with mixed 2,2′-bipyrrole units of different substitution pattern induced transposition of the sterically more congested 2,2′-bipyrrole unit from the crossing point of the figure eight loop to the periphery.