Bibliothek

Notizen: Leaf-gland Pigments: Coleons U, V, W, 14-O-Formyl-coleon-V, and two Royleanones from Plectranthus myrianthus BRIQ.; cis- and trans-A/B-6,7-DioxoroyleanonesFrom leaf-glands of the South-African P. myrianthus (Labiatae) the following diterpenoids have been isolated and their structures established: coleon U, C20H26O5 (6, 11, 12, 14-tetrahydroxy-abieta-5, 8, 11, 13-tetraene-7-one, 2a); coleon V, C20H26O5 (11, 12, 14-trihydroxy-abieta-8, 11, 13-triene-6, 7-dione, 4a); coleon W, C22H28O8 (16(or 17)-acetoxy-6, 11, 12, 14, 17 (or 16)-pentahydroxy-abieta-5, 8, 11, 13-tetraene-7-one, 6); 14-O-formyl-coleon-V, C21H26O6 (14-formyloxy-11, 12-dihydroxy-abieta-8, 11, 13-triene-6, 7-dione, 4b); 7α-formyloxy-6β-hydroxyroyleanone, C21H28O6 (7α-formyloxy-6β, 12-dihydroxy-abieta-8, 12-diene-11, 14-dione, 1a); the already known 6β, 7α-dihydroxyroyleanone (1c) and a dimeric abietane derivative whose structure is not yet elucidated. This is the first record of a co-occurrence of coleons and royleanones in the same plant. In the course of chemical investigations of 4a and 4b the highly oxidized trans- and cis-A/B-6,7-dioxoroyleanones (5a and 5b) were obtained.

Notizen: It is known that the 2l+1 spherical harmonics Ylm can be transformed into cyclically equivalent orbitals, of which only a few examples have so far been given explicitly. In this article the totality of such cyclic sets is derived.It is demonstrated that other kinds of equivalent spherical harmonics do not exist.Finally a set of five equivalent d orbitals related to icosahedral symmetry is introduced.

Notizen: The parameter optimization method of Part I is applied to the exponents of real STOS of first row atoms. In addition to minimum basis ground states, some independently optimized excited states are discussed in the case of Be. Local minima on the energy versus parameter surface are found in 4-configuration functions for the ground state of N. They are not present in either the simpler minimum basis function or in a more complete 8-configuration function.

Notizen: A time independent diagrammatic technique based on the Wick theorem and graphical methods of spin algebras, as outlined in Part I, is applied to a simple open shell case having one unpaired electron in addition to the pure singlet closed shell. Compact explicit expressions for the matrix elements of a spin independent Hamiltonian between conveniently chosen spin symmetry adapted states are given for the ground, mono- and bi-excited configurations.

Notizen: Gaussian orbitals are used to calculate Temple lower bounds for H2+, HeH++, and H3++. Molecular orbitals are constructed from individual Gaussian-type orbitals (GTO) and from GTO contractions adapted for either upper or lower bounds of the hydrogen atoms. The MOS are optimized by minimizing either the upper bound, 〈H〉, or the variance, 〈(H - E)2〉. The best Temple lower bounds achieved by these methods are -0.60336 a.u. for 2+, - 1.06224 a.u. for HeH++, and -0.13003 a.u. for H3++. Comparison is made with other types of molecular orbitals and with the exact wave functions for 2+, HeH++. Analysis of the nuclear cusps is given. A prescription for constructing lower bound molecular orbitals is offered.

Notizen: In this paper static dipole polarizabilities and shielding factors of 3p open-shell atomic systems from A1 to C1 are presented using coupled Hartree-Fock theory in the Roothaan scheme. The calculation was made for the ground as well as for some valence excited states of the ions. A variational approach was adopted to obtain the polarizability values and the results are compared with the existing data wherever possible. The shielding factor values are in good agreement with the theoretical N/Z ratio.

Notizen: New, more accurate, Hartree-Fock limit energies (EHF) for ethane and ethylene are obtained from SCF total molecular energie using Ermler and Kern's procedure. These results, together with EHF values for other small closed shell molecules, are employed to calculate correlation energy (Ec) contributions to reaction heats. Cancellation to within 98% of the total Ec involved, and often to more than 99%, is found for a wide variety of chemical reactions, which strongly suggests that there are systematic regularities in the contribution to Ec from the different kinds of electron pairs in the valence shell. Assuming trictly localized pairs occupying orbitals having strongly directional character, Ec for the valence shell is evaluated in terms of Ec per lone pair, Ec per X—H bond, and Ec per X/X shared pair for Ne and for molecules containing first row atoms, where X is C, N, O, and F.

Notizen: The Hartree-Fock and first natural spin determinants were compared as reference determinants for calculating various one-electron properties such as ρ(0), 〈½∇〉, 〈r-2〉,…, 〈r3〉, and r-112〉. Calculations were made on various small atoms and their positive and negative ions. For nearly all the expectation values studied, the first natural spin orbital determinant gave consistently superior results. In particular, the Hartree-Fock functions gave markedly inferior results for some long range properties such as the magnentic susceptibilities of negative ions. The major correlation error in the expectation values is primarily an orbital effect which may be accounted for by including correlation terms in the one-particle Hamiltonian. Such approximate Brueckner or best overlap orbitals should reproduce most one-electron expectation values accurately.

Notizen: We describe an attempt to use the AMO method for the investigation of insulator metal transitions. One of the main features of the calculation is that it permits an extension of the AMO method to finite temperatures.The ability of the model to account for such transitions is emphasized for the special case of linear antiferromagnetic systems. We discuss possible generalizations by pointing out that there exists a connection with Peierls' model.

Notizen: The theory for treating exchange interactions between atoms or molecules as a perturbation, which was first propoed by Jansen, is extended to general cases by the use of the group algebraic technique and a nonorthogonal basis set. As a result, a new expresion for the perturbation ket and energy of each order is obtained. A comparion of the expression with those presented by other investigators is made.

Notizen: Momentum densities obtained from the Heitler-London (HL) wave functions for diatomic molecules and those from the corresponding valence-bond (VB) wave functions including ionic terms are compared. In each case they shown maxima in the direction perpendicular to the bond. However, the dependence of momentum densities on mutual orientations of the two electronic momenta is quite complex in the latter case. The improvement in the Compton profile on including the ionic terms is illustrated with the example of H2. The momentum denmsities obtained from the VB wave function constructed from orthogonalized atomic orbitals (OAO) have also been examined. The HL wave function with OAOS leads to the same momentum distribution as the repulsive state HL wave function constructed from overlapping AOS.

Notizen: A unitary group formulation of the many-electron problem is employed to give explicit representations of state vectors which are convenient for the discussion of progerties derived from propagatorcalculations. New results are obtained concerning the nature of various random-phase-like approximations and ground state representatives are generated from consistency requirements for the spectral resolution of the polarization propagator. The explicit solution admits the calculation of ground state average values for arbitrary operators and a variational upper bound to the ground state energy.

Notizen: The invariance question int he CNDO and INDO levels of approximation is discussed with particular reference to one-center and two-center two-electron integrals and rotation of molecule-fixed coordinate axes. It is shown that asufficient condition for rotational invariance for the cone-center two-electron integrals is Jμμ = Jμμ, +2Kμμ, where J and K are the Coulomb and exchange integrals over orbitals μ μ′ with the same azimuthal quantum number. CNDO and INDO procedures, which explicitly employ Löwdin's orthogonalized basis set of atomic ortbitals (OAO) and differentiate between s-, p-, and d-orbitals on an atom in calculating various integrals, have also been examined in relation to the rotational invariance requirement. An expression which satisfies rotational invariance for two-electron Coulomb repulsion integrals over OAOS is also given.

Notizen: We investigate the total spin structure of an approximate localized-site wave function for a collection of paramagnetic sites interacting so as to favor a singlet ground state. As the number of sites becomes infinite we obtain the distribution of weights of the different symmetry components of the localized site wave function; further, although only a very small fraction of such nonsymmetric wave functions is actually singlet, we find that it generally yields the same bulk property expectation values as its singlet-projected component.

Notizen: By use of the pseudo-inverse matrix technique the generalization of the Löwdin orthogonalization, given by Kashiwagi and Sasaki, is shown to be valid in a case of singular metric matrices for two basis sets of functions. The application of the same idea to the inverse vibrational problem brings about new procedures for solving this problem in an iterative way.

Notizen: Klein has pointed out that des Cloizeaux's orthonormalization is just another formulation of Löwdin's symmetric orthonormalization. We demonstrate that des Cloizeaux's formulation is convenient for theoretical discussions and that it is intimately connected with polar decomposition--which is a generalization to operators of the fact that any complex number z can be written r exp (iθ) where r is positive and θ real. We generalize two other properties for z and find an interpretation of the Carlson-Keller theorem. Recently Lathouwers found that Löwdin's canonical orthonormalization leads to the eigenvectors of a positive operator. This operator is des Cloizeaux's. We discuss some variational theorems on this background and find the Courant-Hilbert-Löwdin “measure of linear independence” from a simple least squares consideration, closely related to Lathouwers' results.An orthonormalization due to Schweinler and Wigner (1970) is observed to be Löwdin's canonical. The Schweinler-Wigner maximum characterization is referred to a simple general theorem, which also implies a new maximum characterization.In Sections 6 and 7 we consider transformation to an effective Hamiltonian from the point of view of polar decomposition and symmetric orthonormalization. It turns out that the polar part of Bloch's transformation is des Cloizeaux's. The characterizations of this by both Klein and Jørgensen are visualized in a simple way.

Notizen: The method of fractional parentage is extended to the general case of mixed configurations in arbitrary nonsimply reducible groups, G ⊂ SO(3). Particular attention is devoted to the calculation of coefficients of fractional parentage (CFP) and expressions are provided for the matrix elements of F and G type operators between N electron functions.

Notizen: An exact collision theory of unimolecular and bimolecular gas phase reactions is derived from a general quantum-mechanical formulation of reactions rates based on the assumption that the reactants are in thermal equilibrium. In this way the quantum corrections to the classical collision theory expressions are rigorously defined. Approximate formulas for these corrections make it possible to determine well the temperature ranges within which the classical and the semiclassical approximations are valid. A comparison is made between the collision and the transition state theory with emphasis on some conceptual difficulties of the latter in treating the simple decomposition and recombination reactions. It is shown that in the classical (high temperature) limit these theories are incompatible except when the reaction coordinate is entirely separable (i.e., when the transition state theory is no longer useful).

Notizen: Further developments of a recent semiempirical, variable effective charge MO theory for calculation of ionization potentials (IP) and electron affinities (EA) as energy differences between separately minimized ground and ionized states are reported. The method is extended to adiabatic as well as vertical IPS and EAS by including core repulsion and σ bond compression energies in the total energy. The method is generalized to heteroatomic systems and is simplified by neglecting penetration integrals. As before, only two molecular parameters, the vertical IPS of benzene and naphthalene, are required to set the magnitude of the σ changes associated with the polarization of the core during loss or gain of a π charge. Twenty-seven aromatic molecules are studied, including polyacenes, condensed ring compounds, nonbenzenoids with five and seven member rings, nonplanar molecules, and heteroatomics with N+, as in pyridine, N+2, as in pyrrole, and O+2, as in furan. The results are within 0.2 eV of the photoelectron spectroscopic vertical IPS and the predicted vertical-adiabatic separation is consistent with the shape of the first band. The calculated EAS are within 0.2 eV of the observed values.The calculation is used to predict the IP and EA of the ionic photosensitizing cyanine dye, pinacyanol. The values obtained are consistent with the latest measured IP and EA of the adsorbed dye, corrected for surface and aggregation polarization effects.

Notizen: A full set of harmonics which are at the basis of all irreducible representations of the cubic point group and having order l ≤ 16 has been calculated in terms of Cartesian coordinates. Due to their complication, former calculations of harmonics in Cartesian coordinates for half of the irreducible representations did not exceed l = 6. The method presented in this paper is a modification of that originally given by Von der Lage and Bethe; it can be readily applied to the calculation of harmonics of arbitrary order for any irreducible representation of the cubic point group.

Notizen: Following Kohn (reference 4), Schlosser and Marcus (reference 3), and Weare and Parr (reference 2), an energy functional is defined for a molecular problem which is stationary in the neighborhood of the exact solution and permits the use of trial functions that are discontinuous. The functional differs from the functional of the standard Rayleigh-Ritz method in the replacement of the usual kinetic energy operators T̂(μ) with operators T̂′(μ) = T̂(μ) + Î(μ), where Î(μ) generates contributions from surfaces of nonsmooth behavior. If one uses the ∇Ψ · ∇Ψ way of writing the usual kinetic energy contributions, one must add surface integrals of the product of the average of ∇Ψ and the change of ∇Ψ across surfaces of discontinuity.

Notizen: A method for calculating the vertical ionization potentials and electron affinities according to their fundamental definition as differences between energies of the singlet ground and doublet ionized states is developed for cyclic hydrocarbons. The method adopts a new approach based on the central idea of a recent ab initio IP and EA calculation in which orbital exponents are optimized for both ground and ionized states. Hence, all the semi-empirical parameters of the MO theory are written as functions of the effective nuclear charge which, in turn, is made self-consistent with the molecular electronic charge distribution of the species. Although the MO theory is developed in the π electron approximation, the changes in the σ electron density, resulting from the loss or gain of a π electron, are explicitly considered in the calculation. The theory is compared to the earlier work of Hoyland and Goodman and tested against the first five polyacenes and on the condensed ring aromatics phenanthrene, pyrene, and perylene. Except for perylene, the results are in close agreement with the latest photoelectron spectroscopic measurements.

Notizen: A computational procedure which introduces some electron correlation into quantum mechanical calculations is described. Diverse applications are given. Among these, the method gives values of 65.6 kcal/mole for the dissociation energy of LiH, 62.0 kcal/mole for the ring-opening energy of cyclopropane, and 9.123 × 155 dynes/cm for the O-H stretching force constant of H2O. These results, and others given, suggest that our procedure has great potential and provides a very economical method for introducing electron correlation into a wave-function.

Notizen: Parseval's identity for orthonormal bases in Hilbert space is generalised to characterise uniquely biorthonormal bases among biorthonormal systems.

Notizen: This paper studies the decay, due to the spin-lattice coupling, of two ½ spins with slightly different Zeeman energies when the lattice is thermally excited. The analysis is based on obtaining, by means of the Nakajima-Zwanzig projection operator technique, an equation for the evolution of the reduced density operator of the spin system which manifests the influence of one spin on the relaxation process of the other. The zero-order solutions obtained for the evolution of the expectation values of the spin dynamics operators are essentially equivalent to the Bloch equations; higher order solutions are also obtained.

Notizen: A new algorithm for the computation of the density of states distributions of stereoregular polymers is presented. It is related to the Gilat-Raubenheimer technique for three dimensional systems. Its application to polyethylene is briefly described.

Notizen: Basic Metals. II. Protonation and Alkylation Reactions of π-Cyclopentadienyl-metal-bis(tert.-phosphite) ComplexesFür «Basische Metalle. I» siehe [1].The complexes C5H5Co[P(OR)3]2 (R = CH3, C2H5) and C5H5Rh[P(OR)3]2 (R = CH3, C2H5, C6H5, C6H4-o-CH3) react with electrophilic agents E+, e.g. H+ and CH3+, to give [C5H5ME(P(OR)3)2]+. Salts of these cation have been isolated with BF4- and PF6- as the anions. The formation of compounds with direct M-H and M-CH3 bonds points to the pronounced Lewis-base properties of the metal atom in the starting complexes. The NMR. data of the cations [C5H5MH(P(OR)3)2]+ and [C5H5MCH3(P(OR)3)2]+ will be discussed.

Notizen: The synthesis of phenathrenes substituted by nitrogen and oxygen atoms in position 9 and 10 by photolysis of 4,5-diphenyl-oxazol-2-ones (cf. Scheme 4) is described. Moreover an improved general procedure for the synthesis of benzoins in aprotic solvent (tetra-t-butylammonium cyanide in DMF/DMSO) is developed.

Notizen: 1H-NMR.-spectra of a series of alloxazines and isoalloxazines and certain cationic derivatives were investigated (Tab. 2 and 5). Unequivocal assignment of all resonance signals was achieved in some compounds by selective deuteriation also by double resonance technique. The coupling constants were verified by computer simulation. Considerable enhancement of the signals due to H-C(9) and H-C(6) is found on decoupling of H3C-C(7), H3C-C(8) and H3C-N(10), resp. These results are compared with those obtained with FAD. The methyl resonance signal of the H3C-C(7) compounds give doublets due to coupling with H-C(6). The difference in chemical shifts observed upon successive formal introduction of methyl groups into the benzene nucleus of (iso)alloxazines indicates that the molecule becomes less planar thereby. The pyrimidine ring of (iso)alloxazines does not contribute to the ring current except by indirect effects via the carbonyl groups. The experimental data are compared with published MO calculations and discussed.

Notizen: A series of isoalloxazine and alloxazine derivatives have been investigated by 13C-NMR. The synthesis of selectively 13C-enriched derivatives made it possible to assign unambiguously the signals due to the quaternary carbon atoms at position 4, 4a and 10a of the isoalloxazine ring system. The assignment of the other resonances was ensured by the use of selectively deuteriated and chemically modified compounds as well as by decoupling techniques. The assignments differ in part from those published by Breitmaier & Voelter [2] on FMN and FAD. The solvent dependence of the resonances has been studied in dioxan/water mixtures. The experimental data are compared with published MO calculations and discussed.

Notizen: The Different Behaviour of Lysine Methyl Ester and its N,N′-Diacetyl Derivative under Electron ImpactThe base peak in the spectrum of lysine methyl ester is due to the fragment ion C5H10N (m/e 84), for which the cyclic structure g (Scheme 1) is deduced. During its formation from the [M-COOCH3]-ion an equilibration of both nitrogen atoms takes place (ion c, Scheme 1). The cyclic nature of ion m/e 84 is in agreement with the intensity of the corresponding ions in the spectra of homologues of lysine methyl ester (Fig. 1). Although in comparison with lysine methyl ester (1) N,N′-diacetyl-lysine methyl ester (7) shows the same general fragmentation pathway with formation of the ions [M-COOCH3] and [M-COOCH3-H2NCOCH3] (m/e 126), the exact fragmentation mechanism proves to the different. Two mechanisms are discussed for the formation of the ion m/e 126 from 7 (Schemes 2 and 3). The results are based on the spectra of labelled derivatives.

Notizen: The pKa* values for nine acyclic, mono- and bicyclic α-, β- and γ-(trimethyl)ammonio acids, 1(α-γ), 2(α-γ) and 3(α-γ), respectively, have been measured in 50% aqueous ethanol. The comparison of these values with those for the nine homomorphous α-, β- and γ-acids, 4(α-γ), 5(α-γ) and 6(α-γ), respectively, permits an evaluation of the steric effect of the (trimethyl)ammonio groups which is super-imposed on their polar effect in the former acids. The pKa* values, corrected for the steric effect, correlate very well with the reciprocal distance between the positive nitrogen atom and the dissociable proton. This confirms our earlier conclusion that the strength of these acids is determined by the field effect of the (trimethyl)ammonio groups only, the inductive model failing to account for the results. The distinction between two different transmission mechanisms for the polar effect therefore becomes unnecessary, the inductive model appearing as an atomistic description of the field effect.

Notizen: The configurations of a series of mono- and bis-Fe(CO)3 complexes of 12-oxa[4.4.3]-propella-2,4,7,9-tetraene (1) and of 11,13-dioxo-12-methyl-12-aza[4.4.3]propella-2,4,7,9-tetraene (7) as well as of a trienic aza-propellane complex have been studied in solution by 13C- and 1H-NMR. spectroscopy. Praseodymium-induced 13C-shifts of the metalcarbonyl carbon atoms and of the central carbon atom of the complexed diene systems are particularly sensitive and useful to prove exo- or endo-configuration of the tricarbonyliron ligand. In addition, H,H- and C,H-coupling constants of the complexes and parent compounds are reported and discussed.

Notizen: Acetals of 1,2,3,4-tetraoxobutane: preparation and structure determination of rac- and meso-2,3,3,4,4,5-hexamethoxy-tetrahydrofuranOxidation of 3,4-dimethoxyfuran with 2 equiv. of bromine at -75° in the presence of triethylamine and methanol leads to a mixture of rac- and meso-2,3,3,4,4,5-hexamethoxy-tetrahydrofuran (cf. Scheme 1, 4 and 5). The structure of the crystalline rac-compound has been determined by X-ray analysis.

Notizen: Synthesis and Transformations of Isoxazolidine-NucleosidesReaction of the oxime 12 with formaldehyde, acetaldehyde or acetone in the presence of methacrylic acid methylester leads in a highly stereoselective 1,3 dipolar cycloaddition of the corresponding nitrones to the protected isoxazolidine ribosides 13, 14, 20, 21 and 26 (Scheme 1 and 2).Using a new, mild procedure to effect detriylation, the cycloaddition products were transformed into the alcohols 16-19, 22-25 and 27.Cleavage of a mixture of the glycosides 16 and 17 yielded the N-unsubstituted isoxazolidine 29 in 65% optical purity while the cleavage of 27 gave optically pure 28.Alternatively, the isoxazolidine ribosides 13, 14, 16-18 and 26 were transformed via reductive cleavage of the isoxazolidine N-O bond and subsequent lactamization into the corresponding pyrrolidinone-ribosides 30, 33, 35, 42, 49 and 50, the ribitolyl pyrrolidinones 31, 34, 36-39 and 43-46 (see Scheme 4) and the ribitolyl isoxazolidine 47.

Notizen: The crystal structure of 5-formyl-6,7-dimethyl-5,6,7,8-tetrahydropterineThe crystal structure of the title compound, a tetrahydropterine, has been determined by X-ray analysis (direct method) and refined with 1579 structure amplitudes to R = 0.054. The crystal system is triclinic, space group P1, with unit cell dimensions a = 7.171, b = 7.255, c = 12.369 Å, α = 100.64, β = 93.32, γ = 98.27°. The tetrahydropyrazine ring exists in a distinctly flattened conformation. The C(13)- and C(14)-CH3-groups possess a cis-configuration with axial position for C(13)-CH3 and equatorial for C(14)-CH3. The carbonyl-group of the N-formyl function has an (E)-configuration.

Notizen: Nucleophilic Substitution Reactions of Hydroxysteroids using Triphenylphosphane/diethylazodicarboxylateNucleophilic substitution reactions by means of the title reagent on various more or less hindered steroid alcohols with suitable nucleophils in benzene is described. It was not possible to run this substitution process in the hitherto used solvent THF. Cholestan-3α-ol (1) was transformed to the 3β-substituted products 3β-benzoyloxy-cholestane (1a) and 3β-azido-cholestane (1b). Testosterone (2) affords with the corresponding nucleophils after short heating in benzene the inverted 17α-substituted products 3a, 3b and 3c. Analogously the 17α-azido-derivative 5a arises from 17β-hydroxy-androst-3-on (4). In the presence of a ketogroup in the substrate a competitive reaction can occur as it is shown in the case of cholestan-3-on (6): the products are the en-hydrazo-dicarboxylate-steroids 7a and 7b. The sterically very hindered 11α-position in 11α-hydroxy-4-pregnen-3,20-dion (8) can be transformed also to the 11β-azide 9a. The substitution of a 6β-hydroxy group in androstane-3β, 6β, 17β-triol-3,17-diacetate (10) to the 6α-azide 11a affords the elimination product 12 as main component. Trans-diaxial vicinal diols such as cholestane-2β,3α-diol (13) give a mixture of the α- and β-oxiranes 14a and 14b.

Notizen: A gas chromatographic method of measuring the olive oil-gas partition coefficients is described. It is based on the relationship existing between the retention time of each substance and its solubility in olive oil used as a stationary liquid phase. The validity of this method has been tested by varying the length of the column, the percentage of liquid phase and the flow rate of the carrier gas. Using this technique, the partition coefficients of 24 hydrocarbons, 8 aliphatic, 6 aromatic and 10 chlorinated, have been determined (see Table 4).

Notizen: The synthesis of mixed-ligand cobalt(III) complexes with (S)-aspartic-N-monoacetic acid ((S)-AMA) and different amino-acids Na[Co((S)-AMA)(AA)] (AA = gly, (R)- and (S)-ala, val, phe, ser and leu) leads to a mixture of cis-N- and trans-N-isomers. These isomers are formed stereospecifically. VIS., CD.- and NMR.-spectra are reported and a proposal is given for the absolute configuration of all the compounds isolated.

Notizen: The cis-N/trans-N interconversion of the title compound containing glycine and (R)- or (S)-leucine has been studied by polarimetric and spectrophotometric techniques. Equilibrium constants were determined on the basis of kinetic and thermodynamic data. It is shown that the chirality of the bidentate amino-acid has a pronounced influence on the cis-trans equilibrium of these systems. Possible mechanisms of the interconversion reaction are discussed.

Notizen: Steric effects on the dissociation constants of acyclic, mono- and bicyclic carboxylic acidsApparent pKa* values for the series of acyclic, mono- and bicyclic acids 1-14 have been measured in 50% (W/W) ethanol (see the Table). The dissociation constants of these acids decrease as the access of the solvent to the carboxylate group is hindered by the rest of the molecule. These results emphasize the importance of solvation in determining acid strength. New or improved syntheses of several of the acids investigated are reported.

Notizen: Two acetylenic steroids, cholest-5-en-23-yn-3β-ol (5) and 26,27-dinorcholest-5-en-23-yn-3β-ol (3), and another unsaturated steroidalcohol, stigmasta-5,23-dien-3β-ol (7), were isolated from the sponge Calyx nicaaensis. The structures of these two acetylenic steroids were established by synthesis. Several attempts to synthesize the marine steroids alcohol calysterol (1), with a cyclopropene-containing side chain, starting from cholest-5-en-23-yn-3β-ol are also recorded. Addition of ethyl-diazo-acetate to the triple bond was performed, but the reduction to the methyl derivative yielded decomposition products.

Notizen: 1H-NMR. behaviour of 1,3-diaryltriazenes in neutral and acidic solventsFormation and decomposition of 1,3-di-aryltriazenes can be studied by 1H-NMR. Triazenes decompose in acidic medium or by addition of isoamylnitrite: in the last case, the spectrum shows emission lines characteristic of the CINDP effect. At -80° the prototropic rate is slow enough to permit the observation of two aromatic systems.

Notizen: Copper(0) does not catalyze the decomposition of dialkylcarbamoyl azides 5a-e but instead it is oxidized to copper(II) while the azides 5 are reduced by uptaking one electron per molecule and eliminating nitrogen. A probable explanation for the formation of the resulting copper(II) diisocyanate diamine complexes 8a, b (see Scheme 2) as well as the other reaction products is given. A mechanism involving a carbamoyl nitrene as well as a Curtius rearrangement can be excluded.

Notizen: The hydroformylation of α-[2H]-styrene in the presence of an asymmetric rhodium-catalyst afforded two optically active isomeric aldehydes. The origin of the asymmetric induction is discussed on the basis of the chirality and the optical purity of the two products.

Notizen: A Note on Methods for the Transformation of 1,2-Dicarboxylic Acids into α, β-Unsaturated Monocarboxylic Acids.A model study using the Diels-Alder adduct of maleic anhydride and butadiene (see scheme 3) exemplifies the conversion of the succinic acid type of structure into α, β-unsaturated carboxylic acids via two complementary fragmentations of 3,6-dioxo-perhydro-1,2-oxazine derivatives.

Notizen: Synthesis of (±)-α-ChamigreneCis- and trans-β-ionol (cis and trans-1) underwent acid catalysed dehydration to a mixture of the tetraenes 2-5 in 70-80% yield (Table 1). Irradiation of this mixtures made the 6-(Z), 8-(Z)-isomer 5 accessible (columns 3 and 4 in Table 1). Pyrolysis of the different mixtures at 170° showed, that both isomers, 3 and 5 respectively undergo electrocyclization to dehydrochamigrene (6). The latter was reduced to α-chamigrene (7) by hydrogen on Lindlar catalyst.

Notizen: Synthesis of 5,6-Dimethyl-4-oxo-1,3,4,5-tetrahydro-imidazo[4,5-c][1,2,6]thiadiazin 2,2-dioxide and 7-Methyl-4-oxo-1H-3,4-dihydropyrimido[4,5-c][1,2,6]thiadiazin 2,2-dioxideThe derivatives of the above heterocyclic ring systems were prepared by reaction of the corresponding o-amino esters with sulfamoylchloride.

Notizen: Studies in Stereochemistry XIV. Diels-Alder adducts in the resin series; action of peracids and acid-catalysed ring opening of epoxidesThe synthesis of Diels-Alder compounds of type 2 with a 17-nor-13(14)-atisène skeleton is described (cf. Schemes 1-3). Depending on the nature and configuration of substituents R1 and R2 on the carbon atoms 15 and 16, an epoxide (24-33) or a ketone (35-38) or a mixture of epoxide, ketone and lactone is obtained by the action of p-nitroperbenzoic acid on the double bond of these adducts (cf. Scheme 4). A simplified reaction scheme is suggested to explain the formation of the various products. In an acid-catalysed reaction, the epoxides isomerize mainly into ketones. Nevertherless, in some cases, dienes (e.g. 52) or hydroxy-γ-lactones of (13R*, 14S*)-configuration (e.g. 50) resulting from the opening of the epoxide ring with retention of configuration were obtained.

Notizen: Bridged helicenes: 3,15-ethano- and 3,15-(2-oxapropano)-[7]heliceneThe title compounds (35 and 33, see Scheme 4) have been synthesized from a common intermediate: 3,15-dimethoxycarbonyl-[7]helicene (26). The conformation of the bridged [7]helicenes (X-ray diffraction) and their 1H-NMR. spectra have been compared to the conformation and 1H-NMR. spectra of [7]helicene and 3,15-dimethyl-[7]helicene (10).

Notizen: On the structure of Papulacandin B, a new antibiotic with antifungal activityStructure 1 has been established for Papulacandin B (C47H64O17), a new antibiotic from Papularia sphaerosperma (PERS.) HÖhnel by means of spectral analysis of 1 and some derivatives and degradation products. Base catalysed hydrolysis of 1 gave the two unsaturated fatty acids 2 and 3 and the spirocyclic diglycosid 4. The structure of 4 was determined by further degradation reactions.

Notizen: Photochemistry of tricyclic β, γ-γ′, δ′-unsaturated ketonesThe easily available tricyclic ketone 1 (cf. Scheme 1) with a homotwistane skeleton yielded upon direct irradiation the cyclobutanone derivative 3 by a 1,3-acyl shift. Further irradiation converted 3 into the tricyclic hydrocarbon 4. However, acetone sensitized irradiation of 1 gave the tetracyclic ketone 5 by an oxa-di-π-methane rearrangement. Again with acetone as a sensitizer the ketone 5 was quantitatively converted to the pentacyclic ketone 6. The conversion 5 → 6 represents a novel photochemical 1,4-acyl shift. The possible mechanisms are discussed (see Scheme 7). The tricyclic ketone 2 underwent similar types of photoreactions as 1 (Scheme 2). Unlike 5 the tetracyclic ketone 9 did not undergo a photochemical 1,4-acyl shift. The epoxides 10 and 14 derived from the ketones 1 and 2, respectively, underwent a 1,3-acyl shift upon irradiation followed by decarbonylation, and the oxa-di-π-methane rearrangement (Schemes 3 and 4). The diketone 18 derived from 1 behaved in the same way (Scheme 5). The tetracyclic diketone 21 cyclized very easily to the internal aldol product 22 under the influence of traces of base (Scheme 5). Upon irradiation the γ, δ-unsaturated ketone 24 underwent only the Norrish type I cleavage to yield the aldehyde 25 (Scheme 6).

Notizen: The silver ion-catalysed ring-opening of 2-t-butyl-1-chloro-1-fluoro-2-methyl-cyclopropane (see Scheme 2) gave the expected mixture of primary and tertiary fluoroalkenols, whereas a tricyclic analog (bornane-spiro-chlorofluorocyclopropane) (see Scheme 3) exclusively underwent a Wagner/Meerwein rearrangement upon ionization to lose finally a proton affording a 2-fluoro-1,4-diene.

Notizen: Synthesis and reactions of 5,6-dideoxy-6-halogeno-α-D-xylo-hept-5-eno-furanurononitrilesThe 5,6-dideoxy-6-chloro-, 6-iodo- and 6-fluoro-3-O-methyl-α-D-xylo-hept-5-eno-furanurononitriles have been prepared, their properties described as well as the methods used for the assignment of the configuration of the geometrical isomers. Some new reactions of the 6-bromo analog (1) of these compounds are reported. For example, when reacted with 2-mercaptoethanol or N,N′-dimethyl-ethylenediamine in the presence of NaOH, 1 gave the corresponding six-membered ring, stereo-isomers of an oxathiane or of a perhydrodiazine respectively. When the base used was Et3N and the binucleophile the N-methyl-ethanolamine or the N,N′-dimethyl-ethylene-diamine the major product was a cyano-enamine which could be hydrolysed to a β-cyanoketone or cyclized to a five-membered ring, an oxazolidine or an imidazolidine respectively.

Notizen: Stereoselective Reductive Dimerisation of α-Cyano-β-(4-pyridyl)acrylic Acid DerivativesCatalytic hydrogenation of the α-substituted β-(4-pyridyl)acrylonitriles 3 and 4 (see Scheme 3) yields via stereoselective reductive dimerization the substituted cyclo-pentene derivatives 7 and 8 (see Scheme 4 and 5) instead of the expected dihydro-products 5 and 6. The mechanism of this reaction is discussed. The structure and relative configuration of 10 have been established by X-ray single crystal analysis.

Notizen: HeIα excited photoelectron spectra of pentatetraene and the inferred ionization energies are reported. The first band has a characteristic Franck-Condon envelope similar to the first photoelectron bands of allene and butatriene. The four bands found below 16 eV ionization energy have been assigned to the X̃2E, Ã2E, B̃2E and C̃2B2 states of the radical cation of pentatetraene by comparison with STO-3G and SPINDO calculations on the cumulene series. The correlation scheme includes the 2s shell ionization energies of ethylene, allene and butatriene. The π-orbital ionization trends of the cumulenes are discussed in the framework of localized orbitals calculated with the STO-3G basis set.

Notizen: Chemical and Pharmacological Studies on Derivatives of Benzo[de]quinoline, IISpirocompounds of type V (12-18) were synthesized by a carbenium ion cyclization reaction of the intermediates 7 and 11, respectively. 7 was prepared from 2-oxocyclopentanepropionic acid via 1, 2, and 4-6; 11 from the same starting material via 1, 2, and 8-10. - The spiro[7H-benzo[de]quinolin-7,1′-cyclohexan]-2′-one 27 and other compounds of type VI could be synthesized from the (1-isoquinolinyl)ethyl-cyclohexanone 25: 25 is hydroxylated to the hydroxyketone 26; treatment of 26 with a mixture of sulfuric acid and oleum gives 27. The structure of 27 has been proved by transformation into the known spirocyclohexane 33. - Aporphine analogues of type VII (38, 39) were synthesized from the cyclic ketone 34 via either the formylketone 35 and its methyl vinyl ketone adducts 36 and 37 or the methyl ethynyl ketone adduct 40. Compound 40 has also been cyclized to the 10-hydroxy-aporphine 42. 9 compounds of the types mentioned have been screened for hypotensive action in rats, and partly in cats and dogs. Only compound 13 · HCl proved to be (moderately) active in rats and dogs.

Notizen: Synthesis of endo- and exo-1,3-dimethyl-2,9-dioxabicyclo[3.3.1]nonaneThe synthesis of a host-specific substance in norway spruce infested by Trypodendron lineatum OLIV. is described (cf. scheme 1 and 2). Alkylation of the acetyl-acetone di-anion (II) with 3-methyl-3-buten-1-yl-bromide (I) followed by sodium boro-hydride reduction yields erythro- and threo-8-methyl-8-nonen-2,4-diol (IV and V) which are separated by chromatography. Their configurations were established by converting them under equilibrium conditions into one (VI) or two (VII and VIII) benzal derivatives. Oxidative cleavage with ozone of the terminal double bond in the erythro diol IV produces a dihydroxy ketone IX which spontaneously cyclizes to endo-1,3-dimethyl-2,9-dioxa-bicyclo[3.3.1]nonane (X). The threo diol V is converted by the same reaction sequence exclusively into exo-1,3-dimethyl-2,9-dioxa-bicyclo-[3.3.1]nonane (XII). Comparison of the NMR. data of the two acetals X and XII with that of the natural product establishes the endo configuration of the latter. A second, more convenient, synthesis of a mixture of the acetals X and XII starting from the bromo-acetal XIII is also reported.

Notizen: Exo- and endo-Tricarbonyliron Complexes of Bicyclic 2,3-Dimethylidene Compounds.The preparation of exo- and endo-tricarbonyliron complexes (exo- and endo-5, -6, -8, and 9) of 2,3-dimethylidene-5-bicyclo[2.2.1]heptene(1), -bicyclo[2.2.1]-heptane (2), -5-bicyclo[2.2.2]octene (3) and -bicyclo[2.2.2]octane (4) is described. The complexes are obtained by thermal reaction of the bicyclic butadienes with di-ironenneacarbonyl in hexane solution. exo- and endo-5 are also formed photochemically from ironpentacarbonyl and 1 in pentane solution at -35°. The structural assignment of exo- and endo-5 and -6 is based on their mass-spectra and on coordination shifts in 1H- and 13C-NMR.-spectra exo- and endo-6 are correlated with exo- and endo-5, respectively, by hydrogenation. Hydrogenation of the uncomplexed double bond in exo- and endo-5 occurs in both complexes from the exo side as shown by deuteration experiments. The free ligand 1 reacts in the same stereospecific manner.

Notizen: It has been possible to submit the crude hexane extract of the barks of a medicinal plant directly to preparative liquid chromatography. A two step solvent elution gave 6 peaks, four of which readily afforded crystalline material. The entire process required 2-3 hours whereas conventional chromatography required ca. 2 weeks.

Notizen: Dysidin, a novel chlorine containing natural product from the sponge Dysidea herbaceaDysidin (1) has been isolated from the marine sponge Dysidea herbacea. It structure has been determined by degradation studies and spectroscopic methods. The synthesis of a degradation product is described. The relative and absolute configuration is established by X-ray diffraction methods.

Notizen: Total Synthesis of Betalainescis-4-Oxo-2,6-piperidinedicarboxylic acid dimethyl ester (10) was transformed (44%) into the semicarbazone of 2,3-dihydrobetalamic acid dimethyl ester (13/14) by a modified Horner-Wittig reagent 12. Oxidation of 13/14 afforded 41% of a mixture of stereoisomers of betalamic-acid-dimethyl-ester semicarbazone (4), key intermediate for the synthesis of betalaine pigments. The utility of 4 in this respect was demonstrated on a small scale by its conversion to the dimethyl ester of indicaxanthine (9, 11%) and to the trimethyl ester of betanidine (7, 87%). Hydrolysis of 7 gave betanidine (6).We further describe the synthesis of the trimethyl ester of an oxidized form of betalamic acid (20/21) as well as model condensation reactions on the carbonyl group of cyclohexanone, cis-4-oxo-2,6-diphenylpiperidine (23) and its N-formyl derivative 27.Reaction of 4-oxo-1,2,3,4-tetrahydro-2,6-pyridinedicarboxylic-acid dimethyl ester (40) with acetic anhydride or with triethyloxonium tetrafluoroborate resulted in O-acylation or in O-alkylation along with dehydrogenative aromatization to yield the derivatives 39 or 42, respectively, of chelidamic acid.

Notizen: Metal Complexes of N-substituted 3-Imino-isoindolinonesThe condensation of 3-imino-isoindolinone 4 and benzimidazoles or benzthiazoles containing activated methyl-, methylen- or aminogroups (5 resp. 6), yields the iso-indolinone-ligands 1 and 2. Metal ions such as Co2+, Ni2+, Cu2+ and Zn2+ form (1:2)-complexes with these ligands of very high chemical and photochemical stabilities. The magnetic properties of these complexes indicate that the geometry around the central atoms is distorted tetrahedral. A X-ray diffraction study of one of the Co(II)-complexes confirms these findings.

Notizen: Austauschversuche mit radioaktivem Nickel zeigen, dass Ni2+ und Pd2+ in Mercaptoäthylamin(MEA-)-Komplexen austauschbar sind. Aus UV./VIS.- und 1H-NMR.-spektroskopischen Daten geht hervor, dass die Anordnung der Metallionen in Ni2Pd(MEA)4Cl2 symmetrisch ist (Ni Pd Ni), in NiPd2(MEA)4Cl2 dagegen asymmetrisch (Ni Pd Pd).

Notizen: ESR. spectra of the chlorine substituted phenoxy radicals listed in Table 1, which were produced by photo-oxidation of the parent phenols in aprotic solvents, are reported. In most cases the chlorine splittings could be resolved and analysed in detail. Experimental data as well as quantum chemical calculations were used for assignment of all measured chlorine couplings and determination of their relative signs.Spin density distributions and polarization parameters for chlorine are discussed and compared with the results from current semiempirical molecular orbital theories.Chlorine couplings, associated with the larger splittings are found positive in sign, whereas signs of small couplings appear difficult to establish. Limitations in the applicability of McConnell or Karplus-Fraenkel type relations to chlorine substituted aromatic radicals will be discussed and related to peculiar properties of the spin density matrix of such systems.

Notizen: On the regioselectivity of cycloaddition reactions of photochemically generated benzonitrile-isopropylidesThis paper deals with the physical and chemical differences of zwitterionic benzo-nitrile-isopropylides, which differ by a p-substituent in the phenyl ring (H, F, OCH3; Scheme 2). These dipolar species (4-6) are produced by irradiation of the corresponding 2 H-azirines (1-3; Scheme 1) in a 2-methylpentane glass at -185°. Their UV. spectra are reproduced in the Figure. The spectra of 4 and 5 are characterized by an ‘aromatic band’ at short wavelength, and a longer wavelength band at approximately 275 nm, which is considered to be characteristic of the nitrile-ylide system. The UV. spectrum of the methoxy derivative 6, which shows a broad absorption at 260 nm, arises by an addition of the ‘nitrile-ylide band’ and the anisole band. The three dipolar species 4-6 do not show any significant differences in the regioselectivity of the cycloaddition with methyl α-methacrylate even though F and OCH3 have quite different σ-constants (Scheme 1). The addition according to modus A is very much preferred (B/A = 0,076). - It seems, that the substituents F and OCH3 do not affect the physical and chemical behaviour of the parent benzonitrile-isopropylide (4). All three dipolar species 4-6 react regiospecifically according to modus A with methyl trifluoroacetate (Scheme 1). The regioselectivity is reduced in the cycloaddition of 4 with methyl propiolate and ethyl phenylpropiolate (B/A = 0,04 and 0,28, respectively). The reduced regioselectivity in the latter case may be attributed to a reduced polarity of the triple bond in the dipolarophile.

Notizen: Structure of Cantharidine, C10H12O4An X-ray structure determination of the title compound confirms the correctness of the molecular stereochemistry as deduced earlier from chemical considerations.

Notizen: Model Calculations on Hexacyano- and Pentacyanoferrate Complexes with Aromatic Nitrogen HeterocyclesUsing the extended Hückel method, theoretically predicted chemical, photochemical and spectroscopic properties of these complexes are compared with experimental data. A better understanding of the photochemistry is attempted by analysis of the low energy CT absorption. Starting from the amminopentacyanoferrate the spectroscopic properties of the pentacyanoferrate complexes with aromatic heterocycles are described by adding the ‘d-π*’ MLCT and the π-π* transitions. The results obtained on the mononuclear pyrazine compounds suggest a very simple way to understand the binuclear pyrazine complexes. Some properties of the hexacyanoferrates can be better explained if all valence orbitals of the ligands are considered. In all examples the influence of the ‘π-backbonding’ is discussed.

Notizen: The Photochemistry of Conjugated Epoxy-Inones: Photolysis of 5,6-Epoxy-5-isopropyl-6-methyl-hept-3-in-2-onThis paper continues the series of investigations of the photochemistry of α,β-unsaturated γ,δ-epoxyketones by examining the hitherto unknown photochemical behaviour of α,β-acetylenic-γ,δ-epoxy-ketones. As model compound, the aliphatic epoxy-ynone 7 (thermally stable at 180°) was synthesized (Scheme 1). It can be converted with BF3O (C2H5)2 in good yields to the 1,5-diketone 8, the yne-1,4-diketone 49 and in small amounts to the fluorhydrine 50 (Scheme 1).On n,π*- or π, π*-excitation, 7 shows mainly cleavage of the C (γ)-O-bond to give a diradical a (Scheme 11), whose ultimate fate is strongly solvent dependent. In acetonitrile a mainly rearranges to the 1,5-diketone 8 and, to a smaller extent, shows fragmentation to acetone and formation of polymers. Except for small amounts of the dimeric products 9A,9B and biphenyl, the same compounds are obtained in benzene. In cyclopentane, however, a gives only little of 8, and mainly a plethora of compounds formed by a radical process like H-abstraction from solvent, incorporation of cyclopentylradicals, dimerization and fragmentation reactions (9A, 9B, 11-20) (Scheme 3). Irradiation of 7 in propan-2-ol or in dioxane yields products of analogous radical processes as well of photoreduction (Scheme 4). However, the analogous epoxyenone 32 gives mainly products of photoisomerizations without interference by the solvent [6].On photochemical excitation in acetonitrile, the 1,5-diketone 8 shows unspecific decomposition, but in cyclopentane it yields the reduction products 12, 26A, 26B, 27, 28 plus cyclopentylcyclopentane (15) (Scheme 6).

Notizen: The chemical resolution of γ,γ′-di-t-butyl DL-N-benzyloxycarbonyl-γ-carboxy-glutamate is described in detail (preliminary account see [1]). The D (-)-derivative was obtained as a crystalline quinine salt, and the L (+)-derivative as a crystalline salt with (-)-ephedrine in yields of 44 and 70%, respectively. Physical data are indicated for the enantiomers of γ,γ′-di-t-butyl N-benzyloxycarbonyl-γ-carboxyglutamate, γ,γ′-di-t-butyl γ-carboxyglutamate, and γ-carboxyglutamic acid. The absolute configurations and optical purities of the γ,γ′-di-t-butyl (+)- and (-)-N-benzyloxycarbonyl-γ-carboxyglutamates were determined by removal of the protecting groups and decarboxylation to optically active glutamic acid.

Notizen: The purpose of this communication is to describe the preparation and some properties of the first two synthetic peptides containing D- and L-γ-carboxyglutamic acid. Use was made of N-protected γ,γ′-di-t-butyl-γ-carboxyglutamic acids (D, L, and DL) described earlier [1 a]. Preliminary 1H-NMR. data (360 MHz) indicate a restricted rotation of the Gla side chain in the free amino acid as well as in the C-terminal Gla of Gla-Gla in H2O solution at acid pH. The proton dissociation from Gla and Gla-Gla was studied by potentiometric titration and NMR. methods. The pH titration in the presence of Ca2+ ions shows that Gla-Gla has a much higher association constant for this cation than Gla. It is almost as great as that of prothrombin (pCa2+ = 3.2 vs. 3.5).

Notizen: Photochemical Cyclization of o-, m-, p-Allylanisoles and o-AllylanilinesThe compounds irradiated are summarized in Scheme 1. 2-Allylaniline and N-Alkyl Derivatives. Irradiation (ca. 3 h) of compounds 1-3 with a high pressure mercury lamp in benzene solution under argon (quartz vessel) gave in 40-80% yield the corresponding 2-methylindolines 20, 22 and 25, respectively (Scheme 3). Tetrahydroquinolines (23, 26) were formed only in minor amounts (0,5%). Irradiation in methanol solution yielded in addition to the indolines the 2-(2′-methoxypropyl)-anilines 21,24 and 27, respectively, in a ratio of ca. 0.3, 1.5 and 1.0 with respect to the indolines (Scheme 3). Similar results were obtained in ethanol solution. The observation that the photoreactions in benzene or methanol are not quenched by (E)-piperylene or sensitized by acetone suggests that the transformation starts from the singlet manifold of the aniline chromophor. As outlined in Scheme 11 it is proposed that the excited molecules undergo an intramolecular electron transfer to give an acceptor(olefinic side chain)/donor(aniline part) complex (EDA complex; see [28]) of type {a,b} in which the positive charge is mainly located at the nitrogen atom and the negative charge at C(3′) of the allyl substituent. That the negative charge resides predominantly at C (3′) - independently of alkyl substitution at C (3′) (see experiments cited in [26]) - may be due to electrostatic attraction of the charges. Thus, the following H-transfer occurs almost regiospecifically to give the singlet diradical c which cyclizes directly or via the spirocyclopropane derivative d to the indoline derivative 22. Intermediate d is also responsible for the formation of the 2′-methoxypropyl compounds: It is suggested that in the polar solvent methanol d is partially converted to the zwitterion e, the immediate precursor of 24. Experiments with the deuteriated reactants N-d-2 and 2′-d1-2 (Scheme 3) are in agreement with the proposed mechanism.N, N-Dialkyl-2-allylanilines and Allylanisoles. Upon irradiation in methanol or benzene, these aniline derivatives undergo cyclization to give as the only products the corresponding 2-cyclopropylanilines in 50-70% yield (Scheme 4). 2-, 3- and 4- allylated anisoles behave in the same way on irradiation (Schemes 6-8) as long as the allyl group carries no substituent (CH3, Cl) at the double bond (Schemes 9, 10). No photolytic cyclopropane ring formation is observed with the naphthalene derivatives 7, 8, 17 or 18 (Scheme 1). Experiments with the deuteriated compounds 2′-d1-4 and 1′, 1′-d2-11 - synthesized according to Scheme 2 - indicate that in all cases the cyclopropane formation occurs with concomitant 1,2 aryl migration (Schemes 5, 6) which characterizes the reaction as an aromatic di-π-methane rearrangement (Scheme 14). In contrast to the photoreactions described above the cyclopropane ring formation can be sensitized by acetone or quenched totally by (E)-piperylene. A comparison of the triplet energies (ET) of the aromatic and olefinic chromophor of the reactants (cf. Table 4) shows that the di-π-methane rearrangement is only effective when ET of the aryl part is lower than that of the olefinic part, but not by more than 20 kcal/mol. In substrates carrying substituents at the olefinic double bond the energy of T1 of the allyl group drops beneath that of the aryl part. In these cases no di-π-methane rearrangement is observed because an effective deactivation of T1 of the aryl part occurs by (E)/(Z) isomerization of the side chain as is demonstrated by the photochemical behaviour of compound 10 (Scheme 10). This concept seems to be of general significance for related di-π-methane rearrangements in cyclic systems (cf. Scheme 16; further examples: Scheme 15).

Notizen: On the incorporation of geraniol and farnesol into cantharidinEarlier investigations [1] have shown that cantharidin (1) is biosynthesized by the male Lytta vesicatoria L. (Meloidae, Coleoptera) from the common terpenoid precursors mevalonate and farnesol (3). To prove if geraniol (2) is incorporated via farnesol (3) into cantharidin (1) the following geraniols have been synthesized and injected into either larvae or male adult Lytta vesicatoria, partly in a mixture with synthetic 11′, 12-[3H]-farnesol as an internal standard: 2-[14C]-, 7-[14C]-, 7′, 8-[14C]-, 7′, 8-[3H]-geraniol. Unexpectedly, geraniol (2) was not specifically incorporated into cantharidin (1) perhaps due to its higher toxicity or its faster degradation relative to the other precursors before incorporation. The incorporation of U-[14C]-leucine, U-[14C]-isoleucine and 1-[14C]-glucose into cantharidin (1) via their metabolites is evident by degradation studies, whereas 1-[14C]- and 2-[14C]-glycine do not serve as precursors for cantharidin (1).

Notizen: Bildung von 5-Hydroxy-indan-2-on bei Hydrolyseversuchen mit 9-Äthylendioxy-bicyclo[3.3.1]nonan-3,7-dionVerschiedene Versuche, 9-Äthylendioxy-bicyclo[3.3.1]nonan-3,7-dion (2) durch Hydrolyse in das entsprechende Triketon 3 umzuwandeln, führten nur zu 5-Hydroxy-indan-2-on (4) und in einem Fall auch noch zu etwas 7,9-Bis(äthylendioxy)-bicyclo-[3.3.1]nonan-3-on (5). Unter milderen Hydrolysebedingungen reagierte 2 gar nicht.Die Bildung von 4 aus 2 wird über eine Wagner-Meerwein-Umlagerung und nach-folgende Eliminierung von Äthylenglycol formuliert. Das so entstandene Äthylenglycol reagiert mit noch vorhandenem Acetal 2 zum Bis-acetal 5, was als weitere Bestätigung der Resistenz von 2 gegen Hydrolyse gelten darf.

Notizen: Starting from ethyl 2-cyclohexen-1-carboxylate (3) the total synthesis of the perhydrohistrionicotoxin intermediate 23 was achieved in 25% overall-yield. The two key steps involve a positionally specific addition of HOBr to the oxime-olefin 7 and the alkylation of bromooxime 17 with 1-lithio-1-butyne. The latter represents a novel method for stereospecific and position-specific introduction of a nucleophilic butyl equivalent in α-position to a ketonic carbonyl group.

Notizen: Experiments on the competitive incorporation of farnesol-stereoisomers into cantharidinFarnesol (2) has been demonstrated to be an efficient precursor for cantharidin (1), into which it is transformed by elimination of C(1), C(5), C(6), C(7) and C(7′) [1]. The following incorporation experiments with doubly labelled (3H and 14C) stereoisomers of farnesol present strong evidence that (E,E)- farnesol ((E,E)-2) in fact is the precursor for cantharidin, whereas (2E, 6Z)-2 and (Z,Z)-2 are not utilized for the biosynthesis of cantharidin. A possible mechanism for the incorporation of (2Z,6E)-farnesol ((2Z,6E)-2) to an extent of 56,8% relative to (E,E)-2 is discussed.

Notizen: The influence of errors in molecular integrals on the calculated RHF energy values is considered for two models which correspond to round-off and shift errors. The energy variations induced by errors in elements of one- and two-electron matrices and the overlap matrix are represented in a quadratic approximation and the same degree of accuracy is maintained for mean values and standard deviations. The formulas given point out that mean values are less than zero when some of the errors are non-shifted. Special care is required when Gaussian lobe functions are used.

Notizen: A derivation of most general existence conditions for surface states of a semi-infinite Kronig-Penney crystal is reported. They reduce to Steslicka's conditions under a subsidiary restriction and also indicate that the surface-state energies may lie in the allowed bulk bands. Numerical computations supporting the qualitative conclusions are provided.

Notizen: The goodness of the local fit of an approximate wave-function, \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \psi $\end{document}, to the exact function, ψ0, is \documentclass{article}\pagestyle{empty}\begin{document}$ |\tilde \psi - \psi _0 | $\end{document}. From this quantity the global accuracy of \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \psi $\end{document} is defined and a “working supposition” is presented, which quantitatively relates the global accuracy to the accuracy of expectation values. Two criteria based on the accuracy of the reduced local energy and the density respectively, are presented as alternatives to \documentclass{article}\pagestyle{empty}\begin{document}$ |\tilde \psi - \psi _0 | $\end{document}. The relative global accuracies of eight wave-functions for H2 are determined using the two criteria. The ‘working supposition’ is applied and predictions are made concerning the relative accuracies of the expectation values of the following operators: z2, r2, x2 + y2, 3z2 -; r2, ξ, rA-1, r12-1, and EL (the reduced local energy). The success rate is high (〉90%) except for those operators which are sensitive to interelectron coordinates or derivatives of the wave-function.

Notizen: Ab initio calculations have been performed on selected first-row hydrides with a large Gaussian basis set. Energy localized molecular orbitals (LMO'S) were computed and analysed in terms of their sizes and shapes. The total molecular electronic energy was partitioned into components which may be associated with an MO, and the relationship between the sizes and energies of such orbitals was examined. It was found that a simple energy-size relationship exists for core LMO'S but only approximately holds for bond LMO'S.

Notizen: The Thomas-Fermi-Dirac equation for the electron density in a homonuclear diatomic system is solved numerically. The problems arising and methods of dealing with them are discussed and attention is given to the accuracy of the calculated energies. Comparisons are made to previously published work employing approximations, permitting a discussion of their utility.

Notizen: Relativistic symmetry orbitals are given for the double group D3h. For atomic orbitals at the symmetry center a general expression is presented. The atomic orbitals of the s, p½, and p3/2 variety outside the center are also considered. The representation matrices are given in explicit form.

Notizen: We use a variation-perturbation method to calculate the electric polarizabilities and the electric dipole moment of the LiH molecule. We obtain 4.455 for the perpendicular polarizability and 4.001 (×10-24 cm3) for the parallel polarizability. Our result for the electric dipole moment at equilibrium nuclear distance is 5.866, which is in excellent agreement with the experimental value 5.828 debye units.

Notizen: A semi-analytical solution for the nucleus and the internuclear midpoint centred partial wave equations representing the Schrödinger equation for the H2+-like molecule is discussed. Explicit proton and internuclear midpoint centred results for the interaction energy and the wave function for the 1sσg state of H2+ are obtained as a function of the internuclear distance R and the number of coupled differential equation N N ≦ 14 used to represent the Schrödinger equation for the molecule. These, together with some energy optimized floating one centre results for the interaction energy, are used to (1) discuss the convergence of the partial wave calculation as a function of R,N, and the position of the expansion centre, (2) discuss the concept of Coulomb versus electron exchange interaction energies, and (3) discuss briefly the convergence problems of analogous one centre perturbation theory treatments for the ground state H2+ molecule. The electron exchange H2+ (1sσg) molecule provides a severe test for the uefulness of partial wave methods.

Notizen: Three simplifying methodds are discussed and applied to the four lowest valence states of CH2(3B1, 1A1, 1B1 and 1Σg+(1A1*)) and to the two lowest of CH2+(2A1 and 2∏u(2B1)). These methods concern: (1) the development of polarization functions for Gaussian-lobe basis sets by least-square fitting of numebrical multiconfigurational atomic fuinctions (this approach is tested also on (C2H2, (2) the use of intermediate Hamiltonians to calculate avoided crossings between potential hypersurfaces, and (3) thecalculation of correlation energies using an atoms-in-molecule approach.The calculated equilibrium geometries of the CH2 States are within 0.02 Å and 5° of available experimental data. The calculated term values and ionization potentials, Te(1A1 = 0.35 eV, Te (1B1) = 1.22 eV, Te (1Σg+(1A1*)) 2.48 eV, I.P. (2A1) = 10.39 eV and I. P. (2∏u(2B1)) = 10.58 eV, are in agreement with some recent theoretical studies, and are very close to existing experimental information.

Notizen: The focal point of our discussion is the examination of truncated basis sets used in obtaining an accurate first principles clculation of the effective valence shell Hamiltonian by the canonical transformation-cluster expansion approasch. Subsequent diagonalization of this effecitve valence shell hamiltonian yields the valence shell transition energies. A detailed analysis of numerical results obtained using a number of different basis sets of hydrogen-like orbitals together with rigorous symmetry arguments celarly demonstrates the special role played by d orbitals in computing the 3P → 1D transition energy in carbon. The failure of early attempts to calculate the effective Hamiltonian for ethylene from first principles is examined in the light of recent ab initio calculations on ethylene involving d orbitals and the computations reported in this paper. We conclude that accurate calculations of the effective valence shell Hamiltonian for molecules must consider d orbitals in the excited orbital basis set.

Notizen: The localized-site cluster expansion technique is applied to the infinite linear Heisenberg model with both nearest-neighbor and next nearest-neighbor interactions. These cluster ansätze are systematically studied and improved, up to the so-called 5-site approximation. Generally we find the present cluster ansätze yield the most accurate variational results yet available.

Notizen: For orbital optimization within the MC SCF theory a modification of the OEH method is proposed with the direction of descent determined according to the Fletcher-Reeves gradient method. The combined method developed on this basis ensures the convergence of the iterative process when the Hessian singularities occur. The convergence properties of the method proposed are studied by performing the ab initio water molecule calculations using two types of multiconfigurational wave functions.

Notizen: Branching diagram and Serber-type spin functions are ordered according to their diagrams. The method of Graebenstetter et al. is slightly modified; it provides an effective algorithm for the construction of genealogical spin functions. A counterpart of the method is developed for Serber-type spin functions. Special properties of branching diagram functions and Serber-functions are established.

Notizen: A comparison of experimental and theoretical values for Δα = αe - αg, assuming no sigma-electron contribution, shows a great distortion by π-electron calculations. We analyze existing electrochromic data, using this assumption, and report Δα values of 44 Å3 for coronene and 43 Å3 for triphenylene. Some general properties of Δα are discussed in terms of potential energy curves which suggest interesting calculations to relate excited matrix elements with experimental measurements.