Theoretical study of PO and PO−

The diatomic systems, PO and PO^– are studied, using numerical Hartree-Fock (NHF) and coupled-cluster calculations. The latter employs a hybrid NHF and Slater orbital basis set. Highly accurate CCSD methods predict bond lengths accurate to <0.004 Å and frequencies to 60 cm^–1. In addition the electron affinity of PO is computed to be 0.89 eV compared to an experimental value of 1.09±0.01. Comparisons are made with SCF and MBPT(2) results for PO⁺ using conventional basis sets.Dedicated to Professor J. Koutecký on the occasion of his 65th birthdayGuggenheim Fellow     

Ein Computerverfahren für die Massenspektrometrische Untersuchung Organischer Proben bei Fraktionierter Direktverdampfung

A procedure is described for use of an on-line digital computer to acquire and process low resolution mass spectra obtained by a fractionated evaporation technique. The procedure generates unambiguous spectra from uniform solid or liquid organic substances, and characteristic spectra from multicomponent organic solid or liquid samples. The system is realised with minimal hardware configuration.     

Ab initio study of a purine nucleoside: Adenosine

The ab initio SCF LCAO-MO method is used to compute the main electronic properties of a purine nucleoside, adenosine, in two specific conformational arrangements (3′-endo conformation of the ribose, gt orientation of the extracyclic CH₂OH group, anti orientation of the base with respect to the sugar and 3′-endo conformation of the ribose, gg orientation of the extra-cyclic CH₂OH group, syn orientation of the base with respect to the sugar). The results are compared with those performed for the isolated component fragments, adenine and 3′-endo riboses.     

DABCO-directed self-assembly of bisporphyrins (DABCO=1,4-diazabicyclo[2.2.2]octane)

Three isomeric zinc bisporphyrins have been prepared by covalently linking together two aminoporphyrins with an isophthalic acid derivative. The porphyrins differ in the substitution pattern on the meso phenyl groups, that is, ortho, meta, or para. Titrations carried out by UV-visible and 1H NMR spectroscopy have been used to map out the stabilities and the stoichiometries of the complexes formed with 1,4-diazabicyclo[2.2.2]octane (DABCO) in chloroform. The ortho- and meta-substituted bisporphyrins form 1:1 intramolecular sandwich complexes. The para-substituted bisporphyrin cannot adopt the cofacial conformation required for this type of complex and forms a higher order 2:2 intermolecular assembly, which is stable over a wide range of DABCO concentrations.     

Tautomerism and the spectroscopic properties of some 4,6-disubstituted pyrimedines

Tautomerism of some 4,6-disubstituted pyrimidines (with the electron-donor groups such as OH, SH and NH₂) is discussed with regard to their electronic absorption spectra. The spectra of different tautomeric forms of the molecules are satisfactorily interpreted by means of the Pariser—Parr—Pople type of calculations.     

Water environmental effect on tautomeric equilibria of 2- and 4-oxopyridines. A CNDO/2 study

The supermolecule approach is proposed to evaluate the shift of the tautomeric equilibrium of a molecule when going from the vapour phase to water solution. According to the model, a comparison of the stabilization (hydration) energies of different tautomers of a molecule surrounded by water molecules predicts changes in tautomeric equilibrium upon solvation. An application of the model (within the CNDO/2 method) to 2- and 4-oxopyridine shows that the lactam tautomers of the molecules are more stabilized by water molecules than the corresponding lactim forms by about 7–8 kcal/mole.     

7-Substituted prostaglandin analogues. A new synthetic approach

Starting from methyl 7-oxo-7-(1-cyclopentene)-heptanoate, a simple synthesis of the methyl esters of 7-oxo- and 7-hydroxy-9,11-dideoxy-PGF ₁ as a model for 7-substituted prostaglandin analogues is described.

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7-Substituierte Prostaglandin-Analoge — ein neuer Syntheseweg

Zusammenfassung Ausgehend von Methyl-7-oxo-7-(1-cyclopenten)-heptanoat wird eine einfache Synthese der Methylester von 7-Oxo- und 7-Hydroxy-9,11-dideoxy-PGF ₁ als Modellverbindungen für 7-substituierte Prostaglandinanaloge beschrieben.

     

Calculations of substituent and solvent effects on the kinetic isotope effects of Menshutkin reactions

Nitrogen, deuterium, halogen, and carbon kinetic isotope effects have been modeled for the Menshutkin reaction between methyl halides and substituted N,N-dimethylaniline at the HF/6-31G(d) level of theory augmented by the C-PCM continuum solvent model for several solvents. Systematic changes in geometries of the transition states and Gibbs free energies of activation have been found with phenyl ring substituents, solvent, and the leaving group. Kinetic isotope effects also change systematically; however, these changes are predicted to be small, inside the usual precision of the experimental measurements. On the contrary, no correlation has been found between the kinetic isotope effects and the Hammett constants for para substituents. Thus opposite to previous assumptions, our results indicate that kinetic isotope effects on the Menshutkin reaction cannot be used to predict the position of the transition state on the reaction coordinate.     

Acetylene diethers: Dineopentyloxyethyne

Dineopentyloxyethyne has been synthesized fromtrans-2,3-dichloro-1,4-dioxane according to a general procedure already described. In contrast with alkyl neopentyloxyacetylenes, RC=COCH₂Bu^t, which only polymerize when are strongly heated (150°), dineopentyloxyethyne is a kinetically unstable acetylene diether that polymerizes readily at room temperature. However, the compound has been trapped with Co₂(CO)₈ to give either the corresponding hexacarbonyl complex, m.p. 74–75°, or the cyclic trimer, m.p. 205–206°, depending upon the experimental conditions.