Ab initio SCF Calculation of the Fluoronium Ion: Geometry,electronic structure and vibrational constants

An ab initio SCF calculation of 42 points of the energy hypersurface of the fluoronium ion is presented using a contracted F(5s/3p), H(2s) gaussian basis set. In its equilibrium structure a bond length of 1.812 a.u. and a HFH bond angle of 127.2° are predicted. The calculated vibrational frequencies for H₂F⁺, HDF⁺, and D₂F⁺ are in good agreement with the experimental data.     

Photochemische Cycloadditionen von 3-Phenyl-2H-azirinen mit Benzoyl-, Äthoxycarbonyl- und Vinylphosphonaten 34. Mitteilung über Photoreaktionen

The irradiation of the 3-phenyl-2H-azirines 1a–c in the presence of diethyl benzoylphosphonate ( 8 ) in cyclonexane solution, using a mercury high pressure lamp (pyrex filter), yields the diethyl (4, 5-diphenyl-3-oxazolin-5-yl)-phosphonates 9a–c (Scheme 3). In the case of 1b a mixture of two diastereomeric 3-oxazolines, resulting from a regiospecific but non-stereospecific cycloaddition of the benzonitrile-benzylide dipole 2b to the carbonyl group of the phosphonate 8 , was isolated. Benzonitrile-isopropylide ( 2a ), generated from 2,2-dimethyl-3-phenyl-2H-azirine ( 1a ), undergoes a cycloaddition reaction to the ester-carbonyl group of diethyl ethoxycarbonylphosphonate ( 15 ) with the same regiospecificity to give the 3-oxazoline derivative 16 (Scheme 5). The azirines 1a–c , on irradiation in benzene in the presence of diethyl vinylphosphonate ( 17 ) give non-regiospecifically the Δ¹-pyrrolines 13a–c and 14a–c (Scheme 6).     

Photochemische Reaktionen 81. Mitteilung [1] Notiz zur UV.-Bestrahlung von γ, δ-Epoxy-eucarvon und dessen Reaktivität gegenüber Botrifluorid-äthylätherat

UV.-irradiation (λ ≥ 327 nm) of the α,β-unsaturated γ,δ-epoxy ketone 2 in pentane gives the isomers oxidoketone 3 and diketone 4, in high yield. On treatment with BF₃O(C₂H₅)₂, 2 undergoes rearrangement to the diketone 4 and the isomeric lactone 8 and yields also the dimer 9.     

Hydrolyse acide des diazocétones secondaires: Participation des nucléophiles

In the acid hydrolysis of two secondary diazoketones showing rate-determining protonation, 3-diazo-butan-2-one ( 1 ) and 1-phenyl-1-diazo-acetone ( 4 ), the nature of the (rapid) decomposition step of the intermediate diazonium ion was studied by product analysis. In the presence of strong nucleophiles, the reaction with Cl^?, Br^?, I^? and SCN^? follows the Swain-Scott relationship. SCN^? formed thiocyanates; isothiocyanates could not be detected. Both results indicate nucleophilic participation in the substitution step. For the accompanying elimination reaction (the amount of which is independent of added base) the isotope effect k_H/k_D = 2,4 in the hydrolysis of 1–d₃ is in favour of an E2 type mechanism. – Addition of HSCN to methyl-vinylketone at 0° yields nearly exclusively 4-thiocyanato-butan-2-one, which at 25° in the presence of HSCN is slowly rearranged to 4-isothiocyanato-butan-2-one.     

Wurtzitan (Tetracyclo[5.3.1.12,6.04,9]dodecan)

A new synthesis of wurtzitane (13) is described starting from 2-oxo-protoadamant-4-ene (2). The key intermediate ketone 7 was obtained by regiospecific ring expansion of the β-amino alcohol 6. Entry to the wurtzitane system involved solvolysis of the tricyclic unsaturated mesylate 10 (→11).     

The Crystal and Molecular Structures of Two Acid-Catalysed Rearrangement Products of Taxochinon

The structures of two acid catalysed rearrangement products of taxochinone ( 1 ) have been determined by X-ray analysis. One of the products turned out to be a 20 (10→9) abeo-abietane ( 2 ), the other an optically inactive phenalenone ( 3 ). Crystals of the former compound, C₂₀H₂₆O₃, belong to space group P2₁2₁2₁ with four molecules per cell and the structure was refined with 879 significant reflexions to R = 0.032. Crystals of the latter compound, C₂₀H₂₂O₂, belong to space group P2₁/c with 12 molecules per cell and the structure was refined with 1823 significant reflexions to R = 0.058.     

Magnetic field dependence of delayed fluorescence of pyrene in solution

The magnetic field effect on the intensities of monomer (I_M) and excimer (I_D) delayed fluorescence of pyrene has been found to be identical. This result suggests a common spin-selective step in the processes giving rise to I_M and I_D, and is discussed in the light of previously proposed mechanisms. An unusual solvent effect is found on the I_M (I_D) versus field strength curves. This is attributed to photochemical doublet-radical formation. Doublet-radical formation affects the field dependence of I_M and I_D through spin selectivity in the triplet quenching reaction.     

The C—H⋯O hydrogen bond. An ab initio study of nitrosomethane and its hydrogen bonded dimer

In order to study the short C—H?O contact which has been found in several nitroso compounds, a series of ab initio calculations have been performed on nitrosomethane and it's cyclic “hydrogen bonded” dimer. A potential function for the C—H?O contact has been found and the effect of this contact upon the NO and CN bonds has been studied. The potential is shallow with a minimum of only ?2.65 kcal mol^?1 for each contact and the equilibrium C?O distance is 3.524, A. These results indicate that the C—H?O bond is better described as a van der Waal's type contact than a hydrogen bond. The equilibrium length of the NO bond (R_NO) changes in a regular manner with variations in the C?O (R_HYD) distance, i.e. when R_HYD becomes shorter R_NO becomes longer. However, the variations in the CN bond lengths, which in the nitrosomethane monomer molecule is a long and weak bond, are anomalous.