Radikale aus Polymethin-Farbstoffen. IV—Dikation-Radikale aus Polymethincyanin-Farbstoffen mit Indolenin-Endgruppen

Dication radicals have been prepared by electrolytic oxidation of polymethinecyanine dyes. Their e.s.r. spectra confirm the expected structure of the radicals.     

Radikale aus Polymethincyanin-Farbstoffen. I—Polymethincyanine mit Indolenin-Endgruppen

The solution ESR spectra of radicals which have been prepared by electrolytic reduction of dinuclear and trinuclear polymethinecyanine dyes are interpreted. From the values of the coupling constants information can be obtained about the conformation of the radicals.     

Phosphoranes par fermeture trans-annulaire: III—Conformation—configuration—labilité

The analysis of the n.m.r. spectra of the two isomers of 1,6,6-trimethyl-3-phenyl-2,8-dioxa-5-aza-1-phospha ^vbicyclo[3.3.0]octane allows us to propose a conformation for each 5-membered ring and for the configuration of the phosphorus atom. The lability of the H? P proton, revealed by high temperature experiments and by P? H ? P? D exchange, is significantly different in the two isomers.     

Isomere N-Aryltetrazole. III—Massenspektren

The low resolution mass spectra of four pairs of isomeric N-aryltetrazoles have been investigated in order to examine the usefulness of mass spectrometry to distinguish between the isomers. In both series the fragmentation starts by consecutive elimination of N₂ and HCN generating ions of equal masses but different abundances possibly due to different structures. This allows unequivocal identification of the isomers.     

Massenspektrometrische Untersuchung von Amiden: III—Intramolekulare Nucleophile Substitution bei der Methyl-Abspaltung aus Crotonsaurepiperidid und Vinylogen Derivaten

The methyl cleavage from piperidides of type CH₃(CH?CH)_nCONC₅H₁₀ with n = 1 to 3 does not proceed via ring contraction as shown earlier with n = 0. The fragmentation can be formulated with the concept of neighbouring group participation of the amide function which leads to a cyclic transition state. Investigations with a ²H-labelled compound in the case of n = 1 as well as energy measurements (AP, IP, E_k) agree with this assumption.     

Doubly charged ion mass spectra: III—N-alkanes

Doubly charged ion mass spectra have been obtained for 15 n-alkane hydrocarbons. Spectra were measured using a Nier-Johnson geometry Hitachi RMU-7L mass spectrometer operated at 1.6kV accelerating voltage. Fragment ions, which resulted from C? C bond rupture and extensive H loss, dominated the spectra. Molecular ions have not been observed. The most intense ions in the doubly charged ion mass spectra of n-alkanes were [C₂H₄]²⁺, [C₃H₂]²⁺, [C₄H₃]²⁺, [C₅H₂]²⁺, [C₆H₆]²⁺, [C₆H₈]²⁺, [C₇H₆]²⁺, [C₇H₈]²⁺, [C₈H₆]²⁺ and [C₈H₈]²⁺. Appearance energies for forming the prominent doubly charged fragment ions have been measured and range from 27.5 eV to energies greater than 60eV. A geometry optimized SCF approach has been used to compute the energies and structures of prominent ions in the doubly charged mass spectra.     

Carbon-13 nuclear magnetic resonance spectra: III—2-heteroadamantanes

The ¹³C n.m.r. spectra of some 2-heteroadamantanes and 1-substituted 2-heteroadamantanes are reported. The influences of the heteroatoms in the adamantane framework, and those of the substituents attached to it, on the ¹³C chemical shifts of the adamantane carbons are investigated and compared with related compounds such as the corresponding heterocyclohexane derivatives and 2-mono- and 2,2-disubstituted adamantanes. The nonadditivity of the substituent effects for 1-substituted 2-heteroadamantanes, especially for the geminally substituted carbons, is substantially confirmed. In addition, the influences of a missing CH₂ group and of NCH₃ carbons upon the ¹³C chemical shifts of the carbons in the adamantane system are described.     

13C NMR spectra of thiophenes. III—Bromothiophenes

The ¹³C NMR spectra of all bromo substituted thiophenes have been obtained at 15·085 MHz. ¹³C signal assignments for monobromothiophenes have been confirmed by comparison with the spectra of their partially deuteriated derivatives; a revision is made for the assignment in 3-bromothiophene. The substituent effect of bromine is generally additive for the ¹³C chemical shifts. The substituent effect on various types of ¹³C, ¹H coupling constants is also obtained and discussed.     

Mass spectra of liquid crystals. III—phenylpyrimidine derivatives

The 70 eV electron impact mass spectra of 34 1-phenyl-2,5-pyrimidine derivatives are presented. Based on the observed mass shifts by the various substituents, the nature of the main fragment ions is rationalized.     

The photo-oxidation of EPDM rubber: Part III—Mechanistic aspects and stabilization

The kinetics of the photo-oxidation of crude EPDM rubber has been studied in order to propose a mechanism for the sequence of reactions which occurs during the photo-degradation process. The presence of the unsaturation markedly affects the kinetics of the photo-oxidation of EPDM in comparison with that of EPM. We have also studied the stabilization effect of a hindered amine and a hindered phenol on EPDM and compared this with crude EPM rubber. These stabilizers showed poor efficiency, which is explained by the presence of impurities which act as sensitizers for the degradation of the crude rubber.     

Mesomere Kationen: III—13C-Fourier-Transform-NMR-Spektren von Harnstoffen,Thioharnstoffen und Guanidinen

The ¹³C-chemical shifts of methyl substituted ureas, thioureas and related compounds are reported and discussed. π-Electron densities, as obtained by simple HMO calculations, do not reproduce the ¹³C-chemical shift trend. A correlation has been found for the carbonyl and thiocarbonyl resonances which has been discussed as being mainly influenced by the mean excitation energy in the paramagnetic screening term.     

Metastable ion study of organosilicon compounds. Part III—trimethoxyphenylsilane

The unimolecular decomposition of trimethoxyphenylsilane (1) was investigated by mass-analysed ion kinetic energy (MIKE) spectrometry, deuterium-labelling studies and from high resolution data. The characteristic fragmentations of metastable molecular ion of 1 were losses of C₆H₆ and C₇H₇^· with rearrangements. Almost complete H/D scrambling occurred in the molecular ion prior to these decompositions. The other important fragmentation routes corresponded to expulsions of CH₃O^· and C₆H₅^·. These fragmentations were followed by consecutive elimination of an H₂CO molecule, as commonly observed in the mass spectra of alkoxysilanes. In these fragmentation processes, H/D scrambling increased as the internal energy of the molecular ion was lowered. The fragmentations of 1 were compared with those of its carbon analogue, α,α,α-trimethoxytoluene.     

ChemInform Abstract: Fullerene‐Like III—V Clusters: A Density Functional Theory Prediction.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

1H NMR utilization of through-space effects: III—configuration of oximes and analogous compounds

The configurational assignment of Z and E nitrogen derivatives () of 3,5,5-trimethyl-2-cyclohexen-1-one was made taking into consideration the through-space effects on oxime, O-methyloxime, dimethylhydrazone, tert-butylimine, N,N,N -trimethylhydrazonium iodide and oxime hydrochloride derivatives. The relationship between the magnitude of the chemical shifts of the α-protons and the dihedral angle formed by the α-C? H bond and the C?N? OH plane was interpreted in terms of the geometrical dependence of the electric field effect. For the different Y substituents, the change in chemical shift between the Z and the E configuration of the proton near the functional group was mainly dependent on the electric field effect.