Mass spectrometry in structural and stereochemical problems. Part CLIII. Electron impact-promoted fragmentation of n-alkyl cyanides

In spite of previous extensive studies on the mass spectrometry of alkyl cyanides, no good mechanistic insight has as yet been gained into the behavior of straight chain alky1 cyanides. For this reason the possible origins for the principal ions in the mass spectrum of a typical alkyl cyanide (n-hexyl cyanide) have been determined using high resolution mass spectrometry anddeuterium labeling of every carbon atom. The results lead to the conclusion that most of the typical fragmentation processes of n-alkyl cyanides proceed through cyclic intermediates.     

Preparation of chiral triarylphosphines by Pd-catalysed asymmetric P-C cross-coupling

Enantioselective C-P cross-coupling of diarylphosphines and ortho-substituted aryl iodides has been achieved with >90%ee, using an in situ catalyst prepared from Et,Et-FerroTANE, Pd(2)(dba)(3) x CHCl(3) and LiBr.     

Couplage okydatif facile d'anions substitues captodativement

Carbanions carrying captodative substitution are readily oxidized to their dimers.     

Magnetic circular dichroism studies XXXII

CNDO calculations of the MCD spectra of 7- and 9-methyladenine have been carried out in two approximations. A minor modification of the CNDO/S method of Jaffé and coworkers shows an improvement over Jaffé's parameterization with respect to band separations and the signs of the MCDB terms, but is not applicable ton→ π* transitions.     

Field ionization mass spectrometry as a facile method for the study of the thermal formation of radicals

Electron impact spectra of thermolysis products of organic salts heated in the ion source of a mass spectrometer may give rise to organic ions corresponding to the cation of the salt. Field ionization mass spectrometry has been used as a facile method for detemining whether such an ion is due to ionization of the corresponding radical present in the gas phase, or to an electron impact induced fragmentation of a reaction product of higher mass. By comparison of the electron impact and field ionization spectra of a series of N-methyl pyridinium, tropylium and 1,2-dithiolylium salts it has been found possible to identify the radicals formed thermolytically, when present.     

Kinetics of heterogeneous cellulose reactions. I. Cyanoethylation of cotton cellulose

Sakurada's equation and fundamental kinetic laws were applied to the heterogeneous cyanoethylation of cellulose, performed by reacting fiber with liquid acrylonitrile, with sodium hydroxide as the catalyst. The data fit Sakurada's equation better at higher temperatures; deviation occurs at the initial stage, and the rate of reaction falls abruptly at a later stage. The degree of substitution at which the abrupt rate change occurred decreased as the temperature increased from 31 to 60°C. and also as the crystallinity of the fiber decreased. Diluting the reagent with different solvents decreased the rate of reaction and changed its transition points, but did not change the essential nature of the reaction, each segment of which fits Sakurada's equation very well. A uniform distribution of the catalyst (sodium hydroxide) throughout the fiber was attempted, and then the reaction was studied at 50°C. Diffractograms of the samples provided further evidence that the position of the rate change is associated with the change of cellulose (I) crystalline structure. Approximate energy of activation has been calculated, from the specific rate constants, between 31 and 40°C. as 10.6 kcal. and between 45 and 50°C. as 16.7 kcal. At other temperatures the determination was handicapped, due to temperature dependence of the order of reaction. An empirical relation between the constants of Sakurada's equation and the reaction temperature has been sought and correlated with the Arrhenius equation. Energies of activation, determined from this relationship, have been found to be very close to the above values. The change of order of reaction with temperature suggests that the reaction is affected by diffusion and the mechanism is interpreted as a diffusion-controlled reaction where hydrogen bonds play a significant role in diffusion.     

Mass spectrometry in structural and stereochemical problems–CXCV: The structure of the [C6H6O]+˙ ion in the spectrum of phenyl alkyl ethers

The [C₆H₆O]⁺˙ ion from C₆H₅OC₄H₉ is structurally similar to the molecular ion from phenol as demonstrated by ¹³C labeling.     

ESCA: Elektronen-Spektroskopie für chemische Analyse

Eine Substanzprobe, auf die Röntgen-Strahlung einwirkt, emittiert Photo- und Auger-Elektronen. Die Energiespektren der emittierten Elektronen geben Informationen über die Elektronen-struktur in der Probe — und zwar von den innersten atomaren Niveaus und ihrer Abhängigkeit von der chemischen Umgebung bis hin zu den Molekülorbitalen der Valenzelektronen sowie der Bandstruktur bei Festkörpern. Solche Elektronenspektren können jetzt mit hochauflösenden Instrumenten registriert werden; ihre Analyse ergibt neue Aspekte für die Untersuchung der chemischen Bindung. Die zu diesem Zweck entwickelte und inzwischen zu einem hohen Grad von Vollkommenheit ausgebaute Methode der Elektronenspektroskopie wird im folgenden als ESCA (Electron Spectroscopy for Chemical Analysis) bezeichnet.     

An inequality between thep- and (p, 1)-summing norm of finite rank operators fromC(K)-spaces

We show, for any operatorT from aC(K)-space into a Banach space with rank (T)≤n, the inequality , whereC≤4.671 is a numerical constant. The factor (1+logn)^1−1/p is asymptotically correct. This inequality extends a result of Jameson top ≠ 2. Several applications are given — one is a positive solution of a conjecture of Rosenthal and Szarek: For 1≤p<q<2,      

Formal and convergent solutions of singular partial differential equations

We consider the problem of the existence of convergent series solutions for partial differential operators of the form . We give first conditions for P such that the linear equation Pu=f has an analytic solution, then we solve nonlinear equations of the form Pu=F(x,u). For applications we treat also cases with parameters and give a proof of a theorem of S. Kaplan [5]. In the last section we consider a case where small denominators occur.