R. Foster

The absorption spectra of molecular complexes

Abstract The intermolecular charge-transfer absorption spectra of complexes of various p-π aromatic electron donor molecules with a series of p-π aromatic electron acceptor molecules have been measured. The frequencies of the bands of these complexes may be expressed simply as the sum of two terms, characteristic of the donor and acceptor molecules respectively. This relationship fails if the electron donor is weak.

Interaction of electron acceptors with bases—XIII : The interaction of indole with tetracyanoethylene in dichloromethane

Abstract Visible absorption studies of the system indole-tetracyanoethylene in dichloromethane show that an intermolecular charge-transfer complex is initially formed. This decomposes to yield a second product, presumed to be a σ-complex, which finally yields 3-tricyanovinylindole.

The unreliability of association constants or organic charge-transfer complexes derived from optical absorption spectra—I : General considerations

Abstract It is suggested that certain anomalies which arise from the evaluation of equilibrium constants of organic charge-transfer complexes are the result of deviations from Beers law of the optical absorption characteristic of the complexes.

Interaction of electron acceptors with bases—V: The Janovsky and Zimmermann reactions

Abstract When m -dinitrobenzene in excess ketone as solvent is shaken with concentrated aqueous sodium hydroxide (The Janovsky reaction), the conjugate base of the ketone appears to form a σ-addition complex with the m -dinitrobenzene; whereas the product of interaction of m -dinitrobenzene with ketone in ethanolic sodium ethoxide (the Zimmermann reaction) is the conjugate base of the corresponding 2,4 dinitrobenzyl ketone.

Interaction of electron acceptors with bases—XXI : Further studies of the proton magnetic resonance spectra of meisenheimer-like compounds☆

Abstract The structures of σ-complexes formed by the reaction of methoxide ion or acetonate ion with various nitroaromatic compounds are confirmed or established from observations of their PMR. The substrates include: 1-x-2,4-dinitrobenzenes; 1-x-2,6-dinitrobenzenes; 1-x-2,4,6-trinitrobenzenes; 1-x-2,4-dinitronaphthalenes; and 9-x-10-nitroanthracenes.Abstract The structures of σ-complexes formed by the reaction of methoxide ion or acetonate ion with various nitroaromatic compounds are confirmed or established from observations of their PMR. The substrates include: 1-x-2,4-dinitrobenzenes; 1-x-2,6-dinitrobenzenes; 1-x-2,4,6-trinitrobenzenes; 1-x-2,4-dinitronaphthalenes; and 9-x-10-nitroanthracenes.

Interaction of electron acceptors with bases—XVI : Proton magnetic resonance spectra of Meisenheimer compounds

Abstract PMR spectra of several Meisenheimer compounds have been measured in various solvents. Evidence is given that in such products derived from 1,3,5-trinitrobenzene the alkoxy group is readily exchanged in solvolysis by the acetonyl group. Products formed in solution by various concentrations of methoxide on several different polynitroaromatics have also been studied.

The interaction of electron acceptors with bases—II : The spectrum of s-trinitrobenzene in the presence of ammonia and aliphatic amines☆

Abstract The interaction of s-trinitrobenzene with certain aliphatic amines has been studied spectrophotometrically. It is suggested in solutions in ethanol or chloroform, an adduct is initially formed by a dative bond between the nitrogen of the amine molecule and the 2-position in s-trinitrobenzene. The initial reactions are reversed by acid, but in time further irreversible reactions occur.

Interaction of electron acceptors with bases—III : The absorption spectra of substituted polynitrobenzenes in liquid ammonia

Abstract The visible region absorption spectra of a series of substituted polynitrobenzenes in liquid ammonia has been measured. It is suggested that the absorption is produced by the respective pentadienyl anion formed by the attachment of the amide ion to the ring carbon atom of the polynitrobenzene which is ortho or para to the maximum number of nitro groups. Such structures have been proposed by Bunnett as intermediates in aromatic nucleophilic substitution reactions. Of the compounds studied primary and secondary aromatic nitro-anilines are exceptional, in that ionization appears to occur by loss of a proton from the amino group.

The unreliability of association constants of organic charge-transfer complexes derived from optical absorption spectra—II : Apparent isotope effects shown by the tetracyanoethylene complexes of benzene and bezene-d6☆

An attempt to compare optical and thermodynamic properties of the charge-transfer complex benzene-tetracyanoethylene in cyclohexane with those of the corresponding benzene-d6 complex using an optical method has been made. Differences have been noted in the calculated intensity of the intermolecular charge-transfer band, but not in its position. Although the differences in the measured values of association constant at various temperatures are apparently accounted for by differences in the entropy change of complex formation, it is suggested that a failure of Beers law gives a better account of all these differences.

Interaction of electron acceptors with bases—VIII : Further considerations of the Janovsky reaction☆

Abstract Deuterium exchange is observed in methanolic solutions of m-dinitrobenzene in the presence of the methoxide ion. No visible absorption characteristic of the Janovsky reaction is observed in this system. Consequently there appears to be little support for the suggestion (based on similar exchange reactions) that the blue colour obtained with the same system in dimethylformamide or dimethylsulphoxide is necessarily due to the dinitrophenyl anion. Many compounds which have weakly acidic hydrogen atoms appear to be effective in the Janovsky reaction.