Charge-resonance spectra

There are some exceptions to this, e.g, the spectra in concentrated sulfuric acid of phthalocyanine pigments and certain vat dyes and the charge-resonance spectra of hepta- and higher polymethine-cyanines and of the beta-carotene-antimony trichloride complex [ ], all of which have peaks in the near infrared beyond 800 m/i. 

Kirkpatrick, E.S., Muller, K.A., and Rubins, R.S. 1964. Strong axial electron paramagnetic resonance spectrum of Fe3+ in SrTi03 due to nearest-neighbor charge compensation. Physical Review 135 A86-A90. 

The third radical cation structure type for hexadiene systems is formed by radical cation addition without fragmentation. Two hexadiene derivatives were mentioned earlier in this review, allylcyclopropene (Sect. 4.4) [245] and dicyclopropenyl (Sect. 5.3) [369], The products formed upon electron transfer from either substrate can be rationalized via an intramolecular cycloaddition reaction which is arrested after the first step (e.g. -> 133). Recent ESR observations on the parent hexadiene system indicated the formation of a cyclohexane-1,4-diyl radical cation (141). The spectrum shows six nuclei with identical couplings of 11.9G, assigned to four axial p- and two a-protons (Fig. 29) [397-399]. The free electron spin is shared between two carbons, which may explain the blue color of the sample ( charge resonance). At temperatures above 90 K, cyclohexane-1,4-diyl radical cation is converted to that of cyclohexene thus, the ESR results do not support a radical cation Cope rearrangement. 

Of the four monohydroxybenzo[c]cinnolines the 2- and the 4-isomers are potentially tautomeric with the corresponding quinonimines, e.g., 90 91. While the ultraviolet spectrum of 2-hydroxybenzo[c]cinnoIine shows close correspondence to that of the 2-methoxy compound in neutral solution, spectra of the conjugate acid and conjugate base both indicate appreciable charge-resonance between the 2- and 6-positions, and methylation of 90 with dimethyl sulfate or diazomethane gives rise to mixtures of 2-methoxy-benzo[c]cinnoline and the quinonimine 92. ... 

By use of both deuterated compounds and proton-spin decoupling, the resonance spectrum of purine has been analysed. A correlation of the data with the theoretical estimates of charge distribution was found in purine, although a polarization effects may be important especially for the carbon atoms 2 and 8 centred between two nitrogen atoms (IS). 

Fig. 8. Electron spin resonance spectrum of the electrochemically formed nitropropane radical anion, (b) Calculated spectrum coupling constants On = 2.48 mX, flH = 0.998 mX. Most likely charge distribution in the radical cation. For further details, see [111].

The proton magnetic resonance spectrum of the pyridinium ion shows low-field displacement for all the protons, most marked for the y-proton, almost equally strong for the jS-proton and much smaller for the a-proton. These results have been used to estimate the amount by which the charge densities around the pyridine nucleus are altered by cation formation. About 60 per cent of the unit charge deficiency in the pyridinium ion is centred on the nitrogen atom a. 

Trimethyl-4-pteridinone is an acid of pZ 9.5 and is therefore hydrated in the anion. The hydroxyl group is thought to be attached to C-7 and the negative charge to resonate between N-1 and N-3. The neutral species cannot be appreciably hydrated because its ultraviolet spectrum is very different from that of the anion. 

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