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The 60-Mc/sec proton magnetic resonance spectra of N-methyl-2,4,6-trinitroaniline (I) and of N-methyl-2,6-dinitroaniline (II), as well as of the analogous N-diphenylamino compounds, show that the 3- and 5-phenyl protons are inequivalent at low temperatures in solution, but act as equivalent at sufficiently high temperatures. The N-unsubstituted anilines and N,N-dimethyl anilines corresponding to I and II show no such inequivalence. The coalescence with temperature of the AB quartet of the picryl protons in the picrylaniline (I) and diphenylpicrylhydrazine in dichloromethane solution could be described quantitatively by the line-shape equations for two coupled protons exchanging with each other. The analysis yielded the lifetimes of the ground state configurations of these molecules, with Arrhenius activation energies of 14.5±0.3 and 12.5 ± 0.2 kcal/mole and frequency factors of 1.4×1015 and 6×1010 sec—1, respectively, for the intramolecular exchange process. A model for these observations, including Hückel MO calculations, is presented in terms of the barrier to rotation about the amino nitrogen-ring carbon bond, the orientation of the nitro groups ortho to the amino group, and hydrogen bonding between the amino group and these nitro groups. The chemical shift and spin—spin coupling parameters for these compounds and for the 2,4-dinitro analogs are tabulated and compared. The chemical shift values exhibit regularities in excellent agreement with the model introduced.

The adsorption of dyes and particularly of cyanines at silver halide, silver or mica substrates is generally accompanied by changes in the dye spectra. Depending on the system, these changes have been quantitatively evaluated either by reflectance measurements with application of the KubelkaMunk relation or by transmission spectroscopy. Surface concentrations and saturation coverages of the dyes as well as surface areas and average particle dimensions of the substrates were obtained. These values generally agreed well with independently determined measurements and yielded Langmuir adsorption coefficients, apparent standard free energies of adsorption, and probable orientations of the adsorbed dyes.Tt is the purpose of this paper to describe methods for determining and A interpreting dye spectra in aqueous dispersions of silver halides and other substrates. Such spectra can be utilized for the direct measurement of surface concentrations of dyes from which, in turn, the surface area of the substrate can be derived. The techniques involved are not limited to a specific dye class but will be illustrated in this paper by the behavior of cyanine dyes.The known factors which influence the solution spectra of cyanines have been recently reviewed (14,46,73). It will be sufficient to sum marize here some of the concentration-dependent spectral properties for the specific case of l,l'-diethyl-2,2'-cyanine; this cyanine was employed in many of the present experiments. In alcohol as in dilute water solutions this dye, which will be referred to as Pseudocyanine, although it has also been called Pseudoisocyanine, appears to exist only in an extended con figuration and has its maximum absorption near 523 n.m. This transition 173 Downloaded by UCSF LIB CKM RSCS MGMT on December 2, 2014 |

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Hoboken, N. J.