chromophores, especially MA2 where the metal ion bridged two such resonating ligands.The role of chloride in these complexes could not be studied by the present method, but it is probable that chloride ions occupy vacant coordination positions on Sn(IV). It is suggested, also, that chloride-bridge structures are important in the dinuclear, M2A, complex.

Carboxymethylcellulose (CMC) was hydrolyzed in aqueous sulfuric acid at -90 OC to yield substituted glucoses which were analyzed by proton nuclear magnetic resonance. A procedure for the measurement of the degree of substitution (DS) of CMC was developed. Agreement of the DS determlned in thls procedure with that obtalned from a standard ASTM method is generally good. Additionally, the average distribution of the carboxymethyl substituents in CMC was also measured from the same spectrum. This result showed that the reactivity of the hydroxyls in cellulose toward carboxymethylation varied in the order OH(2) > OH(6) > OH(3), where the numbers In parentheses represent the carbon posllions in the anhydroglucose unit.Carboxymethylcellulose (CMC) is an important industrial polymer which finds wide application in detergents, textiles, paper, food, drugs, and oil well drilling operations, among others. In 1974, over 75 million pounds were produced in the United States alone ( I ) . Many of the properties of CMC in actual applications depend to a large extent on two key structural parameters, namely, the degree of substitution (DS) of the hydroxyl groups on the anhydroglucose unit and the distribution of the carboxymethyl substituents.A spectrophotometer is described in which a linear photoarray using charge-coupled technology is used as a detector. The device can access 260 nm of the visible spectrum in as little as 8 ms. Using the detector's integrating character, the exposure time is programmed by computer so that the signalto-noise ratio can be substantially Improved. A model for the variance as a function of wavelength and absorbance was developed and validated.

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Large proton magnetic resonance contact shifts were observed for ethylenediamines coordinated with nickel(l1) ion in aqueous solution. The observed spectra are highly sensitive to the conformational states of the ligand molecule, and considerable structural information can be obtained by investigating the effects of alkyl substitution and of temperature on the spectra. The chelated ligand was found to exist in various gauche forms, with fast conformational exchange between corresponding k and k ' forms and with slow exchange between configurations that require Ni-N bond rupture for interconversion. The alkyl substituents are shown to prefer the pseudo-equatorial position in the ring; the N-methyl group, for example, was found to be 0.43 kcal/mole more stable thermodynamically at this position than at the pseudo-axial position for the tetraaquo-N,N'-dimethylethylenediaminenickel(l1) ion.CONSIDERABLE EVIDENCE, based on X-ray and infrared studies in the solid-state, has now been accumulated ( I , 2) to establish convincingly that the ethylenediamine molecule in coordination complexes exists as a puckered five-membered ring and in a gauche configuration; much earlier it had been tacitly assumed that a planar cis configuration was predominant. Conformational energy differences estimated on the basis of a theoretical model proposed by Corey and Bailar (3) also suggest the gauche form to be the preferred configuration. Several attempts to acquire experimental proof of this preference by the nuclear magnetic resonance (NMR) technique (1,(4)(5)(6) have been reported. However, in the most thoroughly studied example, tris-ethylenediaminecobalt(II1) ion, the methylene protons do not exhibit well refined NMR splitting, which would theoretically be an AzBz system in gauche configuration and in the absence of additional splitting from N, Co, and NH protons. A broad, highly overlapping pattern was observed in HzO, D20, DzSOd, and in trifluoroacetic acid, even over a range of temperatures. This had been rationalized as arising either from too small differences in the chemical shifts between the magnetically different protons or too great mobility of the ring in the gauche form.In this report, conformational studies were carried out, for a number of reasons, on various N-alkylethylenediamines coordinated with nickel(I1) ion in D20. Because of the strong magnetic moment of the unpaired electron spins of the para-

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