Electronegativity values derived from various methods are compared, and a complete electronegativity scale is arranged for all the elements. A chart is given which shows a systematic relation of electronegativity to the periodic system of the elements. A linear relationship is found between electronegativity and the work function of metals.

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and Summary.-Analysis of the electron spin resonance (ESR) of a 'y-irradiated single crystal of L-tyrosine-HCl reveals a free radical formed by loss of an H from the hydroxyl group attached to the ring. Principal g values of the radical are g. = 2.0023 A 0.0005, g, = 2.0067 + 0.0005, and g, = 2.0045 ± 0.0005, with gx perpendicular to the plane of the ring and g, along the CO bond to the ring. Analysis of the hyperfine structure of the spectra shows electron spin density on C(2) and C(6) to be 0.24 and on C(4) to be 0.32. Corresponding spin densities calculated from molecular orbital theory are 0.26 and 0.31, respectively.Radiation effects on various derivatives of tyrosine in the powdered or polycrystalline form have been investigated before with electron spin resonance.1-' By bombardment of the sample with H atoms, Liming and Gordy4 recently showed that one type of radical produced results from H addition on the tyrosine ring. However, there are other ESR signals produced by ionizing irradiation of tyrosine and its derivatives which cannot be attributed to H-addition radicals. Also, when H-addition radicals are formed by ionizing irradiation of pure tyrosine, it is evident that the added H atoms must be released from some other part of the molecule. As the possible explanation of the ESR patterns observed in 7y-irradiated samples of powdered tyrosine and polytyrosine, radicals formed by loss of the hydrogen from the OH group on the ring have been postulated,1' 2 but this postulate could not be proved from the unresolved structure of the resonance of the powdered samples. We have undertaken this study on single crystals in the hope of correctly identifying the radicals formed and obtaining quantitative information about them.The Tyrosine-HCl Crystal.-Single crystals of L-tyrosine-HCl were grown at room temperature by slow evaporation of L-tyrosine dissolved in 30 per cent hydrochloric acid.The dimensions of the crystal used in this study were 1 X 1 X 8 mm. When the crystal was rotated about the c axis (see Fig. 1), six faces were observed. The approximate angles between these faces were measured by an optical goniometer, and the values were compared with the ones calculated from the unit cell dimensions.

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