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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A relation of the form k=aN(xAxB/d2)34+bhas been found to hold accurately for a large number of diatomic and simple polyatomic molecules in their ground states. (The average deviation of k calculated from k observed for seventy-one cases is 1.84 percent.) Here k is the bond-stretching force constant, d the bond length, N the bond order, and xA and xB are the electronegativities of the bonded atoms. If k is measured in dynes/cm×10−5 and d in Angstrom units, a and b have the values 1.67 and 0.30, respectively, for stable molecules exhibiting their normal covalencies, except those in which both bonded atoms have only one electron in the valence shell; for diatomic molecules of the alkali metals, Na2, NaK, etc., a and b are 1.180 and −0.013, respectively; for hydrides of elements having a single electron in the valence shell, 1.180 and 0.040, respectively; and for diatomic hydrides of elements having two to four electrons in the valence shell, 1.42 and 0.08, respectively. Numerous applications of the relation are made and certain exceptions are pointed out.

The Q-branch rotational lines of H2S2 have been measured in the frequency range 80-200 Gc/sec, those of D 2 S2, in the range from 60 to 220 Gc/sec. For HSSH, measurements were made on the torsional vibrational state Vt= 1, and the S-S bond-stretching vibrational state "11,= 1 as well as on the ground state. The molecules are the most nearly accidentally symmetric tops of any so far reported. Wang's asymmetry parameter bp = (C-B) / (2A -B -C) for the ground vibrational state of H32S32SH is found to have the value bp = -1.10X 10-5 ; fOL H32S84SH, bp = -1.07XlO-5 ; for D32S32SD, bp = -2.10XIQ-6. The asymmetry increases markedly with the torsional oscillation: for H32S32SH when "IIt=l, bp = -4.055XlO-5; it decreases with the S-S stretching: for H32S32SH when "11.= 1, bp = -7.72XlO-o. The molecule is found to have the nonplanar chain structure HSSH, with the structural parameters having the values: daR = 1.327 A, daB = 2.055 A, L HSS = 91.32°, and the dihedral angle '1=90°36'. The barrier to relative internal rotation of the two SH groups is evidently very high, much higher than in H20 2• The internal rotational splitting of the ground vibrational state is too small to be resolved. In the torsional vibrational state Vt= 1 it was found to be 2Av= 15.99 Mc/sec. The near orthogonality of the bond angles, the S-S length, and the high barrier to internal rotation indicate significant 7T" bonding through the mechanism of hyperconjugation.

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