the very small (3.0 f 3.0 cc.) apparent orientation polarization observed. -4lthough a small tfipole niornent is entirely possible from the ddtct. no reasonable structure has been proposed for this substance for which one would predict an electric moment of the magnitude 0.5 D Most of the structures proposed recently for nitrogen tetrasulfide such as the cradle form of the eight-membered ring iavored by Lu m d Donohue,l or the closely r e l a t d ring structure proposed by Hassel m d Viervoll,L would be non-polar ; on the other hand a branched chain structure with several multiple bonds, such as that of Ruff and Geisel,lb would probably have a considerably larger moment. \Ye favor the idea that nitrogen tetrasulfide is nonpolar but shows an an abnormally lai-ge ~ t o m i c polarization (about 0.15 MRD). Phosphorus sesquisulfide was assigned a structure in which sulfur atoms are inserted between three of the six P-P bonds of tjie Pd molecule, L PSP = 100" and P-S = 2.15 A. The P-Sbond moment is not known but if we use the observed nionient of P4S3 and the above data, a value P-S = 0 36 D is calculated which is close to the 0.40 D predicted froin electronegativity differences" and, along with the agreement between observed and calculated molar refractions, lends some support to the structure of Hassel and Petterson. The electric moment of S(CN)2indicates that it is a bent molecule and, choosing L CSC = 1 O j " (as i n dimethyl sulfideiY),the S C S bond moment I$ found to be 2.25 in good agreement with the \ector sum, 2 12, of tlie C-S :mi Chi niornents
We assume that See(CN)., has a straight chain structure analogous to the trisulfidesi9 with bond angles L Se-Se-Se, L Se---Se-C = 105" and dihedral angles 41(Se-Se-Se-C1) and +z(Se-Se-Se-Cll) = 90". The electric moments of the three isomers (see ref. (30))of Ses(CN)2are then calculated to be 1.45 (q5i = 90",42 = ' i o " ) , 1.45 ($1 = Z o o , ~$2 = R O O ) and 5.09 (41 = +2 = goo), using a value 3.6 D for the Se-CN bond moment (slightly larger than observed above for the SCN bond moment) ; on the other hand p = 3.64 D would be predicted for free rotation about all single bonds of the tnolecule. The observed value could be accounted ior about equally well by assuming free rotation or by postulating a mixture of isomers resulting from hindered rotation. The mean electric moment of perchloroniethyl mercaptan in the two solvents studied is 0.62 D. Since the Cl.(-C bond moment (0.sj and the C-S bond moment (0%) are nearly equal and opposite, the S-CI bond moment derived from our results is 0.ti2 D. This is close to both the value 0.45 observed previously' and the value 0.5 predicted from electronegativity differences. l 7 The iiioinent of SsC12 calculated for a linear chain molecule using S-C1 = 0 . E D , L SSCl = 105", and dihedral angle C1-S-S-Cl = 90",is 0.85 D; this agrees fairly well with the values 0.92," 1.0y2and 0.932yreported previously but not with the value 1.6 reported by Snlyth, at 0!.3
(19) J. Uonohue and V . Schiiinaker, J . Chcm. Phys., 16, 9 2 (l%C3~. (20) C . C. Woodrow, 11. Cnrninck and J, G. Miller, ibid , 19. K s I (1951). (21) G. Scheihe and 0.Stoll, B I T . ,71B, 1571 (1938). (16) 0 Ruff atid F Geisel. Ber , 37, 1373 (1901) (22) Y. hlorina and S. AIizushima, Sci. P u p e r r I n l . Pliys. Clirm. (1;) 1, PdUllng, "hiature of t h e C h c m i ~ r 13111l, l ' Second I d i l i ~ ~ n , Z
