Oct. ,5, 1955
COMMUNICATIONS TO THE EDITOR
higher than t h a t of its optically active components. Since Grewe and Pachaly have proved their compound to have a 2,5-di-O-tosyl structure rather than the 4,5-di-O-tosyl structure t h a t we had guessed for our compound, the latter may now be written with confidence as 1,3-0-benzylidene-2,5di-O-p-tolylsulfonyl-D-arabitol. The analogous, partially tosylated 1,3-0-methylene-~-arabitol (m.p. 161-163') to which we assigned tentatively a 4,sdi-0-tosyl structure, now appears more likely to be 1,3-0-methylene-2,5-di- 0 - p - tolylsulfonyl-D-arabitol.
5181)
of chloroform, and the mixture diluted with n-pentane as the racemate began to crystallize in clusters of needles. After two recrystallizations from chloroform-pentane and one from ethanol, the product melted a t 152-154" and showed no detectable rotation in chloroform ( c 0 . 8 , 1 4 ) . Anal. Calcd. for C2eHsaOySs: C, 56.92: H, 5.14; S , 11.69. Found: C,56.77; H,4.88; S , 11.71.
Acknowledgment.-The authors wish to thank Dr. William C. Alford and his associates for the microanalyses, Mr. William M. Jones for the infrared data, and Mr. Vernon M. Mosley and Dr. Norman E. Sharpless, all of this Institute, for the X-ray data.
NATIONAL INSTITUTE OF ARTHRITIS Experimental AND METABOLIC DISEASES INSTITUTES OF HEALTH 1,J-O-Benzylidene-P, 5-di-O-p-tolylsulfonyl-~~-arabitol.-NATIONAL About 0.15 g. of each enantiomorph was dissolved in 5 ml. BETHESDA 14, MARYLAND
COMMUNICATIONS T O T H E EDITOR THE STABILITIES OF 1,3,5-TRINITROBENZENE C O M PLEXES OF ORTHO SUBSTITUTED BIPHENYLS
Sir: X-Ray diffraction studies of crystalline 1: 1 complexes of aromatic substances with 1,3,5-trinitrobenzene or benzoquinone, both of which seem to function as electron acceptors in the interactions, show that the acceptor molecule is oriented in the complex with its ring plaae parallel to and separated by somewhat over 3 A. from the plane of the donor ring.' Studies are in progress in this Laboratory to test whether or not the attainment of this parallel plane configuration by the complex components is highly critical for the achievement of maximum complex stability. A clearly positive answer to this question has now been obtained through the evaluation of equilibrium constants for formation of 1 : l complexes of a series of methyl substituted biphenyls with l13,5-trinitrobenzene in carbon tetrachloride a t 25". These were determined through colorimetric investigation in the 340-415 mp region, in which the complexes show characteristic absorption, of a series of solutions in which the biphenyl concentrations varied from 0.05-0.5 M and the concentration of the nitro compound ranged from to l o p 4 M.2 The equilibrium constant, K1 (see equation 1) measured for the complex of KI
=
(complex)/(biphenyl) (TNB)
(1)
biphenyl itself was 0.92 mole-' 1. The corresponding constants for the isomeric monomethyl biphenyls were 0.35 (ortho), 1.38 (meta) and 1.70 (para). For symmetrically substituted dimethylbiphenyls values of 0.34 ( o , ~ ' ) ,1.65 (m,m')and 2.40 (p,p') were obtained, and for bimesityl K1was
