.I172
NOTES
..C
notic properties of a barbituric acid with a 3-alkyl substituent containing a nitro group, i t was thought to be of interest to prepare the barbituric acid from the above compound. Considerable difficulty was experienced in bringi:ig about the condensation between urea and ethyl ethyl- (I -1iietliy1 1 -nitrorthyl)-malonate. The desired compound was firidly obtained in 9% yield using a modification of a procdure described hy AZcElvain arid Gorst .'The pharmacological properties of the sodium salt of the conipound were studied by Lk. J. S . Spencer of the Phdrrnacology 1)epartment ot this 1,aboratory. He reports the following properties. Intraperitoneal LDaU(iiiici 360 mg./kg. 490 mg /kg Oral LD50 (mice) Hypnotic dose (EL) in mice) 110 mg./kg KO hypnotic action observed follo~%iiig oral administration in i i i i u ~ Experimental 5-Ethyl-5-( 1-methyl-1 -nitroethyl) -barbituric Acid ,-To a mixture of 4.8 g. (0.08 mole) of urea, 11 g. (0.04 mole) of ethyl ethyl-(l-methyi-l-nitrc~thyl) malonate, and 100 ml. of dry t-butyl alcohol was added 0.5 g. of sodium methoxide. The alcohol was distilled from the stirred mixture at about 30 ml. per hour and fresh t-butyl alcohol was added continuously at the same mte. One-half gram portions of sodium methoxide were added every hour until 3.5 g. had been added. One hour after the last portion of sodium methoxide had been added, the t-butyl alcohol was distilled under reduced pressure. The residue was cooled, 100 ml. of water was added, and, after a short period of stirring, the water was extracted with 50 ml. of ether. Acidification of the water with concd. hydrochloric acid gave 0.9 g . of white ppt., in. p. 233-237". Recrystallization from ethanol raised the in. p . (cor.) to 238-240" (dec.). Anal. Calcd. for C9€11&305: C, 44.44; H , 5.31; S , 17.27. Found: C, 44.53; 11, 5.46; N, 17.00. iMcElvdin and Goesez had used sodium 6-butoxide as a catalyst In the reaction reported the more readily available sodium niethox~rlcwLi\ found to give equally good rcsul t i (2)
S bl McLSlvain and 31 1 C O C ~ P THIS , JOURNAL, 66, 222G
i1943)
PHARMACEUTICAL RESEARCH U~vrsrolr COMMERCIAL SOLVEVTS CORPORATION RECEIVED J U V E 5, 1950 'rERRE H ?UTE, I VDiAYA
The Resonance Energy of Benzene BY L)c,i. ' i r n 1' HC)RNI(.
Only a small displaceiiient of the carbon atoms is necessary to distort a normal benzene molecule with 1.39 A. C-C bonds t o a configuration where C-C bonds are alternately 1.34 and 1.51 -Le.,
a.;
the configuration represented by a single Kekul6 structure without resonance. Since the displacements are small, the energy expended in distorting the molecule can be obtained from the force constants derived from the vibrational spectrum. If, as is sometimes assumed, the bond length is a sufficient criterion of bond type, this energy might be expected to equal the resonance energy.
Vol. 72
Since the C-H distance and H-C-C angle of KekulC benzene are the same as those of benzene, the distortion involves otily the two symmetry coordinate$' 0 >,I
= (l/v'f;)(rl
+
c
Y?
= (l/dt3)(yJ -
Y-
r3
+ + + rd
-t y 3 -
rl
rd
y5
+ I:, -
ih)
whose forms are illustrated in Fig. 1. The 7's are the changes in the C-C bond lengths. The force constants corresponding to these symmetry coordinates have been designated A, and A2 by Crawford and &filler1who found that AI = 7.83 X 1Oj dynelcm. Inserting the frequencies of the Bz, vibrations obtained by Mair and Hornig2 (Table I) into the equations of Crawford and Miller, two possible sets of force constants for the 132,, species are obtained. They are given in Table 11. TABLE I FREQUENCY OF BzuVIBRATIONS IN BENZENE Cornpound
VI#,
CfiHG CtJL,
cni
ns, cm. - 1
--I
1311 1887
1147 825
TABLE I1 HI / u i i # ! o r u % .i, l i ? ~ .6, , 111 (l!IXl).
