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316
Vol. 85
CgHlz(AgNO&: C, 17.16;H , 1.92;Ag, 51.35. Found: another less symmetric arrangement, Ia, which can C, 17.46; H, 2.06; Ag, 51.40). I was regenerated by exist in any of six equivalent conformations. The treating the silver nitrate adduct with excess amunusual absorption of the methylene hydrogens (Fig. monia. Sublimation a t room temperature (25 mm.) 1, 7.17 T ) is the result of ;L dynamic equi1ibr;ttioii. gave white needles (having a high vapor pressure), The appearance of this peak i.; cxtremely temperature m.p. 50-51’ cor. (Anal. Calcd. for CgH12: C, dependent. Heating the sainple causes the niethylene 89.94; H, 10.06. Found: C, 89.92; H , 10.12). absorption to narrow and sharpen up. Cooling causes The found molecular weights was 120 (mass spectrothe broad absorption to separate into two peaks of metric determination). The conversion of VI1 to I equal area which sharpen up with further cooling. by a given pyrolysis was 0-14% of the neutral pyrolyThus there is interconversion between two equivalent sate as determined by gas-liquid chromatography (5% symmetrical conformers, I. N.ni.r. spectra have been Carbowax 1500 on Fluoropak 80, 4 m. X 6 mm., 100’ obtained a t various temperatures ranging from - 10 column) .9 to 53.5’. These results are reported in a second paper. l’i Infrared (vapor phase) : strong absorptions at 3.30, A completely rigid structure proof for I has been 3.36, 3.40, 11.40, 13.85 p ; medium absorptions a t obtained by proton-proton spin decoupling experi3.47, 5.94, 6.07, 6.72,6.75,6.80,11.36 p ; ultraviolet: ments. These data along with a detailed analysis of xmax = 198 ml.r (9,300),Xshoulder = 210 mU (4,600) the spectra will be reported. in cyclohexane a t 7.4 X 10-5 mole/l. Whether I shows aromatic character or not will be Exhaustive hydrogenation of I gave cyclononane deferred until studies are completed on the “frozen” whose g.1.c. retention time and infrared spectrum were symmetrical conformer. l 4 However, simple LCAO identical with those of an authentic sample. M O calculations have been carried out for I using Together these data show that the isolated hydroangle parameters of 120’ (sp2 bonds) and 109*28”(sp” carbon is a cyclononatriene. The possible isomers bonds). The result thus obtained is a lower limit for (other than I and cis,cis,tians-l,3,5-~yclononatriene~~) a predicted absolute value for any delocalized energy that were considered are cis,cis,cis-1,3,5-, cis,ck,cisthe molecule might possess since these parameters 1,3,6-and cis,cis,trans-l,4,7-cyclononatrienes.Any isoignore steric repulsion of the three inner methylene mer containing a trans olefin is less plausible because hydrogens, This repulsion is undoubtedly present the infrared absorptions (7.6-7.7, 10.4-10.5 p ) atand would cause the homoallylic overlap to be greater tendant with dialkyl trans olefinsi1 are absent in the than that calculated. The calculations give a value spectrum of the new hydrocarbon. of 25.0% as much 2,4-overlap as that of 1,2-overlap The n.m.r. spectrum12 (Fig. 1) of the isolated comand predicts negligible (0.02%) delocalization energv pound provides evidence to assign its structure. The with the six pi electrons occupying three delocalized orbitals (degenerate pair a t -0.955P and one a t IO 300 400 500 600 (
I
-1.03p).
The author gratefully acknowledges the able technical assistance of Mr. D. J. Martin throughout this research and helpful discussions with Drs. A. A. Bothner-By and H . Conroy. (13) K. G. Untch and R. J. Kurland, J . A m . C h ~ mSoc., . 86, 348 (1003). (14) However, t h e infrared spectrum of V and a ferric chloride test showed n o enol form present.
MELLON INSTITUTE PITTSBURGH 13, PENNSYLVANIA RECEIVED NOVEMBER 19, 1962
K. G. IJwcii
THE CONFORMATIONAL EQUILIBRATION OF
c~s,c~s,c~~-~,~,~-CYCLONONATRIENE; A DETERMINATION OF ACTIVATION ENERGY AND ENTROPY BY N.M.R. 11.
Sir : The synthesis and properties of cis,cis,cis-l,4,7cyclononatriene (I) have been reported.’ We wish to present the results of a detailed investigation of the temperature dependence of the n.m.r. spectra of I. This behavior is displayed (Fig. 1) by the n.m.r. spectra taken a t three representative temperatures. As pointed out previously‘ this temperature dependence reveals that the two equivalent forms of the conformation (Ia), hereafter called the “crown,” are interconverting. After the interconversion of one crown t o its mirror image, the inner and outer methylene hydrogens are exchanged. I may also attain a less symmetrical conformation (Ib), hereafter called the “saddle.”
IU
IS
( I ) K. G. Untch, J . A n . Chcm. SOC.,85, 345 (1963).
Feb. 5, 1063
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The low temperature spectra (
