thoroughly extracted with 6 N hydrochloric acid, the acidic extract was made strongly alkaline by addition of potassium carbonate, and this basic solution was extracted with ether. After drying with anhydrous magnesium sulfate the ether was carefully distilled off leaving a small quantity (ca. 200 mg.) of a white crystalline material with an infrared spectrum identical with that of urethan.In a similar irradiation of a more concentrated solution of I in cyclohexane (1:10 M ratio) a small amount of diethyl hydrazodiformate (IX) was found.Attempted Radical-Initiated Decomposition of Ethyl Azidoformate in Cyclohexane. In a water bath of 49 ± 1°, a solution of 1.060 g. (9 X 10-3 mole) of redistilled ethyl azidoformate in 125 ml. of purified cyclohexane was placed in the flask, and the system was flushed with purified nitrogen and then sealed. A total of about 1.8 X 10-2 moles of diethyl peroxydi-carbonate67 was injected in portions over a 4-day period producing a slow evolution of an unidentified gas; the volume evolved at various intervals is re-(4) R.

E -50--60 --70--80-I I 1 1 h (w). 200 2 50 300 350 Figure 7. in EPA at +25 and -192".Circular dichroism curves of 5a-pregnan-20-one (XI) can be expected for XII. The relevant C.D. curves are shown in Figure 7 and, on the basis of the strong negative rotational strength, conformer XI does indeed seem to be the preferred one. The rotational strength of XI ( R O Z 5 = -6.9 X c.g.s., Ro-lg2 = -7.4 X c.g.s.) is only slightly affected by lowering the temperature. Since the rotational strengths of the two preferred conformations are predicted by the octant rule4 to be appreciably different, this result implies a large free energy for the interconversion of XI and XI1 probably approaching 2 kcal. (see Figure 3), if entropy differences in the two conformers are small. ExperimentalAll measurements were performed in Spectrogride solvents. The EPA solvent consisted of ether-isopentane-ethanol in a ratio of 5 : 5 : 2 by volume; C.D. curves were obtained, using a Baird-Atomic Jouan dichrograph operating with a photomultiplier voltage of 1.2 kv. and following the procedures and molecular ellipticity calculations outlined earlier. 39 We wish to thank Drs. P. Crabbe and A. D. Cross (Syntex, S . A., Mexico City) and Dr. G. Snatzke (University of Bonn) for furnishing pertinent manuscripts. Also, Dr. J. S. Mills (National Gallery, London) provided a sample of 3P-acetoxyhexanordammar-20-0ne,~O and Dr. CrabbC supplied samples of 30-acetoxy-l6P-cyano-A5-pregnen-20-one4l and 3P-acetoxy-16P-methyl-A5-pregnen-20-one. The technical assistance of Ruth Records and W. s. Briggs is gratefully acknowledged.Acknowledgment.

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Das nach diesem Schema zu erwartende Kohlenoxyd konnte nachgewiesen werden. Bei Umsetzung von B r o m o f o r m mit Silbernitrat in wasserigem Dioxan (gleichgiiltig ob in Gegenwart oder Abwesenheit von Cyclohexen) entsteht als Hauptprodukt (ca. 35% Ausb.) ein y-Oxa-E-laeton, dessen Konstitution durch Umwandlung in P-Brompropionsaure und dthylen-bromid rnit konz. Bromwasserstoff festgestellt wurde. \ / 0 0-CO

X-ray structural studies demonstrate that diaryl tellurium diiodides can be constrained by steric factors (ortho-alkyl substituents) to adopt a trigonal pyramidal structure in preference to the expected bisphenoidal structure. DFT calculations are shown to reproduce successfully structural details of the title compounds; they allow one to predict which coordination number should be energetically favored. All compounds are chiral, but the barrier to stereomutation by intra-and intermolecular pathways (60-85 kJmol −1 ) is rather low.

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The tris(didentate) chelates [E(OCR1R2CR3R4O)3], with E = Se and Te, display both configurational (delta or lambda; R or S) and conformational (delta or lambda) chirality. In order to assess the contributions of these three chiral arrays to the Cotton effects of the chelates and to elucidate their stereochemistry in the gas phase and in solution, calculations of the UV and CD spectra (down to 180 nm), and also of the relative stability of the chelates, have been performed at the TDDFT/TZVP/B-P86 level. An extensive conformational analysis has supplied additional information on the relevant conformers in the conformational manifold. It was found that the dominant CD effect reflects mostly the delta/lambda twists of the three five-membered ligand rings, and less so the influence of the A/A core configuration, while the contributions of any R/S chiral carbon atoms of the ligand rings are negligible. The sign, the intensity, and the energy of this dominant CD band are found to depend on the stereochemistry of the chelates in a predictable way. Among the conformers, those with equatorially disposed methyl substituents are much preferred. These results make it possible to determine the absolute configuration (A/A) and conformation (delta/lambda) of the chelates from the CD data.

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