The fluorescence spectra of various dinaphthylalkanes have been studied over the temperature range -100-lOOo. Strong intramolecular excimer formation is found only in the two symmetrical 1,3-dinaphthylpropanes, which implies that the stable excimer configuration is the symmetrical sandwich arrangement. Thermally activated self-quenching of fluorescence is important only in the two species which form stable excimers. The quenching path probably does not involve intersystem crossing to a triplet state and transient photodimer formation is suggested .he question of the geometry of an excimer con-(7) E. A. Chandross, E.

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405potassium r-butoxide in r-butyl alcohol-pyridine. After hydrolysis Acknowledgment. We are grateful to the National and careful work-up to ensure isolation of all hydrocarbon product, s, Army Research nmr analysis showed signals only of starting compounds and no evidence for the trans stereoisomers.Science Foundation and the Office (Durham) for financial support of this research.Abstract: The four stereoisomeric cyclobutanes from thermal cycloaddition of 1 ,l-dichloro-2,2-difluoroethylene ("1 122") to the stereoisomeric 2,4-hexadienes1 at 80" have been isolated by preparative vapor phase chromatography and their configurations as previously assigned have been confirmed by nuclear magnetic resonance. Tetrafluoroethylene at 120" adds to trans,trans-2,4-hexadiene to yield only the two stereoisomeric trans-propenylcyclobutanes in a translcis ratio in the ring of 4.2, and with no isomerization of the recovered diene. At this same temperature the addition of 1122 to trans,trans-2,4-hexadiene is attended by isomerization of the diene and formation of minor amounts of cis-propenylcyclobutanes along with major amounts of the trans-propenylcyclobutanes. The isomerization is interpreted as due to reversal of the initial biradical formation, which may occur after rotation in the biradical. The similar amounts of loss of configuration with tetrafluoroethylene and 1122 lead to the suggestion that the rate of ring closure is controlled, not by the rate constant of radical-radical combination, but by the rate of rotations about the three single bonds of the biradical to bring it into a conformation suitable for ring closure from an original distribution of non-cis conformations. he thermal addition of 1,l-dichloro-2,2-difluoro-T ethylene ("1 122") to the geometrical isomers of 2,4-hexadiene yields mixtures of cyclobutanes of idenChart I \ + F2C=CXz -(-) 1-tt 2 incomplete rotational equilibration of an intermediate biradical 3 (Chart I); from the relative amounts of 4-tt and 4 4 from 1-tt and 1-ct when X = C1, it was 34 t lt 44 t I-ct tical orientation but differing in configuration at the ring.' The proportions of the products correspond to

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Bei Bestrahlung des Propans (I) entsteht das thermisch unbeständige intramolekulare Dimerisierungsprodukt (II), das in das Cyclobutanderivat (III) umgelagert wird.