ENDORANALYSIS OF THE TRIPHENYLPHENOXYL RADICAL
73
Acknowledgments. It is a pleasure to acknowledge the friendly cooperation of Professor K. Dimroth and Dr. A. Berndt at the Institute for Organic Chemistry of the University of Marburg and of Dr. F. Bar of the Physical Chemistry Institute of that university. Dr. Bar answered numerous questions on the triphenylphenoxy1 system and supplied a prepublication manuscript. Dr. A. Berndt synthesized the samples.
greater than the nmr widths. Another coherence effect of an intense nmr field is to couple the different degenerate nmr transitions which are excited. A complicating feature for systems with more than two equivalent protons is that the transition moments for the different degenerate nmr transitions are not the same. The detailed effects of the coherence of the radi& tion field in conjunction with the relaxation mechanisms are quite difficult to analyze, but we are programming this problem to obtain computer solutions.
Discussion
J. S.HYDE. I n our first endor experiment (J. S. Hyde and A. H. Maki, J . Chem. Phys., 40, 3117 (1964)) the endor lines from the four ring protons of Coppinger’s radical showed a small splitting which was attributed to a slight inequivalence of these protons. Subsequently, we have discovered that the splitting is removed if the nuclear radiofrequency power is reduced but that the splitting is not affected by the microwave power. Apparently the four protons are, in fact, equivalent. We are not aware of any coherence effects consistent with these observations.
J. H. FREED(Cornel1 University, Ithaca). With regard to the possible observation of multiple quantum transitions, these are expected to arise from the coherent nature of the irradiating field. Some aspects of these effects are discussed elsewhere (J. H. Freed, J . Chem. Phys., 43, 2312 (1965)), but it may be worthwhile to indicate some of them. First, there is the splitting of the esr resonance signal by the intense nmr field, but this effect will not be important when the esr and nmr transition moments are comparable and the esr widths are significantly
Volume 71,Numbet I
January 1967
