Although several different groups have studied the photolysis of phosphorus ylides, none have utilized e. s. r. to support the postulated decomposition mechanisms. The fundamental question which awaits a definitive answer is which bond breaks first upon photolysis. Tschesche1and de Silva2utilizing the ylides (1) and (2) suggested that the carbon-phosphorus double bond was initially broken while Nagao3using (3) proposed phenyl-phosphorus bond cleavage.