 The reaction mechanism for the Johnson – Corey – Chaykovsky reaction consists of nucleophilic addition of the ylide to the carbonyl or imine group . A negative charge is transferred to the heteroatom and because the sulfonium cation is a good leaving group it gets expelled forming the ring . In the related Wittig reaction , the formation of the much stronger phosphorus @-@ oxygen double bond prevents oxirane formation and instead , olefination takes place through a 4 @-@ membered cyclic intermediate . 
 The reaction mechanism for the Johnson – Corey – Chaykovsky reaction <a href='uninflect' title='1'><mark>consists</mark></a> of nucleophilic addition of the ylide to the carbonyl or imine group . A negative charge is transferred to the heteroatom and because the sulfonium cation <a href='drop_aux' title='2'><mark>is</mark></a>a good leaving group it <a href='uninflect' title='3'><mark>gets</mark></a> expelled forming the ring . In the related Wittig reaction , the formation of the much stronger phosphorus @-@ oxygen double bond <a href='uninflect' title='4'><mark>prevents</mark></a> oxirane formation and instead , olefination <a href='uninflect' title='5'><mark>takes</mark></a> place through a 4 @-@ membered cyclic intermediate . 
The reaction mechanism fir da Johnson – Corey – Chaykovsky reaction consist of nucleophilic addition of the ylide to tdacarbonyl or imine group . A negative charge is transferred to the heteroatom and because thdaulfonium cation a good leavin group it get expelled forming the ring . In thedalated Wittig reaction , the damation of the mda stronger phosphorus @-@ oxygen double bond prevent oxirane formation and instead , olefination take place through a 4 @-@ membered cyclic intermediate .