The breaking of the C-X bond and the formation of the new bond ( often denoted C-Y or C-Nu ) occur simultaneously through a transition state in which the carbon under nucleophilic attack is pentacoordinate , and approximately sp2 hybridised .
The breaking of the C-X bond and the formation of the new C-Nu bond occur simultaneously to form a transition state in which the carbon under nucleophilic attack is pentacoordinate , and approximately sp2 hybridized .