Insertion of singlet chlorocarbenes across C–H bonds in alkanes: Evidence for two phase mechanism

Transition states for the insertion reactions of singlet mono and dichlorocarbenes ( 1 CHCl and 1 CCl2) into C–H bonds of alkanes (methane, ethane, propane and n-butane) have been investigated at MP2 and DFT levels with 6-31g (d, p) basis set. The pπ of 1 CHCl and 1 CCl2 may interact with alkane’s filled fragment orbital of either σ or π symmetry. So chlorocarbenes insertion reactions have been investigated for both (σ/π) approaches. The σ approach has been adjudicated to be the minimum energy path over the π approach both at the MP2 and DFT levels. Mulliken, NPA and ESP derived charge analyses have been carried out along the minimal energy reaction path using the IRC method for 1 CHCl and 1 CCl2 insertions into the primary and secondary C–H bonds of propane. The occurrence of TSs either in the electrophilic or nucleophilic phase has been identified through NBO charge analyses in addition to the net charge flow from alkane to the carbene moiety.