DFT and IQA study of substituent effect on the structure, stability, and bonding properties of CX2 singlet and triplet carbenes

Abstract

Abstract During this study, 6 carbenes with various substitutions (hydrogen, deuterium, fluorine, chlorine, bromine, and methyl) and 24 carbenoids (Li, Na, Be, and Mg) were designed to obtain extensive and comprehensive information about their structures, stabilities, atomic specifications, and bonding properties using MP2/aug-cc-pVTZ level of theory. Moreover, the PBEPBE DFT method was used for IQA analyses. The calculated molecular parameters showed both electronegativity and size of the ligand are effective on the studied structures, and the electronegativity effect is more intense than the size. Atomic hybridizations results showed the p indexes of carbon in triplet carbenes are also smaller than those in singlet carbenes, but this difference in halogen-containing carbenes is smaller than the other carbenes. In population analyses, except for sodium-based carbenoids, all carbenoids have higher Eg values than the carbenes. By considering the α-elimination as a method of preparation of these carbenes, the order of carbenes’ stabilities was obtained as f>c>b>m>h, which is the same as the order of electronegativities of the connected ligands. IQA analyses was performed to evaluate the relative stability of carbenes. It was found that the classical interaction in C-F is attractive (negative) unlike the other mentioned bonds energy for carbenes. This electrostatic term in C-F is larger in the singlet state than the triplet state, which leads to the singlet state of CF2 being more stable and consequently more favorable than its triplet state.