Formation and Stability of C₆H₃⁺Isomers

Abstract

The stability of the five main isomers of C6H3(+) was investigated using quantum chemical calculations. The cyclic isomers are stabilized by two complementary aromatic effects, first 6-electron π aromaticity, and second a more unusual three-center two-electron σ aromaticity. Two cyclic isomers sit at the bottom of the potential energy surface with energies very close to each other, with a third cyclic isomer slightly higher. The reaction barriers for the interconversion of these isomers, as well as to convert to low-energy linear isomers, are found to be very high with transition states that break both the π and the σ aromaticities. Finally, possibilities for forming the cyclic isomers via association reactions are discussed.

IR photofragmentation of the phenyl cation: spectroscopy and fragmentation pathways

“…Direct H-loss from phenylium involves a simple C-H bond breaking requiring 5.09 eV. This value is slightly higher (0.2 eV) than obtained at the CCSD(T) level, 22 which is likely due to the multi-configuration character of the m-benzyne C 6 H 4 + cation. 61 Ring opening-leading to the chain-like intermediate int2-can occur along two different reaction paths.…”

“…25 Whereas there exists a general agreement that the 1 A 1 state is the ground state, the energy difference between the triplet and singlet states is somewhat uncertain, with calculations covering a range from 77 to 137 kJ mol À1 . [22][23][24]26,27 Photoelectron spectroscopy of the phenyl radical did not shed any light on the singlet-triplet (S-T) gap. 28 Some experimental support of a singlet ground state was offered in 2000, when a matrix-isolated IR spectroscopy study of phenylium reported vibrational frequencies at 713 and 3110 cm À1 .…”

“…19,20 Phenylium is currently one of the proposed precursors in the interstellar synthesis of benzene. 21,22 Phenylium's high reactivity stems from its electrophilicity, which is induced in the singlet state by its vacant, non-bonding s orbital. 23 The empty s orbital induces sp hybridization of the C-atom, causing a substantial deformation of the hexagonal frame as is depicted in the left structure in Fig.…”

Searching for double σ- and π-aromaticity in borazine derivatives

“…It is important to note that 1 is the global minimum structure for the C 6 H 3 + combination (at the CCSD(T)-F12b/cc-pVTZ + ZPE(B3LYP/cc-pVTZ)//CCSD(T)/cc-pVTZ level). 68 Thus, in the light of our current density analysis, it is possible to suggest that the high s and p aromatic character must be contributing to ring shaped stabilization of C 6 H 3 + . Whereas system 4, despite its substantial s-diatropic character, is not an energetically competitive isomer.…”

Computation of covalent and noncovalent structural parameters at low computational cost: Efficiency of the DH‐SVPD method

“…Some of them focus on the orbital‐optimization (OO) approach [ 10 ] to correct an artificial spin‐symmetry breaking occurring in spin‐unrestricted systems. [ 11–13 ] Others are based on the range‐separation exchange (RSX) scheme [ 14 ] to (partially) cure the self‐interaction and delocalization errors [ 15 ] (SIE and DE, respectively). [ 16–19 ] However, all of them conserve similar features, that is, a fraction of EXX generally larger than 50% and a fraction of PT2 correlation ranging between 10% and 40%, which allow them to reach the chemical accuracy when modeling a large panel of properties ranging from ground‐state energies [ 20 ] to structures [ 21,22 ] and extending to singlet‐singlet vertical excitation energies.…”