The Jahn-Teller split HOMO of the cyclohexane cation in selectively alkyl-substituted cyclohexanes: an ESR and MNDO/INDO MO study

A study of the dynamic equilibrium between symmetrical and distorted 1,2,3-trimethylcyclohexane radical cations

“…The two hydrogens causing the hf triplet are located on two methyl groups, CI' and C2' with their C-H bonds being coaxial to the C1-C2 bond of the ring in which large part of the unpaired electron spin is located. This is in agreement with the known radical cation structures of a variety of methylsub-stituted cyclohexanes [12][13][14][15][16][17][18][19]. Note the possibility of forming an asymmetrical structure being the mirror image by localizing the unpaired electron in the C2-C3 bond of the two symmetrical isomers and with the assignment of hf splittings due to the symmetry-related hydrogens.…”

“…Previously we have elucidated the electronic structures of cations of a variety of alkyl-substituted derivatives, and particularly for the tases with alkyl-groups in two positions, such as cis and trans isomers of 1,1-, 1,2-, 1,3-and 1,4-substitution [12][13][14][15][16][17][18][19]. The 1,3-substituted cations showed the coexistente of two different ground states [18], implying that the energy difference between the electronic states in cations of this and related structures is small.…”

“…3.4 mT) in all three isomers. This is due to an asymmetrical ground state structure with the unpaired electron localized to the C1-C2 bond and with similarity to both the methylcyclohexane [13], 1,2-dimethylcyclohexane [14] and 1-methylsilacyclohexane [20] radical cations. The approximate SOMO (Singly Occupied Molecular Orbital) for one of the symmetrical isomers is depicted ~ below:…”

“…Cyclic alkanes with degenerate HOMO (Highest Occupied Molecular Orbital) have attracted attention due to the possibility of having Jahn-Teller distorted ground states [6][7][8][9][10][11]. A degenerate HOMO can also be split by introducing substituents, which has encouraged us to investigate a variety of alkyl-substituted cyclohexane cations [12][13][14][15][16][17][18][19].…”

“…It is shown that at low temperature (rigid limit) the cations take ala asymmetrically distorted C~ structure with structural resemblance to the methylcyclohexane [13], 1,2-dimethylcyclohexane [14] and some silacycloalkane [20,21 ] radical cations. A reversible temperature effect on the ESR line-shape between 4 and ca.…”