Abstract
The energy profiles for ring opening of representative type B mesoionic 2,3-diphenyl-1,2,3,4-tetrazolium-5-olates, -thiolates, -aminides and âmethylides and for alternative recyclisation pathways are investigated using ab initio MP2 calculations. The energetics of initial ring opening are found to be comparable for all systems, but the tetrazolium-5-olates are anomalous in that no alternative reaction pathway is accessible. The influence of solvent is explored using the polarised continuum model (PCM) method to simulate aqueous solvation. The only significant solvent effect is found to be solvation of the mesoionic precursors. This solvent effect correlates with dipole moment and disfavours initial valence tautomerism both kinetically and thermodynamically.
Highlights
To gain a better understanding of the reaction pathways available to type B mesoionic tetrazoles, we have undertaken an MP2 ab initio study of the energy barriers to ring opening and recyclisation
We have previously studied the relative energies of ten type B mesoionic rings 1 and their valence tautomers 2
We report a study of the energy barriers associated with reaction pathways available to the mesoionic tetrazole derivatives 3a-d
Summary
To gain a better understanding of the reaction pathways available to type B mesoionic tetrazoles, we have undertaken an MP2 ab initio study of the energy barriers to ring opening and recyclisation. The calculated activation energies ÎG3T1 for ring opening via the transition state T1 (Table 1, Entries 1â4) are all in the range 26â31 kcal Âmolâ1. A significant difference between the sulphur and oxygen derivatives is the activation energy for electrocyclic ring closure (ÎG5T2).
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