Homodesmotic reaction, definition

It is worth noting that Wheeler et al. °° have delineated a hierarchy of reaction schema that define various levels of conserved components. This includes a more rigorous definition of isodesmic and homodesmotic reactions, along with providing higher order reactions that conserve larger fragments of molecnles. 

Although the positive A " values definitely indicate considerable stabilization of the conformation 10 of /3-pnictovinylaldehydes relative to their sterically unstrained trans-s frans conformation 10b, one may conclude that this stabilization is almost exclusively caused by the factors (electrostatic and no Opn R orbital interaction) responsible for the formation of the secondary Pn" 0 bond. This conclusion follows from the data on HSE values computed for 10 on the basis of the homodesmotic reaction 3, similar to that (eq 2) applied for evaluation of the aromatic stabilization of y3-chalcovinylaldehydes and their imines 7. 

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