Electronegativity orbital unsymmetrical

The AOs combine to form new MOs but they do so unsymmetrically. The more electronegative atom, perhaps O or F, contributes more to the bonding orbital and the less electronegative element (carbon is the one we shall usually be interested in) contributes more to the antibonding orbital. This applies both to o bonds and to n bonds so here is an idealized case. 

Both unsymmetrical species F—F—0 (bent) and F—0=F (bent) were predicted [13] on the basis of the MO calculation for diatomic OF (see p. 67), which may form a weak o bond by overlap of a p orbital of a highly electronegative atom with one lobe of its jt orbital. However, this bonding model was criticized and replaced by a three-center model which does not support the unsymmetrical FFO species [16]. Heats of formation, calculated by the MNDO method [14] for (symmetrical) FOF (18.2 kcal/mol) and for FFO (125.8 kcal/mol), show the former to be the more stable species [15]. 

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