Molecular orbitals exact relationships

The appropriate energy content and reactivity of the /8-lactam 0=C-N bond (cf. the problem of 6(7)a-methyl and methoxy substitution and 2-substituted derivatives). Although the molecular orbital calculations on penicillins and cephalosporins [271,272,293] are not enough to yield exact conclusions, it is likely that a parabolic relationship exists between the electron population of the 0=C-N bond and the antimicrobial activity. 

Exact relationship between two sets of molecular orbitals [3,4]... 

Outer electrons, the ones involved in bonding, occupy exactly the sort of molecular orbitals discussed in the previous section with regard to MO calculations. Rather than discuss quantitative characteristics of specific wavefunctions, however, the Lennard-Jones paper highlights the general qualitative relationship between the electron density function corresponding to a particular wavefunction orbital and the energy associated with that orbital. These molecular wavefunctions are functionally more complex than atomic wavefunctions and their energies depend importantly on inter-nuclear distance. 

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