Highest occupied molecular orbital charge distribution

The type of conjugation is also reflected in the frontier orbital profile, the charge distribution, and the permanent dipole moments. The results of semiempirical calculations on l-methylpyridinium-3-olate (16), Malloapeltine (17), Trigollenine (18), and Homarine (19) are presented in Scheme 7. Characteristically for the class of conjugated mesomeric betaines, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are distributed over the entire molecule as examplifled for l-methylpyridinium-3-olate. It was shown that 90% of the... 

Another approach has been to try and determine the positive charge distribution in the reactive ion from consideration of the electron distribution in the highest-occupied molecular orbital (HOMO) of the neutral [390, 391, 392, 549, 733]. The positive charge distribution is used to predict the relative probabilities of different bond scissions [390]. 

If only the electron density of the highest occupied molecular orbital (HOMO) is taken into account, an electrophilic attack is said to be regulated by the frontier electron density index (54JCP1433 79FCF1). In nucleophilic substitutions, the aromatic substrate tends to accept an electron pair in the transition state, and so the frontier orbital is taken as the lowest unoccupied molecular orbital (LUMO). In this case, the frontier electron density is assumed to be as the electron distribution that would be present in the LUMO if it were occupied by two electrons. In contrast to arguments based on the charge or 7c-electron densities, both nucleophilic and electrophilic substitution occur preferentially at the atom with the highest electron density within the appropriate frontier orbital, i.e., LUMO or HOMO, respectively. 

Figure 2.18. Electron affinities of Aui 7g. Predicted shell closings at 8, 20, 34, and 58 are o bserved L The gradual increase in electron affinity, and also the decrease in ionization potential can be nnderstood electrostatically. When a conductive sphere increases in size, the charge can be better accommodated because it can distribute over a larger surface. The low electron affinities are found at the shell closure values, because the empty orbitals have a high energy with respect to the occupied orbitals. The differences in energy between the odd- and even-number clusters reflect differences in energy between the corresponding HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital).

Molecular orbitals are characterized by energies and amplitudes expressing the distribution of electron density over the nuclear framework (1-3). In the linear combination of atomic orbital (LCAO) approximation, the latter are expressed in terms of AO coefficients which in turn can be processed using the Mulliken approach into atomic and overlap populations. These in turn are related to relative charge distribution and atom-atom bonding interactions. Although in principle all occupied MOs are required to describe an observable molecular property, in fact certain aspects of structure and reactivity correlate rather well with the nature of selected filled and unfilled MOs. In particular, the properties of the highest occupied MO (HOMO) and lowest unoccupied MO (LUMO) permit the rationalization of trends in structural and reaction properties (28). A qualitative predictor of stability or, alternatively, a predictor of electron... 

EH molecular orbital calculations have been performed for these systems as well as for the isolated D - A units. Charge distributions, highest occupied and lowest empty levels, 3f -resonance energies have been considered. 

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