Acceptor atom, -orbitals

Obviously, all of the factors which determine bond energies must be taken into account, such as the charges and sizes of A and B, the electronegatives of the donor and acceptor atoms, orbital overlaps, and steric repulsions. The HSAB Principle then refers to an additional stabilization of hard-hard or soft-soft pairs, or a destabilization of hard-soft pairs. 

For electron movement to occur, the donor and acceptor molecules must approach so that the donor HOMO and acceptor LUMO can interact. For example, the LUMO of singlet methylene is a 2p atomic orbital on carbon that is perpendicular to the molecular plane. Donors must approach methylene in a way that allows interaction of the donor HOMO with the 2p orbital. 

A simple, perhaps too-naive, electronic interpretation of these polar states in the snap-out reactions comes from the observation that if one is to form a bond between two already bonded atoms in a molecule then an electron from one must be available to fall into a vacant orbital of the other. But for the activation energy to be low for such a process, the donor atom (base) must become strongly negative in charge and the acceptor atom (acid) must have a low-lying orbital vacant to receive the electron. However, its low-lying orbitals are already filled so that in order for one to become vacant, it must become complimentarily charged, i.e., positive. The sequence of steps may be pictured as ... 

Superexchange is another mechanism of electron transfer over relatively large distances in which the solvent or matrix acts as a bridge between the donor molecule D and the acceptor molecule A. It differs from electron hopping in that the electron is at no time actually localized on a molecule of the medium there is an interaction between the orbitals of the molecules A, B and D which form a sort of very loose supermolecule over which the electron is delocalized (Figure 4.10). This mechanism seems plausible when the relevant orbitals of A, B and D are rather close in energy. This is similar to the requirement for the interaction of atomic orbitals to form a molecule. 

The atom accepting the electron pair must have an unfilled orbital available which the donated electron pair can populate. This can be an unfilled valence shell orbital, as is the case if the acceptor atom has a valence sextet, or it can be an accessible antibonding orbital, either a or it. ... 

Triphenylmethyl (trityl) tetrafluoroborate, on the other hand, is sp2 hybridized but it is also extremely reactive toward electron donors. The acceptor orbital of the trityl cation is an unfilled 2p atomic orbital on the charged carbon. These carbon electrophiles are isolable compounds, but they are extremely reactive with any sort of electron donor (H2O vapor is a common culprit). 

A common case is that the matrix element ( coupling, rq f) is non-zero between donor and bridge at a single atomic orbital which we give index 1. The acceptor is similarly in contact with the last orbital of the bridge, with index n (coupling=9). Most matrices of eq.(27) are thus sparse and it is easy to derive the effective interaction matrix element [19], The energy difference A between and a may be written as ... 

The terms in this matrix element correspond to paths from p on the donor, to atomic orbital in the medium, and from i in the medium to v on the acceptor. 

A similar reasoning applies to virtual transfer of an electron from a filled orbital at an atom of spin S to a half-filled orbital at an acceptor atom. 

Sn-Sn bonding model in [Sn CH(SiMe3)2h]2 (a) overlap of atomic orbitals, (b) representation of the donor-acceptor bonding. 

Maximum acceptor superdelocalizability Artificial Neural Network Atomic Orbital Androgen Receptor Automated Rule-Induction... 

Baetzold used extended Hiickel and complete neglect of differential overlap (CNDO) procedures for computing electronic properties of Pd clusters (102, 103). It appeared that Pd aggregates up to 10 atoms have electronic properties that are different than those of bulk palladium. d-Holes are present in small-size clusters such as Pd2 (atomic configuration 4dw) because the diffuse s atomic orbitals overlap strongly and form a low-energy symmetric orbital. In consequence, electrons occupy this molecular orbital, leaving a vacant d orbital. For a catalytic chemist the most important aspect of these theoretical studies is that the electron affinity calculated for a 10-atom Pd cluster is 8.1 eV. This value, compared to the experimental work function of bulk Pd (4.5 eV), means that small Pd clusters would be better than bulk metal as electron acceptors. 

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