Molecular orbital bond older

By experimental results Coulson presumably means experimentally calibrated theoretical constants associated with molecular structure the turbulent history of molecular structure in the nineteenth century surely qualifies as theoretical any experimental results presented in terms that presuppose it. In comparing the valence-bond and molecular-orbital treatments of bond polarity, he argues that although the molecular orbital presentation is more natural and conceptually the simpler, the structures used in the v.b. description do correspond to pictures long familiar, in classical form, to experimental chemistry. Moreover, this link with the older and more conventional language is of considerable value [Coulson, 1961, 154]. 

A much older description of ethene is known as the bent bond formulation. The double bond is described as the result of overlap of two sp hybrid orbitals on each of the two carbon atoms, as shown in Figure 1.29. This model also predicts that ethene should be a planar molecule, but it predicts H-C-H bond angles of 109.5°— which is even further from the observed 117° than was the prediction based on sp hybridization. Furthermore, except for cyclopropane, we feel imcomfortable about drawing molecular pictures with bonds that... 

Pfeiffer s monumental review (277) systematizes the older literature regarding most kinds of molecular compound formation. Ahr-land et al. (2) have provided a more recent discussion comparing the affinities of different ligand atoms for acceptor molecules and ions. They include a helpful warning that not all ligand atoms interact with acceptor molecules in accordance with basicity order. Most particularly the metal ions in the middle of the Periodic Table such as silver (I), platinum (II), and mercury (II) may supply electrons for TT-bonding from their own lower d-orbitals and should not be compared with protonic acids. 

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