Ethyne model structure

The ligand-model vibrational spectroscopy approach has contributed strongly to fairly reliable identifications on metal surfaces of C2 species of the types 1, 2 (ethene type II spectra) (17), 3 (ethene type I spectra), 4 (ethene type I spectra), 8, and 13 (ethyne type B spectra) as well as to possible identifications of types 5, 7, 15 (ethyne type A spectra), 16, and 20. Approximate band positions and associated intensity distributions in the spectra from normal and perdeutero species should be considered together (/ 7). The correspondence of the infrared spectrum from 4 with type I spectra is less satisfactory for the C2D4 ligand than in most other cases. However an extra structural variable in this case is the degree of nonplanarity of the cyclic C2M2 skeleton, which may differ between the model compound and the surface species. 

We can account for the structure of ethyne on the basis of orbital hybridization as we did for ethane and ethene. In our model for ethane (Section 1.12B) we saw that the carbon orbitals are sp hybridized, and in our model for ethene (Section 1.13) we saw that they are sp hybridized. In our model for ethyne we shall see that the carbon atoms are sp hybridized. 

Describe the accepted model for the bonding of ethene and of ethyne to transition metals. Show how this model accounts for the structural, spectroscopic and reactivity variations of these coordinated ligands. 

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