Carbon compounds bonding orbital hybridization

The same kind of orbital hybridization that accounts for the methane structure also accounts for the bonding together of carbon atoms into chains and rings to make possible many millions of organic compounds. Ethane, C2H6, is the simplest molecule containing a carbon-carbon bond. 

The valence-bond concept of orbital hybridization described in the previous four sections is not limited to carbon compounds. Covalent bonds formed by-other elements can also be described using hybrid orbitals. Look, for instance, at the nitrogen atom in methylamine, CH3NH2, an organic derivative of ammonia (NH3) and the substance responsible for the odor of rotting fish. 

One way in which the n bonds in these compounds may be examined is by calculating natural bond orbitals (NBO) from the molecular wave function." Here, the MOs are localized, and the nature of the localized orbitals may be examined. The p-n localized orbital is found to have decreased occupation as the carbon-carbon bond is distorted, indicating that the p orbitals are being used in part in forming other localized orbitals (i.e., rehybridized). It is also possible to calculate natural hybrid orbitals, and their deviation from the line of centers between the atoms involved. The deviations are included in Table 15.2, and are seen to increase markedly with increased twisting. 

Molecular orbitals don t explain everything and become increasingly more difficult to draw with more than two atoms. We use a model called hybridization to explain other effects, particularly in carbon compounds. Hybridization is a mixing of atomic orbitals to create new orbitals that have a geometry better suited to a particular type of bonding environment. For example, in the formation of the compound BeH2, we would like to be able to explain why this molecule is linear that is, the H-Be-H bond is 180°. 

One of the celebrated successes of orbital hybridization is the elucidation of multiple bonding, which stems from the Lewis formulation of a chemical bond as a shared electron pair. In a compound such as ethylene the saturation of the carbon valence shells can only be achieved by the sharing of two electron pairs between the two carbon atoms. 

The concept ofhybridisiation described in the prexious four j tions is not r 8triclcarbon compounds. Covalent bunds formed by other elements in the periodic table aliio can be described uains hybrid orbitals. Loot at the nitrogen atom in ammonia, NHg, for example. A nitre en atom haa five Quler hell electrons nnd therefore forms three covalent bonds to complete its valence electron octet. 

An isolated carbon atom possesses two electrons in its Is orbital, two electrons in its 2s orbital and two electrons in its 2p orbitals. The types of bonding found in carbon compounds arise from various hybrids of the 2s and 2p orbitals. Combination of one 2s and three 2p orbitals... 

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