Hybridization of Other Atoms Nitrogen and Oxygen

A number of other molecules in addition to those shown in Figures 6-7 and 6-8 are aromatic. The first five possible values of n are 0, 1,2, 3, and 4. These numbers correspond to 4n + 2 values of 2, 6, 10, 14, and 18, respectively. Pyridine (refer to Figure 6-7) illustrates the fact that aromatic compounds are not necessarily hydrocarbons. However, the replacement of the nitrogen in pyridine with oxygen places an sp hybridized atom in the ring, so the system is no longer aromatic. 

The same kind of sp3 hybridization that describes the bonds to carbon in the tetrahedral methane molecule also describes bonds to nitrogen in the trigonal pyramidal ammonia molecule, to oxygen in the bent water molecule, and to all other atoms that VSEPR theory predicts to have a tetrahedral arrangement of four charge clouds. 

It is probably fair to say that life reflects and depends on three chemical aspects (1) hybridization of carbon and oxygen (as well as nitrogen), (2) the facile way carbon atoms may bind to other carbon atoms, and (3) the unique ability of hydrogen to form H-bonds. The catenation and tetrahedral geometry of the carbon atoms are the fundamental features of all organic compounds in cells. However, the most abundant molecule in any living cell is water. 

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