Examples of cluster and factor analyses

Comparisons of the types just described can provide information of great chemical or biochemical interest. A few examples, some already alluded to, follow. 

The ester bond -C0 0-R contains both a C=0 and a C-O-R group. It is found that the electrons are delocalized within this group, resulting in resonance stabilization of the type for benzene  

On the other hand, infra red spectroscopic studies indicate that this resonance stabilization does not occur with thioesters. 

An ester carbonyl group, however, involves an sp carbon atom while the other carbon atom attached to the doubly bonded oxygen atom is sp. The sp bonding results in a shortening of the C-(0,S) bond, and this has to be taken into account in the analysis. 

FIGURE 16.13. Formula for vitamin B12. (a) Simplified formula where Me = CH3, Ac = CH2CONH2, Pr = CH2CH2CONH2. (b) Details of the numbering in the corrin ring system. 

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