Carbon-oxygen bonds, polar nature

The structural features especially the very polar nature of the carbonyl group point clearly to the kind of chemistry we will see for aldehydes and ketones in this chapter The partially positive carbon of C=0 has carbocation character and is electrophilic The planar arrangement of its bonds make this carbon relatively uncrowded and susceptible to attack by nucleophiles Oxygen is partially negative and weakly basic... 

Carbonic anhydrase is an enzyme of central importance to the production of gastric acid. This enzyme, which contains zinc, accelerates the naturally occurring reversible reaction of CO2 with water. Before considering the mechanism of action of the enzyme, note the resonating structure of CO2. The carbon-to-oxygen bonds are polar the molecular structure can be represented by the resonance hybrids shown in Figure 2.54. Note that in two of the three forms shown the central carbon atom has a positive charge. 

Of course a nitrile is not a carbonyl. But nitrile and carbonyl chemistries are similar, and an examination of nitrile reactions naturally belongs in this section. Like carhonyl compounds, nitriles are both electrophiles and nucleophiles. As in carhonyl compounds, a polar resonance form contributes to the structure of nitriles (Fig. 18.44). Consequently, the triple bond is polarized and the carhon acts as a Lewis add. One might antidpate that nudeophiles would add to nitriles, and that idea is correct. These similarities mean that many of the reactions of carhonyl groups are also possible for nitriles, and the mechanisms are generally dosely related. Students sometimes have trouble with the nitrile reactions, however, so it is important not to dismiss them with only a cursory look. For some reason, the analogy between the carbon—oxygen double bond and the carbon—nitrogen triple bond is not always easy to keep in mind. 

Consequently, the presence of the silicone oxygen bond in the material monomer results in the development of a strong structure when compared to other polymers within the same application field, where the polymer chain is composed of carbon atoms instead of silicone. Nevertheless, it must be noted that the polar nature of the silicone oxygen bond results in a material that is vulnerable to the action of hydrolysis [44], which, however, appears to be notable for pH values less than 2.5 or greater than 11 [48]. 

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