Bonds Essential’ double

Fatty acid degradation and synthesis are relatively simple processes that are essentially the reverse of each other. The process of degradation converts an aliphatic compound into a set of activated acetyl units (acetyl CoA) that can be processed by the citric acid cycle (Figure 22.2). An activated fatty acid is oxidized to introduce a double bond the double bond is hydrated to introduce an oxygen the alcohol is oxidized to a ketone and, finally, the four carbon fragment is cleaved by coenzyme A to yield acetyl CoA and a fatty acid chain two carbons shorter. If the fatty acid has an even number of carbon atoms and is saturated, the process is simply repeated until the fatty acid is completely converted into acetyl CoA units. 

R. Korenstein, K. A. Muszkat, and S. Sharafy-Ozeri, Photochromism and thermochromism through partial torsion about an essential double bond. Structure of the B colored isomers of bianthrones, J. Am. Chem Soc. 95, 6177-6181 (1973). 

Oil Saturated (no double bonds) Monounsaturated (one double bond) Polyunsaturated (two or more double bonds - essential ) Cholesterol... 

When a multiple bond is desired, it is necessary only to trace over the single bond one (or two) additional times. LHASA responds by redrawing the bond as double (or triple). Indicating stereochemistry is essentially the same, the appropriate indicator (wedged or dotted) is chosen and the desired bond is traced with the stylus (see below). 

Delete all essential single and essential double bonds. 

Rule 1. If only one classical structure can be written for a molecule, all the bonds in it are essential single or essential double bonds. Such bonds are localized. This has already been shown to hold (see Sections 3.6 and 3.12). 

Rule 2. Bonds that are not essential single bonds or essential double bonds have intermediate strengths and so lengths. This was established in Section 3.10, p. 89. 

Note that in (81), the 2,8,7,6 segment contains only essential single and essential double bonds and so does not take part in the delocalized system. 

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