The very large number ofpreparatively useful reactions of organic chemistry can be classified systematically and clearly by using the common characteristic
of all organic compounds, namely, the carbon skeleton. The following cases can then be differentiated:
1. The carbon skeleton is preformed in the starting material. Examples: benozoic acid from toluene; acetaldehyde from ethanol.
2. The carbon skeleton is built up from two or more molecules with formation of a carbon-carbon bond.
3. The carbon skeleton is a residue obtained by partial degradation of a structure containing more carbon atoms. Examples: Enanthol from castor oil; phthalic acid from naphthalene....

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