An Introduction to Organic Synthesis Polysubstituted Benzenes

How might you prepare diphenylmethane, (Ph)2CH2, from benzene and an appropriate acid chloride More than one step is needed. 

There are many reasons for carrying out the laboratory synthesis of an organic molecule. In the pharmaceutical industry, new molecules are designed and synthesized in the hope that some might be useful new drugs. In the chemical industry, syntheses are done to devise more economical routes to known compounds. In biochemistry laboratories, the synthesis of molecules designed to probe enzyme mechanisms is often undertaken. 

The ability to plan a successful multistep synthesis of a complex molecule requires a working knowledge of the uses and limitations of numerous organic reactions. Not only must you know which reactions to use, you must also know when to use them, because the order in which reactions are carried out is often critical to the success of the overall scheme. 

There s no secret to planning an organic synthesis all it takes is a knowledge of the different reactions and some practice. The only real trick is to work backward, in what is often referred to as a retrosynthetic direction. Don t look at a potential starting material and ask yourself what reactions it might undergo. Instead, look at the final product and ask, What was the immediate 

Let s look at some examples of synthetic planning using polysubstituted aromatic compounds as the targets. First, however, it s necessary to point out that electrophilic substitution on a disubstituted benzene ring is governed by the same resonance and inductive effects that affect monosubstituted rings. The only difference is that it s necessary to consider the additive effects of two groups. In practice, this isn t as difficult as it sounds three rules are usually sufficient  

---