Organic Chemistry Reactions

REACTIONS

Key Notes

Bond formation

Most organic reactions take place between nucleophiles and electrophiles, where the nucleophilic center of the nucleophile forms a bond to the electrophilic center of the electrophile.

Classification of reactions

Reactions can be classified as acid/base reactions, functional group trans-formations or as carbon–carbon bond formations. Reactions can also be classified according to the process or mechanism taking place and these are specific for particular functional groups.

Bond formation

Synthetic organic chemistry is about creating complex molecules from simple starting materials – a process which may involve many different reactions. Designing a synthesis is a bit like chess. A grand master has to know the pieces and the moves that can be made before planning a game strategy. As far as an organic chemist is concerned, he/she has to know the molecules and the sort of reactions which can be carried out before planning a synthetic ‘game strategy’.

Inevitably, there is a lot of memory work involved in knowing reactions, but there is a logic involved as well. Basically, most reactions involve electron-rich molecules forming bonds to electron deficient molecules (i.e. nucleophiles forming bonds to electrophiles). The bond will be formed specifically between the nucleophilic center of the nucleophile and the electrophilic center of the electrophile.

Classification of reactions

There are a large number of reactions in organic chemistry, but we can simplify the picture by grouping these reactions into various categories. To begin with, we can classify reactions as being:

·           acid/base reactions;

·           functional group transformations;

·           carbon–carbon bond formations.

The first category of reaction is relatively simple and involves the reaction of an acid with a base to give a salt. These reactions are covered in Section G. The second category of reaction is where one functional group can be converted into another. Normally these reactions are relatively straightforward and proceed in high yield. The third category of reactions is extremely important to organic chemistry since these are the reactions which allow the chemist to construct complex molecules from simple starting materials. In general, these reactions are the most difficult and temperamental to carry out. Some of these reactions are so important that they are named after the scientists who developed them (e.g. Grignard and Aldol reactions).

Another way of categorizing reactions is to group similar types of reactions together, depending on the process or mechanism involved. This is particularly useful since specific functional groups will undergo certain types of reaction cat-egory. Table 1 serves as a summary of the types of reactions which functional groups normally undergo.