Functional Group Manipulation

FUNCTIONAL GROUP SYNTHESIS

FUNCTIONAL GROUP MANIPULATION

As we have seen in earlier undergraduate organic coursework, organic chemistry is often organized around the chemistry of functional groups. Functional groups are recurring sequences of bonded elements which give typical and characteristic chemical reactions. Recall that there are characteristic reactions of ketones, esters, secondary alcohols, and so on. Consequently, it is very important to be able to introduce a particular functional group into a molecule or to interconvert functional groups in a molecule in order to utilize particular reactions available to them.

To manipulate functional groups, it is first necessary to be able to identify them, understand their bonding and oxidation levels, and recognize the bonding changes that are needed to convert one functional group into another. A variety of functional group reactions are available, and much of the introductory organic chemistry course is devoted to learning reagents and reactions for carrying out functional group interconversions.

Very often these reactions are traditional and illustrative, but they are not nec-essarily the best way to manipulate a particular functional group. Many traditional methods have been replaced, in practice, by newer reactions or reagents which offer certain advantages over older methods. In general, these advantages have to do with mild conditions, selectivity, generality, and/or experimental simplicity. Nevertheless all types of functional group interconversions, new or old, are still based fundamentally on the ideas that have been developed earlier in this book.

This chapter is not meant to serve as a surrogate for an undergraduate text as it does not cover all the functional groups covered in the introductory course. Instead it concentrates on the most common ones. It is assumed that the func-tional group transformations taught at the undergraduate level have already been mastered. If this material has not been learned, it should be reviewed using a standard undergraduate text.

The discussion which follows is organized in the following fashion. First a common undergraduate text was used to provide a list of “standard” or “tra-ditional” preparations for the major functional groups dealt with herein. Most of these reactions should be familiar because they are the ones learned (or not learned) in the undergraduate course in organic chemistry. Although these meth-ods will be listed and perhaps discussed briefly, the discussion in no way serves as a review of these methods.

The main focus of this chapter will be to introduce the most widely used and practical ways (or “real” ways) to introduce the major functional groups. These latter methods have practical synthetic value and are usually the first choices in real laboratory situations, but often they differ from the standard list of prepara-tions. What is important is that these first-choice methods must be integrated into the methods previously encountered so that a wider view of how to manipulate functional groups is achieved.

The functional group order goes from highest oxidation level (carboxylic acid) to lowest oxidation level (alkanes). As might be anticipated, carboxylic acids are most often prepared oxidatively and alkanes are most often prepared reductively. Functional groups of intermediate oxidation level can be accessed either reduc-tively or oxidatively. Furthermore the methods discussed for each functional group are organized by the oxidation level change that is used, that is, oxidative methods followed by methods requiring no change in oxidation level followed by reductive methods.