Chapter 1
Introduction

1.1 SYSTEMATIC IDENTIFICATION OF ORGANIC COMPOUNDS: THE NEED FOR ORGANIC QUALITATIVE ANALYSIS

Qualitative organic chemistry has been in use since long before the advent of modern spectroscopy. Modern spectroscopic techniques have assisted the chemist by providing spectra that can be interpreted to give more detail about the interaction between atoms and functional groups. Some students have difficulty identifying structures using exclusively nuclear magnetic resonance (NMR) spectra, infrared (IR) spectra, and mass spectra. The information obtained through chemical tests allows the student to narrow down the possible functional groups. Additionally, by taking a course in qualitative organic chemistry, a student is given the freedom of selecting, for himself or herself, the functional group classification tests that are needed to identify a compound.

In roughly two dozen chapters or more of a standard organic text, the student encounters many chemical reactions. Literally, millions of different organic compounds have been synthesized. Chemical companies sell thousands of compounds, and industrial‐scale production generates thousands of different compounds on various scales. Characterization of organic compounds can be done by a handful of physical and chemical observations if it is done in a systematic manner. The list of more common and readily available chemicals is much smaller than the millions that are possible.

In this text, we have focused our attention on an even smaller list of compounds that can be used as “unknowns.” The melting point‐boiling point tables give a very accurate idea of the focus of this book. Instructors using this book may very well use other references, such as the CRC reference volumes,1 the Millipore Sigma website, the Fisher Scientific website, and others, for a more extensive list of possibilities for “unknown” compounds.

Organic chemists are often confronted with either of the following extreme situations:

1. Determination of the identity of a compound that has no prior history. This is often the case for a natural‐products chemist who must study a very small amount of sample isolated from a plant or an animal. A similar situation applies to the forensic chemist who analyzes very small samples related to a lawsuit or crime.
2. The industrial chemist or college laboratory chemist who must analyze a sample that contains a major expected product and minor products, all of which could be expected from a given set of reagents and conditions. It is entirely possible that such a sample with a well‐documented history will allow one to have a properly preconceived notion as to how the analysis should be conducted.

The theory and technique for identifying organic compounds constitute an essential introduction to research in organic chemistry. This study organizes the accumulated knowledge concerning physical properties, structures, and reactions of thousands of carbon compounds into a systematic, logical identification scheme. Although its initial aim is the characterization of previously known compounds, the scheme of attack constitutes the first stage in the elucidation of structure of newly prepared organic compounds.

If, for example, two known compounds A and B are dissolved in a solvent C, a catalyst D is added, and the whole subjected to proper reaction conditions of temperature and pressure, a mixture of new products plus unchanged starting materials results.

Immediately two questions arise:

1. What procedure should be chosen to separate the mixture into its components?
2. How are the individual compounds (E through K) to be positively characterized? Which ones are unchanged reactants? Which compounds have been described previously by other chemists? Finally, which products are new?

These two problems are intimately related. Separations of organic mixtures use both chemical and physical processes and are dependent on the structures of the constituents.

The present course of study focuses on the systematic identification of individual compounds first. The specific steps are given in Chapter 3. Physical properties are described in Chapter 4. The use of these principles for devising efficient procedures for the separation of mixtures is outlined in Chapter 5. Solubility techniques are described in Chapter 6. Spectroscopy methods are discussed in Chapters 7–9. The classification tests for functional groups are given in Chapter 10, and the preparation of derivatives is given in Chapter 11.

In recent years, the question of scale has become an issue. Scale has always been a focal point for qualitative analysis. The issue has been recognized at an even earlier point in the chemistry curriculum, and a very large number of colleges now incorporate some sort of microscale or miniscale approach into their sophomore organic courses. Organic qualitative analysis has always been a test tube subject and thus should philosophically be in tune with the microscale revolution. Most of our experiments are at the scale of the past editions of this text and thus many chemistry instructors may wish to scale down. Scaling down to 1/2, 1/5, or 1/10 of the cited amount should be very straightforward in most cases, and thus scale is the option of the course coordinator. The only warning is that certain reactions (for example, conversion of a carboxylic acid to an amide or of an alcohol to a 3,5‐dinitrobenzoate) are notoriously sensitive to the purity of the reagents. Thus, a larger‐scale reaction is likely desirable here.

Cleanup and Waste Disposal

A related, and in some ways bigger, issue is that of waste disposal. The trend at most colleges in recent years is to have waste disposal done by a licensed company under contract with the college. Most instructors are not qualified to dispose of waste and thus they can only provide cleanup guidelines. We have attempted to prepare this edition with that in mind. It is usually the job of the instructor to provide containers for waste disposal. Waste disposal vessels are usually labeled as to their use, such as solids vs. liquids and inorganic vs. organic compounds. Special containers are used for especially toxic wastes such as halogenated organic compounds or heavy metal solutions. Additionally, there are usually special containers for broken glass equipment. There may be places to recycle paper, and finally, there are simple trash cans for garbage. There is usually a classification decision for every act of discarding material. Most importantly, the students should receive instructions from their lab instructors that are in accordance with local regulations.

1.2 SUGGESTIONS TO STUDENTS AND INSTRUCTORS