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

Schedule

An exact time schedule applicable to all schools cannot be set because of the varied use of semester, quarter, trimester, and summer session terms of instructions. However, for a semester of 15 weeks, two 3-hr laboratory periods per week plus one "lab lecture" per week work well. Modifications can be made to adapt the course to individual schools.

Lecture Material

The first lecture should emphasize safety and all safety protocols as described in Chapter 2. Next, the course overview is described as outlined in Chapter 3. Next, a review of spectroscopic techniques, including operating instructions, should be discussed (Chapters 7-9). Physical properties (Chapter 4), including melting point and boiling point, should be described next. Solubility of the unknown should be reviewed (Chapter 5). Recrystallization (Section 4.4) and separation of mixtures (Chapter 6) could be explained. It is not necessary to lecture on all the experiments and procedures (Chapters 10 and 11), but an introduction to the most common tests should be discussed.

After the first one or two unknowns have been completed, it will be valuable to work on some of the problems of Chapter 13 (available on book companion website) in class and discuss the structure correlation with chemical reactions and spectral data. It is the instructor's choice whether or not to make the Solutions Manual available to the students.

Laboratory Work-Unknowns

By use of spectroscopic data and chemical reactions, it is possible for students to work out six to eight single compounds and two mixtures (containing two or three components each) in a 15-week semester.

To get a rapid start and illustrate the systematic scheme, it may be useful to give a titratable acid to each student for a first unknown. The student is told that the substance is titratable and that he or she is to get the elemental analysis, melting or boiling point, and neutralization equivalent and to calculate the possible molecular weights. Then, if the unknown contains halogen or nitrogen, the student is to select and try three or four (but no more) classification tests. Next, a list of possible compounds with derivatives is prepared by consulting the table of acids (Appendix II). One derivative is made and turned in with the report (Sections 3.1 and 3.11). This first unknown should be completed in two 3-hr laboratory periods.

Since many schools run organic qualitative analysis in a lab course connected to the second semester (or last term) of the traditional sophomore course, the decision about how to order the...