Lab Modules from Dr. Linda Schwab Dept. of Chemistry, Wells College Aurora, NY 13026-0500

This module presents an introduction to organic qualitative analysis coupled to introductions to infrared (IR) and nuclear magnetic resonance (NMR) spectrometry. The process of qualitative analysis has always been an exploratory one; this experiment, however. rather than giving the student a flow chart of reactions in advance, allows the student to develop reaction tables, correlation charts, and a flow chart in the course of the experiment, and emphasizes natural products and household chemicals as unknowns.

The first section of the experiment explores the reactivities which distinguish the classes of hydrocarbons, alkanes, alkenes, alkynes and arenes. In this section, students may also develop a simple correlation chart of important IR frequencies. The section culminates with a quantitative experiment which students must design themselves: analysis of the relative unsaturation of edible oils by a visible spectrophotometric method or by NMR.

The second part of the experiment introduces the oxygen-containing functional groups, emphasizing the analysis of the neutral groups (ketones. aldehydes, alcohols and ethers). As students apply the tests to a set of standards, they develop a flow chart of reactions which can be used to determine an unknown natural product. This process can be linked to the study of more complex IR and NMR spectra, and concludes with another self-designed experiment exploring the reactivity of pyridinium chlorochromate as an oxidizing agent.

The parts may be taken in sequence or separately to correspond to the instructor's favored order of topics in the organic chemistry course. Although the experiment is most suited to the organic chemistry course, the experiments on hydrocarbons would complement an introductory course in general. organic and biochemistry.

^†Associate Professor of Chemistry, Wells College: author to which correspondence should be addressed.

Beginning students of organic chemistry are often dismayed by the variety of reagents used for various reactions. The mass of knowledge becomes more manageable when the student becomes aware of the selectivity of many of these reagents, and therefore better able to select a single suitable reagent rather than being lost among the choices. The idea of selectivity can be explored by having the student find out which carbonyl-containing functional groups can be reduced by sodium borohydride, and then extending this knowledge to the modification of a natural product or to an exploration of the best conditions for the reaction (a good introduction to some practical physical organic chemistry).

This experiment fits most one-year organic courses either in the first semester or the beginning of the second (with alcohols and/or with aldehydes and ketones). Students will need to be familiar with the spectroscopic techniques(s) they will use for product identification, and with some use of the literature. Because the experiment can be extended to involve some additional independent work and/or a brief "research proposal", it would be an interesting and appropriate culmination to first-semester work.

The experiment takes two to three weeks; students work in teams of three. NMR and IR are used to determine the structures of the products; IR alone will suffice if NMR is unavailable.

The experiment can also be used or revisited in an upper-level integrated laboratory; further exploration of reaction conditions, determination of product rations using NMR, and applicability of the reaction to synthesis of insect pheromones are all appropriate to such a laboratory. A simplified version of the experiment may find a place in the one-year course in general, organic and biochemistry as an interesting illustration of the prevalence of redox reactions throughout chemistry.

^†Associate Professor of Chemistry, Wells College: author to which correspondence should be addressed.

Chemiluminescent reactions are fascinating to observe, and experiments which include them are always popular with students (and faculty!). This experiment uses a class of luminescent compounds less well-known for this property than luminol and related compounds, though more familiar for their general utility in organic chemistry: p-halophenylmagnesium bromides. examples of aryl Grignard reagents. In this experiment, the four required halobromobenzenes are prepared by a Sandmeyer reaction from the corresponding anilines, illustrating the use of a diazotization reaction to provide regiospecific halogenation; the Grignard reagent is prepared in the usual way and immediately oxidized in a stream of 1~2. Students work in pairs and the class as a whole shares results on the color and intensity of the luminescence reactions of the four Grignard reagents.

The experiment requires two three-hour laboratory periods. Advanced instrumentation is not required, though the structures of the intermediate halobromobenzenes may be confirmed by spectroscopy. An oxygen tank is needed; in addition, a sonicator is suggested as a way to initiate the formation of the Grignard reagent, though of course classic methods will suffice. and a large vacuum desiccator is very helpful. Measurement of the luminescence with simple laboratory photometers may be attempted, though the light produced is at the lower limit of sensitivity of common photometers. If photometers are not used, qualitative description of the luminescence is still interesting, and a semiquantitative comparison may still be made with either commercial luminescent materials ("glow sticks") or other luminescent compounds synthesized as part of the laboratory program.

The experiment is most appropriate late in the organic chemistry course to correlate with the usual placement of related topics such as photochemistry and aromatic amines; it requires command of techniques such as steam distillation and thorough drying of reagents and sufficient familiarity with general technique to decide how to purify the intermediate halobromobenzene. The experiment would make a very good bridge to an integrated upper-level laboratory course.

†Associate Professor of Chemistry, Wells College: author to which correspondence should be addressed.

Learning common laboratory techniques is usually, and justifiably, an important part of the laboratory of organic chemistry. Students need to ]earn safe and accepted practices; in addition, they need to familiarize themselves with the physical properties associated with various classes of organic compounds. These tasks may be combined and made much more interesting. and significant to the student by applying them to the development of an in-house solvent recovery program. (You will also be pleased to see somewhat less of your department budget consumed by solvent purchases and waste disposal costs! ) Students become familiar with handbooks as they check the properties of the materials to be distilled. Use of a gas chromatograph allows them an additional method besides boiling point to assess the purity of their distillate. The other part of the experiment models a process which might be used in designing a solvent recovery program in industry; it involves correlating boiling point with GC retention time and with structure for an homologous (or isomeric) series of alcohols.

The entire experiment may be used in the beginning of the organic chemistry course; it is also suitable for other introductory courses which use some organic chemistry (e.g. General Chemistry, nonmajors chemistry or Environmental Chemistry). If you do not have a GC available, refractometry may be used to check solvent purity, and the study of properties may be done as a literature assignment and/or an introduction to graphing software available in your department. These modifications make the experiment adaptable to use in high schools.

†Associate Professor of Chemistry, Wells College: author to which correspondence should be addressed.

Students of organic chemistry usually find enolate reactions very challenging; applying the mechanism to a realistic problem can help them achieve the "aha!" moment of understanding. In this experiment, students are led to discover the Dieckmann condensation. Although textbooks usually mention this reaction as a subtype of the Claisen condensation, most students do not immediately realize or recall that cyclization can occur with the reagents and conditions given. However, the formation of a ring is just unexpected and intriguing enough to make enolate reactions more interesting and memorable. This topic usually falls in the second half of the second semester of a year-long course in organic chemistry, and the level of technical skill and ability to interpret NMR spectra required by this experiment are also appropriate to a point fairly late in the course sequence. Students gain experience in handling sodium (or solutions of sodium ethoxide, if you prefer to dispense it to the class). The main part of the experiment requires two weeks; if you do not think you can manage to have every student take an NMR, consider having students work in pairs (thus, a team of three students becomes a team of six), or have some students use NMR and some use IR or derivatization to identify the product. It is still possible and worthwhile to use this experiment if you do not have an NMR available at all; students may use IR and derivatization alone to prove the structures of their products. In this case, allow an extra week for the qualitative analysis. The experiment is also very suitable to use or revisit in an advanced organic or integrated upper-level laboratory.

†Associate Professor of Chemistry, Wells College: author to which correspondence should be addressed.

The study of natural products is an important area of contemporary research in organic chemistry, and an excellent way to introduce students to the practice of organic chemistry. Students enjoy discovering the chemistry of familiar plants, and are delighted to begin an experiment with sample collection in the field. This experiment teaches common separation and purification techniques in the context of isolating several components from pine gum. It incorporates material on organic acid-base reactions, stability of alkenes and stereochemistry; it is well suited to use early in the organic course. One might also return to the experiment later in the same course or in an advanced organic course to learn the use of mixed solvents in recrystallization or of Woodward's rules in the structure determination of conjugated alkenes by UV spectroscopy. The isolation of turpentine is also a popular experiment with nonmajors or General Chemistry classes which include an introduction to hydrocarbons. Two periods are required for the experiment; students work in pairs or teams of three. The experiment uses gas chromatography and polarimetry, and some introduction to literature resources. If a gas chromatograph is not available, a refractometer could be used to compare the crude and commercial turpentine.

†Associate Professor of Chemistry, Wells College: author to which correspondence should be addressed.

Any reasonably curious chemistry student is bound to wonder what entitles us to draw detailed conclusions about how reactions occur when we can't see the molecules reacting. Understanding the kind of evidence kinetics can give helps to answer that question. In this experiment, students compare the rate of formation of the purple iron-phenol complex from acetylsalicylic acid and ferric chloride with the rate of hydrolysis of acetylsalicyclic acid in the same aqueous medium. The second part of the experiment introduces the idea that a simple two-phase system may be a reasonable model for the more complex partitions present in biological systems. Both parts of the experiment use spectrophotometry: visible spectrophotometers suffice to follow the formation of the colored complex and a UV instrument is used to monitor the hydrolysis reaction and to determine the partition coefficient of acetylsalicylic acid and other over-the-counter analgetics in octanol-water. The experiment can be used in the General Chemistry course whenever kinetics and equilibrium are treated; it is ideal for a course in chemistry for the health professions; and it is also suitable for Organic Chemistry (ester hydrolysis, solubility properties of different functional groups). This experiment also may be used to introduce students to the use of the graphing and calculation software available in your department.

†Associate Professor of Chemistry, Wells College: author to which correspondence should be addressed.

Organic chemistry may be said to have its formal beginnings in the middle of the nineteenth century; among the earliest analytical and synthetic challenges taken on by chemists in this era were the elucidation of the structures of natural dyes and the attempt to duplicate their colors in the laboratory. The synthesis of dyes and the interaction of dyes with fibers remains a fascinating topic, blending the study of mechanisms and the physicochemical properties of various functional groups with the esthetic appeal of color and the traditions of the artisan. This experiment allows the student of organic chemistry to prepare several dyes, compare the conditions used in the various applications of a single reaction mechanism (electrophilic aromatic substitution), study the acid-base properties of the synthetic dyes, examine the effectiveness of the interaction of these and selected natural dyes with natural fibers in the presence and absence of metal mordants, and relate the results to the physical properties of the functional groups of both dye and fiber. The second part of this experiment, the relation of dyes and fibers, is also suitable to be used by students in a nonmajors chemistry course; it provides these students with the opportunity to use the concepts of functional groups and polarity and to study the important natural polymers wool and cotton. Two periods are required for the complete experiment. Part of a third period may be required if groups of students are assigned the tasks of preparing the natural dyes and/or mordanting the fibers; alternatively, these tasks may be carried out by the teaching assistants or the students may do the assigned preparations during other experiments. The experiment requires no advanced instrumentation.

†Associate Professor of Chemistry, Wells College: author to which correspondence should be addressed.

Author Table

General Chemistry Organic Chemistry

Environmental Chemistry Liberal Arts Chemistry

Analytical Chemistry Upper Level Chemistry

Contact Professor Linda Schwab with feedback on her lab modules at Lschwab@henry.wells.edu