Infrared spectroscopy, laboratory experiments

One of the virtues of spectroscopic approaches is that they are commonly nondestructive and noninvasive, although some procedures involve the attachment of labels chemically at specific sites. The former approaches are particularly valuable for in vivo studies. In laboratory experiments, the amounts of materials required range from the femtomole (10 mol) level for some particularly sensitive fluorescence approaches to milligrams or more for typical EPR, infrared, or X-ray spectroscopy. Ongoing requirements in instrumentation and techniques are continually whittling away at the limits to the amount of material required. 

The ability to identify organic compounds is an important skill that is frequently used in the organic laboratory. Although there are several spectroscopic methods and many chemical and physical tests that can be used for identification, the goal of this experiment is to identify an unknown liquid using infrared spectroscopy and a boiling-point determination. Both methods are introduced in this experiment. 

It is essential that the benzaldehyde used in this experiment be pure. Benzaldehyde is easily oxidized in air to benzoic acid. Even when benzaldehyde appears free of benzoic acid by infrared spectroscopy, you should check the purity of your benzaldehyde and thiamine by following the instructions given in the first paragraph of the Procedure ("Reaction Mixture"). When the benzaldehyde is pure, the solution will be nearly filled with solid benzoin after 2 days (you may need to scratch the inside of the flask to induce crystallization). If no solid appears or very little appears, then there is a problem with the purity of the benzaldehyde. If possible, use a newly opened bottle that has been purchased recently. However, it is essential that you check both the old and new benzaldehyde before doing the laboratory experiment. 

Infrared spectroscopy is an excellent technique for determining the structure of a polymer. For example, polyethylene and polypropylene have relatively simple spectra because they are saturated hydrocarbons. Polyesters have stretching frequencies associated with the C=0 and C—O groups in the polymer chain. Polyamides (nylon) show absorptions that are characteristic for the C=0 stretch and N—H stretch. Polystyrene has characteristic features of a monosubstituted aromatic compound (see Technique 25, Figure 25.12). You may determine the infrared spectra of the linear polyester from Experiment 46A and polystyrene from Experiment 46C in this part of the experiment. Your instructor may ask you to analyze a sample that you bring to the laboratory or one supplied to you. 

Infrared spectroscopy work and ATR studies were carried out by Mr. John P. Falzone of these laboratories. ESCA experiments were carried out by Dr. J.S. Brinen and Mr. W. R. Doughman anodization experiments by Dr. T. B. Reddy and Ms. L. Maxine Mull. 

The combined technique of thermogravimetric analysis - infrared spectroscopy, TGA/IR, provides very useful information to enable the understanding of the degradation scheme of a polymer. In addition to the usual weight loss information that is produced from the TGA portion of the experiment, the infrared spectra that are obtained permit temporal resolution of the gases that are evolved from the degrading polymer. In this paper, several systems that have been studied in these laboratories are reviewed and some of the mechanistic information that has been obtained is elucidated. 

Lillhonga T, Geladi P. Three-way analysis of a designed compost experiment using near-infrared spectroscopy and laboratory measurements. J Chemometr 2011 25 193-200. 

It soon became apparent that there were two types of students with different needs. One group had almost no experience in infrared spectroscopy and wanted fundamental information on apparatus, experimental techniques, and applications. The second group had substantial laboratory experience in infrared spectroscopy and wanted much more emphasis on the interpretation of spectra. Therefore, starting with the third year (1952), two separate courses were given in successive weeks. The first was devoted to experimental aspects. In addition to morning lectures, each smdent had 10 hours of laboratory in the afternoons (2 hours per day for five days). The second course concentrated on the theory and applications of infrared spectra with heavy emphasis on characteristic group frequencies. An important feature was 10 hours devoted to solving problems in the interpretation of unknown spectra. 

In 1970 two new experiments were added, one on Fourier transform infrared spectroscopy and the other on Raman spectroscopy with laser excitation. This was the last year of the laboratory offering. In 1971 there was a precipitous drop in attendance, perhaps related to the sharp economic downturn, and the first week (containing the laboratory) had to be canceled. Only 29 persons attended the second week. MIT informed Professor Lord that it no longer wanted to sponsor the course, so he asked Lippincott, Miller, and Mayo whether any of them wanted to offer the course at their institution. Lippincott and Miller could not do so, but Mayo, who by then was at Bowdoin College in Brunswick, Maine, was enthusiastic. Hence after 22 years at MIT, the course was moved to Bowdoin College, where the 1972... 

Recent work in our laboratory has shown that Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) can be used routinely to measure vibrational spectra of a monolayer on a low area metal surface. To achieve sensitivity and resolution, a pseudo-double beam, polarization modulation technique was integrated into the FT-IR experiment. We have shown applicability of FT-IRRAS to spectral measurements of surface adsorbates in the presence of a surrounding infrared absorbing gas or liquid as well as measurements in the UHV. We now show progress toward situ measurement of thermal and hydration induced conformational changes of adsorbate structure. The design of the cell and some preliminary measurements will be discussed. 

We have already discussed the high-resolution spectroscopy of the OH radical at some length. It occupies a special place in the history of the subject, being the first short-lived free radical to be detected and studied in the laboratory by microwave spectroscopy. The details of the experiment by Dousmanis, Sanders and Townes [4] were described in section 10.1. It was also the first interstellar molecule to be detected by radio-astronomy. In chapter 8 we described the molecular beam electric resonance studies of yl-doubling transitions in the lowest rotational levels, and in chapter 9 we gave a comprehensive discussion of the microwave and far-infrared magnetic resonance spectra of OH. Our quantitative analysis of the magnetic resonance spectra made use of the results of pure field-free microwave studies of the rotational transitions, which we now describe. 

We will mainly discuss studies of radicals to give an overview of this area of research. We briefly describe FT spectroscopy in the infrared and ultraviolet/visible and discuss a few of the experiments carried out in our laboratories. We compare... 

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