Solving Infrared Spectral Problems

Electromagnetic Radiation Molecular Spectroscopy Infrared Spectroscopy 2-4 Interpreting Infrared Spectra 12.5 Solving Infrared Spectral Problems... 

Section 2.21, Alkyl and Aryl Halides, was revised. Section 2.23, How to Solve Infrared Spectral Problems, is a new section. The sections that followed were renumbered. 

One of the problems which must be solved for quantitative measurements by emission is the need for a blackbody source at the temperature of measurement. And a variety of blackbody references have been used including a V-shaped cavity of graphite 164), a metal plate covered with a flat black paint1S6 160) and a cone of black paper l53). However, none of these methods of producing a blackbody reference spectrum are adequate. In most cases the efficiency of the reference has not been established. The most recent recommendation 1S0) is an aluminium cup painted with an Epley-Parsons solar black lacquer which has an emittance of greater than 98% over the infrared spectral range. 

The advent of affordable, research grade FTIR spectrometers was followed by a rapid increase in the amount and diversity of in situ infrared studies, essentially as a result of their inherently high sensitivity, and rapid spectral collection times. As well as effectively solving the sensitivity problem, FTIR spectrometers facilitated the application of simple data collection and manipulation methods, and consequently greatly increased the experimental protocols that could be employed. 

In this chapter you will employ jointly all of the spectroscopic methods we have discussed so far to solve structural problems in organic chemistry. Thirty-four problems are provided to give you practice in applying the principles learned in earlier chapters. The problems involve analysis of the mass spectrum (MS), the infrared (IR) spectrum, and proton and carbon ( H and C) NMR. Ultraviolet (UV) spectral data, if provided in the problem, appear in a tabular form rather than as a spectrum. You will notice as you proceed through this chapter that the problems use different mixes of spectral information. Thus, you may be provided with a mass spectrum, an infrared spectrum, and a proton NMR spectrum in one problem, and in another you may have available the infrared spectrum and both proton and carbon NMR. 

Spectroscopy developed rapidly after the achievements of Bunsen and Kirchhoff, but a knowledge of the real cause and origin of spectral hnes was long in coming. It had to wait for the introduction of quantum theory and quantum mechanics. Two Danes took the decisive steps. In 1912 Niels Bjerrum studied the absorption of infrared radiation in gases. He showed that molecules absorb vibration and rotation energy in distinct quanta. Niels Bohr solved the problem of atomic spectra. 

There is a unique chapter on how to correctly use spectral processing to tackle the thorny problem of mixture analysis. Half the battle in obtaining a good infrared spectrum is proper sample preparation learn to win that battle by reading the Preparing Samples Properly chapter covering in detail the most important development in infrared sample preparation in decades diamond ATRs. The final chapters examine single analyte quantitative analysis and how infrared microscopy is used to catch criminals and solve industrial problems. 

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