Organic Chemistry: Concepts and Applications - Headley Allan D. 2020

Spectroscopy Revisited, A More Detailed Examination
13.1 Introduction

In Section 3.16 of Chapter 3, the topic of spectroscopy, specifically infrared (IR) spectroscopy, was introduced in the context of functional groups and how this type spectroscopy can be used to assist in the identification of specific functional groups of different organic molecules. In this Chapter, IR spectroscopy, along with additional types of spectroscopy, will be examined in greater details. There are literally millions of different types of organic compounds, and everyday new organic compounds are being isolated from natural sources. Many of these compounds are described as natural products. Most have healing and medicinal benefits and they have been reproduced in large quantities by various industries, mainly for pharmaceutical uses. There are other organic compounds that are synthesized in various research labs. Thus, an integral aspect of an organic chemist's work is the utilization of spectroscopy in the determination of the actual structures of newly discovered and synthesized compounds.

The types of spectroscopy that will be covered in this chapter include ultraviolet, IR, mass spectrometry, and nuclear magnetic resonance (NMR) spectroscopy. Spectroscopy involves the interaction of molecules with different forms of energy. Of interest to chemists, and especially to organic chemists, is the nature of the interaction of molecules when they come into contact with energy. Once energy of a specified frequency interacts with a molecule, the molecule becomes excited and undergoes different types of transitions depending on the frequency of the energy. When some molecules are exposed to energy in the form of light, weak bonds are broken to form radicals as the case of peroxides and halogens. On the other hand, when water molecules, for example are excited by microwave energy, they rotate and, as a result, heat is generated, which is used to heat our food in the microwave oven. Based on the nature of the interaction of molecules with energy of different frequencies, important information can be gained about molecules and used to assist in structure determination. The forms of energy that will be used in spectroscopy encountered in this course include visible light, ultraviolet light, IR, and radio waves.