MCAT Organic Chemistry Review

Spectroscopy

Introduction

If we are given an unknown compound, one of the most efficient ways to identify it and determine its properties is by using spectroscopy. Spectroscopy measures the energy differences between the possible states of a molecular system by determining the frequencies of electromagnetic radiation absorbed by the molecules. These possible states are quantized energy levels associated with different types of molecular motion, such as molecular rotation, vibration of bonds, electron absorption, and nuclear spin transitions. Different types of spectroscopy measure different types of molecular properties, allowing us to identify the presence of specific functional groups and to detect the connectivity (backbone) of a molecule.

In a medical context, spectroscopy is important in magnetic resonance imaging (MRI). MRI scanners actually measure 1H–NMR spectra of water molecules in different environments in the body. They then converts these signals into greyscale, allowing excellent visualization of the body, especially soft tissue.

One of the big advantages of laboratory spectroscopy is that only a small quantity of sample is needed. Also, the sample may be reused after a test is performed. The downside of spectroscopy is that it’s difficult to do without special equipment—but as long as you have a chemistry lab available, these are some of the best techniques to identify compounds.