Chapter 6: Structural Identification of Organic Compounds: IR and NMR Spectroscopy
In this chapter, we will focus on the methods for chemists to determine the structure of organic compounds. As part of the efforts for scientists to search for new compounds for medical, material or new energy resource purposes, determining the structures of the new compounds is a very critical step. A number of instrumental spectroscopy techniques have been used broadly for such purposes. Spectroscopy is the study of the interaction of matter and electromagnetic radiation, and how these interactions can be quantified, analyzed, and interpreted to gain information about the structure of matter. To identify the structures of organic compounds, we will specifically study how molecules interact with electromagnetic radiation, so the spectroscopy techniques in our discussions here can also be called molecular spectroscopy.
Specifically, we will have discussions about infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy in this Chapter. IR spectroscopy is a technique applied widely in organic chemistry to detect the presence or absence of a certain functional group, and NMR spectroscopy is a powerful analytical technique that can determine the bonding arrangement, or the structure, of a molecule.
Learning Objectives for this chapter:
- Understand and explain the principle of Infrared (IR) spectroscopy.
- Be able to identify the bands of major organic functional groups in IR spectra.
- Understand and explain the principle of Nuclear Magnetic Resonance (NMR) spectroscopy, including the NMR active nuclei, spin state and magnetic resonance, shielding and de-shielding effects and chemical shift.
- Interpret the NMR spectra of a certain compound by assigning the peaks based on groups of signals, chemical shifts, splitting patterns, and integration.
- Predict the number of peaks expected in the 1H or 13C NMR spectrum of a given compound.
- Determine the structures of unknown compounds based on the structural information given together with IR and NMR spectra.
