Dear Students,

Welcome to the Tutorial section on NMR spectroscopy. Below, you'll find a set of fundamental rules and guidelines to help you interpret both ¹H and ¹³C NMR spectra for solving the structures of organic compounds. Additionally, you can download a free copy of the textbook NMR Spectroscopy for Chemists—a comprehensive resource for deepening your knowledge of NMR spectroscopy techniques and applications in organic chemistry.

Download the textbook

Basic Rules

• Before the analysis of NMR spectra, think about the molecular formula. Is the molecule fully saturated or are there some multiple bonds or rings?
• Identify solvent signals and exclude them from the structural analysis.
• Consider the number of signals, their positions (chemical shifts), intensity, shape and splitting.
• The number of signals corresponds to the number of non-equivalent atoms in the molecule. For example, benzene will have only one carbon signal and one hydrogen signal because all carbon atoms in its structure are equivalent and all hydrogen atoms are equivalent.
• The positions of signals (their chemical shifts) reflect the molecular environment of the atoms. There are specific regions in the spectra, where signals of some functional groups can be found. For example, signals of carbonyl carbon atoms (in ketones and aldehydes) can be found at 190–220 ppm, signals of carboxylic acid derivatives (acids, esters, anhydrides, amides, halides) can be found at 160–180 ppm.
  Typical carbon chemical shifts
  Typical hydrogen chemical shifts
• In the carbon APT spectra, positive signals (up signals) correspond to CH₂ and quaternary carbon atoms, and negative signals (down signals) correspond to CH₃ and CH carbon atoms.
• The intensity of signals reflects the number of equivalent atoms contributing to the signal. Hydrogen spectra can usually be quantified by integration. The integral intensities are shown below the signals. Note that small deviations of the integral intensities from ideal values are normal. Unfortunately, signal intensities in commonly measured carbon spectra can be significantly affected by other effects than the number of equivalent atoms and therefore cannot be quantified.
• The shape of signals may reflect dynamic processes, such as conformational equilibria. Broad signals are often observed for systems with slow dynamics.
• Exchangeable hydrogen atoms are those attached to an oxygen, nitrogen or sulfur atom. Signals of exchangeable protons are often broader than other signals.
• The splitting of signals caused by J-coupling brings information about the number of (mostly) hydrogen atoms in neighboring positions. For example, the signal of the methyl group in an ethoxy fragment (CH₃–CH₂–O) is split to a triplet by the neighboring two hydrogen atoms in the CH₂ group. Similarly, the signal of the CH₂ group is split to a quartet by the neighboring three hydrogen atoms in the methyl group.
  
• The signal splitting in carbon spectra is usually removed by decoupling leading to all carbon signals being observed as singlets.

Have fun with NMR-Challenge!