UW-Madison MRSEC

Nuclear Magnetic Resonance
Proton NMR

Environmental Effects

The chemical environment of the nuclei influences the instrumental response. The information from the spectra can be broken into four categories. They are:

2. Position of Signals - Chemical Shift

3. Intensity of Signals

4. Splitting of Signals

Each of these characteristics gives valuable information about the structure of the molecule.

Number of Signals

The chemical environment of the nucleus determines its resonance frequency. Thus, the number of signals in a NMR spectrum identifies the number of different chemical environments in which the nuclei in the sample reside.

Position of Signal - Chemical Shift

The position of the signal, relative to a reference signal, is called the chemical shift and provides additional information regarding the type of chemical environment surrounding the nucleus responsible for the signal. For proton NMR the chemical shifts have a range of 10-15 ppm. In carbon-13 NMR the chemical shifts range up to 200 ppm.

Intensity of Signal

The intensity of the signal can identify the relative number of nuclei in the environment contributing to the signal.

Splitting of Signals

The pattern into which some signals are split indicates the number of protons on adjacent atoms. There will be n + 1 peaks for n protons on adjacent atoms. The relative peak areas follow the pattern:

The spacing between the peaks in hertz is called the coupling constant, J. Two signals that arise from nuclei that interact with each other will have the same value of J.