The Evans Method: Calculating Unpaired Electrons and Magnetic Susceptibility

Marketing Dept., | 8 min read
Marketing Dept., | 8 min read

The Evans Method is a powerful technique used in chemistry to determine the number of unpaired electrons in a compound, which in turn helps in understanding its magnetic properties. This post will explore the Evans Method, its applications, and how it is used to calculate unpaired electrons and magnetic susceptibility

What is The Evans Method?

The Evans Method involves using NMR spectroscopy to measure the magnetic susceptibility of a sample. Magnetic susceptibility is a measure of how much a substance will become magnetized in an applied magnetic field. It is closely related to the number of unpaired electrons in the substance. Here’s a simplified outline of the process:

  1. Preparation: A solution of the paramagnetic compound is prepared along with a reference compound.
  2. NMR Measurement: The NMR spectra of both the sample and the reference are recorded.
  3. Calculation: The difference in the chemical shift between the sample and the reference is used to calculate the magnetic susceptibility and the number of unpaired electrons.

How to Use Evans Method to Find Unpaired Electrons?

To use Evans method to find unpaired electrons, first dissolve your paramagnetic compound in a deuterated solvent like CDCl3 and prepare a reference sample with just the deuterated solvent. Measure the NMR spectrum of the reference sample to identify the solvent peak, then measure the NMR spectrum of the paramagnetic sample to observe the shifted solvent peak. Calculate the chemical shift difference (Δδ\Delta \delta) between the reference and paramagnetic samples. Use the Evans equation to determine the effective magnetic moment (μeff\mu_{eff}) and then find the number of unpaired electrons (nn). The number of unpaired electrons is calculated using the formula:

μeff=Δδ⋅TK\mu_{eff} = \sqrt{\frac{\Delta \delta \cdot T}{K}} n=4μeff2+1−12n = \frac{\sqrt{4\mu_{eff}^2 + 1} - 1}{2}

Applications of the Evans Method

The Evans Method is widely used in coordination chemistry and materials science to:

  1. Determine the electronic configuration of transition metal complexes.
  2. Study the magnetic properties of new compounds.
  3. Investigate the effects of ligands on the magnetic properties of metal centers.

Beyond basic coordination chemistry, the Evans Method is crucial in the development of advanced materials, including molecular magnets and spintronic devices. Understanding the magnetic susceptibility and the number of unpaired electrons helps in designing materials with specific magnetic properties, essential for high-density data storage and quantum computing.

Furthermore, this method aids in the synthesis and characterization of catalysts used in various chemical reactions. By analyzing the magnetic properties, researchers can infer the oxidation states and electronic environments of metal centers in catalysts, leading to more efficient and selective catalytic processes.


The Evans Method is a crucial technique in the field of chemistry for understanding the magnetic properties of compounds. It provides insights into the electronic structure and behavior of materials, aiding in the development of new magnetic materials and catalysts.

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