Nujol
Definition and meaning of Nujol in chemistry.
Nujol is a viscous mineral oil composed of saturated hydrocarbons, used in analytical chemistry to prepare samples for infrared spectroscopy and X-ray crystallography.
In more detail
In infrared spectroscopy, Nujol is ground with a solid sample to form a 'Nujol mull,' creating a uniform paste for analysis; its characteristic C-H absorption bands (around 2850-2960 cm⁻¹, with additional bending bands near 1460 and 1375 cm⁻¹) must be accounted for during data interpretation. In X-ray crystallography, Nujol serves as an inert mounting medium for crystals because it is largely transparent to X-rays and produces minimal background scattering. Its chemical inertness and low volatility make it ideal for both applications.
Key facts
| Chemical Composition | Mixture of saturated hydrocarbons (alkanes) of higher molecular weight than kerosene, typically C18 and higher |
|---|---|
| Primary Application | Infrared spectroscopy sample preparation (Nujol mull) |
| Secondary Application | X-ray crystallography crystal mounting |
| Field | Analytical Chemistry |
A chemist preparing an unknown solid compound for infrared spectroscopy might grind it with Nujol using a mortar and pestle to form a thick paste (Nujol mull), then place it between two sodium chloride plates for measurement.
Frequently asked questions
Does Nujol interfere with IR spectra?
Yes, Nujol exhibits strong C-H stretching absorption bands around 2850-2960 cm⁻¹ (plus bending bands near 1460 and 1375 cm⁻¹) that appear in spectra, but these regions are well-characterized and easily identified, allowing analysts to distinguish them from sample peaks during interpretation.
Why is Nujol preferred for X-ray crystallography over other mounting media?
Nujol is largely transparent to X-rays and produces minimal background scattering, so it does not interfere with or obscure the crystal diffraction pattern being measured.