Nujol
Definition and meaning of Nujol in chemistry.
Nujol is a thick mineral oil made of heavy saturated hydrocarbons. Chemists use this heavy oil to prepare solid samples for testing. It is especially useful in infrared spectroscopy and X-ray crystallography.
In more detail
Infrared spectroscopy measures how molecules absorb light to identify them. Solid samples often scatter this light and ruin the test. To fix this, a chemist grinds the solid powder with a few drops of Nujol.
This creates a smooth paste called a Nujol mull. The heavy oil coats the particles and stops the light from scattering. Nujol is made of simple carbon and hydrogen chains.
Because of this, Nujol itself absorbs some infrared light. It shows strong stretching signals between 2850 and 2960 cm-1. It also shows smaller bending signals near 1460 and 1375 cm-1.
Chemists must ignore these known Nujol signals when reading the final graph. If the sample absorbs light in those exact same spots, Nujol is a bad choice. Nujol is also very useful in X-ray crystallography.
This technique bounces X-rays off a crystal to find its exact shape. The oil acts as a safe glue to hold the tiny crystal in place. It works perfectly because X-rays pass right through the oil.
It creates almost no background noise on the detector. The oil does not react with most chemicals. It also does not evaporate easily in the open air. This keeps the sample safe and stable during long tests.
Key facts
| Chemical Composition | Mixture of heavy saturated hydrocarbons |
|---|---|
| Typical Chain Length | Usually C18 and higher |
| Primary Use | Making a mull for infrared spectroscopy |
| Secondary Use | Mounting crystals for X-ray tests |
| Key Infrared Signals | 2850 to 2960 cm-1 and near 1460 and 1375 cm-1 |
| Physical State | Thick, viscous liquid at room temperature |
Imagine a student needs to test a mystery white powder. The student puts a small scoop of the powder into a small glass bowl. They add two drops of Nujol oil. The student grinds the mixture firmly until it looks like cloudy petroleum jelly. They smear a thin layer of this paste between two clear salt plates. Finally, they place the stacked plates into the infrared machine to read the hidden chemical bonds.
Frequently asked questions
Does Nujol hide parts of the infrared spectrum?
Yes. It blocks the regions where carbon-hydrogen bonds absorb light, specifically around 2850 to 2960 cm-1. You cannot see sample peaks in these exact spots.
Why use Nujol instead of just melting the solid?
Many solid chemicals will burn or break down if you heat them enough to melt. Grinding them with oil is much safer.
Why is Nujol good for holding crystals in X-ray tests?
It is clear to X-rays and does not dry out. It protects the crystal from air without hiding the crystal structure.