What is Acetonitrile? - Structure, Uses & Properties

Instructor: Korry Barnes

Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.

The focal point of this lesson will be on a specific organic compound known as acetonitrile. Our primary topics of discussion will include its structure, chemical properties, and important uses it finds application towards.

A Multi-Purpose Molecule

When you were in elementary school did you have anyone in your class that no matter what the game or sport was in recess, they always seemed to be good at it? For whatever reason, some people just seem to excel in athletic-type events no matter what they are or what the skills required are. Sometimes, we call those types of people multi-skilled or multi-faceted in their abilities to do a lot of different things at a high level.

Did you know that some organic compounds can be likened to multi-skilled people? There are some compounds out there that are good at doing a lot of things and have such wide application ranges, we can kind of think of them as being like that gifted individual at recess who is multi-talented. The specific compound we are going to be discussing in this lesson is very privileged, and is called acetonitrile. We will be exploring the structure, chemical properties, and primary applications of acetonitrile to see just how versatile it can be. Let's dive in!

Structure of Acetonitrile

Let's begin our explorations by looking at the definition and structure of acetonitrile. Acetonitrile is an organic compound (meaning it's carbon-based) with the chemical formula CH3 CN, and is classified as a nitrile in terms of its functional group. In organic chemistry, a nitrile is defined as a carbon atom that contains a triple bond to a nitrogen atom. Interestingly, acetonitrile is actually the simplest organic nitrile that's possible.

Acetonitrile is the simplest organic nitrile, and contains a carbon-nitrogen triple bond

Acetonitrile also contains a second carbon atom bonded to three hydrogen atoms, which is called a methyl group (-CH3 group). Because of the fact that the central carbon atom contains a triple bond to the nitrogen atom, the bond angle between the methyl group carbon, the central carbon atom, and the nitrogen atom is a perfect 180 degrees.

From a structural standpoint, the reason for this is because bonds are simply electrons, and since electrons are negatively charged they will repel one another if brought into close proximity (like charges repel, opposites attract). The optimal way that the electrons associated with the chemical bonds can get as far from one another as possible and maximize space between them is if the bond angle is 180 degrees.

Properties of Acetonitrile

Now that we're a bit more familiar with the structure of acetonitrile, let's discuss some of the properties it exhibits. One of the most important properties of acetonitrile is its polarity. More specifically, it's classified as a polar compound. What exactly does this mean? It turns out that some atoms have the ability to attract electrons toward themselves more than others. This phenomenon is called electronegativity, we say that the electrons associated with the chemical bonds will always be more attracted to the more electronegative atom.

In the case of acetonitrile nitrogen is much more electronegative than carbon. Since this is the case, the electrons contained within the triple bond tend to 'spend more time' around nitrogen or are attracted to the nitrogen atom to a much greater extent than carbon. This results in an unequal sharing of the electrons, and means that at any given point in time, the carbon atom will carry a partial positive charge and the nitrogen will have a partial negative charge. This is why acetonitrile is classified as a polar compound.

Another important property of acetonitrile is its boiling point, which is about 82 degrees celsius. It's actually a rather high boiling point for such a small molecule, the the value of the boiling point can actually be attributed to the polarity. In general, the more polar the compound, the higher the boiling point will be.

Uses of Acetonitrile

Of the many uses of acetonitrile, it notably can serve as a two-carbon building block in organic synthesis. When chemists are trying to construct large, complex molecules, they utilize simple compounds like acetonitrile as starting materials. Using acetonitrile not only allows two carbon atoms to be added but also a nitrogen as well.

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