Nitriles are named by identifying the longest carbon chain (including the nitrile carbon), then adding the suffix “-nitrile” to the parent alkane name. The carbon of the C≡N group is always numbered as carbon 1. A three-carbon nitrile, for example, is propanenitrile: prop- (three carbons) + -ane + -nitrile.
The Basic IUPAC Method
For simple, open-chain nitriles, follow these steps:
- Count the longest chain including the nitrile carbon (the carbon directly attached to nitrogen). That carbon is C1.
- Name the parent alkane based on that chain length. A four-carbon chain is butane, a five-carbon chain is pentane, and so on.
- Add the suffix -nitrile directly to the alkane name. Four carbons gives you butanenitrile; five gives you pentanenitrile.
- Number substituents from the nitrile carbon (C1) outward. A methyl group on C3 of a five-carbon nitrile would make it 3-methylpentanenitrile.
Because the nitrile carbon is always C1, you don’t need to specify its position with a locant. You never write “1-butanenitrile” since there’s no other place the nitrile group could be on a straight chain.
Naming Nitriles on Rings
When a C≡N group is attached directly to a ring (cycloalkane or aromatic ring), the naming works differently. You can’t include the nitrile carbon in the ring count, so instead of using the “-nitrile” suffix, you add “-carbonitrile” to the name of the ring system. A C≡N group attached to cyclohexane becomes cyclohexanecarbonitrile. The ring carbon bonded to the nitrile group is numbered C1, and other substituents on the ring are numbered from there.
The Carboxylic Acid Shortcut
There’s a second, equally valid IUPAC approach: name the nitrile as a derivative of the corresponding carboxylic acid. You simply swap the acid ending for a nitrile ending. If the acid name ends in “-ic acid” or “-oic acid,” replace that with “-onitrile.” If it ends in “-carboxylic acid,” replace that with “-carbonitrile.”
This means butanoic acid becomes butanonitrile, and benzoic acid becomes benzonitrile. For cyclopentanecarboxylic acid, you get cyclopentanecarbonitrile. This method is especially handy when you already know the name of the parent acid, since the conversion is mechanical.
Common (Non-IUPAC) Names
Several nitriles are almost always referred to by their common names, especially in lab settings. The most important ones to recognize:
- Acetonitrile is the common name for ethanenitrile (two carbons total), derived from acetic acid. It’s one of the most widely used organic solvents.
- Benzonitrile is the nitrile derived from benzoic acid, with C≡N attached directly to a benzene ring. This name happens to match both the common and IUPAC-derived conventions.
- Acrylonitrile is the common name for 2-propenenitrile, a three-carbon nitrile with a double bond. It’s an important industrial chemical.
In most coursework, you’ll be expected to give the systematic IUPAC name, but knowing these common names helps when reading older texts or product labels.
Dinitriles: Two Nitrile Groups
When a molecule has two nitrile groups, one on each end of a chain, you name the full carbon chain (counting both nitrile carbons) and add “-dinitrile” as the suffix. A four-carbon chain with a nitrile at each end is butanedinitrile. The numbering starts at one end and goes to the other, just like a regular alkane, with C1 and C4 each bearing a C≡N group. Since the nitrile groups are symmetric in these cases, you don’t need locant numbers for them.
When Nitrile Isn’t the Main Group
Nitriles rank high in IUPAC’s functional group priority list, but they fall below carboxylic acids. If a molecule contains both a carboxylic acid and a nitrile, the acid takes priority as the principal group and gets the suffix. The nitrile is then treated as a substituent using the prefix “cyano-” with a locant number indicating its position on the chain.
For example, a five-carbon chain with a carboxylic acid at C1 and a C≡N at C5 would be named 5-cyanopentanoic acid. The acid suffix defines the parent name, and the cyano- prefix tells you where the nitrile sits.
The cyano- prefix also shows up when the nitrile group is treated as a substituent on a simple alkane chain, though this is less common in standard naming. In that style, a C≡N group on C1 of a three-carbon chain would be called 1-cyanopropane. The chain is numbered to give the cyano group the lowest possible locant. In practice, you’d almost always name this compound as butanenitrile instead, since the nitrile suffix takes precedence when no higher-priority group is present.
Quick Reference for Naming
- Open-chain nitrile (principal group): count all carbons including C≡N carbon, add -nitrile. Example: CH₃CH₂C≡N = propanenitrile.
- Nitrile on a ring: name the ring, add -carbonitrile. Example: C≡N on cyclopentane = cyclopentanecarbonitrile.
- From acid name: replace -ic acid/-oic acid with -onitrile, or replace -carboxylic acid with -carbonitrile.
- Two nitrile groups: name the full chain, add -dinitrile. Example: N≡C-CH₂CH₂-C≡N = butanedinitrile.
- Nitrile as substituent: use the prefix cyano- with a locant when a higher-priority group (like a carboxylic acid) is present.