The nitril group
A – C≡N group is called "nitril", when the C is part of a main chain.
When a – C≡N group performs as a side chain (the C does not take part of the main chain), than the name 'cyanide' can be used, just like in the inorganic chemistry with cyanide ions: -CN-
Nitril groups can be introduced / made in a substitution reaction of cyanide with a halogene alkane:
This substitution can be considered as a method of chain enlarging.
The Nitril group possesses a threefold bonding. With the consequence that not addition is possible, not just one or two, but even three times..
This is very special.
A special rule is: more than one OH-group connected to the same C in a carbon chain is not stable; water will be produced.
First we add three molecules of water to support the addition, but eventually one molecule of water will return.
You can also see that finally an alkanoic acid and ammonia are formed, the two final products.