Question

In alkyl cyanide, alkyl group is attached with:
A. $C$ of $CN$ group
B. $N$ of $CN$ group
C. either $C$ or $N$ of $CN$ group
D. both $C$and $N$ of $CN$ group

Answer 1

Hint: When a compound is named as a cyanide there is carbon-carbon attachment between the alkyl and the functional group. The attachment sites in the functional group are not interchangeable.The name of the compound changes if the attachment site changes.

Complete step by step answer:
Let us first understand the structure of the molecules.
$R - C \equiv N$
where, $R$ could be any alkyl group.
We can see from the above structure that there is a triple bond between the carbon and the nitrogen of the molecule.
Carbon is tetravalent, and since it only forms three bonds with nitrogen, one electron is free to bond with the alkyl groups.
Nitrogen also has one lone pair on its surface which can be used for donation.
So in technical sense, a molecule with carbon and nitrogen, both of them are essentially capable of forming a bond with the alkyl group.
Now, how we differentiate that which atom in the molecule is getting attached to the alkyl group is using the name.
If the $C$ of $CN$ group is attached to the alkyl group, we name the compound as alkyl cyanide.
If the $N$ of $CN$ group is attached to the alkyl group, we name the compound as alkyl isocyanide.

So, the correct answer is Option A.

Note: In case, there is further addition of sulphur in the molecule, then also there are two possible donor sites. The fundamental of naming remains the same. In case of cyanide, it become thiocyanide and isocyanide becomes isothiocyanide. Thio refers to the sulphur group.