Question

Which of the following compound gives the smell of mustard oil:
(A) Alkyl isocyanate
(B) Alkyl isothiocyanate
(C) Alkyl isocyanide
(D) Alkyl isonitrile

Answer 1

Hint: Mustard oil seeds do not have any smell but sinus opening aroma happens when seeds are grounded and combined with the liquid. Mustard oil’s taste and smell is pungent. And this smell is due to the presence of sulphur elements in any compound. If any compound smells like mustard oil, it means that compound must have a sulphur element.

Complete Step by Step Solution:
Alkyl isocyanate is a compound in which an isocyanate is a functional group. Isocyanate should not be confused with cyanate ester. In Alkyl cyanate,an alkyl group (R) is bonded through oxygen (O) of the cyanate ester functional group. Whereas in Alkyl isocyanate, an alkyl group is bonded through nitrogen (N) of isocyanate functional group such as


As there is no sulphur present thus it cannot smell like mustard oil.
Alkyl isocyanide is an isomer of the nitrile compound.The nitrile group is one in which carbon is bonded with nitrogen and when this nitrile group is attached to an alkyl group (R) through carbon part (CN) it is known as alkyl nitrile and when this nitrile group is attached to an alkyl group (R) through nitrogen (NC) is known as alkyl isonitrile or alkyl isocyanide such as
As this compound also does not contain any sulphur so it also does not smell like mustard oil.

Alkyl isothiocyanate is the one that contains sulphur. In this compound, the alkyl group is attached to the isothiocyanate group through nitrogen such as


Thus, the correct option is B.

Note: Word ‘thio’ as a prefix is used in chemical nomenclature. This word represents sulphur element. Thus, the word is used as a prefix when an oxygen atom is replaced with a sulphur atom.