Question

Which of the set of compounds do not have a conjugated system?

A. (ii), (iv), (v) and (vi)
B. (i), (ii), (v) and (vii)
C. (ii), (iii), (v) and (vi)
D. None of these.

Answer 1

Non aromatic or aromatic compounds can be checked by certain rules, if it follows then, aromatic and if not then, not aromatic. Aromaticity is a special property which is seen in organic compounds of ring-shaped, flat structures with a ring of conjugated systems that gives increased stability.

Complete step by step answer:
An aromatic compound contains a set of covalent bonds with specific characteristics
A delocalized conjugated system of electrons, which is an arrangement of alternating single and double bonds. It should be a coplanar structure having all the atoms in the same plane. It should follow Huckel’s rule, a number of delocalized electrons$\left( 4n+2 \right)$, where $n=0,1,2,3,$ and so on. Atoms should be arranged in one or more rings.
In a conjugated system, electrons are delocalized with the alternate single and double bond. Lone pairs can also be part of the system. Compounds (i),(iii) and (vii) have a conjugated system.
Therefore correct answer is option C that is three compounds which do not have a conjugated system are (ii),(iv),(v) and (vi)

So, the correct answer is Option C

Note: Note that the compound’s’ does not seem to be aromatic by its structure because the ring has $4$ electrons, which does not satisfy Huckel’s rule. But on resonance, with other atoms, a resonating structure is formed which is aromatic. So, do not judge Aromaticity by just looking at the compound, it can be aromatic in one form or another.