Question

Which one of the following statements is True:

(A) $PhLi$ adds to both compounds with equal ease
(B) $PhLi$ does not add to either of the compounds
(C) $PhLi$ reacts readily with 1 but does not add to 2
(D) $PhLi$ reacts readily with 2 but does not add to 1

Answer 1

To solve this question, we must first some basic knowledge about Phenyllithium $(PhLi)$ and also we must understand the basic concepts of Aromaticity. Then we need to assess the properties of $PhLi$ and then use the rules for Aromaticity to determine that what will be the action of $PhLi$ on $1\,\,and\,\,2$ and then only we can conclude the correct answer.

Complete step-by-step answer: $PhLi$ : Phenyllithium or lithobenzene is an organometallic agent with the empirical formula ${C_6}{H_5}Li$ . It is most commonly used as a metalating agent in organic syntheses and a substitute for Grignard reagents for introducing phenyl groups in organic syntheses.Aromaticity: It is defined as a property of the conjugated cycloalkenes which enhances the stability of a molecule due to the delocalization of electrons present in the π-π orbitals.
The aromatics compounds are said to exhibit some special characteristics or called as rules which are given below-
1.Aromatic compounds are always cyclic structures.
2.Each element of the ring within the structure must and should have a p-orbital ring which is in a perpendicular form to the ring, and this makes it a planar molecule
3.All the compounds obey the Huckel’s Rule, i.e. all the aromatic compounds should have the $\left( {4n + 2} \right)\pi$ number of electrons.
4.The organic compound has to be flat.
Step 1: For the first compound:

So very clearly we can see in the above structures that it is an aromatic compound.
Step2:For the second compound:

So very clearly we can see in the above structures that it is an antiaromatic compound.And Hence, the first compound will be more reactive towards $PhLi$ and the second compound will be unreactive towards $PhLi$ .Conclusion: $PhLi$ reacts readily with 1 but does not add to 2

So, clearly we can conclude that the correct answer is Option (C).

Note: Crystalline phenyllithium is colorless; however, solutions of phenyllithium are various shades of brown or red depending on the solvent used and the impurities present in the solute.