Question

Rank the following compounds in order of decreasing electron density in the benzene.
Chlorobenzene (2) 4- nitrocholorbenzene (3) 2,4 – dinitrocholorbenzene (4) 2,4,6- trinitrochlorobenzene
A.1 > 2 > 3 > 4
B.1 > 3 > 2 > 4
C.3 > 1 > 4 > 2
D.4 > 3 > 2 > 1

Answer 1

Hint: Before solving this question, we should first know about the electron density of each benzene ring and then compare which one has greater and arrange it in decreasing order accordingly. Electron Density depends on the electronegativity of the element. The highly electronegative elements have more electrons.

Complete answer:
Greater electron density is represented by a partial negative charge whereas a partial positive charge represents less electron density.
 

In Chlorobenzene, Cl is there which is a high electronegative element. It withdraws the electrons from the benzene ring.
 

In 4-nitrochlorobenzene, Cl is there which withdraws the electrons and $N{{O}_{2}}$is also present which also has electron withdrawing property, so electron density decreases here.
 

In 2,4-dinitrochlorobenzene, Cl is there which withdraws the electrons and two nitro groups are present which withdraws the electrons from the benzene ring decreasing the electron density.
 

In 2,4,6- trinitrochlorobenzene, Cl is there which withdraws the electrons and three nitro groups are present which withdraws the electrons from the benzene ring decreasing the electron density.

Note:
The probability to find an electron in a certain place in a proximity of an atom or molecule, This calculation gives a quantity that is called Electron Density. Generally, The place where the electron density is high is the most prominent place for the electron to be found.