Questions dealing with electrophilic aromatic substitution

1. The nitration of N,N-dimethylaniline, C₆H₅N(CH₃)₂, in 85% H₂SO₄ gives 45% m-nitro product and 38% p-nitro product.
1. What is the species actually undergoing nitration to give the meta product?



2. How is it formed?

 See a) above 

3. What is its relative reactivity to that of benzene?  

It is less reactive than benzene as electron withdrawal by the nitrogen destabilizes the transition state, thereby increasing the activation energy for carbocation formation. 



4. Why does this species under go meta substitution?

The nitrogen has no ability to donate electrons as there is no lone pair on the nitrogen.

2. The nitroso group, -N=O, is ortho-para directing but deactivating. Explain in terms of resonance and inductive effects. 

Electronegativity explains deactivation: 



 Resonance explains o,p direction due to electron release. E.g. look at ortho attack:



3. Hexachlorophene, a substance used in the manufacture of germicidal soaps, is prepared by reaction of 2,4,5-trichlorophenol with formaldehyde in concentrated sulfuric acid. Propose a mechanism.



 



 

4. Propose a synthesis of 2-bromo-4-nitrotoluene from benzene.



 

5. Two alcohols, "A" and "B", have the same molecular formula C₉H₁₀O and react with sulfuric acid to give the same hydrocarbon "C". Compound "A" is optically active and compound "B" is not. Catalytic hydrogenation of "C" gives a hydrocarbon "D", C₉H₁₀, which gives two and only two products when nitrated once with HNO₃/H₂SO₄. Give the structures of "A", "B", "C", and "D".

 Comparing C₉H₁₀ with the formula of the equivalent alkane, C₉H₂₀, indicates five units of unsaturation. Nitration indicates an aromatic ring. The fact that there are only two mononitrated products indicates that there are only two different types of hydrogen on the aromatic ring. D must be:

 

Thus, C must be:



And A must be:

 

And optically inactive B must be:



6. Propose a mechanism for the following reaction: