See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Electrophilic Aromatic Substitution (EAS) and directing effects. The target molecule is 1-tert-butyl-4-nitrobenzene (para-nitro-tert-butylbenzene). It has a tert-butyl group and a nitro group in para positions relative to each other. Step 1 - Identify the directing effects: - The tert-butyl group (-C(CH3)3) is an ortho/para director and ring activator. - The nitro group (-NO2) is a meta director and ring deactivator. Step 2 - Determine the correct order of substitution: - To get the para product, we need to introduce the tert-butyl group FIRST (Friedel-Crafts alkylation), which activates the ring and directs the incoming electrophile to the ortho and para positions. - Then, nitration (HNO3/H2SO4) will introduce -NO2 preferentially at the para position relative to the tert-butyl group (para is favored over ortho due to steric bulk of the tert-butyl group), giving 4-tert-butyl-1-nitrobenzene. Step 3 - Why option (b) is best: - Option (b): Step 1 is Me3CCl/AlCl3 (Friedel-Crafts alkylation to give tert-butylbenzene), Step 2 is HNO3/H2SO4 (nitration). The tert-butyl group directs nitration predominantly to the para position due to steric hindrance at ortho positions, yielding the desired 4-nitro-tert-butylbenzene. This is the correct sequence. Step 4 - Why other options fail: - Option (a): Nitration is done first, giving nitrobenzene. Nitro group is a strong meta director and deactivator, so subsequent Friedel-Crafts alkylation would be directed to the meta position, not para. Also, Friedel-Crafts reactions are generally unsuccessful on strongly deactivated rings. Wrong product and poor yield. - Option (c): Uses isobutyl chloride (CH3-CH(CH3)-CH2-Cl) instead of tert-butyl chloride. Under Friedel-Crafts conditions with AlCl3, the isobutyl carbocation can rearrange to the tert-butyl carbocation, so it might still give tert-butylbenzene, but this is less direct and less reliable; however, the main issue is that the order (alkylation first, then nitration) in (c) is the same as (b) in terms of sequence, BUT this uses the isobutyl/neopentyl system which is less ideal than directly using Me3CCl. Actually option (c) could also work via rearrangement, but option (b) is more direct and reliable. - Option (d): Nitration first (giving nitrobenzene), then attempted Friedel-Crafts with isobutyl chloride/AlCl3 — same problems as (a): deactivated ring, meta direction, reaction unlikely to proceed well. Therefore, the correct answer is B.