Benzene, C6H6, reacts with Br2 in the presence of FeBr3 as a catalyst to give an organic compound wi — Stoichiometry / Organic Chemistry / Solutions Chemistry Question
Problem Context
Benzene, C6H6, reacts with Br2 in the presence of FeBr3 as a catalyst to give an organic compound with the percentage composition by mass; C 30.55%, H 1.71%, Br 67.74% and hydrogen bromide.
Determine the empirical formula of the compound.
Model Answer
convert masses to moles:
These numbers are whole numbers, so the empirical formula must be C3H2Br
When 0.115 g of this compound are dissolved in 4.36 g of naphthalene the solution freezes at 79.51 ˚C. Pure naphthalene freezes at 80.29 ˚C and has a kf = 6.94 ˚C·m–1. Determine the molar mass and molecular formula of the compound.
Model Answer
ΔT = 80.29 – 79.51 = 0.78 ˚C. Plugging this value into the formula for freezing point depression gives,
240 / 117.9 = 2.03 which is approximately 2, so the molecular formula must be C6H4Br2
Write a balanced equation for the reaction.
Model Answer
C6H6 + 2Br2 → C6H4Br2 + 2HBr
Calculate the theoretical yield for the organic compound when 4.33 g of of benzene is reacted with an excess of bromine.
Model Answer
The theoretical yield is:
= 13.1 g C6H4Br2
If the actual yield of the reaction is 5.67 g, what is the percentage yield?
Model Answer
Percent yield is:
= 43.4%
Write structures for the possible isomers that could be formed in this reaction.
Model Answer
The possible isomers for i. are,
Identify the major isomer(s) formed in this reaction and explain your reasoning.
Model Answer
ii. the major products are,
because –Br is an ortho-para director. The para isomer should be the most prominent product because of steric hindrance for the ortho product.