Question

Part a) Each student will receive one of bromobenzene, toluene, benzaldehyde, anisole, or biphenyl, and will need to add 14.0 mmol of their compound to their reaction. Calculate the mass of 14.0 mmol of each compound.

Part b) What do you think will be the relative rate of reaction for the compounds? Which will undergo substitution most quickly? What is your reasoning for your order?

Part c) You will be tracking the progress of your reaction using TLC. If you use a silica plate and a 10% ethyl acetate in hexanes eluent, where do you expect your product spot to appear in relation to your starting material?

Answer 1

Part a)

Molar mass 1 mole 1 mmole 14 mmole

Bromobenzene 157.01 g/mol 157.01 g 0.15701 g 2.19814 g

Toluene 92.14 g/mol 92.14 g 0.09214 g 1.28996 g

Benzaldehyde 106.12 g/mol 106.21 g 0.10621 g 1.48694 g

Anisole 108.14 g/mol 108.14 g 0.10814 g 1.51396 g

Biphenyl 154.21 g/mol 154.21 g 0.15421 g 2.15894 g

Part b:

For electrophilic substitution reaction, Anisole will be the most reactive, since the lone pair of electron on oxygen atom of methoxy group will increase the electron density of the benzene ring.

anisole > toluene > biphenyl > bromobenzene > benzaldehyde.

Part C:

This is a generic question, since you didn't mention which substitution reaction. For alkylation the top to bottom order of the compounds in TLC are as

biphenyl

toluene

bromobenzene

benzaldehyde

anisole

Even at 10% ethyl acetate in hexanes eluent, you will not be able to distinguish the spots between biphenyl, toluene and bromobenzene.