Question

I need to know from least to greatest the polarity of caffeine, acetaminophen, aspirin, and ibuprofen. I am very confused cause many people have asked this question on chegg but lots of people have given different answers. This is to see which would have greatest Rf value in TLC. Please help.

Answer 1

To answer your question, first get the structures of all the compounds. Then see which compound has more polar groups.

let us see,

caffeine

acetaminophen

aspirin

ibuprofen

Caffeine has more amines, so it has more charge separtion, so it is polar then all the listed compunds.

Next comes acetaminophen. because it has more H-bond donors and acceptors. it has one NH and One OH

aspirin and ibuprofen more are less like equal and aspirin is little bit more polar then ibuprofen. ibuprofen has only alkyl and aromatic groups with one COOH. So it is less polar then aspirin

Caffeine > Acetaminophen > phenacetin > Aspirin > Ibuprofen