# How can we determine the polarity of fat molecules?

I'm trying to solve a question in a biochemistry quiz, which is asking for classifying a set of lipidic derivatives, by increasing polarity. Unfortunately, we didn't cover the classification of different liposoluble molecules by polarity in Biochemistry class. I find myself buried in details every time I use google seeking a good explanation. So:

How can we determine either if one molecule is more/less polar than other ?

For example, classifying Cholesterol, Triglyceride, Phosphatidylcholine, Phosphatidylserine, by increasing polarity.

PS : I'm not searching for the answer of that example too. I just need the exact method for determining how strong a polar fat molecule is. I'm sorry for my bad english.

• Please read our homework policy, then edit your question to include what you've learned so far, what your thinking is regarding the polarity of the different molecules, and where exactly you're stuck. We're not here to do your homework for you, but we are here to help you learn. – MattDMo Aug 20 '15 at 17:10
• This is not homework. I'm just practising some random exercises from the internet in order to develop my knowledge and skills in Biochemistry. I asked for the method, not the answer to the exercice. And this example I provided is not the set provided in the exercise. :) – Younesse Bagachoul Aug 20 '15 at 17:17
• You determine polarity, generally, by looking at the composition and the functional groups on the molecule, and the geometry of the molecule. Do you expect a separation of charge, or something uniform? Water is polar because the draw on the net electrons for the molecule is to the oxygen atom, resulting in a more negative charge in that region. Carbon dioxide is nonpolar because of it's linear geometry, even though there are two oxygen atoms. – CKM Aug 20 '15 at 18:21
• Not that. For example, a fatty acid have a hydrophilic region and a hydrophobic region right? and a phospholipid also do. But, they differ in composition of the polar head (Hydrophilic part). So, I want to classify these two molecules, by their hydrophilic part polarity. Which one is more polar and can interact with water more than other. Got it ? – Younesse Bagachoul Aug 20 '15 at 19:02
• chemistry.stackexchange.com/questions/18589/… I managed to find a good answer in the chem stack exchange. Otherwise you'd use column liquid chromatography and a gradient elution technique to determine experimentally which one is more polar. – CKM Aug 20 '15 at 21:07