Which of these Functional Groups are polar ? ?

Question

Are all these Functional Groups polar ? :

a. Hydroxyl ( - OH )

b. Carbonyl

c. Carboxyl (-COOH)

d. Amino (-NH2) the 2 is a subscript

e. Sulfhydryl (-SH)

f. Phosphate

I've got that [a, c, and d] are polar so far, but I'm not sure if that's correct and don't know about the rest. I've read that if a molecule is polar, then it is hydrophilic, if they're all polar, this makes them hydrophilic too then, right ?

Any help would be greatly appreciated at the moment. =) Thanks in advance.

Answer 1

So far you are correct, but there are a few that were left out.

One of the main reasons that these molecules are polar is because of a large electronegativity difference. So, the carbonyl group, which is C=O (carbon double bonded to a oxygen), has an electronegativity difference and will be polar. The same can be said for the carboxyl COOH, it to is polar because of the differecnce in electronegativity.

The sulfhydryl group or called the thiol is somewhat polar. Since the electronegativity difference is small, the molecule is considered to be non-polar. For the phosphate group is polar because of a electronegativity difference between the four oxygens.

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Answer is: A, B, C, D, F.

Now I was talking about electronegativity to solve the problem. Now you also have to think of the structure, which is called the VSEPR model. Now that takes the shape of the molecule into affect.

So for phosphate, electronegatity alone cannot give you a definitive answer for why phosphate is polar. Since the phosphate  (to be simple) has a tetrahedral shape, it forms an inbalance between the 4 oxygens and creates and stronger pull to one side of the molecule and hence making it polar.

good luck.