Question

why are polyunsaturated fatty acids liquid at room temperature

Answer 1

is that a question out of interest, or homework?

Answer 2

homework @Schleifspur

Answer 3

mhkay. then you should be figuring out some things before I can really help you.

- what does 'unsaturated' mean?
- does it require energy to make a saturated fatty acid unsaturated?
- how do saturated fatty acids interact with each other?

Answer 4

so unsaturated is multiple bonds and not sure about the second question also not sure about the last question

Answer 5

okay. you're right about my first question. so, unsaturated means that there is a double bond between some of the carbon atoms.

to my second question: yes, it certainly does take more energy to make an unsaturated fatty acid by taking out two H atoms. remember that energy is NEVER lost. you can assume that the energy is partly stored in the double bond that you created by taking away the hydrogen.

to my third question: there are three kinds of interaction forces that are relevant between molecules, but only one that is relevant for fatty acids. the three are: hydrogen bonds, ionic interaction, van der waals interaction. which do you think is most relevant, and why could that be?

Answer 6

Would it be a Hydrogen bond because we are dealing with Hydrogen and its the strongest bond?

Answer 7

for a hydrogen bond you need hydrogen (duh) and a free electron pair, which is not present in fatty acids. it is the strongest bond, you're right about that, but there is a way stronger force in fatty acids. :-)

Answer 8

instead, we count on van der waals interactions, which are basically attractive forces between molecules. they are stronger if the molecules are bigger. but: molecules need their atoms to be close together for van der waals forces to be really strong.

if you have an unsaturated bond, it causes a molecular kink in the normally straight structure of the fatty acid. thus, the fatty acids can not bond via van der waals as well. and that is why they are liquid instead of solid =)

I will draw for you.