The generic structural formula for a 1-alkyl-3-methylimid- azolium cation is where R is a -CH2(CH2)nCH3 alkyl group. The melting points of the salts that form between 1-alkyl-3-methylimidazolium cation and the PF6- anion are as follows: R = CH2CH3 (m.p. = 60 °C), R = CH2CH2CH3 (m.p. = 40 °C), r = CH2CH2CH2CH3 (m.p. = 10 °C), and R = CH2CH2CH2CH2CH2CH3 (m.p. = -61 °C). Why does the melting point decrease as the length of alkyl group increases?

Video transcript

Hey everyone, we're told that a carb oxalic acid is an organic compound with the general formula R. C 00. H, where R is a hydrocarbon chain. The melting points of several carb oxalic acids are shown below. Let's go ahead and assess this chart. Looking at our first carb oxalic acid, we can see that we have a total of two carbons. Moving down the list, we have three carbons, four carbons, five carbons and finally six carbons. And this is including the carbon in our car box silic acid. And as we can see right here, all of our even number of carbons have higher melting points in comparison to our odd numbered carbons which have lower melting points. Now, let's go ahead and draw this out comparing our even numbered carbons and our odd numbered carbons. We can see that we have a symmetrical shape and the symmetrical shape allows our car box cilic assets to pack more efficiently in a solid form, which is why we see an increase in our melting points with our even numbered carbons. So that is going to be the answer to this question. Now, I hope that made sense. And let us know if you have any questions