AAMC 10 PS #40 / Solvents in general

[Tenebrus]

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Hey guys,

I'm having some some trouble with solvent questions. I'm familiar with like dissolves like, but to what extent is something considered polar or nonpolar for solvent purposes? Take this question for example:

40. Which of the following solents could NOT be used to dissolve the hydrocarbon portion of oleic acid?
A. Acetic Acid
B. Benzene
C. Diethyl Ether
D. Chloroform


Correct answer is A.

I correctly eliminated B and C since they aren't polar, but isn't chloroform polar as well? Also, how do carbonyl's and nitrogen containing compounds work with regards to their polarity and use as a solvent?


Thanks for any help!

 

[richkaj]

I believe chloroform is CHCl3 which makes it a tetrahedral with a molecular geometry that is trigonal pyrimidal. The Cl cancel and leaving the C-H bond to be the dipole moment. The acetic acid is more polar by the C=O bond and the O-H bond making it the more polar reagent. Yes, you are correct chloroform is polar but not as polar as acetic acid.

The carbons involved in carbonyls in certain compounds can be based on the (electrophilicity) (ability to attract nucleophiles in certain reactions) because there is a dipole produced in carbonyls as the oxygen takes more of the double bond since it is more electronegative in the carbonyl bond leaving carbon more positive. Nitrogens can act as nucleophiles to carbonyls if they have lone pairs of electrons (act as a lewis acid)... the atoms that the nitrogen is attached to will determine it's ability to react in a reaction.

If you see some examples of nitrogen containing compounds that look different this would be helpful in explaining the difference. Ammonium ion and Ammonia will react in a different manner... I hope this helps... if I missed something, please comment.

 

[Tenebrus]

Thanks, that makes sense. I should have gone with the more polar answer 😛