Kaplan Item 34 BS Section Test

[Simran1031]

which simple test can be used to distinguish 2 compounds?
1. para methyl phenol
2. benzyl alcohol

a. Compound 2's solubility on NaOCH3
b. compound 1's solubility in NaOH
c. compound 1's ability to decolorize a bromine solution
d. compound 1's solubility in NaHCO3
answer: compound 1's solubility in NaOH

I am not sure how to get to this answer..and im not sure how to determine solubulities of these compounds in general. someone please help!

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[Phlame217]

Organic chemistry 101

You have to know how to identify an Ortho/Para or Meta Director and also determine the polarity of substituants.

P-Methyl-Phenol is a very neutrally charged molecule (Phenol is benzene with OH group which is very polar) but the methyl balances out the charge.

On the other hand, benzyl alcohol is a very similar molecule to Phenol there for its very polar.

Next realize "like dissolves like" so you should know that benzyl alcohol would dissolve in a polar solvent and that p-Methyl-Phenol would dissolve somewhat in NaOH or better in a non polar substance.

A) Both would dissolve in this because its polar and both would undergo a reaction with this, not very pratical.

B) BA would readily dissolve in this, PMP would somewhat dissolve.

C) Br will not react with either compound (both require energy or catalyst)

D) NaHCO3 is a neutral buffer and would dissolve PMP, not BA.

So answer is B

 

[Simran1031]

so basically its because benzyl alcohol is more polar and would more likey dissolved in NAOH( a polar substance) more than para methyl phenol. and is this because the methyl group reduces the acidity and the polarity of the structure?

so acidity and polarity go hand and hand correct? sorry if i am starting to sound silly..havent done orgo since 3 years ago..officially starting my 3 month review next week but tackling a few questions here and there.

 

[Phlame217]

Dont get acidity and polarity confused.

Neither are acidic or basic, you should be examing the concentration of elections.

 

[Simran1031]

so basically concerntration of electrons..whether it is electron donating or withdrawing is this what you mean?

 

[Phlame217]

Pretty much, look up the definition of OP (ortho para) and Meta directors

 

[isaacmn]

[Actually, it has nothing to do with polarity, since the two structures have OH bonding. What makes the para methyl phenol and phenol in general distinct is their acidic properties. Their OH can easily give up its proton than any other benzyl alcohol subsitutents. So being that it has acidic properties, it can react with NaOH, more like an acid and base reaction. Where as the benzyl alcohol cant because they do not share the same distinct properties like phenol does.