2ne1

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Which of the following compound is least likely to be protonated by H2SO4?

a. 2,2 dimethyl propane
b. CH3CH=CH2
c.CH3CH2CH2OH
d. CH3OCH3
e. CH3COOH

Thanks!!:)
 
Dec 14, 2009
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question is same as which compound is the least acidic?

Alkane> alkene > alkyne > ether > alcohol > carboxylic acid (the most acidic)

so answer is a) someone correct me if I am wrong
 

AmpedUp

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question is same as which compound is the least acidic?

Alkane> alkene > alkyne > ether > alcohol > carboxylic acid (the most acidic)

so answer is a) someone correct me if I am wrong
not exactly

the question just asks if a molecule can be protonated or not. all of them can except choice A. Only thing that reacts with alkanes are halogens e.g. Br2 and Cl2 (as far as I know - and NBS?).
 
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AmpedUp I advise you to learn the principle instead of memorizing reactions.
 
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2ne1

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It is A. alkane.

kpark, acids get deprotonated..if the question asks which is least likely to be protonated, wouldn't it mean to find the most acidic compound?
 
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2ne1

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Sorry, it feels like I am posting questions in every 5 seconds, but I have DAT coming up real soon and got stuck doing practice probs!
Now the question...

benzyl alcohol reacting with HCl and heat will produce what?

I thought it would go through elimination, but since it's a benzene, it cannot.
I checked with Kaplan BB and it said alchols get dehydrated in a strongly acidic solution(like H2SO4) with heat.
The answer says that the -OH group becomes -Cl.....
I thought displacement of hydroxyl groups in substiution rxn is rare since OH- is poor leaving group so if you want to convert the alchol into alkyl halides, you need to use things like SOCl2.
Can anybody clarify this? Thanks!
 
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The right answer is A, the saturated hydrocarbon is very stable and will be extremely destabilized by an H+

B) The pi electrons from the double bond can accommodate protons

C-E) The lone pairs on the Oxygens can handle the protonation in acidic conditions.
 

AmpedUp

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AmpedUp I advise you to learn the principle instead of memorizing reactions.
what do you mean?

you'd know it by now after a million synthesis problems in OChem...

draw all of these molecules out...Does it make sense that the alkane can be PROTONATED by an acid? No. An alkane has no room for another hydrogen (because carbon can't bond to more than 4 "things").

Just saying...I hate memorizing as much as the next person, but when you do so many problems, you kinda know it off the back of your hand...know what i mean by that?
 
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Dec 14, 2009
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least protonated by H2SO4 = least deprotonated = least acidic
remember ! acid is the proton donor. Also you need to know (somewhat general chemistry)
The best conductor of electricity (strong electrolyte = strong acid) will be the solution that contains the most charged particles. HNO3 is the strong acid, so the acid has dissociated completely in the solution into H+ and No3-.

Second question is pretty simple, alcohol is very volatile substances but like you said, OH group is terrible leaving group. That's why you need a heat to make it better leaving group, so alcohol get even more volatile with heat (boil water with heat, so vapor pressure increase with temperature increase)
 
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Hey AmpedUp, I think that the question asked about protonation, not deprotonation (which is what you wrote in your first reply).

Your reasoning is right, just applied in the opposite direction.
 

AmpedUp

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oops. sorry for that. i caught that first time around when i answered "A", but i had it in reverse in my last post.

aaagghhh so much studying this week...fail.
 
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Mar 15, 2010
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Hi Kpark102,

Increased temperature doesn't make OH a better leaving group, though it does increase the average kinetic energy which means that reactions are more likely to take place by overcoming the activation energy barrier. It is the protonating of the -OH group, making water, which is a good leaving group, that lets this reaction proceed in (reasonably) good yield.

I still say the best way to swap an OH for a Cl on a benzene ring is with thionyl chloride (SOCl2), but I guess you gotta make due with the chemicals you got!
 
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2ne1

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Thanks for your effort to explain your answer, but I think the reason why the answer was A was better explained by other repliers.
Acids are proton donors(according to bronsted lawry acid base theory). They get deprotonated by donating protons and bases get protonated by accepting protons. Right?
So if something is least likely to be protonated by acid means that it is NOT a good base since bases get protonated by acid. Therefore, something that is least likely to be deportonated is something that is most acidic.
 
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