Why is it E2?

[Isradoc1983]

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ok just some question from a kaplan orgo subject test that really confused me
CH3 KOH
H3C-CH-CH2-CH-CH3-------->
Cl Alcohol

why is it a E2? OH- isn't a bulky base and alcohol is protic polar, so why E2?
its an easy question but I am just confused
Also, E2 works best with Strong Bulky bases and polar aprotic solvents right?
I thought I am good with E1/E2 until I saw this simple question

 

[doc3232]

ok just some question from a kaplan orgo subject test that really confused me
CH3 KOH
H3C-CH-CH2-CH-CH3-------->
Cl Alcohol

why is it a E2? OH- isn't a bulky base and alcohol is protic polar, so why E2?
its an easy question but I am just confused
Also, E2 works best with Strong Bulky bases and polar aprotic solvents right?
I thought I am good with E1/E2 until I saw this simple question

I am lost...can you rewrite that?

 

[glk2101]

cant really tell what the substrate is from what you wrote, but it looks like a secondary carbon with Cl bonded..
anyways, whenever you see a strong base such as KOH, most of the time its E2 regardless of whether its a primary, secondary, or tertiary carbon, and polar aprotic limits SN2 not E2 if I remember correctly.
E1 would be very slow with a secondary carbon, and also a strong base disfavors E1
hope this helps

 

[glk2101]

also, the effect of a strong bulky base is to favor the hoffman product

 

[Isradoc1983]

ahhh sorry my post got messed up when i submitted it

its 2-chloro isopentane or 2 chloro 5 methyl pentane

the reaction uses KOH and alcohol. Kaplan says its E2, but I'd think its E1 cause its polar protic solvent.

 

[doc3232]

cant really tell what the substrate is from what you wrote, but it looks like a secondary carbon with Cl bonded..
anyways, whenever you see a strong base such as KOH, most of the time its E2 regardless of whether its a primary, secondary, or tertiary carbon, and polar aprotic limits SN2 not E2 if I remember correctly.
E1 would be very slow with a secondary carbon, and also a strong base disfavors E2
hope this helps

Hmmmm...you contradicted yourself, which is it?
I am a little weak when it comes to O-chem basics.

 

[doc3232]

...................CH3
...................|
H3C-CH-CH2-CH-CH3-------->
.......|
.......Cl

it goes with KOH and alcohol.

I think this is what the OP means

Now I see what is happening.

 

[glk2101]

sorry strong base disfavors E1

 

[doc3232]

ahhh sorry my post got messed up when i submitted it

its 2-chloro isopentane or 2 chloro 5 methyl pentane

the reaction uses KOH and alcohol. Kaplan says its E2, but I'd think its E1 cause its polar protic solvent.

How can a solution be protic when there is KOH as a reagent? Even though there is alcohol, there is a strong base to not let it be protic.

 

[Isradoc1983]

ok i might have missed it in my studying what is the hoffman product ?
are you talking about rearrangement for the most stable carbocation?

 

[glk2101]

an alcohol would be polar because of unequal sharing of electrons and protic because of the presence of the proton on the oxygen

 

[glk2101]

the hoffman product is the less stable product, so if you have a bulky base then it might be hard to form a tetrasubstituted alkene. instead you might be able to only form a disubstituted alkene, which overides zaitsev's rule..
in destroyer road maps they show this btw

 

[doc3232]

ok i might have missed it in my studying what is the hoffman product ?
are you talking about rearrangement for the most stable carbocation?

Hofman product is the product with the least substituted double bond. Bulky bases can't get too close so they take the first proton they can get their hands on so they don't target tertiary, but rather primary (or secondary if primary is not available).

KOH or an alcohol would be polar because of unequal sharing of electrons and protic because of the presence of the proton on the oxygen

A protic solvent is a solvent with protons floating around. The H on OH is not going anywhere. For example: CH4 has protons on it, is it a protic solvent?

 

[glk2101]

from one of my books:
"a protic solvent is a solvent that has a proton connected to an electronegative atom(for example, H2O or EtOH). It is called protic because the solvent can serve as a source of protons. In other words, the solvent can give a proton because the solvent can stabilize a negative charge."

 

[doc3232]

from one of my books:
"a protic solvent is a solvent that has a proton connected to an electronegative atom(for example, H2O or EtOH). It is called protic because the solvent can serve as a source of protons. In other words, the solvent can give a proton because the solvent can stabilize a negative charge."

So you are saying that OH- is going to give a proton and become O--(as in 2 minus charge)?

The examples they gave are not bases.
Your book is wrong, not any Hydrogen connected to an electroneg atom is a protic solvent.

 

[glk2101]

no KOH is not going to give an H , but water is a polar protic solvent

 

[Isradoc1983]

ok guys maybe i didn't emphasized when i ment that the solvent is polar protic i meant its an alcohol not KOH
the Nuc is OH- and the solvent is alcohol.So can anyone explain to me why this is a E2 and not E1 ? or is kaplan just wrong
thanks for the hoffman. I remember I saw it in destroyer need to go over it again.

 

[glk2101]

ok, since KOH is a strong base, it favors the E2 and disfavors the E1, thats about all you need to know for the reason

however if it was tertiary and the base was weak, then E1 could work better than E2

 

[doc3232]

ok guys maybe i didn't emphasized when i ment that the solvent is polar protic i meant its an alcohol not KOH
the Nuc is OH- and the solvent is alcohol.So can anyone explain to me why this is a E2 and not E1 ? or is kaplan just wrong
thanks for the hoffman. I remember I saw it in destroyer need to go over it again.

The way I think about it is that a aprotic solvent favors E2.
But first you would have to accept that this is a aprotic solvent.
IMO, a base as a reagent makes the solution aprotic.

 

[Electrons]

KOH is a strong base, it will grab the proton H from the C3 and form alkene between C2 & C3. OH + H will form H2O, that will be the protic solvent

Is that the correct answer?

 

[Albuterol]

^ thats what i was thinking....

 

[Isradoc1983]

well the question just asked what would be the product which was easy, but the explanation said that its E2. This confused me cause they said the solvent is alcohol...
so i guess my question was what will determine the rxn OH- (strong base,E2) or polar protic (part of E1)