Orgo help!!!

[flin5845]

Ok I have attached a question that I am not sure I understand.

The answer was after the first step you would make propene. Then with the bromination you would add bromine in an anti fashion to yield 1,2-dibromopropane.

Here is my question. I am not sure how in the world this thing would do an elimination. There is no way a primary alcohol is going to go E1 which leaves E2. I do not see a base either. Unless there is another reaction that yields alkenes that I am forgetting about.

I thought that the alcohol would be protanated making water a good leaving group. So I thought the bromine would just add to the primary carbon yielding 1-bromopropane in an SN2 fashion.

am I missing something?!!?

This question came from an Achievers exam.

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[Tyrangiel]

The H+, Heat step will add a proton to the alcohol group and then it will leave on its own, resulting in a carbocation intermediate. Because propane isn't very large the carbocation won't rearrange and bromine will attack leaving you with the product.

 

[Tyrangiel]

Well i guess that doesn't work with what they say will happen...

 

[AllahIsGreater]

i would say elimination, and then addition of two Br's anti.

 

[flin5845]

how will you do elimination with out a base. It wont go E1 a primary carbocation will not form

 

[bharat008]

Once OH is protonated it leaves as H20 leaving you a carbocation. So, now the carbocation can act as a ACID since its positively charged and H2O can act as a base; therefore H2O will remove the H giving you an alkene..

 

[UBCStudent128]

H+, heat can be just thought as dehydration.

Remember whenever a reagent says heat think elimination.
-H2O !

So OH from one side of the Carbon-Carbon bond and a hydrogen atom from the other side will be dehydrated, forming a double bond.


How would you hydrate an alkene? You would add H+ and H2O. This is the reverse reaction of that.