[evan043]

Alright so these questions are a cumulation of more difficult exam questions that I missed (and our professor gives us the exams back to keep, so it is ok that you are helping me).
   
 - I will list where I went wrong, from top to bottum, and explain what I am confused about.

***The numbers aren't in order because they are from different exams.

5. Omit

9. b) I understand the coupling reaction of 1. Li, Hexane 2. 1 CuI, Ether to an alkyl halide forms a Gilman Reagent, but I don't understand what the intermediate would be if I only used 1/2 CuI.

2. Alkyl Shift- I've put a decent amount of thought into this one, lets see if I am on the right track now....
    -Should have pulled the C-C double bond apart using both electrons to form a covalent bond with the protonated H^t
    -At that point I would have a carbocation on the dimethyl pentane structure, and a Bromide nucleophile.
    -Before the Bromide nucleophile comes in (I suppose in an S_N2 Reaction), a more stable carbocation could come in via rearrangement from a secondary carbon to the tertiary carbon.
    -Bromide Ion attaches to the tertiary carbon.

Sound about right?

13. In this question my prof. wants the mechanism to both products explained, #1 which I attempted and #2 I am still clue less about.

  #1, Most of what I did was retarded.
  -Forgot to the second step where water leaves the hexane forming the carbocation.
  -I would understand a simple rearrangement of methyl groups to form the proposed structure, but then again there would be no reason to.... and even if I did that where would the double bond come from?
          ^----That is my main question.

   #2... I am at a lose for words, and so is probably about 50% of my honors class.

2. a) Omit.
     

[qw098]

Any reason you can't ask your professor?

I'm not trying to be a dink or anything

[evan043]

Thats a good question. I will give my professor the fact the he is brilliant, but he doesnt communicate very well, and often times he is in a hurry making it hard to get a detailed response because he is the head of the organic chemistry lab department. He actually only teaches one class every semester, and only one section, so most of his time is invested elsewhere...

[Dan]

9. b) I understand the coupling reaction of 1. Li, Hexane 2. 1 CuI, Ether to an alkyl halide forms a Gilman Reagent, but I don't understand what the intermediate would be if I only used 1/2 CuI.

What is the oxidation state of Cu in CuI?

You have proposed:

RLi + CuI RCuLi

Can you see the problem? What is the oxidation state of Cu in RCuLi? Is the equation balanced?

For Q2, what you describe sounds fine, but without a drawing I can't really say.

13. In this question my prof. wants the mechanism to both products explained, #1 which I attempted and #2 I am still clue less about.

  #1, Most of what I did was retarded.
  -Forgot to the second step where water leaves the hexane forming the carbocation.
  -I would understand a simple rearrangement of methyl groups to form the proposed structure, but then again there would be no reason to.... and even if I did that where would the double bond come from?
          ^----That is my main question.

Ok, so you have identified: 1. Loss of water to form a carbocation; 2. A 1,2 methyl shift. What you are left with is still a carbocation. In order to become neutral, it will lose something else... (hint: E1 elimination).

   #2... I am at a lose for words, and so is probably about 50% of my honors class.

Look at the 1,2 methyl shift step in the previous mechanism. Are there any other groups that could migrate other than a methyl?

[evan043]

Dan, thank you for your thoughtful response. I will rework, and repost my solutions in a couple hours. I really appreciate this. -Evan