[masdfgh]

Hi, I'm not really gonna ask you to answer any questions, I just want to know if the following summary of reactions for alkenes are correct (the arrows and products). I don't want to review this summary of mine if any of them is incorrect.

These reactions are:
I. Electrophilic Addition
1. Addition of HX
2. Addition of X2
3. Halohydrin Formation
4. Addition of H2) (ROH)
5.Oxymercuration-Demercuration
6. Hydroboration Oxidation

II. Reduction reaction
III. Oxidation Reaction

I hope this isn't too much.
Anyway, if you find my draft messy and hard to understand , I'm fine with rewriting it.
Oh, I don't really have any problems with II and III so you can leave that out if you want to.




Thanks! 

[discodermolide]

Sorry but I find the draft messy and hard to understand, it is out of focus on my screen and I can just about make it out, but not with certainty.

[masdfgh]

Sorry but I find the draft messy and hard to understand, it is out of focus on my screen and I can just about make it out, but not with certainty.

Okay no problem. I'll rewrite it.

[Schrödinger]

I'm kind of in a hurry here, so I'll tell you what's wrong with I 1. Addition of HX. The exception is not HBr. It's HBr in the presence of a peroxide. Normal HBr reacts pretty much in the same manner as the other haloacids.

[masdfgh]

Oh, yeah, peroxide. I forgot.

I hope this is better now.

[discodermolide]

In 6) the hydroboration. The peroxide attacks the boron, this then rearranges to place the oxygen between the carbon and the boron, C-O-BR2,
OH then hydrolyses the O-B bond to give the alcohol and the boronic acid.

[AWK]

In 6) the hydroboration. The peroxide attacks the boron, this then rearranges to place the oxygen between the carbon and the boron, C-O-BR2,
OH then hydrolyses the O-B bond to give the alcohol and the boronic acid.

Hydroboration means - reaction with BH₃
Do you mean - radical hydrobromination?

[discodermolide]

In 6) the hydroboration. The peroxide attacks the boron, this then rearranges to place the oxygen between the carbon and the boron, C-O-BR2,
OH then hydrolyses the O-B bond to give the alcohol and the boronic acid.

Hydroboration means - reaction with BH₃
Do you mean - radical hydrobromination?

I am referring to the second picture answer F, looks like BH3 to me.

[AWK]

ie  C-O-BR2 means COBH₂?

[discodermolide]

ie  C-O-BR2 means COBH₂?

Yes

[orgopete]

I like that the bromination was written stepwise. I prefer it written like that. Then the other reactions can all have an analogous mechanism. The alkene electrons do not have to behave differently with different reagent. I am not troubled that an intramolecular addition of a pair of electrons on a neighboring atom can be very fast.

I would caution the use of the curved arrows. In the first example F, the curved arrows must start with the electrons of the B-H bond. It is the same as the bromination, but with a proton attached.

A was shown without the rearrangement, D is often used as an example that does rearrange, E can give the unrearranged product because the electrons on mercury intercept the carbocation intermediate. If you write out the oxidation mechanism of the hydroboration, it will be helpful for other reactions.

[masdfgh]

Thanks everyone!

[masdfgh]

follow-up question:

Addition of H2 and Oxy/Demercuration to an alkene both give an OH. How do I know which to use?

For example if I am given a question like:

1-methylcyclopentene ---?---> 2-methylcyclopentanol

Do I answer 1.(HgOAc)2/H2O/2.NaBH/OH or H2O/H+?

Alternatively, 1.BH3/THF/2.H2O/OH is also possible for me (though I may be wrong) since hydroboration-oxidation is anti-markovnikov, and OH is attached to the secondary carbon (less substituted) and not to the tertiary carbon where methyl is attached.

A better example would be:

Propene ---?---> 2-propanol

1.(HgOAc)2/H2O/2.NaBH/OH or H2O/H+?

[discodermolide]

follow-up question:

Addition of H2 and Oxy/Demercuration to an alkene both give an OH. How do I know which to use?

For example if I am given a question like:

1-methylcyclopentene ---?---> 2-methylcyclopentanol

Do I answer 1.(HgOAc)2/H2O/2.NaBH/OH or H2O/H+?

Alternatively, 1.BH3/THF/2.H2O/OH is also possible for me (though I may be wrong) since hydroboration-oxidation is anti-markovnikov, and OH is attached to the secondary carbon (less substituted) and not to the tertiary carbon where methyl is attached.

A better example would be:

Propene ---?---> 2-propanol

1.(HgOAc)2/H2O/2.NaBH/OH or H2O/H+?

Choose the one you like best from the examples you gave

[orgopete]

follow-up question:

Do I answer 1.(HgOAc)2/H2O/2.NaBH/OH or H2O/H+?

Propene ---?---> 2-propanol

1.(HgOAc)2/H2O/2.NaBH/OH or H2O/H+?

In that example, it wouldn't matter greatly (on paper). In the lab, propene would be reluctant and the mercury would be better. The more electron rich the alkene, the easier would an acid catalyzed addition be. I believe McMurry writes the addition of water to ethylene and propylene to proceed by a bisulfate ester intermediate which must be hydrolyzed to complete the conversion to the alcohol.

I think you will find many books will give the acid catalyzed addition of water to 3-methylbut-1-ene will give 2-methylbutan-2-ol. I would expect a level of rearrangement would accompany this reaction though I think a mixture will result. If mercury were used, non-bonded electrons of mercury can capture the neighboring carbocation more efficiently than the tertiary C-H electrons (the rearranging hydride to tertiary carbocation). (If anyone can quote a literature result of this reaction, please report actual yields.)