[boostar]

Hi fellow forumers,

I have a question in a revision test that I am studying for, and it is really confusing me. It is as follows:

What is the product int he following reaction?

C-C-C-C-C=C (1-hexene) ---------> 

It is first treated with BH₃, and then the product of this is treated with H₂O₂/^-OH

Is it:

A) C-C-C-C-C-C-OH  (A primary alcohol)

B) C-C-C-C-C-C    (A secondary Alcohol)
                  \
                   OH
         
C) C-C-C-C-C-C   (An alkane)

D) C-C-C-C-C-C  (:: represents a double bond - this is a ketone)
                 ::
                 O 

                O
                ::
E) C-C-C-C-C-CH (An aldehyde)

Out of the above - which would be the answer? From what I gather, the B would act as a electrophile, while the H would act as nucleophiles. This would mean the B attacks the double bond. Once this occurs, a hydrogen from BH₃ then goes to the other carbon. So after the first reaction, I think we have something like this:

                                 H
                                 [
                 C-C-C-C-C-C
                              [
                              BH₂

So then H₂O₂/^-OH somehow comes into the picture - and I'm not really sure what would happen. Could someone explain in terms of electrophiles and nucleophiles what would occur? Any help would be appreciated.

Thanks in advance.

[omegasynthesis999]

Boron is influence by steric factors (it can approach a less substituted carbon more easily) and electronic factors. In terms of the latter, the carbon to which the boron does not attach develops a partial positive charge in an intermediate so you need to look at which carbon is able to bear the partial positive charge better, one with more electron releasing groups or those with fewer. Overall the rxn is anti-markovnikov.

In terms of Nucleophiles/Electrophiles, the pi electrons of the double bond are the nucleophile and the Boron is electrophilic (part of the mechanism can be found on Wikipedia).

Based on this info, I think you should re-evaluate the answer you chose.

[boostar]

So the answer is A? I am still confused about the mechanism though:
                                 
                                 +
                 C-C-C-C-C-C
                              [
                              BH₃

So this is what you get after the first step? Then you treat it with:
H₂O₂/-OH

Would the -OH connect to the terminal C+ and then the BH₃ get replaced with a H from H₂O₂?

[macman104]

google Hydroboration Oxidation

[g-bones]

hydroboration oxidizes at the least hindered terminus of the alkene, so the correct placement of the alcohol would be at the primary position