21

1H-borepine is isoelectronic to the cycloheptatrienyl cation. In both cases, you have a planar ring of seven atoms, whose hybridisation is close enough to $\mathrm{sp^2}$ to allow for a third p-orbital to be perpendicular to the ring plane. And in both, you are then filling these seven π orbitals with 6 π electrons, resulting in a Hückel-aromatic ...


15

Acetic acid effects protonolysis of the borane: If AcOD is used then RD (instead of RH) is formed.


14

For the hydroboration of isobutene there is a steric aspect: And though sterics may play some part, it doesn't explain near 100% regioselectivity. More important in determining regiochemistry, I would say, are the electronics of the transition state: Boron is electrophilic, and as such will draw the electron density of the alkene π-bond towards itself. ...


10

Organoboranes react with chloramine to give the corresponding amine as reported by Brown et al. [1], so P is n-propylamine (propan‐1‐amine). The mechanism is similar to the oxidation of boranes using $\ce{H2O2}/\ce{NaOH}$, but instead of migration to an oxygen atom, the alkyl chain migrates to a nitrogen atom. The $\ce{N-B}$ bond is cleaved in the same way. ...


8

I like Waylander's answer, which is 100% correct. However, I have a little concern about the question itself. The conditions given in OP's question are not exactly correct. It may mislead the viewers and people seeking answers for similar type of questions. H. C. Brown had specifically noted (Ref.1) the following condition for his groundbreaking discovery (I ...


7

The second step is a syn addition of the boron hydride. As depicted below, it will result in an anti-Markovnikov product with the boron on the less-substituted carbon. Both hydrogen and boron are on the same side of the former double bond and these two are the ones we refer to when we say syn addition. The final step, the oxidation by hydrogen peroxide, is ...


3

This figure from this reference (p. 170). might help you visualize things. As you can see, the stereochemistry is given by electronic repulsion between the carbonyl group and the incoming aldehyde.


2

Both hydroxide and alcoholate can be displaced from the tetracoordinated intermediate. The difference is that displacing the hydroxide is just the back reaction of the inital attack while displacing the alcoholate will move the reaction forward. You cannot argue that $\ce{X}$ is a stronger base than $\ce{Y}$ and therefore $\ce{X}$ will always get displaced. ...


1

Hydroboration With the simplest hydroborating agent $\ce{BH3.THF}$, the hydroboration/oxidation of 1-phenylpropene proceeds to give 1-phenylpropan-1-ol as the major product.[1] The isomer of the substrate used was not reported. There is some ambiguity in the above source, as the labels 8 and 8′ (which the paper uses to refer to the two regioisomers) are ...


Only top voted, non community-wiki answers of a minimum length are eligible