1- bromo-4-methylhexane

Methylhexane undergoes radical bromination to yield optically inactive 3-bromo-3-methylhexane as the major product. Is the product chiral What conclusions can you draw about the radical intermediate ... 

Heating optically active (5)-3-bromo-3-methylhexane with aqueous acetone results in the formation of racemic 3-methyl-3-hexanol. 

The chiral tertiary alcohol (/ )-3-methyl-3-hexanol reacts with HBr by an SnI pathway. HBr protonates the hydroxyl group, which dissociates to yield a planar, achiral carbocation. Reaction with the nucleophilic bromide anion can occur from either side of the carbocation to produce ( )3-bromo-3-methylhexane. 

The reactions considered in the previous two sections involve additions toa achiral alkenes, and optically inactive products are formed in all cases. Whatfl would happen, though, if we were to carry out a reaction on a single enaa tiomer of a chiral reactant For example, what stereochemical result would J be obtained from addition of HBr to a chiral alkene, such as (fl>4-methy - 1-hexene The product of the reaction, 2-bromo-4-methylhexane, has two chirality centers and four possible stereoisomers. 1 ... 

What about the configuration at C2, the newly formed chirality center As illustrated in Figure 9.19, the stereochemistry at C2 is established by attack of Br ion on a carbocation intermediate in the usual manner. But this carbocation does not have a plane of symmetry it is chiral because of the chirality center at C4. Since the carbocation has no plane of symmetry, it is not attacked equally well from top and bottom faces. One of the two faces is likely, for steric reasons, to be a bit more accessible than the other face, leading to a mixture of R and S products in some ratio other than 50 50, Thus, two diastereomeric products, (2/ ,4fi)-2-bromo-4-methylhexane and (2S,4/i)-2-bromo-4-methylhexane, are formed in unequal amounts, and the mixture is optically active. 

Reaction of HBr with (R)-3-methyl-3-hexanol leads to racemic 3-bromo-3-methylhexane. Explain. 

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