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Which stereoisomer of 3-hexene forms a meso compound when it reacts with #Br_2# ?

Answer 1

trans-Hex-3-ene forms a meso compound when it reacts with bromine.

The bromination of an alkene involves the formation of an intermediate cyclic bromonium ion, followed by the anti-addition of a bromide ion to form the product.

The rigidity of the ring controls the stereochemistry of the reaction.

This means that the bromination of a trans alkene gives a meso dibromide.

For example, the bromination of trans-but-2-ene yields a meso compound.

Similarly, the bromination of hex-3-ene gives meso-2,3-dibromohexane as the product.

Attack of #"Br"^-# at C-3 gives (#3S,4R#)-3,4-dibromohexane.

Attack of #"Br"^-# at C-4 gives (#3R,4S#)-3,4-dibromohexane.

These two structures are superimposable on each other, so the product is a meso compound.

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Answer 2

Nicholas Antonuccio

The cis stereoisomer of 3-hexene forms a meso compound when it reacts with Br2.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.