How can I explain the mechanism for hydrohalogenation with a hydride-shift (carbocation rearrangement)?

Answer 1

A carbocation intermediate that can become more stable by a hydride shift will do so.

We must always consider the possibility of rearrangements when a mechanism involves a carbocation intermediate.

Consider the addition of hydrogen chloride to 3-methylbut-1-ene.

#"CH"_2"=CH-CH(CH"_3)_2 + "HCl" → "?"#

In Step 1, the #"H"^+# adds to the alkene according to the Markovnikov Rule.

#"H-Cl " + "CH"_2"=CHCH(CH"_3")"_2 → "CH"_3"-"stackrel(+)("C")"H-CH(CH"_3")"_2 + "Cl"^-#

This is a 2° carbocation.

If the #"H"# migrates in Step 2 from C-3 to C-2, we will get a 3° carbocation.

#"CH"_3"-"stackrel(+)("C")"H-CH(CH"_3")"_2 → "CH"_3"-CH"_2"-"stackrel(+)("C")"(CH"_3")"_2#

Since the new carbocation is more stable, the rearrangement will occur.

Then in Step 3 the #"Cl"^-# adds to the carbocation to form the rearranged product.

#"CH"_3"-CH"_2"-"stackrel(+)("C")"(CH"_3")"_2 → "CH"_3"-CH"_2"-C(CH"_3")"_2"Cl"#

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Answer 2

Hydrohalogenation with a hydride-shift involves the migration of a hydride ion to stabilize a carbocation intermediate, leading to the formation of a more stable alkyl halide. This process occurs when a secondary carbocation can rearrange to a more stable tertiary carbocation through the migration of a neighboring hydride ion. The nucleophile, a halide ion, then attacks the carbocation to yield the final product.

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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.

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.

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.

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.

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