A. Explain why a single pure product is obtained from...

a. Explain why a single pure product is obtained from hydroboration-oxidation of 2 -butyne, whereas two products are obtained from hydroboration-oxidation of 2 -pentyne.
b. Name two other internal alkynes that will yield only one product on hydroboration-oxidation.

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Key Concepts

Hydroboration-Oxidation Reaction Mechanism

This reaction involves the addition of boron and hydrogen across a multiple bond followed by oxidation to yield an alcohol. The initial addition is syn, meaning both the hydrogen and boron add to the same face of the alkyne or alkene, and the process typically proceeds under mild conditions with high stereoselectivity.

Molecular Symmetry in Internal Alkynes

Internal alkynes that are symmetric have identical substituents on either end of the triple bond, which leads to a single reactive concentration and, subsequently, only one product upon addition. In contrast, unsymmetric internal alkynes have different groups on each side of the triple bond, leading to the possibility of regioisomer formation during the addition step.

Regioselectivity in Addition Reactions

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over possible others. In hydroboration-oxidation, the orientation of the addition to unsymmetric alkynes is influenced by factors like electronic and steric effects, resulting in multiple products for unsymmetrical substrates and a single product for symmetrical ones.

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