Chapter 9.SE, Problem 22MP

Interpretation Introduction

a)

Interpretation:

The product formed and the electron pushing mechanism for its formation, when 2-pentyne is reduced with Li in NH₃ is to be given.

Concept introduction:

Lithium metal donates an electron to the alkyne to give an anion radical which in the next step abstracts a proton from ammonia solvent to yield a vinylic radical. In the third step the vinylic radical accepts a second electron from another Li atom to produce a vinylic anion which in the fourth step abstracts another proton from ammonia solvent to yield the final trans product.

The addition takes place with trans stereochemistry. The stereochemistry is established in the third step when the less hindered vinylic anion is formed from vinylic radical.

To propose:

The product formed and the electron pushing mechanism for its formation, when 2-pentyne is reduced with Li in NH₃.

Interpretation Introduction

b)

Interpretation:

The product formed and the electron pushing mechanism for its formation, when 3-methyl-1-butyne is reduced with Li in ND₃ is to be given.

Concept introduction:

Lithium metal donates an electron to the alkyne to give an anion radical which in the next step abstracts a proton from deuteratedammonia solvent to yield a vinylic radical. In the third step the vinylic radical accepts a second electron from another Li atom to produce a vinylic anion which in the fourth step abstracts another proton from the solvent to yield the final trans product.

The addition takes place with trans stereochemistry. The stereochemistry is established in the third step when the less hindered vinylic anion is formed from vinylic radical.

To propose:

The product formed and the electron pushing mechanism for its formation, when 3-methyl-1-butyne is reduced with Li in ND₃.

Interpretation Introduction

c)

Interpretation:

The product formed and the electron pushing mechanism for its formation, when propynylbenzene is reduced with Li in NH₃ is to be given.

Concept introduction:

Lithium metal donates an electron to the alkyne to give an anion radical which in the next step abstracts a proton from ammonia solvent to yield a vinylic radical. In the third step the vinylic radical accepts a second electron from another Li atom to produce a vinylic anion which in the fourth step abstracts another proton from ammonia solvent to yield the final trans product.

The addition takes place with trans stereochemistry. The stereochemistry is established in the third step when the less hindered vinylic anion is formed from vinylic radical.

To propose:

The product formed and the electron pushing mechanism for its formation, when propynylbenzene is reduced with Li in NH₃.