Chapter 9.SE, Problem 32AP

Interpretation Introduction

a)

Interpretation:

The product formed when 5-decyne reacts with H2 in the presence of Lindlar catalyst.

Concept introduction:

Alkynes can be reduced by treatment with hydrogen in the presence of a catalyst. The hydrogenation occurs with syn stereochemistry to give a cis alkene as product if Lindler catalyst is used.

To predict:

The product formed when 5-decyne reacts with H₂ in the presence of Lindlar catalyst.

Answer to Problem 32AP

The product formed when 5-decyne reacts with H₂ in the presence of Lindlar catalyst is cis-5-decene

Explanation of Solution

When 5-decyne reacts with hydrogen in the presence of Lindlar catalyst, the addition of hydrogens to both carbons in triple bond takes place resulting in the formation of cis-5-decene.

Conclusion

The product expected when 5-decyne reacts with H₂ in the presence of Lindlar catalyst is cis-5-decene.

Interpretation Introduction

b)

Interpretation:

The product formed when 5-decyne reacts with Li in ammonia.

Concept introduction:

Alkynes can be reduced by treatment with hydrogen in the presence of a catalyst. The hydrogenation occurs with anti stereochemistry to give a trans-alkene as product if Li in ammonia is used.

To predict:

The product formed when 5-decyne reacts with Li in ammonia.

Answer to Problem 32AP

The product formed when 5-decyne reacts with Li in ammonia is trans-5-decene.

Explanation of Solution

When 5-decyne reacts with hydrogen in the presence of Li in ammonia, the addition of hydrogens to both carbons in triple bond takes place following antistereochemistry resulting in the formation of trans-5-decene.

Conclusion

The product expected when 5-decyne reacts with Li in ammonia is trans-5-decene.

Interpretation Introduction

c)

Interpretation:

The product formed when 5-decyne reacts with one equivalent of bromine.

Concept introduction:

Alkynes undergo addition reactions with anti stereochemistry when treated with bromine. When treated with one equivalent of bromine a trans-dibromoalkene results as product by the addition of bromine atoms to the carbons in triple bond from opposite faces.

To predict:

The product formed when 5-decyne reacts with one equivalent of bromine.

Answer to Problem 32AP

The product formed when 5-decyne reacts with one equivalent of bromine is trans-5,6-dibromo-5-hexene.

Explanation of Solution

When 5-decyne reacts with bromine, the addition of bromine to both carbons in triple bond takes place following anti stereochemistry, resulting in the formation of trans-5,6-dibromo-5-decene as the product.

Conclusion

The product formed when 5-decyne reacts with one equivalent of bromine is trans-5,6-dibromo-5-decene.

Interpretation Introduction

d)

Interpretation:

The product formed when 5-decyne reacts with BH₃ in THF followed by with H₂O₂, OH-.

Concept introduction:

Alkynes get hydrated in the hydroboration oxidation reaction. The reaction occurs with syn stereochemistry following anti Markovnikov regiochemistry to produce an enol. The enol then tautomerizes to yield a ketone as the product.

To predict:

The product formed when 5-decyne reacts with BH₃ in THF followed by with H₂O₂, OH-.

Answer to Problem 32AP

The product formed when 5-decyne reacts with BH₃ in THF followed by with H₂O₂, OH- is 6-decanone.

Explanation of Solution

When 5-decyne is treated with BH₃ in THF followed by with H₂O₂, OH-, the reaction occurs with syn stereochemistry following anti Markovnikov regiochemistry to produce an enol. The enol then tautomerizes to yield a ketone as the product. The Boron and hence the OH group adds to the less highly substituted carbon in triple bond and H adds to the more highly substituted carbon atom in the triple bond to produce an enol. The enol then tautomerizes to yield the ketone as the product.

Conclusion

The product formed when 5-decyne reacts with BH₃ in THF followed by with H₂O₂, OH-is 6-decanone.

Interpretation Introduction

e)

Interpretation:

The product formed when 5-decyne reacts with H₂O, H₂SO₄ in the presence of HgSO₄ is to be given.

Concept introduction:

When treated with H₂O, H₂SO₄ in the presence of HgSO₄ alkynes get hydrated to produce enols. The addition of water to unsymmetrical alkynes follows Markonikov regiochemistry while it cannot be applied in the case of symmetrical alkynes. The enols produced then undergo tautomerization to give a ketone as the product.

To predict:

The product formed when 5-decyne reacts with H₂O, H₂SO₄ in the presence of HgSO₄.

Answer to Problem 32AP

The product formed when 5-decyne reacts with H₂O, H₂SO₄ in the presence of HgSO₄ is 5-decanone.

Explanation of Solution

5-Decyne is a symmetrical alkyne. Hence Markonikov regiochemistry is not applicable. When treated with dilute H₂SO₄ in the presence of HgSO₄, the OH group adds to a carbon in triple bond and H adds to the other carbon in triple bond to yield an enol. The enol then tautomerizes to yield the ketone, 5-decanone.

Conclusion

The product formed when 5-decyne reacts with H₂O, H₂SO₄ in the presence of HgSO₄ is 5-decanone.

Interpretation Introduction

f)

Interpretation:

The product formed when 5-decyne reacts with excess H₂ in the presence of Pd/C is to be given.

Concept introduction:

When treated with excess H₂, Pd/C catalyst the alkynes react with two molar equivalents of hydrogen to give the parent alkane as the product.

To predict:

The product formed when 5-decyne reacts with excess H₂ in the presence of Pd/C.

Answer to Problem 32AP

The product formed when 5-decyne reacts with excess H₂ in the presence of Pd/C is n-decane.

Explanation of Solution

When 5-Decyne is treated with excess H₂ in the presence of Pd/C, two molar equivalents of hydrogens add to the triple bond. The corresponding alkane, n-decane is the product.

Conclusion

The product formed when 5-decyne reacts with excess H₂ in the presence of Pd/C is n-decane.