Chapter 12, Problem 12.27P

Interpretation Introduction

(a)

Interpretation:

The complete mechanism and the major organic product are to be drawn for the given reaction.

Concept introduction:

Haloforms (${\text{CHX}}_3$, X = halogen) can be deprotonated by strong bases like alkoxide ions. The resulting tri halo anion undergoes heterolysis to produce a dihalo-carbene. The dihalo-carbene can react with an alkene or alkyne to produce a dihalo-substituted cyclopropane (or cyclopropene) ring. The lone pair of the carbene forms a bond with one of the initially double-bonded carbons. Simultaneously, the $\text{π}$ bond pair from the alkene/alkyne forms a bond with the carbene carbon. The cis/trans stereochemistry of the starting alkene is preserved. If the alkene has a cis geometry, the two substituents are on the same side of the ring in the product. If it has a trans geometry, the two substituents are on the opposite sides of the ring in the product.

If the starting alkene is achiral and the product chiral, then a racemic mixture of two enantiomers is produced. If the starting alkene and the product are both chiral, an unequal mixture of enantiomers is produced.

Interpretation Introduction

(b)

Interpretation:

The complete mechanism and the major organic product are to be drawn for the given reaction.

Concept introduction:

Haloforms (${\text{CHX}}_3$, X = halogen) can be deprotonated by strong bases like alkoxide ions. The resulting tri halo anion undergoes heterolysis to produce a dihalo-carbene. The dihalo-carbene can react with an alkene or alkyne to produce a dihalo-substituted cyclopropane (or cyclopropene) ring. The lone pair of the carbene forms a bond with one of the initially double-bonded carbons. Simultaneously, the $\text{π}$ bond pair from the alkene/alkyne forms a bond with the carbene carbon. The cis/trans stereochemistry of the starting alkene is preserved. If the alkene has a cis geometry, the two substituents are on the same side of the ring in the product. If it has a trans geometry, the two substituents are on the opposite sides of the ring in the product.

If the starting alkene is achiral and the product chiral, then a racemic mixture of two enantiomers is produced. If the starting alkene and the product are both chiral, an unequal mixture of enantiomers is produced.

Interpretation Introduction

(c)

Interpretation:

The complete mechanism and the major organic product are to be drawn for the given reaction.

Concept introduction:

Haloforms (${\text{CHX}}_3$, X = halogen) can be deprotonated by strong bases like alkoxide ions. The resulting tri halo anion undergoes heterolysis to produce a dihalo-carbene. The dihalo-carbene can react with an alkene or alkyne to produce a dihalo-substituted cyclopropane (or cyclopropene) ring. The lone pair of the carbene forms a bond with one of the initially double-bonded carbons. Simultaneously, the $\text{π}$ bond pair from the alkene/alkyne forms a bond with the carbene carbon. The cis/trans stereochemistry of the starting alkene is preserved. If the alkene has a cis geometry, the two substituents are on the same side of the ring in the product. If it has a trans geometry, the two substituents are on the opposite sides of the ring in the product.

If the starting alkene is achiral and the product chiral, then a racemic mixture of two enantiomers is produced. If the starting alkene and the product are both chiral, an unequal mixture of enantiomers is produced.