Chapter 12, Problem 12.3P

Interpretation Introduction

Interpretation:

The complete, detailed mechanism for the given reaction is to be drawn. The products are to be predicted with the help of the mechanism, paying close attention to stereochemistry.

Concept introduction:

A carbene is a species containing a carbon atom that has a lone pair of electrons and two bonds. Carbenes are typically highly electrophilic due to the lack of an octet and are ${\text{sp}}^{\text{2}}$ hybridized. The lone pair of electrons occupies a hybrid orbital, leaving the p orbital empty. Thus, carbenes resemble a carbocation and are generally highly electron-deficient.

Chloroform is a precursor to generate a carbene. When an alkyl trihalide is treated with a strong base in the presence of cyclohexane, a dihalocarbene is generated in two steps via $\text{α}$- elimination. The base first deprotonates the alkyl trihalide, which is weakly acidic. In step two, the halogen atom departs to generate a carbene.

In an electrophilic addition reaction, alkenes react with carbenes, forming a three-membered ring. The reaction consists of addition of the alkene to an electrophilic carbene. The lone pair can donate back so that a carbocation does not actually form in same step. The stereochemistry of the substituents in the alkene is conserved in the product.