When 2,2-dibromo-1-phenylpropane is heated overnight with sodium amide at 150 °C, the major product (after addition of water) is a different foul-smelling compound of formula C9H8. Propose a structure for this product, and give a mechanism to account for its formation.

Verified step by step guidance

1. Identify the starting material: 2,2-dibromo-1-phenylpropane. This compound has a phenyl group (C6H5) attached to a propane chain with two bromine atoms on the second carbon.
2. Recognize the reagent and conditions: Sodium amide (NaNH2) is a strong base, and heating at 150 °C suggests an elimination reaction is likely to occur.
3. Consider the elimination mechanism: Sodium amide can deprotonate the hydrogen atoms adjacent to the bromine atoms, leading to the formation of a carbanion. This can result in the elimination of bromine atoms, forming a triple bond (alkyne).
4. Determine the structure of the product: The molecular formula C9H8 suggests a degree of unsaturation consistent with an alkyne. The elimination of two bromine atoms from 2,2-dibromo-1-phenylpropane can lead to the formation of phenylacetylene (C6H5C≡CH).
5. Propose the mechanism: The reaction likely proceeds through a double elimination (E2 mechanism) where sodium amide deprotonates the carbon adjacent to the bromine, forming a carbanion, which then expels the bromide ion to form a double bond. A second deprotonation and elimination step forms the triple bond, resulting in phenylacetylene.

Key Concepts

Elimination Reactions

Elimination reactions involve the removal of atoms or groups from a molecule, resulting in the formation of a double bond. In the context of 2,2-dibromo-1-phenylpropane, heating with sodium amide promotes the elimination of bromine atoms, leading to the formation of an alkene. Understanding this process is crucial for predicting the structure of the major product formed after the reaction.

Nucleophilic Substitution

Nucleophilic substitution is a fundamental reaction in organic chemistry where a nucleophile replaces a leaving group in a molecule. In this case, sodium amide acts as a strong nucleophile, facilitating the substitution of bromine atoms in 2,2-dibromo-1-phenylpropane. Recognizing how nucleophiles interact with electrophiles helps in understanding the mechanism leading to the final product.

Rearrangement Reactions

Rearrangement reactions involve the structural reorganization of a molecule, often leading to more stable or reactive forms. After the elimination and substitution processes, the resulting compound may undergo rearrangement to form a more stable structure, which is essential for predicting the foul-smelling product with the formula C9H8. This concept is key to understanding how the final product differs from the starting material.