Tetrahedral Intermediate

Definition

A tetrahedral intermediate is a key reaction step that occurs in many organic chemistry reactions, where a trigonal planar carbonyl carbon temporarily becomes a tetrahedral carbon with four bonded atoms. This transient intermediate is crucial for understanding the mechanisms of various nucleophilic addition and substitution reactions.

5 Must Know Facts For Your Next Test

1. The tetrahedral intermediate forms when a nucleophile attacks the carbonyl carbon, temporarily changing the carbonyl's planar geometry to a tetrahedral shape.
2. The tetrahedral intermediate is a key step in the mechanism of the Grignard reaction, where a Grignard reagent adds to a carbonyl compound.
3. In the hydration of aldehydes and ketones, a tetrahedral intermediate is formed when water adds to the carbonyl carbon.
4. Imine and enamine formation from the nucleophilic addition of amines to carbonyls also involves a tetrahedral intermediate.
5. The Wolff-Kishner reduction, which converts a carbonyl to an alkane, proceeds through a tetrahedral hydrazine intermediate.

Review Questions

• Explain the role of the tetrahedral intermediate in the Grignard reaction and how it leads to the formation of alcohols from carbonyl compounds.
  • In the Grignard reaction, a Grignard reagent (an organomagnesium compound) acts as a nucleophile and adds to the carbonyl carbon of an aldehyde or ketone. This forms a tetrahedral intermediate where the carbonyl carbon is temporarily bonded to four atoms. The magnesium-containing group then rearranges, displacing the original substituent and resulting in the formation of a new carbon-carbon bond. Finally, the addition of water hydrolyzes the magnesium-oxygen bond, yielding the corresponding alcohol product.
• Describe the role of the tetrahedral intermediate in the nucleophilic addition reactions of aldehydes and ketones, such as hydration, imine formation, and the Wolff-Kishner reduction.
  • In the nucleophilic addition reactions of aldehydes and ketones, a tetrahedral intermediate is a crucial step. For example, in the hydration of a carbonyl, water acts as the nucleophile and adds to the carbonyl carbon, forming a tetrahedral intermediate. This intermediate then rearranges to give the corresponding geminal diol. Similarly, in imine and enamine formation from the addition of amines, a tetrahedral intermediate is formed before the elimination of water. The Wolff-Kishner reduction also proceeds through a tetrahedral hydrazine intermediate before the final deoxygenation step. In each case, the transient tetrahedral intermediate is a key mechanistic step that enables the overall transformation.
• Analyze how the formation and rearrangement of the tetrahedral intermediate is involved in nucleophilic acyl substitution reactions, such as the conversion of carboxylic acids to esters, amides, and nitriles.
  • Nucleophilic acyl substitution reactions, which convert carboxylic acid derivatives into other functional groups, involve the formation and rearrangement of a tetrahedral intermediate. When a nucleophile attacks the carbonyl carbon of a carboxylic acid, ester, or amide, a tetrahedral intermediate is formed. This intermediate then collapses, expelling the original leaving group (e.g., an alkoxide, hydroxide, or amine) and forming the new acyl-nucleophile product. The ability of the tetrahedral intermediate to accommodate this rearrangement is crucial for the success of these substitution reactions, which are widely used in organic synthesis to interconvert important functional groups like esters, amides, and nitriles.

Related terms

Nucleophilic Addition:

A reaction where a nucleophile adds to a carbonyl carbon, forming a tetrahedral intermediate before rearranging to the final product.

Nucleophilic Substitution:

A reaction where a nucleophile replaces a leaving group, often passing through a tetrahedral intermediate.

Carbonyl Carbon:

The carbon atom in a carbonyl group (C=O) that is partially positively charged and susceptible to nucleophilic attack.