Question

Which of the following statements is false? (l) According to Lewis theory electrophiles are Lewis acids while nucleophiles are Lewis bases. (2) In Friedel-Crafts reaction, the catalysts used are Lewis acids. (3) In complex compounds, metal ions are Lewis bases while ligands are Lewis acids. (4) Electron-deficient molecules are Lewis acids.

Short answer

Statement (3) is false.

Step-by-step solution

Understanding Lewis Acids and Bases

Review the definitions: Electrophiles are electron pair acceptors (Lewis acids), while nucleophiles are electron pair donors (Lewis bases).

Friedel-Crafts Reaction and Catalysts

Recognize that Friedel-Crafts reactions use catalysts such as AlCl3, which is a Lewis acid.

Metal Ions and Ligands in Complex Compounds

In complex compounds, metal ions typically act as Lewis acids because they accept electron pairs from ligands, which act as Lewis bases.

Electron-Deficient Molecules

Electron-deficient molecules are Lewis acids because they can accept electron pairs.

Identifying the False Statement

Analyze all the statements again. Statements (1), (2), and (4) are true based on the definitions and analyses. However, (3) is incorrect because in complex compounds, metal ions are Lewis acids, not Lewis bases.

Key concepts

Lewis Acids

Lewis acids are chemical species that can accept an electron pair. This characteristic makes them electrophiles, which seek electrons to achieve a more stable electronic configuration.
Common examples of Lewis acids include:

• Hydrogen ions (H⁺)
• Metal ions such as Fe³⁺ or Al³⁺
• Electron-deficient molecules like BF₃ or AlCl₃

These species generally have vacant orbitals, enabling them to accept electron pairs from Lewis bases. Understanding Lewis acids is essential when discussing catalytic processes, coordination complexes, and many organic reactions.

Lewis Bases

Lewis bases are compounds that can donate an electron pair. This makes them nucleophiles, meaning they seek positively charged or electron-deficient sites.
Examples of Lewis bases include:

• Ammonia (NH₃)
• Hydroxide ions (OH^-)
• Water (H₂O)
• Ligands in metal complexes like ethylenediamine

Lewis bases have lone pairs of electrons that they can share with Lewis acids, facilitating the formation of a coordinate bond. This interaction forms the foundation for many reactions, including acid-base interactions and complex formation.

Friedel-Crafts Reaction

The Friedel-Crafts reaction is a type of organic reaction used to attach substituents onto aromatic rings. There are two types: Friedel-Crafts alkylation and Friedel-Crafts acylation.
Key points include:

• AlCl₃ or FeCl₃ are common catalysts used in these reactions
• These catalysts are Lewis acids that accept electron pairs
• The reaction allows for the formation of new carbon-carbon bonds

During the reaction, the catalyst helps to generate a more reactive electrophile which then reacts with the aromatic compound. Understanding the role of Lewis acids in this reaction is crucial for mastering many synthetic pathways in organic chemistry.

Metal-Ligand Complexes

In coordination chemistry, metal-ligand complexes play a fundamental role in many chemical processes.
Key aspects include:

• Metal ions are Lewis acids: They accept electron pairs
• Ligands are Lewis bases: They donate electron pairs
• The metal-ligand interaction is through a coordinate bond

For example, in a complex like [Fe(CN)₆]^3-, Fe³⁺ is the Lewis acid, and the cyanide ions (CN^-) are the Lewis bases. The interaction between the metal and the ligands stabilizes the metal ion and modifies its chemical properties.
Understanding these interactions is essential for fields like bioinorganic chemistry, catalysis, and materials science.