Problem 42 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is an organometallic compound (a) lithium methoxide (b) lithium acetate (c) lithium dimethylamide (d) methyl lithium

Step-by-Step Solution

Answer

Option D: Methyl lithium is the organometallic compound.

Step 1: Understanding Organometallic Compounds

Organometallic compounds contain a metal bonded to carbon atoms of organic groups. The bond is typically a metal-carbon bond, which distinguishes organometallic compounds from other types of metal compounds.

Step 2: Analyzing Option A

Lithium methoxide (CH3OLi) does not contain a metal-carbon bond directly attached to a metal. The oxygen atom in this compound bridges the carbon and metal (lithium), so it is not considered organometallic.

Step 3: Analyzing Option B

Lithium acetate (CH3COOLi) contains metal and carbon but the carbon atom is not directly bonded to the lithium. Instead, it's bonded through the oxygen atom, thus excluding it as organometallic.

Step 4: Analyzing Option C

Lithium dimethylamide [(CH3)2NLi] involves nitrogen bonded to the carbon rather than the lithium directly to the carbon. Consequently, it does not qualify as an organometallic compound.

Step 5: Analyzing Option D

Methyl lithium (CH3Li) contains a direct carbon-metal bond between the lithium and the methyl group. Therefore, it qualifies as an organometallic compound.

Key Concepts

Metal-Carbon Bond

A metal-carbon bond is a defining characteristic of organometallic compounds. It is a chemical bond formed between a metal atom and a carbon atom of an organic moiety. This bond is crucial because it imparts unique properties to the compounds, allowing them to participate in a variety of chemical reactions not possible for other metal compounds.

The strength and nature of the metal-carbon bond can vary significantly. For transition metals, these bonds can show partial covalent characteristics due to the overlap of metal d-orbitals and carbon p-orbitals. In contrast, main group metals like lithium tend to form more ionic bonds with carbon, which is simpler in nature. The bond strength and type can influence the reactivity and stability of the organometallic compound. Understanding these bonds is critical in organic chemistry, particularly when predicting reaction outcomes or designing new molecules.

Types of Metal Compounds

Metal compounds can be classified into a few types depending on their bonding and structure. Organometallic compounds are just one of these classifications, characterized by the presence of at least one metal-carbon bond.

Other types of metal compounds include:

• Inorganic Metal Compounds: These do not contain carbon bonded to the metal. Examples include metal oxides, such as CuO, and metal halides like FeCl₃.
• Coordination Compounds: These feature metal ions coordinated to molecules or anions called ligands, but without a direct metal-carbon bond. A classic example is [Fe(CN)₆]⁴⁻.
• Metal-Organic Frameworks (MOFs): Although containing metal and organic structures, MOFs do not fall under organometallic since the metal and organic linkers do not form direct metal-carbon bonds.

Identifying these types helps in understanding the nature and potential applications of the compound.

Organic Chemistry

Organic chemistry is the branch of chemistry dealing with carbon-containing compounds. Organometallic chemistry sits at the intersection of organic and inorganic chemistry, focusing on metal-containing compounds bonded to organic moieties.

In organic chemistry, the study of carbon compounds is not limited to simple organic molecules but can include large, complex structures like proteins and polymers. However, the introduction of metal bonds, as seen in organometallic compounds, opens new pathways for reaction mechanisms. These compounds serve as catalysts in organic synthesis, aiding processes such as polymerization and hydrogenation.

• Organometallic compounds are crucial in facilitating organic transformations, offering pathways like the Grignard reaction which converts ketones to alcohols.
• They play a pivotal role in industrial applications, acting as catalysts in organic reactions that produce pharmaceuticals, plastics, and fuels.

Thus, the incorporation of metal-carbon bonds expands the toolkit available to chemists working in organic synthesis and industrial applications.