Question

The molecule benzyne \(\left(\mathrm{C}_{6} \mathrm{H}_{4}\right)\) is a very reactive species. It resembles benzene in that it has a sixmembered ring of carbon atoms. Draw a Lewis structure of the molecule and account for the molecule's high reactivity.

Short answer

Benzyne is very reactive due to its triple bond, causing electron deficiency and ring strain.

Step-by-step solution

Understand the Structure of Benzyne

Begin by recognizing that benzyne ( C_{6}H_{4}) is a derivative of benzene where two hydrogen atoms are removed, and an extra bond appears between two adjacent carbon atoms. This results in one carbon-carbon triple bond in the structure.

Draw the Base Benzene Structure

Draw a hexagonal ring with alternating double and single bonds, representing benzene, C_{6}H_{6}. This forms the foundation for benzyne.

Modify Benzene to Form Benzyne

Remove two hydrogen atoms from adjacent carbons on the benzene ring to account for the C_{6}H_{4} formula. Change one double bond between these two carbons to a triple bond to get the benzyne structure.

Identify Electron Deficiency

Recognize that the formation of a triple bond in place of a double bond causes a high level of strain and electron deficiency on the adjacent carbons. This electron deficiency increases the molecule's reactivity, making benzyne a highly reactive intermediate in chemical reactions.

Key concepts

Reactivity

Benzyne is known for its high reactivity, which sets it apart from many other chemical compounds. This reactivity comes down to the structure of benzyne. When compared to benzene, benzyne has two hydrogen atoms removed, allowing a carbon-carbon triple bond to form. Due to this triple bond, the molecule experiences a significant amount of strain. This strain makes the electrons more available and reactive, which means benzyne can readily participate in chemical reactions. In essence, this inherent instability is what fuels its reactivity. Benzyne is considered an intermediate, meaning it's a temporary form that often appears in the midst of a larger chemical reaction. Because of this, it's not commonly found in stable forms and reacts quickly to form more stable compounds. This makes benzyne a crucial player in creating complex molecules during synthetic reactions.

Electron Deficiency

The concept of electron deficiency is central to understanding why benzyne is so reactive. In chemistry, electron deficiency occurs when a compound does not have enough electrons to form stable bonds. This directly results from the carbon-carbon triple bond in benzyne. In benzene, each carbon atom is bonded in a stable configuration with alternating single and double bonds. However, in benzyne, two hydrogen atoms are removed, and a triple bond takes their place. While this triple bond attempts to share electrons between the two carbon atoms, it doesn't provide the optimal electron sharing found in the usual double bond structure. Consequently, each carbon in the triple-bonded pair has fewer electrons than needed to stabilize the ring with typical aromatic stability. This makes benzyne electron deficient and results in high reactivity. The electron deficiency creates an urge to react with other molecules to gain stability, making it eager to undergo chemical transformations.

Derivative of Benzene

Benzyne is essentially a derivative of benzene, which is a very stable and well-known aromatic compound. Benzene's structure features a perfect hexagonal ring with alternating double bonds, sometimes depicted as a resonance-stabilized compound with a ring of electrons distributed evenly around it. In benzyne, however, slight changes take place, resulting in a structure far less stable than benzene. By removing two hydrogen atoms from adjacent carbon atoms in benzene, an extra bond forms between these carbons, creating a triple bond. This alteration turns the molecule into benzyne As a derivative, benzyne inherits some structural aspects of benzene, but the triple bond changes the reactivity drastically compared to benzene's stable form. You can think of benzyne as benzene altered under the right conditions to become a reactive intermediate. Understanding benzyne as a derivative is crucial because it highlights the importance of structural changes and the resulting shifts in chemical behavior. This knowledge is vital when dealing with organic synthesis and reactions involving aromatic compounds.