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Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure
Chapter 8, Problem 71

Benzyne, C6H4, is a highly energetic and reactive molecule. What hybridization do you expect for the two triply bonded carbon atoms? What are the 'theoretical' values for the C¬C‚C bond angles? Why do you suppose benzyne is so reactive? Structural formula of benzyne, C6H4, showing its reactive triply bonded carbon atoms.

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Identify the hybridization of the two triply bonded carbon atoms in benzyne. Since each of these carbon atoms forms three sigma bonds and one pi bond, they are sp-hybridized.
Determine the theoretical bond angles for sp-hybridized carbon atoms. The ideal bond angle for sp-hybridized atoms is 180 degrees.
Analyze the structure of benzyne to understand the bond angles around the triply bonded carbon atoms. Due to the ring strain in the benzene ring, the actual bond angles will be less than the ideal 180 degrees.
Consider why benzyne is highly reactive. The strain in the benzene ring and the presence of the highly reactive triple bond make benzyne very reactive.
Summarize the findings: The two triply bonded carbon atoms in benzyne are sp-hybridized, the theoretical bond angles are 180 degrees, but due to ring strain, the actual bond angles are less. The high reactivity of benzyne is due to the ring strain and the presence of the triple bond.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that can accommodate the bonding requirements of a molecule. In the case of benzyne, the two triply bonded carbon atoms are expected to exhibit sp hybridization, which involves the mixing of one s orbital and one p orbital, resulting in two sp hybrid orbitals that are oriented linearly.
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Bond Angles

Theoretical bond angles are determined by the hybridization of the atoms involved. For sp hybridized carbon atoms, the ideal bond angle is 180 degrees, as the hybrid orbitals are arranged linearly. In benzyne, the presence of the triple bond influences the geometry, leading to bond angles that may deviate slightly from the ideal due to steric and electronic effects.
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Reactivity of Benzyne

Benzyne is highly reactive due to the presence of a triple bond between two carbon atoms, which creates significant electron density and strain in the molecule. This reactivity is further enhanced by the instability of the benzyne structure, making it prone to undergo various chemical reactions, such as nucleophilic attacks, to relieve the strain and achieve a more stable configuration.
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