Question

Rank C―H σ the following bonds in terms of their bond length. Explain your ranking ( 1= longest ; 3 = shortest).

Accepted Answer

Step 1: Understand the relationship between bond length and hybridization. Bond length is influenced by the hybridization of the carbon atom bonded to hydrogen. The more s-character in the hybrid orbital, the shorter the bond length. For example, sp hybridized carbons have the shortest bond length, followed by sp2, and then sp3 hybridized carbons. Step 2: Analyze the structures provided. The first structure is a benzene ring with an sp2 hybridized carbon bonded to hydrogen. The second structure is a terminal alkyne with an sp hybridized carbon bonded to hydrogen. The third structure is a cyclopentane ring with an sp3 hybridized carbon bonded to hydrogen. Step 3: Compare the hybridization of the carbon atoms. The sp hybridized carbon in the alkyne has the highest s-character (50%), resulting in the shortest bond length. The sp2 hybridized carbon in the benzene ring has intermediate s-character (33%), resulting in a bond length longer than sp but shorter than sp3. The sp3 hybridized carbon in cyclopentane has the lowest s-character (25%), resulting in the longest bond length. Step 4: Rank the bond lengths based on the hybridization. The bond length ranking is as follows: (1) Cyclopentane (sp3, longest bond length), (2) Benzene (sp2, intermediate bond length), (3) Terminal alkyne (sp, shortest bond length). Step 5: Summarize the reasoning. The bond length decreases as the s-character of the hybrid orbital increases. This is because orbitals with higher s-character are closer to the nucleus, pulling the bonded atoms closer together and shortening the bond length.

Rank C―H σ the following bonds in terms of their bond length. Explain your ranking ( 1= longest ; 3 = shortest).

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Key Concepts

Bond Length

σ Bonds

Factors Affecting Bond Length