When rigorously examining the nature of the carbon-halogen bond across various structural substrates — Haloalkanes and Haloarenes Chemistry Question
Question
When rigorously examining the nature of the carbon-halogen bond across various structural substrates, which of the following specific bonds possesses the lowest $s$ -character at the carbon center, resulting in the longest relative bond length and highest susceptibility to classical $S_N2$ displacement?
💡 Solution & Explanation
The $s$ -character of a hybridized orbital strongly influences bond length and electronegativity. Greater $s$ -character means the electrons are held closer to the nucleus, making the bond shorter and stronger. Chloroethyne ($HC\equiv C-Cl$) features an $sp$ hybridized carbon ($50\%$ $s$ -character). Chlorobenzene and vinyl chloride both feature an $sp^2$ hybridized carbon ($33.3\%$ $s$ -character). Cyclohexyl chloride features an $sp^3$ hybridized aliphatic carbon ($25\%$ $s$ -character). Because $25\%$ is the lowest $s$ -character among these options, the $C-Cl$ bond in cyclohexyl chloride is the longest, the least tightly held, and by far the most susceptible to classical backside nucleophilic attack ($S_N2$).