Q.The $\text{C--Cl}$ bond in chlorobenzene (about $1.69\ \text{\AA}$) is shorter than the $\text{C--Cl}$ bond in a saturated chloroalkane such as $\text{CH}_3\text{Cl}$ (about $1.77$--$1.78\ \text{\AA}$). Explain this difference in terms of bonding.

In chlorobenzene, chlorine's lone pair can delocalise by resonance into the aromatic ring's $\pi$ system, since the chlorine sits on an $sp^2$ carbon whose $p$ orbital is properly aligned to conjugate with the ring. This delocalisation mixes some double-bond character into what would otherwise be treated as a pure single bond, and a bond with partial double-bond character is intrinsically shorter (and stronger) than a pure single bond. A second, independent contribution comes from the hybridisation of the ring carbon itself: an $sp^2$ orbital has more $s$ character than an $sp^3$ orbital, and orbitals with more $s$ character form shorter sigma bonds regardless of resonance. Both effects act in the same direct …

Attribute the shortening to two compounding causes -- resonance (partial double-bond character) and hybridisation (more s …

Citing only the electronegativity of chlorine as the explanation -- electronegativity alone does not explain why this bond differs from the C--Cl bond in a …