For the $\mathrm{S_N2}$ reaction between chloroacetone and iodide, my professor has drawn a donor-acceptor interaction between the iodine lone pair attacking the Cl-substituted carbon and the π antibonding $\ce{C-O}$ orbital of the molecule.

If $\mathrm{S_N2}$ requires overlap between the σ* $\ce{C-Cl}$ orbital and the nucleophilic lone pair of I with σ symmetry, how can that lone pair participate in a donor-acceptor interaction with orbitals of π symmetry? I believed these orbitals did not interact as they are orthogonal to one another and thus experience no overlap.

Could it be that the lone pairs my professor is referring to are the other lone pairs on iodine in p orbitals that extend through the appropriate symmetry planes?



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