We used NBO theory to analyse the frontier orbitals on iodine that were used to engage in covalent and secondary bonding in intermediates A, A′, and B; and we used Natural Population Analysis (NPA) to determine atomic charges on C1 of the transferring phenyl group and on the nitrogen of DABCO. In intermediate A the iodine uses 12.5% s-orbital character in the covalent bond (a) with the transferring phenyl group, and C1 has a corresponding NPA charge of -0.233 (Scheme 7 and Table and). On the other hand, in intermediate A′ the iodine uses 10.5% s-character to bond (f) with the transferring phenyl group (Scheme 7 and Table ). We attribute the lesser amount of s-orbital character used by iodine in A′ to greater amount of p-orbital character that results from the secondary bond with the triflate trans to the transferring phenyl group. The NPA charge on C1 in A′ is more negative than that in A at -0.264 (Table ). Zhdankin and Ochiai have previously described a trans influence scale on hypervalent 3-iodanes; 28 however, our computational structures do not reveal an increase in bond length in a comparison of bond f in A′ and bond (a) in A as a result of secondary bonding (Table ). Our data do suggest, on the other hand, that the existence of a secondary bond trans to the transferring group results in a higher barrier and slower ligand coupling reaction. We attribute this effect to the decrease in s-orbital character on iodine in A′ (f) and thereby poorer stabilization of the migrating electron pair from bond (f/h) (Scheme 7). Our computational results regarding the relative energies of transition states from A and A′ are consistent with other's findings that reductive elimination from three-coordinate complex is lower in energy than from a four-coordinate complex. Moreover, our results provide the first rationalisation for this observation based on the frontier orbitals on iodine and NPA charges on the carbon of the transferring aryl group. The iodine atom in intermediate B uses 11.6% s-orbital character to bond with the transferring phenyl group (bond k in B; Scheme 7 and Table ), which is less s-orbital character than found in the corresponding bond (a) in intermediate A. The computational results (larger G ‡ and less s-orbital character) found for intermediate B (relative to A) are consistent with the lower krel value experimentally obtained for compound 7 (Table ). An additional factor that may contribute to the higher transition state energy from B relative to A is increased electron-pair repulsion between the mesityl and phenyl groups. As observed in all three transition states (Scheme 7), the C4-C1-I angle bends and the CPh-I-CMes angles contracts (Scheme 7). Therefore, in the case of B with a more sterically bulky mesityl group the distance between the transferring phenyl and the mesityl group in the transition state is relatively short (~ 2.4 Å) compared to the distance between the two phenyl groups in the transition state from A (3.2 Å; Scheme 7). The combined effect of frontier orbitals on iodine and steric effects of the bulky mesityl group are the underlying factors that result in a slower phenylation of DABCO with 7 in comparison with compound 1 (Table ).