However, when both ortho positions are substituted (substrate 1b), the ortho addition at the mesityl group is suppressed due to the lack of protons for rearomatization. In contrast, the transition state formed by ipso addition to sulfur (12.5 kcal/mol) was more stable than the ortho addition to the aromatic group attached to nitrogen (14.1 kcal/mol). No ortho addition product was isolated experimentally which aligns well with this computational prediction (Scheme 2B). To further explore the influence of ortho substituents, a substrate with only one ortho position occupied (1c) was also investigated. Surprisingly, the transition state of ipso addition is still the most stable (13.4 kcal/mol) compared to the two ortho additions (14.8, N-aryl and 15.1 R2NSO2-aryl, in kcal/mol), corresponding again to the experimental results where aryl-migration is the predominant product (Scheme 2B). Our analysis suggests that an increase of steric hindrance at the ortho position destabilises the substrate by twisting the aromatic ring. This steric strain thus increases the ground state energy bringing it closer to the transition state energy for ipso attack where the ipso carbon becomes sp 3 hybridised.