Next, variable time normalization analysis (VTNA) was used to estimate the orders in each of the reaction components: the amine catalyst, each copper source, the base and the other reagents (Figure ). We identified an order of 1 in aldehyde, transient directing group and K2CO3. Fractional orders were observed for both the sulfinate and CuF2 (0.75 and 0.5 respectively), and a zero order in Cu(OAc)2. Together with the optimization studies was clear that the sulfinate has a competing inhibitory effect on the reaction, presumably by blocking copper coordination sites and thus leading to the complex order observed. In order to better understand the C-H activation step itself, we employed deuteration and kinetic isotope effect experiments. When performing the reaction in HFIP-d2, no obvious deuteration was observed in either starting material or product, implying that both C-H activation is irreversible under the reaction conditions and there are likely no further cyclometallation events between copper and the product. A significant primary kinetic isotope effect was observed in both parallel (KIEparallel = 2.42) and competition experiments (KIEcompetition = 3.25) which indicates C-H bond cleavage is intimately linked to the turnover limiting step (Figure ). Further investigation into the electronics of this step by Hammett analysis revealed a negative correlation (Figure ). This implies a build-up of positive charge on the arene ring in the turnover limiting step, therefore implying an unusual turnover limiting mechanism of C-H activation via a partially dearomatized transition state. Considering these findings together, we propose a concerted asynchronous cleavage of the C-H bond and formation of the C-Cu bond, which involves nucleophilic attack from the aryl p-system to the copper centre leading to a partial Wheland-type transition state followed by deprotonation by the carbonate base. This may occur through either an inner or outer sphere mechanism (Figure