The four-parameter model consists of two terms for both the substrate and catalyst. The natural bond orbital (NBO) partial charge of the substituent at the C6′-position on the quinoline classified the different substituents installed at this site (orange, Figure ). The more electron-rich (larger negative value) alkoxy-substituted catalysts give higher selectivities than the aryl or protio analogs. The buried volume collected within a 5 Å radius of C9 reads out the catalyst pocket established by the phosphinate substitution (red, Figure ). The larger buried volume provided by the cyclohexyl substituents (3e) restricts the pocket size, resulting in the most selective catalyst. The sulfonimidamide substrate is described by its molar volume (gray, Figure ). Although not independently correlated to the observed selectivity, we hypothesize this parameter accounts for substrate-catalyst steric matching in the selectivity-determining transition state (vide infra). Lastly, the C NMR chemical shift of the α-carbon (green, Figure ) serves to classify the aryl from the pseudo-aliphatic (i.e., benzyl, allyl, and cyclopropyl) substrates, which exhibit lower selectivities. Having established quantitative structure-enantioselectivity relationships, we began kinetic investigations into the mechanism of catalysis to inform subsequent computational models. We selected in situ infrared (IR) spectroscopy as our analytical technique of choice to monitor the reaction's progress. Both the consumption of the starting electrophile 2a and the formation of product 4aa could be monitored via resolved peaks in the carbonyl region of the IR spectra (Figure ). From the outset of this study, we suspected that an uncatalyzed background acylation reaction might play an impactful role in the process and be competitive with the cinchona-catalyzed acylation. To gain further insight into the rate of the uncatalyzed background reaction, the reaction was performed and monitored in the absence of a catalyst (black, Figure ). A tenfold difference in the initial rates was observed between the 3e-catalyzed and uncatalyzed processes. Therefore, it is presumed that an aggregate rate of the cinchonacatalyzed reaction with a contribution from an uncatalyzed background reaction contributes to the reaction profile and observed selectivity. Importantly, precisely quantifying the exact background reaction contribution for each catalyst-substrate combination is challenging, but we estimate a ~5-30% background rate depending on the catalyst-substrate combination. This limits the selectivity ceiling to ~97:3 er for most examples.