This section examines the outliers associated with the test set for the best regression model; see Table . Generally, the regression model struggles to accurately predict the C-H pK a values at bridgehead positions (comp69, comp70, comp321). Bridgehead deprotonation is often energetically unfavorable, leading to an unstable anion. Since our descriptor vector solely describes CM5 charges, it fails to account for the steric strain associated with the bridgehead position. The regression model also encounters difficulties when an anion gains extra stability through charge delocalization via resonance, as shown in Figure . It is expected that our model may struggle to describe the additional stability arising from conjugation since the descriptor vector for CM5 charges originates from the neutral molecule.