The kinetics for surface-catalyzed alcohol dehydration reactions often depends on the structure of the alcohol.Studies of structure-activity relations across primary, secondary, and tertiary alcohols can provide fundamental information onthe nature of active sites on the surface. Here, we investigated the dehydration of 1-butanol, 2-butanol and tert-butanol overTiO2 anatase catalysts modified with various phosphonic acid (PA) self-assembled monolayers (SAMs). As a response to thepresence of PAs, the three C4 alcohol isomers showed different dehydration rates, with 1-butanol dehydration being enhancedto the greatest extent by PA modification. Furthermore, the fluorinated, more polar 4-fluorobenzyl phosphonic acid outperformedalkyl PAs across all alcohols. Steady-state kinetic measurements and temperature programmed desorption studiesindicated that PA SAMs significantly lowered the dehydration activation barrier; the extent of reduction in the barrier wassensitive to both the substitution of the alcohol and the charge distribution on the PA in a way that was consistent withstabilization of a carbenium-like transition state. Overall, the effect of PA modifiers on alcohol dehydration rates was found tobe determined from a balance between transition state stabilization and active site blocking effects, with the potential to tuneactivity and selectivity based on the structure and coverage of the SAM.