We had a recent #openaccess paper published in Environ. Sci. Technol. on the photohydrolysis of Ar-CF3 groups to Ar-CO2H, focusing on the effect of substituents (pubs.acs.org/doi/full/10.10…). I thought I would do a short thread. 1/n 
The work is the last chapter of Ale Manfrin's (@AlchemistAle) doctoral thesis. Thanks again to @KarlGademann and @JanssenLilli for being part of the defense committee. mcneill-group.org/single-post/20… 2/n
The central reaction in the paper is the photohydrolysis of trifluoromethyl-substituted arenas giving carboxylic acids as products. The reaction has been known for quite a while and has been studied a fair amount in Switzerland. 3/n
Scott Mabury's group and some other groups have studied examples of this reaction in an environmental context. 4/n
Ale tried to get to the bottom of the substituent effects by examining 16 different substituents in ortho, meta, and para to the CF3 group. What he found is two main effects: Modulation of the compounds' absorbance spectra and modulation of their quantum yields 5/n
Absorption spectra effects. What I learned from this project (and was already known) is that almost any substituent causes a red-shift in substituted benzenes and that there is basically no connection between classical Hammett-type substituent parameters and absorbance. 6/n
The larger the red-shift, the larger the increase in absorbance by our solar-simulating Xe lamp, with a handful of substituents giving a large enough shift to lead to significant absorbance under environmental conditions, like NO2, NR2, OR, COCH3. 7/n
The quantum yields did seem to care whether the substituent was electron donating (good) or electron withdrawing (bad) and also were highest for ortho and meta substitution. Photochemical reactions are known to not follow the ground state pattern of ortho ~ para ≠ meta. 8/n
The bottom line is that if you want to see photohydrolysis of an Ar-CF3 compound, having an ortho or meta OH or NH2 substituent will really help and having an electron withdrawing group will probably hurt. Now you can predict which of these will photoreact faster. 9/n
(The answer is flufenamic acid) 10/n
Finally, if you liked this reaction, a really cool analogue is the photohydrolysis of -SF5 substituted arenes giving sulfonic acids, reported by Jackson and Mabury (Environ. Toxicol. Chem. 2009, Vol. 28, 1866–1873). 11/11
