A high‐level theoretical study into the atmospheric phase hydration , bond dissociation enthalpies, and acidity of aldehydes

CBS‐Q//B3, G4(MP2), and G4 composite method calculations were used to estimate atmospheric phase standard state (298.15 K, 1 atm) free energies of hydration (Δ hydr G° (g) ), hydration equilibrium constants (log K hydr,(g) ), bond dissociation enthalpies (BDEs), and enthalpies (Δ d H° (g) ) and free energies (Δ d G° (g) ) of aldehydic proton acid dissociation for various substituted aldehydes with electron withdrawing and electron releasing groups. Good quality log K hydr,(g) correlations with the Swain–Lupton resonance effect parameters R and R + were found, allowing extension of the model to predict log K hydr,(g) values for 487 substituted aldehydes having available R‐values and 108 substituted aldehydes having available R + values. Good correlations were also found between experimental aqueous phase hydration equilibrium constants (log K hydr,(aq) ) and summative R / R + values for peripheral substituents on a range of carbonyl derivatives (aldehydes, ketones, esters, and amides), suggesting that the structure–reactivity modeling approach can be extended to include all possible combinations of R 1 C(O) R 2 carbonyl substitution in both gas and aqueous systems. Computationally derived BDEs and Δ d H° (g) /Δ d G° (g) were in good agreement with the limited experimental and theoretical datasets. BDEs did not generally correlate with any of the Hammett substituent constants or Swain–Lupton parameters considered. Gas phase acidities exhibited high correlation coefficients with Hammett inductive substituent constants ( σ I ) and field effect parameters ( F ), allowing these to be employed as surrogates for estimating the gas phase aldehydic proton acidities of a larger potential compound range. The resulting models will be of use in predicting the environmental behavior for a broad range of environmentally relevant compounds containing carbonyl functionalities. Copyright © 2016 John Wiley & Sons, Ltd.