The ground state basicities of a series of substituted crotonaldehyde

DFT (B3LYP 6-31G(d)) calculations with complete geometry optimizations are carried out on a series of substituted crotonaldehyde and their O-protonated counterparts. The gas phase O-protonation turns out to be exothermic case and the local stereochemical disposition of the proton is found to be almost the same in each case. The presence of substituent is seen to cause very little change of the protonation energies (PE) relative to the unsubstituted crotonaldehyde. Electron releasing substituents increase PE by 0.002–0.004 hartree and the electron withdrawing substituents decrease it by 0.01 hartree. Computed protonation energies are sought to be correlated with a number of computed system parameters such as the net charge on the carbonyl oxygen, charge on the proton of the unprotonated and the protonated species.