The Li+ Affinities of a Series of Substituted Crotonaldehyde in Their Lowest-Lying Excited Triplet State: A DFT Study

Abstract

DFT (B3LYP6-311G(d,p)) calculations of Li+ affinities on a series of substituted crotonaldehyde (aliphatic unsaturated conjugated system) and their O–Li+ counterparts were performed with complete geometry optimizations in the relevant excited state. The gas phase O–Li+ complexation turns out to be the exothermic case and the local stereochemical disposition of the Li+ is found to be almost the same in each case. The presence of substituent is seen to cause change of the Li+ affinity (ΔE) relative to the unsubstituted crotonaldehyde. Electron releasing or electron withdrawing substituents change it by 12.55-37.65 Kcal/mol. Computed Li+ affinities are sought to be correlated with a number of computed system parameters such as the net charge on the Li+ and the carbonyl oxygen of the Li+ complexes and the net charge on the carbonyl oxygen of the free bases and also the computed hardness of the free bases. The Li+ ion induced shifts are in general red shifts except for the oxychloro compound where it is a blue shift. The energetics, structural and electronic properties of the complexes indicate that the interaction between the Li+ ion and a carbonyl base is predominantly an ion–dipole attraction and the ioninduced dipole interaction as well rather than a covalent interaction.