Solvent effects resulting from frontier molecular-orbital interactions. Part 2. The Diels–Alder reaction between 5-substituted 1,4-naphthoquinones and 2,3-dimethylbutadiene

The rates of the Diels–Alder reactions between 2,3-dimethylbutadiene and 5-substituted 1,4-naphthoquinones in different solvents have been measured and found to give hyperbolic correlations with the acceptor numbers of the solvents. This can be interpreted in terms of FMO interactions between the solvent, acting as an electrophile, and naphthoquinones, which influence the LUMO energy of the solvated quinones. Linearization of the hyperbolic functions and comparison of their slopes suggest that the substituent has little influence on the solvent effect.