Role of p(Z)–π(Ar/Nap) conjugation in structures of 1-(arylchalcogena)naphthalenes for Z = Te versus Se, S and O: experimental and theoretical investigations

Abstract

Magnitudes of the p(Z)–π(Ar/Nap) conjugation were evaluated for 1-(arylchalcogena)naphthalenes (1-(ArZ)Nap, 1-(p-YC₆H₄Z)C₁₀H₇; 1 (Z = Te), 2 (Se), 3 (S) and 4 (O)). Structures of 1 were determined by X-ray analysis for Y = NMe₂ (b), OMe (c) and CN (i). For 1b and 1c that have electron donating Y, the Z–C_Ar bond is located on the naphthyl plane with Z–C_Nap being perpendicular to the aryl plane, which we define as (B: pd). On the other hand, the structure of 1i with electron donating Y is (A: pl), of which Z–C_Ar is placed almost perpendicular to the naphthyl plane with Z–C_Nap being located on the aryl plane. Each structure of 1a (Y = H), 1b, 1c, 1d (Me), 1e (F), 1f (Cl), 1g (Br), 1h (COOEt), 1i and 1j (NO₂) was determined by NMR in chloroform-d. Structures of 1 in the solutions are (B: pd) for b, c and e that have electron donating Y, (A: pl) for f–j with electron accepting Y, and in equilibrium between (B: pd) and (A: pl) for a and d of which Y are rather neutral. The results for 2–4 are very similar to those of 1 in solutions. Quantum chemical calculations were performed on 1–4 with Y of a, b′ (NH₂), d, f and j. Magnitudes of the p(Z)–π(Ar/Nap) conjugation were well-evaluated by NBO (natural bond orbital) analysis. The values were 12.6 and 13.0 kcal mol⁻¹ for the typical forms of (A: pl) and (B: pd) of 1a, respectively, resulting in a much smaller energy difference between the two (0.4 kcal mol⁻¹), which should correspond to the observed result. It is well-demonstrated that the p(Te)–π(Ar/Nap) conjugation operates effectively in 1, although the magnitudes increase in the order of Z = Te < Se < S < O. Thermal effect of the Gibbs free energies is shown to play an important role in the energy profiles of 1a–4a.