Electronic Structure of Symmetric Homocojugated Dienes. Circular Dichroism of (1S)-2-Deuterio- and 2-Methylnorbornadiene and (1S)-2-Deuterio- and 2-Methylbicyclooctadiene

Article abstract of DOI:10.1021/ja00538a009

(1S)-<2-(2)H>Bicyclo<2.2.1>hepta-2,5-diene (1), (1S)-2-methylbicyclo<2.2.1>hepta-2,5-diene (3), (1S)-<2-(2)H>bicyclo<2.2.2>octa-2,5-diene (4), and (1S)-2-methylbicyclo<2.2.2>octadiene (6) were prepared by reaction of the corresponding chiral β,γ-unsaturated ketone tosylhydrazone with CH3Li followed by either D2O or CH3I quenching.The circular dichroism Cotton effects of 1 (Δε₂₃₇ = -0.032, Δε₂₁₆ = +0.14, Δε₂₀₅ = -0.37) and 4 (Δε₂₂₂ = -0.027) are the first examples obtained from deuterated olefins or dienes whose chirality is due only to isotopic substitution.Both the deuterated and the methylated dienes exhibited multiple Cotton effects (3, Δε₂₄₉ = +2.38, Δε₂₂₂ = -0.25, Δε₂₁₉ = -0.54, Δε₂₁₄ = +0.62, Δε₂₀₄ = -0.94; 6, Δε₂₃₁ = +0.90, Δε₂₁₁ = +0.48, Δε₂₀₀ = -0.24), demonstrating the existence of interchromophoric interaction and electronic transitions that are only difficulty seen in their ultraviolet spectra.We present ab initio localized orbital RPA calculations on 1 that allow a consistent assignment of norbornadiene transitions.