Conformational And Electronic Interaction Studies Of 2-Seleno-Substituted Carbonyl Compounds And The Comparison With The 2-Thio-Analogues. XIII. α-Phenylseleno-p-Substituted Propiophenones¹

Abstract

The ν_CO IR analysis of α-phenylseleno-p-substituted propiophenones (I) indicates the existence of the cis-gauche rotational isomerism, the gauche conformer is predominant and the more polar one. The carbonyl frequency shifts for the gauche conformer of the title compounds are rather more negative than the δν_CO gauche shifts of the previously studied ω-phenylthio-p-substituted acetophenones (II). The title compounds (I) present practically no variation of the δν_CO absolute values on going from electron-donating to electron-attracting substituents in comparison to compounds of series (II) where this variation is significant. The Non Additivity Effect of the α-methyne carbon chemical shifts for series (I) is close to the NAE values of the α-methylene carbon for series (II). The bathochromic shifts of the n → π_CO∗ transition for compounds of series (I) and (II) in relation to their parent compounds are quite close. The obtained data indicate an interplay of the π_CO∗/ρ_C-X·π_CO∗/n_X and π_CO/ρ_C-X∗ orbital interactions which act on both series of compounds but in a larger extent for the selenium derivatives than for the sulfur derivatives. The π_CO/ρ_C-Se∗ interaction is the one which prevails in greater extent over the π_CO/ρ_C-S∗ interaction.

Key Words:

• Conformational studies
• electronic interactions
• IR
• ¹³C NMR and UV spectroscopies
• α-phenylseleno-p-substituted propiophenones