13C NMR chemical shifts and substituent effects transmission in 1,7,7‐trimethyl‐3‐[(E)‐2′‐arylethenyl]‐2‐oxabicyclo[4.4.0]deca‐3,5‐dienes

Abstract

Abstract13C NMR chemical shifts were determined for all carbons in a number of 1,7,7‐trimethyl‐3‐[(E)‐2′‐arylethenyl]‐2‐oxabicyclo[4.4.0]deca‐3,5‐dienes [aryl = C6H5, C6H4CH3‐p, C6H4F‐p, C6H4Cl‐p, C6H4Br‐p, C6H4CN‐p, C6H4NO2‐p, C6H4OCH3‐p, C6H3(OCH3)2‐m, p and α‐furyl]. Substituent chemical shift (Δδ13C) values for C‐1, C‐3, C‐4, C‐5, C‐6, C‐1′, C‐2′, C‐3′ and C‐4′,8′ were correlated with various Hammett parameters by singleparameter analysis. The correlations revealed that the substituent effects are transmitted across three π‐bonds in conjugation with the aryl ring. Dual‐substituent‐parameter treatment of the substituent chemical shifts revealed that resonance plays a major role in the substituent effect transmission. Hammett parameters were also derived for the α‐furyl substituent.