Influence of substituent and push‐pull effect on the chemical shifts of the carbon in bridging bond of 1‐furyl/thienyl‐2‐arylethylene

Abstract

Sixty‐six samples of 1‐furyl/thienyl‐2‐arylethylene model compounds XCHCHArY (abbreviated XEBY) were synthesized. The nuclear magnetic resonance spectra (NMR) of model compounds were determined. The chemical shift δC(X) and δC(Y) of the carbon atoms in bridging bond CHCH which connected to the X group and the ArY group, respectively, were confirmed with the two‐dimensional NMR method. The effect of substituent on the δC(X) and δC(Y) was studied, meanwhile, the push‐pull effect of substituent on ΔδC = δC(Y) − δC(X) and δC(Y/X) = δC(Y)/δC(X) were discussed. The results show the following: (a) Both the δC(X) and δC(Y) are affected by excited‐state substituent constant σCCex()X of group X, Hammett constant σ(Y), and excited‐state substituent constant 0.25emσCCex()Y of group Y. The effect of σ(Y) on the δC(X) is positive, whereas that on the δC(Y) is negative. That is to say, the σ(Y) of group Y has an alternative influence on the δC(X) and δC(Y). (b) Compared with furyl, there is a p‐d effect formed by the 3d orbit of S atom and the p electron of the π system in thienyl, which increase the chemical shift of the carbon atoms in bridging bond. (c) The push‐pull effect between substituent X and Y is not only affected by the σ parameter but also related to the σCCex parameter, which results from the combined effect of the two parameters σ and σCCex. The observation of this paper provides a new perspective in understanding the push‐pull effect of substituent.

A new insight into the push‐pull effect of substituents via the stilbene‐like model compounds

“…The stilbene‐like model compounds (Scheme 1) were synthesized via the methods reported in our previous work [31–35], and their 13 C NMR chemical shifts δ C (X) and δ C (Y) of the carbon atoms in bridging bond CH=CH and CMe=CH were measured with a Bruker AV 500 MHz nuclear magnetic resonance spectrometer. The δ C values of the model compounds were listed in Table 1.…”

“…The model compounds A , B , and C were synthesized according to the methods of author's previous reports [31–35, 40, 41], and Seus's work [42], as shown in Figure 3. The experimental methods are as follows.…”

“…Recently, authors [31, 32] investigated quantitatively the influence of substituent effect on the push‐pull effect (chemical shift difference of the bridging bond carbon atoms) of 1‐furyl/thienyl‐ 2‐arylethylene and further firstly established a relationship between the solid‐state fluorescence wavelength and the push‐pull effect for the mentioned compounds. In the process of studying the push‐pull effect of substituents, a very interesting phenomenon was observed: The maximum push‐pull effect is not always between the strong electron‐donating D and strong electron‐accepting A groups, which is inconsistent with our usual understanding of push‐pull effect.…”

Push‐Pull Effect at Formation of Sitting‐Atop Metal‐Porphyrin Complex in Solvating Media: H‐Bonding and Electrostatic Repulsion

“…Push‐pull effect on the geometrical, optical and charge transfer properties of disubstituted derivatives of mer ‐tris(4‐hydroxy‐1,5‐naphthyridinato) aluminum was used for design of new optical materials [43] . A noticeable push‐pull effect is exerted on NMR carbon chemical shifts in bridging bond [44] …”

Substituent Effect Study for 13Cβ SCS in a Meta-Styrene Series. Reynolds Dual Substituent Parameter Model Investigation

“…4,5 Recently investigators have examined the pull− push effects of X and Y on the chemical shifts of the carbon in the bridging bond of XCHCHArY using the single substituent parameter (MSP) model. 6 The dual substituent parameter (DSP) model has been successfully applied to the modeling of the 13 C SCS for the para-disubstituted benzene ring. 7−14 However, the meta-disubstituted benzene ring has not been well-investigated, primarily due to the improper choice of substituent parameters, which must be used in the model to reproduce the 13 C SCS.…”