Comparison of the substituent effects on the (13) C NMR with the (1) H NMR chemical shifts of CH=N in substituted benzylideneanilines.

Research article Received: 4 December 2014

Revised: 1 February 2015

Accepted: 19 March 2015

Published online in Wiley Online Library: 1 June 2015

(wileyonlinelibrary.com) DOI 10.1002/mrc.4248

Comparison of the substituent effects on the 13C NMR with the 1H NMR chemical shifts of CH¼N in substituted benzylideneanilines Linyan Wang,a,b Chaotun Caob and Chenzhong Caoa,b* Fifty-two samples of substituted benzylideneanilines XPhCH¼NPhYs (XBAYs) were synthesized, and their NMR spectra were determined in this paper. Together with the NMR data of other 77 samples of XBAYs quoted from literatures, the 1H NMR chemical shifts (δH(CH¼N)) and 13C NMR chemical shifts (δC(CH¼N)) of the CH¼N bridging group were investigated for total of 129 samples of XBAYs. The result shows that the δH(CH¼N) and δC(CH¼N) have no distinctive linear relationship, which is contrary to the theoretical thought that declared the δH(CH¼N) values would increase as the δC(CH¼N) values increase. With the in-depth analysis, we found that the effects of σF and σR of X/Y group on the δH(CH¼N) and the δC(CH¼N) are opposite; the effects of the substituent specific cross-interaction effect between X and Y (Δσ2) on the δH(CH¼N) and the δC(CH¼N) are different; the contributions of parameters in the regression equations of the δH(CH¼N) and the δC(CH¼N) [Eqns (4 and 7), respectively] also have an obvious difference. Copyright © 2015 John Wiley & Sons, Ltd. Keywords: benzylideneanilines; substituent effects; 1H NMR chemical shifts; 13C NMR chemical shifts; substituent specific cross-interaction

Introduction

520

The benzylideneanilines XPhCH¼NPhYs (abbreviated XBAYs) are a kind of typical compounds with π conjugate system and have been applied extensively in the fields of liquid crystal and nonlinear optical material.[1–3] In the molecule of XBAY, CH¼N is a bridge linking two aromatic rings, in which one ring carries substituent X and another ring carries substituent Y. The substituents X and Y can act as electron donors and/or electron acceptors. Changes of X and Y in XBAY can affect its molecular overall electron distribution and the properties of optoelectronic materials containing the molecule of XBAY. Therefore, the substituent effects on the performance of the CH¼N bridging group attained great interest in recent years.[4–11] As we know, the NMR shielding is affected by the electron density, and the field of resonance increases with the increasing electron density of the protons and carbon nucleus in the molecule.[12,13] So the NMR chemical shifts of CH¼N (δH(CH¼N) and δC(CH¼N)) were always applied by many researchers to study the substituent effects on the molecules in the past years.[4–6,8,14,15] Echevarria et al.[14] have made sketchy studies about the 1H NMR and 13C NMR of CH¼N by employing 24 samples of substituted benzylideneanilines and discussed the linear relationship between the δH(CH¼N) values or δC(CH¼N) values and the Hammett substituent constant σp. They obtained results: the δH(CH¼N) presented linear relation with σp of the benzaldehyde ring substituents but did not present linear relation with the σp of the aniline ring substituents; in addition, the effects of the aniline ring substituents on the δC(CH¼N) were larger than that of the benzaldehyde ring substituents. Afterwards, the substituent effects on the δC(CH¼N) of some title compounds were analyzed by employing several different single and dual substituent parameter approaches, and the relatively best equation [Eqn (1)] was attained by Neuvonen et al.[7,16] In their research, they pointed out that the presence of the substituent

Magn. Reson. Chem. 2015, 53, 520–525

specific cross-interaction between X and Y could be verified. Although they did not quantify the cross-interaction, their works strongly promotes the research of the substituent effects on the δC(CH¼N) of title compounds. In our recent work,[17] the substituent specific cross-interaction effects was quantified with the item Δσ 2 (Δσ2 = (σX σY)2) and a more effective five-parameter equation [Eqn (2)] was proposed to quantify the δC(CH¼N) of substituted benzylideneanilines by adding Δσ 2 item to Eqn (1). σF is the inductive effect; σR is the conjugative effect; Δσ 2 is the substituent specific cross-interaction effect; ρ is the coefficient of corresponding parameter. δC ðCH ¼ NÞ ¼ constant þ ρF ðXÞσ F ðXÞ þ ρF ðYÞσ F ðYÞ þ ρR ðXÞ σ R ðXÞ þ ρR ðYÞ σ R ðYÞ δC ðCH ¼ NÞ ¼ constant þ ρF ðXÞ σ F ðXÞ þ ρF ðYÞ σ F ðYÞ þ ρR ðXÞ σ R ðXÞ þ ρR ðYÞ σ R ðYÞ þ ρðΔσ2 Þ Δσ 2

(1)

(2)

* Correspondence to: Chenzhong Cao, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Key Laboratory of Theoretical Organic Chemistry and Function Molecule (Hunan University of Science and Technology), Ministry of Education, Hunan Provincial University Key Laboratory of QSAR/QSPR, Xiangtan 411201, China. E--mail: [email protected] a School of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China b School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Key Laboratory of Theoretical Organic Chemistry and Function Molecule (Hunan University of Science and Technology), Ministry of Education, Hunan Provincial University Key Laboratory of QSAR/QSPR, Xiangtan 411201, China

Copyright © 2015 John Wiley & Sons, Ltd.

Substituent effects on the 13C NMR and the 1H NMR chemical shifts Now that the 1H NMR and 13C NMR chemical shifts are all affected by the electron density, and it was generally believed that the δH(CH¼N) values should increase as the δC(CH¼N) values increase in a same set of compounds. Is it true? Based on a wide set of 129 samples of substituted benzylideneanilines (as shown in Scheme 1), the plot of δC(CH¼N) values versus δH(CH¼N) values was carried out (Fig. 1). Figure 1 shows a surprising result that there is a bad correlation between the δH(CH¼N) and δC(CH¼N) of XBAYs, the correlation coefficient is only 0.6347. It implies that the effects of substituents X and Y on the δH(CH¼N) and on the δC(CH¼N) are different. What are the reasons bringing out the aforementioned phenomenon? In this paper, we made an investigation on this topic using the 129 samples of title compounds and attained a meaningful result.

Results and discussions The δC(CH¼N) values and δH(CH¼N) values of title compounds were collected and listed in Table 1. Some of them were measured in this work, and the rest were quoted from the literatures. The substituents X and Y in molecules of title compounds are of electronwithdrawing substituents (e.g. NO2 and CN) and electron-donating substituents (e.g. NMe2 and OMe); in addition, X and Y are of parasubstituted and meta-substituted. Taking Eqns (1 and 2) as models, corresponding regression equations were attained [Eqns (3 and 4)] for the 129 δC(CH¼N) values in Table 1. δC ðCH ¼ NÞ ¼ 160:25 4:68 σ F ðXÞ þ 3:19 σ F ðYÞ 0:86 σ R ðXÞ þ 5:04σ R ðYÞ

(3)

R ¼ 0:9860; R2 ¼ 0:9722; S ¼ 0:37; F ¼ 1084:48; n ¼ 129 δC ðCH ¼ NÞ ¼ 160:30 4:38 σ F ðXÞ þ 3:07 σ F ðYÞ 1:11 σ R ðXÞ þ 4:63 σ R ðYÞ 0:61Δσ 2

(4)

R ¼ 0:9938; R2 ¼ 0:9877; S ¼ 0:25; F ¼ 1968:77; n ¼ 129 One can observe that Eqn (4) is superior to Eqn (3) obviously. The correlation coefficient R of Eqn (4) is larger than that of Eqn (3), and the standard error S of Eqn (4) is smaller than that of Eqn (3). Equation (4) shows that the σF and σR of X group decrease

Scheme 1. Title compounds used in this paper.

the δC(CH¼N), while the σF and σR of Y group increase the δC(CH¼N). What we want to know is how do the X and Y groups affect the δH(CH¼N). We made discussions as follows. Based on 129 samples of title compounds, the regression analysis of the δH(CH¼N) values of Hammett constant σp/m of X and Y was carried out in this paper, and Eqn (5) was obtained (Table 2). In Eqn (5), the ration of |ρ(X)/ρ(Y)| is 2.00, which means that the effect of X on the δH(CH¼N) is 2.00 times higher than Y on δH(CH¼N), and the effect of Y on the δH(CH¼N) is not ignorable. On the other hand, Eqn (5) shows that the σp/m of X group increases the δH(CH¼N), while the σp/m of Y group decreases the δH(CH¼N). It is just opposite with the effects of substituents on the δC(CH¼N). As we know, σ = σF + σR. In the report of Cao et al.,[17] the regression equation of the δC(CH¼N) became better when Hammett constant σ was divided to the inductive constant σF and conjugative constant σR; therefore, the different contributions of inductive and conjugative effects were taken into account in the regression analysis of the δH(CH¼N) values in this paper, and Eqn (6) was obtained (Table 2). Comparing the correlation coefficient (R), the standard errors (S), and F value of Eqn (6) with these of Eqn (5), the results show that Eqn (6) has no improvement after dividing σ to σF and σR. That is to say, the inductive and conjugative effects of substituents on δH (CH¼N) are almost the same intensity, and they can be merged in the correlation equation. It is different from the results of regression analysis of the δC(CH¼N) by Cao et al.[17] It is known that the substituent specific cross-interaction effects Δσ2 between X and Y is a necessary item in quantifying δC(CH¼N),[17] additionally for the comparison with Eqn (4), so this item was also added into Eqn (6) to carry out the regression analysis against the δH(CH¼N) values, then Eqn (7) was obtained (Table 2). The results of Table 2 show that the correlation coefficient (R) and the standard errors (S) of Eqns (5 and 7) are almost the same; but the F value of Eqn (5) is larger than that of Eqn 7. Also, the average absolute errors between the calculated values and experimental values of the two equations are all equal to 0.03 ppm. In conclusion, the Eqn (5) is enough to quantify the substituent effects on the δH(CH¼N), and the substituent specific cross-interaction effects Δσ2 on the δH(CH¼N) is negligible, which is different from the effect of Δσ2 on the δC(CH¼N).[17] In the report of Cao et al.,[17] the substituent specific cross-interaction effect on the δC(CH¼N) is indispensable. The reason leading to the difference of substituent effects on the δC(CH¼N) and δH(CH¼N) may be the deviation of hydrogen atom from the conjugated main chain in the molecules of XBAYs. In addition, the parameter effects on the δC(CH¼N) and δH(CH¼N) are different. For that, Eqns (4 and 7) have the same parameters and the regression results of Eqn (7) are close to that of Eqn (5). So here the relative importance of parameters in Eqns (4 and 7) are investigated from the relative contributions (ψγ) or fraction contributions (ψf) of the corresponding parameters to the δC(CH¼N) and δH(CH¼N).[20,21] ψγ ¼ mi X i (8) R2 ψγ ðiÞ 100% ψf ðiÞ ¼ X (9) ψ ðiÞ γ

i

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Figure 1. The plot of δH(CH¼N) values versus δC(CH¼N) values of title compounds.

The mi and X i are the coefficient and the average value of the ith parameter in Eqn (4 or 7), respectively, and the R are the correlation coefficients of Eqn (4 or 7). The sum is over the parameters in the equations. The contribution results for the corresponding parameters of Eqns (4 and 7) are all shown in Table 3.

L. Wang, C. Cao and C. Cao Table 1. The data of δC(CH¼N) and δH(CH¼N) of 129 samples of title compounds Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

2a

X

Y

σF (X)a

σF (Y)a

σR (X)a

σR (Y)a

Δσ

m-F m-F m-F m-F m-Br m-Br m-Br m-Br m-Br m-CN m-CN m-CN m-CN m-CN m-OMe p-NMe2 p-OMe p-Cl p-CF3 p-CN p-NO2 p-NMe2 p-OMe p-Me p-Cl p-CN p-NO2 p-NMe2 p-OMe p-Me p-Cl p-CN p-NO2 p-NMe2 p-CN p-NO2 p-Cl p-CN m-OMe m-Me m-Me m-Me m-F m-F m-F m-CN m-CN m-CN m-CN m-Br m-Br m-Br m-Me m-Cl m-NO2 m-Cl m-NO2

p-NMe2 p-OMe p-Me p-Cl p-NMe2 p-OMe p-Me p-F p-Cl p-NMe2 p-OMe p-Me p-Cl p-CN p-NMe2 m-Me m-Me m-Me m-Me m-Me m-Me m-F m-F m-F m-F m-F m-F m-Br m-Br m-Br m-Br m-Br m-Br m-OMe m-OMe m-OMe m-CN m-CN m-CN m-OMe m-Me m-F m-Me m-F m-Br m-OMe m-Me m-F m-CN m-Me m-CN m-Br p-OMe p-OMe p-OMe p-COOEt p-COOEt

0.34 0.34 0.34 0.34 0.39 0.39 0.39 0.39 0.39 0.56 0.56 0.56 0.56 0.56 0.12 0.15 0.29 0.42 0.38 0.51 0.65 0.15 0.29 0.01 0.42 0.51 0.65 0.15 0.29 0.01 0.42 0.51 0.65 0.15 0.51 0.65 0.42 0.51 0.12 0.07 0.07 0.07 0.34 0.34 0.34 0.56 0.56 0.56 0.56 0.39 0.39 0.39 0.07 0.37 0.71 0.37 0.71

0.15 0.29 0.01 0.42 0.15 0.29 0.01 0.45 0.42 0.15 0.29 0.01 0.42 0.51 0.15 0.07 0.07 0.07 0.07 0.07 0.07 0.34 0.34 0.34 0.34 0.34 0.34 0.39 0.39 0.39 0.39 0.39 0.39 0.12 0.12 0.12 0.56 0.56 0.56 0.12 0.07 0.34 0.07 0.34 0.39 0.12 0.07 0.34 0.56 0.07 0.56 0.39 0.29 0.29 0.29 0.34 0.34

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.98 0.56 0.19 0.16 0.15 0.13 0.98 0.56 0.18 0.19 0.15 0.13 0.98 0.56 0.18 0.19 0.15 0.13 0.98 0.15 0.13 0.19 0.15 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.98 0.56 0.18 0.19 0.98 0.56 0.18 0.39 0.19 0.98 0.56 0.18 0.19 0.15 0.98 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.56 0.56 0.56 0.11 0.11

1.37 0.37 0.26 0.01 1.49 0.44 0.31 0.11 0.03 1.93 0.69 0.53 0.11 0.01 0.90 0.58 0.04 0.09 0.37 0.53 0.72 1.37 0.37 0.26 0.01 0.10 0.19 1.49 0.44 0.31 0.03 0.07 0.15 0.90 0.29 0.44 0.11 0.01 0.19 0.04 0.00 0.17 0.17 0.00 0.00 0.19 0.40 0.05 0.00 0.21 0.03 0.00 0.04 0.41 0.96 0.01 0.07

δCb

δHc

δC.calcd.d

δH.calcd.e

153.99 156.66 158.00 159.17 153.58 156.28 157.61 158.23 158.84 151.96 154.93 156.38 157.66 159.69 155.83 160.06 159.50 158.60 158.32 157.63 157.10 160.98 160.51 161.19 159.71 158.83 158.35 161.06 160.60 161.30 159.81 158.92 158.44 160.16 158.09 157.54 160.77 159.97 162.15 160.28 160.38 161.52 158.59 159.71 159.82 157.55 157.11 158.32 159.47 158.24 160.44 159.51 158.74 156.45 154.76 160.00 158.68

8.49 8.46 8.45 8.41 8.45 8.42 8.41 8.38 8.37 8.51 8.48 8.47 8.44 8.43 8.49 8.33 8.35 8.42 8.51 8.49 8.55 8.32 8.36 8.40 8.40 8.47 8.53 8.27 8.38 8.40 8.38 8.46 8.52 8.33 8.49 8.55 8.39 8.48 8.38 8.44 8.44 8.40 8.43 8.41 8.39 8.46 8.46 8.44 8.45 8.39 8.36 8.35 8.45 8.43 8.57 8.40 8.54

153.89 156.88 157.85 159.22 153.60 156.62 157.60 158.10 158.98 152.58 155.72 156.72 158.19 160.10 155.14 160.16 159.41 158.40 158.02 157.36 156.65 160.94 160.47 161.34 159.71 158.88 158.24 161.02 160.58 161.46 159.85 159.06 158.42 160.55 158.09 157.41 160.33 159.61 161.38 160.95 160.39 161.55 158.49 159.86 160.01 158.10 157.39 158.86 159.57 158.25 160.29 159.79 158.88 156.73 154.90 160.23 158.70

8.51 8.48 8.47 8.44 8.52 8.48 8.48 8.46 8.45 8.54 8.50 8.50 8.47 8.44 8.48 8.32 8.39 8.45 8.49 8.50 8.52 8.30 8.36 8.38 8.42 8.48 8.49 8.29 8.36 8.37 8.42 8.47 8.49 8.31 8.49 8.50 8.41 8.46 8.40 8.40 8.41 8.39 8.46 8.44 8.43 8.48 8.49 8.46 8.45 8.47 8.43 8.44 8.43 8.48 8.52 8.43 8.48

522

(Continues)



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Substituent effects on the 13C NMR and the 1H NMR chemical shifts

Table 1. (Continued) Number 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113

2a

X

Y

σF (X)a

σF (Y)a

σR (X)a

σR (Y)a

Δσ

m-Me p-CN p-CF3 p-F p-Cl p-Me p-NO2 H p-NMe2 p-OMe p-NO2 p-NO2 p-NO2 p-NO2 p-NO2 p-NO2 p-NO2 p-CN p-CN p-CN p-CN p-CN p-CN p-CN p-F p-F p-F p-F p-F p-F p-F p-Cl p-Cl p-Cl p-Cl p-Cl p-Cl p-Cl H H H H H H p-Me p-Me p-Me p-Me p-Me p-Me p-Me p-OMe p-OMe p-OMe p-OMe p-OMe

p-COOEt p-COOEt p-COOEt p-COOEt p-COOEt p-COOEt p-COOEt p-COOEt p-COOEt p-COOEt p-CN p-F p-Cl H p-Me p-OMe p-NMe2 p-CN p-F p-Cl H p-Me p-OMe p-NMe2 p-CN p-F p-Cl H p-Me p-OMe p-NMe2 p-CN p-F p-Cl H p-Me p-OMe p-NMe2 p-F p-Cl H Me p-OMe p-NMe2 p-CN p-F p-Cl H p-Me p-OMe p-NMe2 p-CN p-F p-Cl H p-Me

0.07 0.51 0.38 0.45 0.42 0.01 0.65 0.00 0.15 0.29 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.51 0.51 0.51 0.51 0.51 0.51 0.51 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.29 0.29 0.29 0.29 0.29

0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.51 0.45 0.42 0.00 0.01 0.29 0.15 0.51 0.45 0.42 0.00 0.01 0.29 0.15 0.51 0.45 0.42 0.00 0.01 0.29 0.15 0.51 0.45 0.42 0.00 0.01 0.29 0.15 0.45 0.42 0.00 0.01 0.29 0.15 0.51 0.45 0.42 0.00 0.01 0.29 0.15 0.51 0.45 0.42 0.00 0.01

0.00 0.15 0.16 0.39 0.19 0.18 0.13 0.00 0.98 0.56 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.19 0.19 0.19 0.19 0.19 0.19 0.19 0.00 0.00 0.00 0.00 0.00 0.00 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.56 0.56 0.56 0.56 0.56

0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.15 0.39 0.19 0.00 0.18 0.56 0.98 0.15 0.39 0.19 0.00 0.18 0.56 0.98 0.15 0.39 0.19 0.00 0.18 0.56 0.98 0.15 0.39 0.19 0.00 0.18 0.56 0.98 0.39 0.19 0.00 0.18 0.56 0.98 0.15 0.39 0.19 0.00 0.18 0.56 0.98 0.15 0.39 0.19 0.00 0.18

0.27 0.04 0.01 0.15 0.05 0.38 0.11 0.20 1.64 0.52 0.01 0.52 0.30 0.61 0.90 1.10 2.59 0.00 0.36 0.18 0.44 0.69 0.86 2.22 0.36 0.00 0.03 0.00 0.05 0.11 0.79 0.18 0.03 0.00 0.05 0.16 0.25 1.12 0.00 0.05 0.00 0.03 0.07 0.69 0.69 0.05 0.16 0.03 0.00 0.01 0.44 0.86 0.11 0.25 0.07 0.01

δCb

δHc

δC.calcd.d

δH.calcd.e

161.92 159.33 159.93 160.05 160.11 161.56 158.86 161.67 161.30 160.84 159.75 156.96 157.64 157.33 156.32 154.76 151.51 160.21 157.48 158.14 157.82 156.85 155.35 152.22 160.82 158.57 159.11 158.76 158.00 156.81 154.37 160.90 158.52 159.11 158.74 157.94 156.68 154.07 160.16 160.71 160.34 159.59 158.41 155.97 162.29 160.15 160.67 160.30 159.58 158.46 156.15 161.54 159.49 159.99 159.64 158.94

8.41 8.50 8.50 8.41 8.41 8.40 8.55 8.44 8.30 8.36 8.52 8.56 8.54 8.56 8.56 8.48 8.60 8.46 8.49 8.48 8.50 8.51 8.52 8.55 8.37 8.41 8.39 8.42 8.42 8.44 8.48 8.37 8.41 8.40 8.41 8.42 8.44 8.47 8.46 8.43 8.45 8.47 8.48 8.52 8.36 8.40 8.38 8.42 8.43 8.44 8.48 8.33 8.40 8.35 8.38 8.39

162.00 159.43 160.01 160.23 160.20 161.78 158.80 161.73 161.28 160.89 159.56 156.57 157.54 156.94 155.95 154.93 151.64 160.16 157.26 158.20 157.63 156.67 155.67 152.46 160.80 158.34 159.16 158.76 157.93 156.99 154.20 160.82 158.23 159.08 158.64 157.77 156.82 153.91 159.88 160.68 160.30 159.48 158.55 155.80 162.29 160.00 160.77 160.44 159.65 158.75 156.11 161.39 159.16 159.91 159.61 158.85

8.38 8.47 8.45 8.40 8.42 8.37 8.48 8.39 8.29 8.36 8.47 8.51 8.50 8.51 8.52 8.53 8.56 8.46 8.49 8.48 8.50 8.51 8.51 8.55 8.38 8.42 8.41 8.42 8.44 8.44 8.48 8.40 8.44 8.43 8.45 8.46 8.46 8.50 8.41 8.40 8.42 8.43 8.43 8.47 8.36 8.39 8.38 8.40 8.41 8.41 8.45 8.34 8.38 8.37 8.38 8.40

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523

(Continues)

L. Wang, C. Cao and C. Cao

Table 1. (Continued) Number 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129

X

Y

p-OMe p-OMe p-NMe2 p-NMe2 p-NMe2 p-NMe2 p-NMe2 p-NMe2 p-NMe2 p-CF3 p-CF3 p-CF3 p-CF3 p-CF3 p-CF3 p-CF3

p-OMe p-NMe2 p-CN p-F p-Cl H p-Me p-OMe p-NMe2 p-CN p-F p-Cl H p-Me p-OMe p-NMe2

2a

σF (X)a

σF (Y)a

σR (X)a

σR (Y)a

Δσ

0.29 0.29 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.38 0.38 0.38 0.38 0.38 0.38 0.38

0.29 0.15 0.51 0.45 0.42 0.00 0.01 0.29 0.15 0.51 0.45 0.42 0.00 0.01 0.29 0.15

0.56 0.56 0.98 0.98 0.98 0.98 0.98 0.98 0.98 0.16 0.16 0.16 0.16 0.16 0.16 0.16

0.56 0.98 0.15 0.39 0.19 0.00 0.18 0.56 0.98 0.15 0.39 0.19 0.00 0.18 0.56 0.98

0.00 0.31 2.22 0.79 1.12 0.69 0.44 0.31 0.00 0.01 0.23 0.10 0.29 0.50 0.66 1.88

2

δCb

δHc

δC.calcd.d

δH.calcd.e

157.88 155.69 161.86 160.08 160.51 160.21 159.57 158.65 156.73 160.76 158.22 158.85 158.51 157.62 156.24 153.39

8.43 8.44 8.26 8.30 8.29 8.32 8.33 8.34 8.37 8.46 8.50 8.49 8.51 8.52 8.54 8.56

157.95 155.39 161.63 159.82 160.46 160.31 159.66 158.84 156.66 160.71 157.89 158.81 158.28 157.35 156.35 153.23

8.40 8.44 8.28 8.31 8.30 8.32 8.33 8.33 8.37 8.44 8.48 8.47 8.48 8.49 8.50 8.53

2

The values of parameters were taken from Hansch et al.;[18] Δσ = (σX σY) . δC is the δC(CH¼N). The δC(CH¼N) of numbers 1–52 were measured in this work; the δC(CH¼N) of numbers 53–67 were taken from our previous work;[17] the δC(CH¼N) of 68–129 were taken from Neuvonen et al.[7] c δH is the δH(CH¼N).The δH(CH¼N) of numbers 1–52 were measured in this work; the δH(CH¼N) of numbers 53–67 were taken from our previous work;[17] the δH(CH¼N) of 68–129 were taken from our unpublished work (the master’s dissertation of B. Lu).[19] d δC.calcd. is the δC(CH¼N) values calculated in Eqn (4). e δH.calcd. is the δΗ(CH¼N) values calculated in Eqn (5). a

b

Table 2. The correlation equations between the δH(CH¼N) values and the substituent effect constants for compounds XBAYs

δH(CH = N) = 8.42 + 0.12σ(X) 0.06σ(Y) 2 R = 0.8811, R = 0.7764, S = 0.03, F = 218.77, n = 129 δH(CH = N) = 8.44 + 0.09σ F(X) 0.07σ F(Y) + 0.14σ R(X) 0.06σ R(Y) 2 R = 0.8879, R = 0.7884, S = 0.03, F = 115.53, n = 129 δH(CH = N) = 8.43 + 0.08σ F(X) 0.07σ F(Y) + 2 0.14σ R(X) 0.05σ R(Y) + 0.008Δσ 2 R = 0.8895, R = 0.7913, S = 0.03, F = 93.25, n = 129

Eqn (5) Eqn (6)

larger than the σ of X, while to the change of δH(CH¼N), the σ of X is much more than the σ of Y. On the other hand, the plots of the δC(CH¼N) and δH(CH¼N) values calculated by Eqns ((4) and (5)), respectively, versus the corresponding experimental ones were made, shown as in Figs 2 and 3 (all the values were listed in Table 1). As seen from the figures, good relevance in Fig. 2 was presented, and relatively poor relevance in Fig. 3 could be accepted because the range of the experimental δH(CH¼N) values is only 0.34 ppm.

Eqn (7)

XBAYs, XPhCH¼NPhYs.

Table 3. The relative and fraction contribution (ψγ and ψf) of parameters to the δC(CH¼N) and δH(CH¼N) of XBAYs σ(X)

Parameter

Eqn (4) Eqn (7)

ψγ ψf (%) ψγ ψf (%)

2

σ(Y)

Δσ

σF (X)

σR (X)

σF (Y)

σR (Y)

1.4997 40.33 0.0274 33.82

0.1736 4.67 0.0182 22.45

0.7975 21.45 0.0219 27.02

0.9623 25.88 0.0104 12.83

0.2398 6.45 0.0031 3.88

524

One can observe in Table 3 that the contributions of parameters to the changes of δC(CH¼N) and δH(CH¼N) are very different. σR(X) contributes more to δH(CH¼N) than δC(CH¼N), while σR(Y) and Δσ2 contribute more to δC(CH¼N) than δH(CH¼N). On the whole, for the contributions to the change of δC(CH¼N), the σ of Y is somewhat


Figure 2. The plot of the δC(CH¼N) values calculated in Eqn (4) versus the experimental δC(CH¼N) values of title compounds.

Figure 3. The plot of the δH(CH¼N) values calculated in Eqn (5) versus the experimental δH(CH¼N) values of title compounds.


Magn. Reson. Chem. 2015, 53, 520–525

Substituent effects on the 13C NMR and the 1H NMR chemical shifts

Conclusions

References

In contrast to empirical prediction, there is no distinctive linear relationship between the δH(CH¼N) and δC(CH¼N) of title compounds. Equations (4 and 5) show that the δC(CH¼N) and δH(CH¼N) are dominated by different substituent effects. As seen in Eqn (4), the σF and σR of X group decrease the δC(CH¼N), while the σF and σR of Y group increase the δC(CH¼N). However, the effects of X and Y groups on the δH(CH¼N) have opposite behaviors [Eqn (5)]. In addition, the result shows that the effect of substituent specific cross-interaction effects between X and Y (Δσ2) on the δH(CH¼N) is negligible, while it is indispensable on the δC(CH¼N). Finally, the contributions of parameters to the change of δC(CH¼N) and δH(CH¼N) are different, for the change of δH(CH¼N), the contribution of σ(X) is much larger than that of σ(Y); while for the change of δC(CH¼N), the contribution of σ(Y) is somewhat larger than that of σ(X). Why substituents X and Y present the different effects on the δH (CH¼N) and δC(CH¼N) of title compounds is still an interesting topic and need to be further investigated deeply.

[1] T. Donaldson, P. A. Henderson, M. F. Achard, C. T. Imrie. Liq. Cryst. 2011, 38, 1331–1339. [2] L. Callau, M. Giamberini, J. A. Reina, A. Mantecón. J. Polym. Sci. Pol. Chem. 2006, 44, 1877–1889. [3] T. Kawamoto, M. Nishiwaki, Y. Tsunekawa, K. Nozaki, T. Konno. Inorg. Chem. 2008, 47, 3095–3104. [4] P. Novak, Z. Meić, D. Vikić-Topić, V. Smrečki, J. Plavec. Spectrochim. Acta A. 1998, 54, 327–333. [5] V. Koleva, T. Dudev, I. Wawer. J. Mol. Struct. 1997, 412, 153–159. [6] G. Odian, N. I. Yang, Y. Wei. Magn. Reson. Chem. 1985, 23, 908–915. [7] H. Neuvonen, K. Neuvonen, F. Fülöp. J. Org. Chem. 2006, 71, 3141–3148. [8] A. Kawasaki. J. Chem. Soc. Perk. T. 2. 1990, 223–228. [9] G. F. Chen, C. Z. Cao, B. T. Lu, B. Sheng. J. Phys. Org. Chem. 2012, 25, 327–333. [10] Z. J. Fang, C. Z. Cao, G. F. Chen. J. Phys. Org. Chem. 2012, 25, 1343–1350. [11] Z. J. Fang, C. Z. Cao, W. H. Wu, L. Wang. J. Phys. Org. Chem. 2013, 26, 249–255. [12] S. T. Lin, C. C. Lee, D. W. Liang. Tetrahedron 2000, 56, 9619–9623. [13] K. Matsumoto, H. Katsura, T. Uchida, K. Aoyama, T. Machiguchi. Heterocycles. 1997, 45, 2443–2448. [14] A. Echevarria, J. Miller, M. G. Nascimento. Magn. Reson. in Chem. 1985, 23, 809–813. [15] A. Cherkasov, M. Jonsson. J. Chem. Inf. Comp. Sci. 1999, 39, 1057–1063. [16] H. Neuvonen, K. Neuvonen, A. Koch, E. Kleinpeter. J. Mol. StrucTheochem. 2007, 815, 95–104. [17] C. Z. Cao, B. T. Lu, G. F. Chen. J. Phys. Org. Chem. 2011, 24, 335–341. [18] C. Hansch, A. Leo, R. W. Taft. Chem. Rev. 1991, 91, 165–195. [19] B. T. Lu. Master dissertation. Hunan, Hunan University of Science and Technology, 2011. [20] D. E. Needham, I. C. Wei, P. G. Seybold. J. Am. Chem. Soc. 1988, 110, 4186–4194. [21] F. P. Liu, Y. Z. Liang, C. Z. Cao, N. Zhou. Anal. Chim. Acta 2007, 594, 279–289. [22] J. Schmeyers, F. Toda, J. Boy, G. Kaupp. J. Chem. Soc., Perk. T. 2. 1998, 989–994.

Dataset The substituted benzylideneanilines were all synthesized with the solvent-free method according to Scheme 1.[17,22] They were purified with anhydrous alcohol and were confirmed with 1H NMR and 13C NMR. The NMR spectra were recorded with Bruker AV 500 MHz in CDCl3 at room temperature at an approximate concentration. The NMR chemical shifts are expressed in parts per million relative to TMS (0.00 ppm), which is used as an internal reference. The detailed data of the synthesized compounds are available in the Supporting Information. Acknowledgements

Supporting information

The project was supported by the National Natural Science Foundation of China (no. 21272063), the Scientific Research Fund of Hunan Provincial Education Department (no. 14C0466) and the Natural Science Foundation of Hunan (no. 14JJ3112).

Additional supporting information may be found in the online version of this article at the publisher’s web-site.

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