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

Article abstract of DOI:10.1002/mrc.4248

Fifty-two samples of substituted benzylideneanilines XPhCH=NPhYs (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

Full text of DOI:10.1002/mrc.4248

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
13
1
C NMR with the H 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 deter-
mined 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 theoret-
ical 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
specific cross-interaction between X and Y could be verified. Al-
though they did not quantify the cross-interaction, their works
Introduction
The benzylideneanilines XPhCH¼NPhYs (abbreviated XBAYs) are a
strongly promotes the research of the substituent effects on the
δC(CH¼N) of title compounds. In our recent work,[17] the substitu-
kind of typical compounds with π conjugate system and have been
applied extensively in the fields of liquid crystal and nonlinear opti-
cal material.[1–3] In the molecule of XBAY, CH¼N is a bridge linking
two aromatic rings, in which one ring carries substituent X and an-
other 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]
ent specific cross-interaction effects was quantified with the item
Δσ2 (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 Δσ2 item to Eqn (1). σF is the induc-
tive effect; σR is the conjugative effect; Δσ2 is the substituent spe-
cific cross-interaction effect; ρ is the coefficient of corresponding
parameter.
δCðCH ¼ NÞ ¼ constant þ ρFðXÞσFðXÞ þ ρFðYÞσF ðYÞ
(1)
þ ρRðXÞ σRðXÞ þ ρRðYÞ σRðYÞ
As we know, the NMR shielding is affected by the electron den-
sity, and the field of resonance increases with the increasing elec-
tron 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 substit-
uent 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 substit-
uents; in addition, the effects of the aniline ring substituents on the
δC(CH¼N) were larger than that of the benzaldehyde ring substitu-
ents. Afterwards, the substituent effects on the δC(CH¼N) of some
title compounds were analyzed by employing several different sin-
gle 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
δCðCH ¼ NÞ ¼ constant þ ρFðXÞσFðXÞ þ ρFðYÞσFðYÞ
(2)
þ ρRðXÞσRðXÞ þ ρRðYÞσRðYÞ þ ρ
Δσ2
ðΔσ2Þ
*
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: czcao@hnust.edu.cn
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
Magn. Reson. Chem. 2015, 53, 520–525
Copyright © 2015 John Wiley & Sons, Ltd.

Substituent effects on the 13C NMR and the 1H NMR chemical shifts
1
Now that the H NMR and 13C NMR chemical shifts are all af-
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).
fected by the electron density, and it was generally believed that
the δH(CH¼N) values should increase as the δC(CH¼N) values in-
crease 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 co-
efficient 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.
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 contribu-
tions 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]
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 sub-
stituents X and Y in molecules of title compounds are of electron-
withdrawing substituents (e.g. NO2 and CN) and electron-donating
substituents (e.g. NMe2 and OMe); in addition, X and Y are of para-
substituted 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.
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).
δCðCH ¼ NÞ ¼ 160:25 ꢀ 4:68σFðXÞ þ 3:19σFðYÞ
(3)
ꢀ 0:86σRðXÞ þ 5:04σRðYÞ
R ¼ 0:9860; R2 ¼ 0:9722; S ¼ 0:37; F ¼ 1084:48; n ¼ 129
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.
δCðCH ¼ NÞ ¼ 160:30 ꢀ 4:38σFðXÞ þ 3:07σFðYÞ
(4)
ꢀ 1:11σRðXÞ þ 4:63σRðYÞ ꢀ 0:61Δσ2
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
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 contri-
butions (ψf) of the corresponding parameters to the δC(CH¼N) and
δH(CH¼N).[20,21]
Scheme 1. Title compounds used in this paper.
ψγ ¼ miXi
(8)
ꢀ
ꢀ
ꢀ
ꢀ
2
R ψγðiÞ
X
ꢀ
ꢀ
ψfðiÞ ¼
ꢁ100%
(9)
ꢀ
ꢀ
ψγðiÞ
i
The mi and Xi 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 parame-
ters of Eqns (4 and 7) are all shown in Table 3.
Figure 1. The plot of δH(CH¼N) values versus δC(CH¼N) values of title
compounds.
Magn. Reson. Chem. 2015, 53, 520–525
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc

L. Wang, C. Cao and C. Cao
Table 1. The data of δC(CH¼N) and δH(CH¼N) of 129 samples of title compounds
σF (X)a
σF (Y)a
σR (X)a
σR (Y)a
Δσ2a
δC
δH
δC.calcd.
δH.calcd.
b
c
d
e
Number
X
Y
1
m-F
p-NMe2
p-OMe
p-Me
p-Cl
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
ꢀ0.98
ꢀ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
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
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
2
m-F
3
m-F
0.00
4
m-F
0.00
5
m-Br
p-NMe2
p-OMe
p-Me
p-F
0.00
6
m-Br
0.00
7
m-Br
0.00
8
m-Br
0.00
9
m-Br
p-Cl
0.00
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
m-CN
m-CN
m-CN
m-CN
m-CN
m-OMe
p-NMe2
p-OMe
p-Cl
p-NMe2
p-OMe
p-Me
p-Cl
0.00
0.00
0.00
0.00
p-CN
0.00
p-NMe2
m-Me
m-Me
m-Me
m-Me
m-Me
m-Me
m-F
0.00
ꢀ0.98
0.00
ꢀ0.98
ꢀ0.56
ꢀ0.19
0.16
0.00
0.00
p-CF3
p-CN
p-NO2
p-NMe2
p-OMe
p-Me
p-Cl
0.00
0.15
0.00
0.13
0.00
ꢀ0.98
ꢀ0.56
ꢀ0.18
ꢀ0.19
0.15
0.00
m-F
0.00
m-F
0.00
m-F
0.00
p-CN
p-NO2
p-NMe2
p-OMe
p-Me
p-Cl
m-F
0.00
m-F
0.13
0.00
m-Br
ꢀ0.98
ꢀ0.56
ꢀ0.18
ꢀ0.19
0.15
0.00
m-Br
0.00
m-Br
0.00
m-Br
0.00
p-CN
p-NO2
p-NMe2
p-CN
p-NO2
p-Cl
m-Br
0.00
m-Br
0.13
0.00
m-OMe
m-OMe
m-OMe
m-CN
m-CN
m-CN
m-OMe
m-Me
m-F
ꢀ0.98
0.15
0.00
0.00
0.13
0.00
ꢀ0.19
0.15
0.00
p-CN
m-OMe
m-Me
m-Me
m-Me
m-F
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
m-Me
m-F
0.00
0.00
m-F
0.00
0.00
m-F
m-Br
0.00
0.00
m-CN
m-CN
m-CN
m-CN
m-Br
m-OMe
m-Me
m-F
0.00
0.00
0.00
0.00
0.00
0.00
m-CN
m-Me
m-CN
m-Br
0.00
0.00
0.00
0.00
m-Br
0.00
0.00
m-Br
0.00
0.00
m-Me
m-Cl
p-OMe
p-OMe
p-OMe
p-COOEt
p-COOEt
0.00
ꢀ0.56
ꢀ0.56
ꢀ0.56
0.11
0.00
m-NO2
m-Cl
0.00
0.00
m-NO2
0.00
0.11
(Continues)
wileyonlinelibrary.com/journal/mrc
Copyright © 2015 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2015, 53, 520–525

Substituent effects on the 13C NMR and the 1H NMR chemical shifts
Table 1. (Continued)
σF (X)a
σF (Y)a
σR (X)a
σR (Y)a
Δσ2a
δC
δH
δC.calcd.
δH.calcd.
b
c
d
e
Number
X
Y
58
m-Me
p-CN
p-CF3
p-F
p-COOEt
p-COOEt
p-COOEt
p-COOEt
p-COOEt
p-COOEt
p-COOEt
p-COOEt
p-COOEt
p-COOEt
p-CN
p-F
ꢀ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
0.11
0.11
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
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
59
60
0.16
0.11
61
ꢀ0.39
ꢀ0.19
ꢀ0.18
0.13
0.11
62
p-Cl
0.11
63
p-Me
p-NO2
H
0.11
64
0.11
65
0.00
0.11
66
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
ꢀ0.98
ꢀ0.56
0.13
0.11
67
0.11
68
0.15
69
0.13
ꢀ0.39
ꢀ0.19
0.00
70
p-Cl
0.13
71
H
0.13
72
p-Me
p-OMe
p-NMe2
p-CN
p-F
0.13
ꢀ0.18
ꢀ0.56
ꢀ0.98
0.15
73
0.13
74
0.13
75
0.15
76
0.15
ꢀ0.39
ꢀ0.19
0.00
77
p-Cl
0.15
78
H
0.15
79
p-Me
p-OMe
p-NMe2
p-CN
p-F
0.15
ꢀ0.18
ꢀ0.56
ꢀ0.98
0.15
80
0.15
81
0.15
82
ꢀ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
83
p-F
ꢀ0.39
ꢀ0.19
0.00
84
p-F
p-Cl
85
p-F
H
86
p-F
p-Me
p-OMe
p-NMe2
p-CN
p-F
ꢀ0.18
ꢀ0.56
ꢀ0.98
0.15
87
p-F
88
p-F
89
p-Cl
90
p-Cl
ꢀ0.39
ꢀ0.19
0.00
91
p-Cl
p-Cl
92
p-Cl
H
93
p-Cl
p-Me
p-OMe
p-NMe2
p-F
ꢀ0.18
ꢀ0.56
ꢀ0.98
ꢀ0.39
ꢀ0.19
0.00
94
p-Cl
95
p-Cl
96
H
97
H
p-Cl
0.00
98
H
H
0.00
99
H
Me
0.00
ꢀ0.18
ꢀ0.56
ꢀ0.98
0.15
100
101
102
103
104
105
106
107
108
109
110
111
112
113
H
p-OMe
p-NMe2
p-CN
p-F
0.00
H
0.00
p-Me
p-Me
p-Me
p-Me
p-Me
p-Me
p-Me
p-OMe
p-OMe
p-OMe
p-OMe
p-OMe
ꢀ0.18
ꢀ0.18
ꢀ0.18
ꢀ0.18
ꢀ0.18
ꢀ0.18
ꢀ0.18
ꢀ0.56
ꢀ0.56
ꢀ0.56
ꢀ0.56
ꢀ0.56
ꢀ0.39
ꢀ0.19
0.00
p-Cl
H
p-Me
p-OMe
p-NMe2
p-CN
p-F
ꢀ0.18
ꢀ0.56
ꢀ0.98
0.15
ꢀ0.39
ꢀ0.19
0.00
p-Cl
H
p-Me
ꢀ0.18
(Continues)
Magn. Reson. Chem. 2015, 53, 520–525
Copyright © 2015 John Wiley & Sons, Ltd.
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L. Wang, C. Cao and C. Cao
Table 1. (Continued)
σF (X)a
σF (Y)a
σR (X)a
σR (Y)a
Δσ2a
δC
δH
δC.calcd.
δH.calcd.
b
c
d
e
Number
X
Y
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
p-OMe
p-OMe
p-NMe2
p-NMe2
p-NMe2
p-NMe2
p-NMe2
p-NMe2
p-NMe2
p-CF3
p-OMe
p-NMe2
p-CN
p-F
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
ꢀ0.56
ꢀ0.98
0.15
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
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
ꢀ0.39
ꢀ0.19
0.00
p-Cl
H
p-Me
p-OMe
p-NMe2
p-CN
p-F
ꢀ0.18
ꢀ0.56
ꢀ0.98
0.15
p-CF3
0.16
ꢀ0.39
ꢀ0.19
0.00
p-CF3
p-Cl
0.16
p-CF3
H
0.16
p-CF3
p-Me
p-OMe
p-NMe2
0.16
ꢀ0.18
ꢀ0.56
ꢀ0.98
p-CF3
0.16
p-CF3
0.16
aThe values of parameters were taken from Hansch et al.;[18] Δσ2 = (σX ꢀ σY)2.
bδC 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]
cδH 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]
dδC.calcd. is the δC(CH¼N) values calculated in Eqn (4).
eδH.calcd. is the δΗ(CH¼N) values calculated in Eqn (5).
larger than the σ of X, while to the change of δH(CH¼N), the σ of
Table 2. The correlation equations between the δH(CH¼N) values and
X is much more than the σ of Y.
the substituent effect constants for compounds XBAYs
On the other hand, the plots of the δC(CH¼N) and δH(CH¼N)
values calculated by Eqns ((4) and (5)), respectively, versus the corre-
sponding 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.
δH(CH = N) = 8.42 + 0.12σ(X) ꢀ 0.06σ(Y)
R = 0.8811, R2 = 0.7764, S = 0.03, F = 218.77, n = 129
δH(CH = N) = 8.44 + 0.09σF(X) ꢀ 0.07σF(Y) +
0.14σR(X) ꢀ 0.06σR(Y)
Eqn (5)
Eqn (6)
R = 0.8879, R2 = 0.7884, S = 0.03, F = 115.53, n = 129
δH(CH = N) = 8.43 + 0.08σF(X) ꢀ 0.07σF(Y) +
0.14σR(X) ꢀ 0.05σR(Y) + 0.008Δσ2
Eqn (7)
R = 0.8895, R2 = 0.7913, S = 0.03, F = 93.25, n = 129
XBAYs, XPhCH¼NPhYs.
Table 3. The relative and fraction contribution (ψγ and ψf) of parame-
ters to the δC(CH¼N) and δH(CH¼N) of XBAYs
Parameter
σ(X)
σ(Y)
Δσ2
Figure 2. The plot of the δC(CH¼N) values calculated in Eqn (4) versus the
experimental δC(CH¼N) values of title compounds.
σF (X)
ꢀ1.4997
σR (X)
σF (Y)
σR (Y)
Eqn (4) ψγ
0.1736
4.67
0.7975 ꢀ0.9623 ꢀ0.2398
ψf (%) 40.33
Eqn (7) ψγ
ψf (%) 33.82
21.45
25.88
0.0104
12.83
6.45
0.0274 ꢀ0.0182 ꢀ0.0219
22.45 27.02
0.0031
3.88
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 3. The plot of the δH(CH¼N) values calculated in Eqn (5) versus the
experimental δH(CH¼N) values of title compounds.
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Copyright © 2015 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2015, 53, 520–525

Substituent effects on the 13C NMR and the 1H NMR chemical shifts
Conclusions
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the contribution of σ(Y) is somewhat larger than that of σ(X).
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Dataset
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The substituted benzylideneanilines were all synthesized with the
solvent-free method according to Scheme 1.[17,22] They were puri-
fied 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 concen-
tration. The NMR chemical shifts are expressed in parts per million
relative to TMS (0.00ppm), which is used as an internal reference.
The detailed data of the synthesized compounds are available in
the Supporting Information.
Supporting information
Acknowledgements
The project was supported by the National Natural Science Founda-
tion 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 ver-
sion of this article at the publisher’s web-site.
Magn. Reson. Chem. 2015, 53, 520–525
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc