Comparison of the 13C (C=N) chemical shifts of substituted N-(phenyl-ethylene)-anilines and substituted N-(benzylidene)-anilines

Article abstract of DOI:10.1002/poc.3450

Comparison of ¹³C NMR of C=N bond chemical shifts δ_C(C=N) in substituted N-(phenyl-ethylene)-anilines XArC(Me)=NArY (XPEAYs) with that in substituted N-(benzylidene)-anilines XArCH=NArY (XBAYs) was carried out. The δ_C(C=N)

Full text of DOI:10.1002/poc.3450

Research article
Received: 17 November 2014,
Revised: 17 January 2015,
Accepted: 23 March 2015,
Published online in Wiley Online Library: 25 May 2015
(wileyonlinelibrary.com) DOI: 10.1002/poc.3450
13
Comparison of the C (C=N) chemical shifts of
substituted N-(phenyl-ethylene)-anilines and
substituted N-(benzylidene)-anilines
Zhongzhong Caoa,b, Chaotun Caoa,b and Chenzhong Caoa,b*
Comparison of 13C NMR of C = N bond chemical shifts δC(C = N) in substituted N-(phenyl-ethylene)-anilines XArC(Me) = NArY
(XPEAYs) with that in substituted N-(benzylidene)-anilines XArCH = NArY (XBAYs) was carried out. The δC(C= N) of 61 samples
of XPEAYs were measured, and the substituent effect on their δC(C= N) were investigated. The results show the factors affecting
the δC(C= N) of XPEAYs are quite different from that of XBAYs. A penta-parameter correlation equation was obtained for the 61
compounds, which has correlation coefficient 0.9922 and standard error 0.12 ppm. The result indicates that, in XPEAYs, the
inductive effects of substituents X and Y are major factors affecting the δC(C= N), while the conjugative effect of them have very
little effect on the δC(C= N) and can be ignored. The substituent-specific cross-interaction effects between X and Y and between
Me of C = N bond and substituent Y are important factors affecting the δC(C= N). Also, the excited-state substituent parameter of
substitute Y has certain contribution to the δC(C= N). Copyright © 2015 John Wiley & Sons, Ltd.
Keywords: 13C NMR chemical shifts; excited-state substituent parameter; inductive effect of substituent; N-(phenyl-ethylene)-anilines;
substituent specific cross-interaction effect
and Y to quantify the δC(C = N). The obtained equation has good
predictability. Basing on the previous research, we come up with
INTRODUCTION
another series of compounds, substituted N-(phenyl-ethylene)-
anilines XArC(Me) = NArY (abbreviated XPEAYs), whose mole-
cular structure is similar to the XBAYs. In XPEAYs, a group Me
replaces the atom H in CH = N of XBAYs, and results in more
complicated cross-interactions of the substituted groups. For
the compounds XBAYs, there are four situations[18] of interac-
tions among the substituents X and Y, while in the XPEAYs, Me
is an EDG and will act with X and Y through the conjugate chain,
respectively. It is a very attractive topic whether the change reg-
ularity of the δC(C = N) in XPEAYs is as the same as that in XBAYs
or not. Therefore, we investigated the aforementioned topic and
obtained meaningful results in this work.
The substituted anilines XArCR = NArY have been attracted wide-
spread attention because of its special nonlinear optical proper-
ties.[1–10] Their molecules have a π-electron conjugate system
carrying a group at one end and another group at the opposite
end, so their optical and electrical properties are more suscep-
tible to subtle changes of the molecular structures. Therefore, it
is a meaningful work to probe the substituent effect on its regu-
larity of molecular internal charge distribution for understanding
and predicting the physicochemical property of this kind of com-
pounds.[10–17] The NMR spectra are often used for investiga-
ting[5–7] the substituent effect on its regularity of molecular
internal charge distribution by measuring the chemical shifts of
the atom in molecular specific position.
Neuvonen[3–12] has investigated the substituent effects on the
electronic characteristic of the C = N bridging group in
substituted N-(benzylidene)-anilines XArCH = NArY (abbreviated
XBAYs) with the 13C NMR chemical shifts δC(C = N) of C = N bond
and obtained the valuable results: (1) for the X-substituents:
electron-withdrawing group (EWG) cause shielding, while
electron-donating group (EDG) behave oppositely; (2) in con-
trast, for the Y-substituents: EWG cause deshielding, while EDG
cause shielding of the C = N bond. Neuvonen[9,10] pointed out:
‘the presence of the specific cross-interaction between X and Y
could be verified’, but this specific cross-interaction effect was
not be quantified at that time. Recently, Cao[18–20] et al. deve-
loped Neuvonen’s research by exploring the other properties
of XBAYs and proposed the parameter Δσ2 to measure the
substituent-specific cross-interaction effect between substitu-
ents X and Y. Here, Δσ2 = [σx ꢀ σy]2 = {[σF(X) + σR(X)]-[σF(Y) + σR
(Y)]}2. They combined the electronic effects of substituents X
and Y with the substituent specific cross-interaction between X
EXPERIMENTAL SECTIONS
Materials prepared
The target compounds were synthesized by heating reflux method.[21–24]
The substituted actophenone (10 mmol) and the substituted aniline
(11 mmol) were mixed in a 50 ml round-bottom flask with 5 ml toluene
* Correspondence to: C. Cao, School of Chemistry and Chemical Engineering,
Hunan University of Science and Technology, Xiangtan, 411201, China.
E-mail: czcao@hnust.edu.cn
a Z. Cao, C. Cao, C. Cao
School of Chemistry and Chemical Engineering, Hunan University of Science
and Technology, Xiangtan, 411201, China
b Z. Cao, C. Cao, C. Cao
Key Laboratory of Theoretical Organic Chemistry and Function Molecule,
Ministry of Education, Hunan University of Science and Technology, Xiangtan,
411201, China
J. Phys. Org. Chem. 2015, 28 564–569
Copyright © 2015 John Wiley & Sons, Ltd.

Comparison of the 13C (C = N) Chemical Shifts of XArC(Me) = NArY and XArCH = NArY
added. Then the mixture was heated at 140° Celsius for 10 h, cooled to
room temperature, and purified by recrystallization or column chroma-
tography. The obtained products were characterized by NMR.
compounds with the same pairs of substituents X and Y were
employed. It was surprising that there is no linear relationship
of the δC(C = N) values of XBAYs versus that of XPEAYs.
Based on Fig. 1 and Eqn (2), we try to add the excited-state
substituent parameters σ of X and Y[26] into Eqn (2); then Eqn
ex
Spectroscopic measurement
cc
ex
cc
ex
cc
(3) was obtained by adding σ (X) and σ (Y).
The products were vacuum dried for a whole day before measurements.
The NMR spectra of compounds XPEAYs in Table 1 were recorded in
CDCl3 at 293 K. The 13C NMR chemical shifts are expressed in ppm rela-
tive to CDCl3 (77.00 ppm) at 126 MHz, and the 1H NMR chemical shifts
are expressed in ppm relative to TMS (0.00 ppm) at 500 MHz. All samples to
be measured were made up at an appropriate concentration (32 mg/ml CDCl3).
The 1H NMR and 13C NMR spectral date and spectrum are given in the
Supporting Information.
δCðC ¼ NÞ ¼ 165:43 – 2:80σFðXÞ þ 2:06σFðYÞ þ 0:04σRðXÞ
þ0:19σRðYÞ–0:25Δσ2–0:09σeccxðXÞ þ 0:38σcecxðYÞ
R ¼ 0:9907; R2 ¼ 0:9814; S ¼ 0:13; n ¼ 61; F ¼ 399:44 (3)
It was observed that Eqn (3) has better correlation than Eqn (2);
the standard error was 0.13 ppm, which is within the experimental
uncertainties. It indicates that the excited-state substituent para-
meter of substituents X and Y play a role of affecting the δC(C = N)
of XPEAYs. In addition, there is a group Me attached to the C = N
bond in XPEAYs. Because the C = N bond is a polar double bond,
the electronegativity of N atom is bigger than that of C atom; the
π-electron flow from C to N. Maybe the electron-donating group
Me affects the δC(C = N) by means of the substituent specific cross-
interaction effect between Me and Y. So we further put this item,
namely χ2 =[σP(Me)ꢀσ(Y)]2 =[ꢀ0.17ꢀσ(Y)]2 into Eqn 3 and then
obtained Eqn (4).
It is known that the concentration of a compound will influence its
13C NMR chemical shifts. In order to investigate this effect, we choose
p-O2NPEAMe-p as an example to measure its δC(C = N) at a gradient
concentration of 30, 35, and 50 mg/ml in the solvent of CDCl3. The
δC(C = N) are 163.57, 163.59, and 163.57 ppm, respectively, which are all
close to the value 163.54 ppm measured at concentration of 32 mg/ml in
CDCl3. It is to say that a small change of the concentration has unobvious
effect on the δC(C = N) values for the target compounds XPEAYs.
In addition, different values of δC(C = N) for a compound will be ob-
tained in a variety of solvent. Thus, we choose some XPEAYs as model
compounds (e.g., HPEACN-m, HPEAMeO-p, p-F3CPEAMeO-p, p-O2NPEAH)
to measure their δC(C = N) in the solvent DMSO-d6. The obtained δC(C = N)
values are 166.88, 164.96, 164.16, and 164.12 ppm, respectively, which
matches the variation trend of δC(C = N) measured in CDCl3.
δCðC ¼ NÞ ¼ 165:43– 2:76σFðXÞ þ 1:74σFðYÞ þ 0:08σRðXÞ
ꢀ0:01σRðYÞ ꢀ 0:34Δσ2 ꢀ 0:1σecxcðXÞ þ 0:48σcexcðYÞ
þ0:42χ2
METHODS AND DISCUSSION
Cao[18] proposed Eqn (1) to correlate the δC(C = N) of XBAYs, in
R ¼ 0:9931; R2 ¼ 0:9862; S ¼ 0:11; n ¼ 61; F ¼ 466:69 (4)
which the standard error is only 0.17 ppm.
δCðC ¼ NÞ ¼ 160:25 ꢀ 4:18σFðXÞ þ 3:24σFðYÞ ꢀ 1:15σRðXÞ
þ4:67σRðYÞ –0:59Δσ2
The result of Eqn (4) has better improvement than Eqn (3), and
its standard error is down to 0.11 ppm. What we also want to
know if there is substituent specific cross-interaction effect
between Me and substituent X. Thus, we added a corresponding
item, ω2 = [σP(Me)ꢀσ(X)]2, into Eqn (3) and carried out a regres-
sion analysis. The obtained result shows that the effect of ω2
on the δC(C = N) is very little and can be ignored.
R ¼ 0:9975; R2 ¼ 0:9950; S ¼ 0:17; n ¼ 80; F ¼ 2937:31 (1)
Where σF(X) and σF(Y) are the inductive parameters of substit-
uents X and Y, σR(X), and σR(Y) are the conjugative parameters of
X and Y, respectively, Δσ2 is the substituent specific cross-
interaction effect between substituents X and Y.
In order to compare with the compounds XBAYs, here, 61
samples of XPEAYs were synthesized; their 13C NMR of C = N
bonds chemical shifts were measured, which were listed in
Table 1. Firstly, the variants of Eqn (1) were employed to quantify
the δC(C = N) of XPEAYs. Thus, the experimental values of the
δC(C = N) of XPEAYs in Table 1 were regressed against the five
parameters σF(X), σF(Y), σR(X), σR(Y), and Δσ2 according to Eqn (1),
and Eqn (2) was obtained.
By analyzing the t-values (Table 2) of the coefficients of Eqn (4),
we can see that the contributions of items σR(X), σR(Y), and σeccx(X)
are relatively small. Thus, we remove these three items, that is,
2
2
ex
cc
using the five items σF(X), σF(Y), Δσ , σ (Y), and χ to carry out
regression analysis again. Equation (5) was obtained.
δCðC ¼ NÞ ¼ 165:41– 2:67σFðXÞ þ 1:77σFðYÞ ꢀ 0:29Δσ2
ex
þ0:50σ ðYÞ þ 0:39χ2
cc
R ¼ 0:9922; R2 ¼ 0:9844; S ¼ 0:12; n ¼ 61; F ¼ 692:06 (5)
δCðC ¼ NÞ ¼ 165:47 – 2:71σFðXÞ þ 2:19σFðYÞ þ 0:26σRðXÞ
þ0:60σRðYÞ ꢀ 0:42Δσ2
It can be seen that the results of Eqn (5) rival to that of Eqn (4),
in spite of the three parameters, were reduced in the former.
Equation (5) shows that there are five main factors affecting
the δC(C = N) of XPEAYs, which include both inductive effects of
substituents X and Y (σF(X) and σF(Y)), the excited-state substitu-
R ¼ 0:9784; R2 ¼ 0:9573; S ¼ 0:20; n ¼ 61; F ¼ 246:90 (2)
ex
ent parameter of Y (σ (Y)), the two substituent specific cross-
Equation (2) has also good correlation, because the molecular
structure of XPEAYs has certain similarity with that of XBAYs. Its
standard error 0.20 ppm is larger than that of Eqn (1)[18]; maybe
there are some others factors affecting the δC(C = N) of XPEAYs.
To seek out this difference, we plot the experimental δC(C = N)
of XBAYs against that of corresponding XPEAYs (e.g., p-MeBAF-p
versus p-MePEAF-p), and obtained Fig. 1, in which 45 couples of
cc
interaction effects between X and Y (Δσ2) and between Me and Y
(χ2). The factors affecting the δC(C= N) of XPEAYs are quite diffe-
rent from that of XBAYs. Hence, we recommended Eqn (5) to quan-
tify the δC(C= N) of XPEAYs. The values calculated by Eqn (5) were
listed in the last column of Table 1. Figure 2 is the plot of calculated
values of δC(C= N) versus the experimental ones.
J. Phys. Org. Chem. 2015, 28 564–569
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

Z. CAO, C. CAO AND C. CAO
ex
Table 1. The values of δC(C = N),σF, σR, σeccx (X), and σ (Y) for the XArC(Me) = NArY (δ(CDCl3) = 77.00 ppm)
cc
σF(X) a
σF(Y)a
σR(X)a
σR(Y)a
σ
(X)b
σ
(Y)b
δC(C = N)exp.
δC(C = N)cal.
c
d
ex
cc
ex
cc
No.
X
Y
1
2
3
4
5
6
7
8
p-OMe
p-OMe
p-OMe
p-OMe
p-OMe
p-OMe
p-OMe
p-Me
p-Me
p-Me
p-Me
p-Me
p-Me
p-Me
H
H
H
H
p-Cl
p-Cl
p-Cl
p-Cl
p-Cl
p-NMe2
p-OMe
p-Me
H
p-Cl
p-F
p-CN
p-NMe2
p-OMe
p-Me
H
p-Cl
p-F
p-CN
p-OMe
H
p-Cl
p-F
p-NMe2
p-OMe
p-Me
H
0.29
0.29
0.29
0.29
0.29
0.29
0.29
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0
0.15
0.29
0.01
0
0.42
0.45
0.51
0.15
0.29
0.01
0
0.42
0.45
0.51
0.29
0
0.42
0.45
0.15
0.29
0.01
0
0.42
0.45
0.51
0.15
0.29
0.01
0
0.42
0.45
0.51
0.15
0.29
0.01
0
0.42
0.45
0.15
0.29
0.01
0
ꢀ0.56
ꢀ0.56
ꢀ0.56
ꢀ0.56
ꢀ0.56
ꢀ0.56
ꢀ0.56
ꢀ0.18
ꢀ0.18
ꢀ0.18
ꢀ0.18
ꢀ0.18
ꢀ0.18
ꢀ0.18
0
ꢀ0.98
ꢀ0.56
ꢀ0.18
0
ꢀ0.19
ꢀ0.39
0.15
ꢀ0.98
ꢀ0.56
ꢀ0.18
0
ꢀ0.19
ꢀ0.39
0.15
ꢀ0.50
ꢀ0.50
ꢀ0.50
ꢀ0.50
ꢀ0.50
ꢀ0.50
ꢀ0.50
ꢀ0.17
ꢀ0.17
ꢀ0.17
ꢀ0.17
ꢀ0.17
ꢀ0.17
ꢀ0.17
0
ꢀ1.81
ꢀ0.50
ꢀ0.17
0
164.15
165.09
164.56
164.51
165.26
165.36
165.14
164.84
165.57
165.31
165.25
166.04
166.13
165.92
165.75
165.53
166.26
166.33
163.52
164.45
164.25
164.26
165.02
165.08
165.02
163.64
164.40
164.07
164.15
164.90
164.97
164.85
163.39
164.42
164.28
164.36
165.05
165.08
162.21
163.58
163.54
163.67
164.38
164.37
164.51
166.59
164.36
164.16
165.01
165.03
164.02
163.94
163.42
164.97
164.84
164.40
166.77
164.07
164.90
164.56
164.62
165.25
165.45
165.20
164.78
165.64
165.31
165.38
166.03
166.21
166.00
165.65
165.42
166.09
166.25
163.49
164.48
164.17
164.28
164.98
165.12
165.05
163.50
164.44
164.12
164.21
164.89
165.05
164.92
163.37
164.47
164.18
164.32
165.06
165.17
162.45
163.62
163.34
163.50
164.28
164.37
164.49
166.42
164.61
164.30
165.26
165.24
164.10
164.05
163.27
164.91
164.84
164.15
166.72
ꢀ0.22
0.06
ꢀ0.70
ꢀ1.81
ꢀ0.50
ꢀ0.17
0
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
ꢀ0.22
0.06
ꢀ0.70
ꢀ0.50
0
ꢀ0.56
0
0
0
0
0
0
0
0
0
0
ꢀ0.19
ꢀ0.39
ꢀ0.98
ꢀ0.56
ꢀ0.18
0
ꢀ0.19
ꢀ0.39
0.15
ꢀ0.98
ꢀ0.56
ꢀ0.18
0
ꢀ0.19
ꢀ0.39
0.15
ꢀ0.98
ꢀ0.56
ꢀ0.18
0
ꢀ0.19
ꢀ0.39
ꢀ0.98
ꢀ0.56
ꢀ0.18
0
ꢀ0.19
ꢀ0.39
0.15
ꢀ0.39
ꢀ0.56
ꢀ0.18
ꢀ0.39
0
ꢀ0.22
0.06
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.38
0.38
0.38
0.38
0.38
0.38
0.65
0.65
0.65
0.65
0.65
0.65
0.65
ꢀ0.07
0.37
0.37
0.37
0.01
0.42
0.45
0.65
0.42
0.45
0.65
0.01
ꢀ0.19
ꢀ0.19
ꢀ0.19
ꢀ0.19
ꢀ0.19
ꢀ0.19
ꢀ0.19
ꢀ0.39
ꢀ0.39
ꢀ0.39
ꢀ0.39
ꢀ0.39
ꢀ0.39
ꢀ0.39
0.16
0.16
0.16
0.16
0.16
0.16
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0
0
0
0
ꢀ0.18
ꢀ0.19
ꢀ0.39
0.13
ꢀ0.19
ꢀ0.39
0.13
ꢀ0.22
ꢀ0.22
ꢀ0.22
ꢀ0.22
ꢀ0.22
ꢀ0.22
ꢀ0.22
0.06
0.06
0.06
0.06
0.06
ꢀ1.81
ꢀ0.50
ꢀ0.17
0
p-Cl
p-F
ꢀ0.22
p-Cl
p-Cl
p-F
p-F
p-F
p-F
p-F
p-F
0.06
p-CN
p-NMe2
p-OMe
p-Me
H
ꢀ0.70
ꢀ1.81
ꢀ0.50
ꢀ0.17
0
p-Cl
p-F
ꢀ0.22
0.06
0.06
0.06
p-F
p-CN
p-NMe2
p-OMe
p-Me
H
p-Cl
p-F
p-NMe2
p-OMe
p-Me
H
ꢀ0.70
ꢀ1.81
ꢀ0.50
ꢀ0.17
0
p-CF3
p-CF3
p-CF3
p-CF3
p-CF3
p-CF3
p-NO2
p-NO2
p-NO2
p-NO2
p-NO2
p-NO2
p-NO2
m-Me
m-Cl
m-Cl
m-Cl
p-Me
p-Cl
ꢀ0.12
ꢀ0.12
ꢀ0.12
ꢀ0.12
ꢀ0.12
ꢀ0.12
ꢀ1.17
ꢀ1.17
ꢀ1.17
ꢀ1.17
ꢀ1.17
ꢀ
ꢀ0.22
0.06
ꢀ1.81
ꢀ0.50
ꢀ0.17
0
p-Cl
p-F
0.42
0.45
0.51
0.45
0.29
0.01
0.45
ꢀ0.07
ꢀ0.07
ꢀ0.07
ꢀ0.07
0.34
0.34
0.34
0.56
ꢀ0.22
0.06
p-CN
p-F
p-OMe
p-Me
p-F
m-Me
m-Me
m-Me
m-Me
m-F
ꢀ1.17
ꢀ0.03
0
0
0
ꢀ0.17
ꢀ0.22
0.06
ꢀ1.17
ꢀ0.22
0.06
ꢀ0.70
0.06
ꢀ0.50
ꢀ0.17
0.06
ꢀ0.03
ꢀ0.03
ꢀ0.03
ꢀ0.03
0.02
0
0
0
0
0
0
0
p-F
p-NO2
p-Cl
p-F
p-NO2
p-Me
m-F
m-F
m-CN
0.02
0.02
0.56
ꢀ1.17
ꢀ0.18
ꢀ0.17
(continues)
wileyonlinelibrary.com/journal/poc
Copyright © 2015 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2015, 28 564–569

Comparison of the 13C (C = N) Chemical Shifts of XArC(Me) = NArY and XArCH = NArY
Table 1. (Continued)
a
c
d
σF(Y)a
σR(X)a
σR(Y)a
σ
(X)b
σ
(Y)b
δC(C = N)exp.
δC(C = N)cal.
ex
cc
ex
cc
No.
X
Y
σF(X)
58
59
60
61
H
p-F
p-Cl
p-NO2
m-CN
m-CN
m-CN
m-CN
0
0.56
0.56
0.56
0.56
0
0
0
0
0
0
0.56
0.56
0.56
0.56
167.02
165.65
165.58
165.24
166.82
165.64
165.77
165.21
0.45
0.42
0.65
ꢀ0.39
ꢀ0.19
0.13
ꢀ0.22
ꢀ0.22
ꢀ1.17
aThe values were taken from Reference.[25]
bThe values were taken from Reference.[26]
cThe values were measured by this work.
dCalculated values with Eqn (5).
Figure 2. Plot of the calculated values of δC(C = N) versus experimental
ones for XPEAYs
Figure 1. Plot of the experimental δC(C = N) of XPEAYs versus experi-
mental ones of XBAYs
Effect of substituents X and Y on the δC(C = N)
Effect of parameters in Equation (5) on the δC(C = N)
Table 3 also showed that the inductive effect of substituents X
and Y are dominant factors affecting the δC(C = N). It can be
observed from Eqn (5) that the coefficient ρF(X) of σF(X) is nega-
tive, while the coefficient ρF(Y) of σF(Y) is positive; it indicates that
For the five parameters in Eqn (5), we can investigate their relative
importance from the relative contributions (ψr) or fraction contri-
butions (ψ f) of the corresponding parameters to the δC(C= N).[27,28]
Ψγ ¼ miXi
(6)
ꢀ
ꢀ
ꢀ
ꢀ
2
Table 3. The relative and fraction contribution (ψr and ψf) of
variants σF(X), σF(Y), Δσ2, σcecx (Y), and χ2 to the δC (C = N) of
XArC(Me) = NArY in Equation (5)
R ΨγðiÞ
X
Ψf ðiÞ ¼
ꢀ
ꢀ ꢁ100%
(7)
ꢀ
ꢀ
ΨγðiÞ
i
Variant
σF(X)
σF(Y)
Δσ2
σ
(Y)
χ2
ex
cc
Where the mi and Xi are the coefficient and the average value
of the parameter in Eqn (5), and the R is the correlation coeffi-
cient of Eqn (5). The sum is over the parameters in the equation.
The contribution results for the five parameters in Eqn (5) are
shown in Table 3.
ψr
ψf (%)
0.9042
53.42
0.4746 0.0936 0.1470 0.0745
28.04 5.46 8.68 4.40
It can be observed in Table 3 that the inductive effect of
substituents of both substituents X and Y have major effect on
the δC(C = N), and the contribution of substituent X is more than
that of substituent Y; the reason may be that the distance
between X and the C atom of C = N bond is shorter than that
between Y and the C atom. The contributions of Δσ2, χ2, and
σeccx(Y) to the δC(C = N) are 5.46%, 4.40%, and 8.68%, respectively.
Although the contributions of these three items are far less than
that of the inductive effects of the substituents X and Y, they are
essential to calculate the δC(C = N) of XPEAYs accurately.
Table 4. The relative and fraction contribution (ψr and ψf) of
variants σF(X), σF(Y), σR(X), σR(Y), and Δσ2 to the δC (C = N) of
XArCH = NArY in equation (1)a
Variant
σF(X)
σF(Y)
σR(X)
σR(Y)
Δσ2
ψ
ψ
1.3306
34.39
0.9717 0.2075
25.11 5.36
1.0741 0.2616
27.76 6.76
r
f (%)
aEquation (1) was reported by Reference.[18]
Table 2. The t-stat values of parameters in Equation (4)
Δσ2
σ
(X)
σ
(Y)
χ2
4.292
ex
cc
ex
cc
Parameter
t-Stat
σF(X)
σF(Y)
σR(X)
σR(Y)
ꢀ32.99
16.82
1.135
ꢀ0.1597
ꢀ6.883
ꢀ2.189
10.13
J. Phys. Org. Chem. 2015, 28 564–569
Copyright © 2015 John Wiley & Sons, Ltd.
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Z. CAO, C. CAO AND C. CAO
Table 5. The δC(C = N) of XArCH = NArY and XArC(Me) = NArY (ppm) with some special substituents
X
Y
XPEAY
XBAYa
X
Y
XPEAY
XBAYa
p-OMe
p-NMe2
p-OMe
p-Me
H
p-Cl
p-F
p-CN
p-NMe2
p-OMe
p-Me
H
164.31
165.25
164.72
164.67
165.42
165.52
165.30
162.37
163.74
163.70
163.83
164.54
164.53
164.67
155.69
157.88
158.94
159.64
159.99
159.49
161.54
151.51
154.76
156.32
157.33
157.64
156.96
159.75
p-OMe
p-Me
p-Cl
p-NMe2
164.31
165.00
163.68
163.80
162.37
166.08
165.18
165.01
155.69
156.15
154.07
154.37
151.51
162.29
160.90
160.82
p-F
p-NO2
p-Me
p-Cl
p-CN
p-NO2
p-F
p-Cl
p-F
p-CN
aThe values of δC(C = N) were taken from Reference.[18]
XBAYs, XArCH = NArY; XPEAYs, XArC(Me) = NArY.
they have an opposite effect on the δC(C = N). The details are as
follows: For the substituents X, the EWG decreases the δC(C = N),
while EDG increases the δC(C = N). In contrast, for the substituents
Y, the EWG increases the δC(C = N), while the EDG decreases the
δC(C = N). The values of ρF(X) and ρF(Y) are ꢀ2.67 and +1.77,
respectively, and the numerical value for the ratio |ρF(X)/ρF(Y)|
is 1.51. It means that the change of the δC(C = N) is more
sensitive to the inductive effect of substituent X than to that
of substituent Y.
in XPEAYs. Maybe it is due to the effect of the Me attached to the
C = N bond on the δC(C = N). In XPEAYs, the valence-electron
cloud of C atom in the C(Me) = N bond is bounded more tightly
than that in the CH = N bond of XBAYs because of the lager elec-
tronegativity of C atom in Me versus H atom. Thus, the valence-
electron cloud in C(Me) = N is harder to depart from its C atom,
receiving the effect of substituents X,Y or the circular current of
benzene ring.
It can be seen from the Table 4. In XBAYs, the conjugative
effect of substituents X and Y are also important factors to the
δC(C = N),[18] while they have little effect on the δC(C = N) in
XPEAYs and can be ignored. The reason may be that the two
benzene rings get more serious deviation from the plane of
the C = N bond in XPEAYs than in XBAYs, so it weakens the
conjugative effect of substituents X and Y in XPEAYs.
CONCLUSION
There is no linear relationship between the δC(C = N) of XPEAYs
and XBAYs. By comparing the change of the δC(C = N) in XPEAYs
with that of in XBAYs, we get the conclusion that the effects of
the substituents X and Y on the δC(C = N) are obviously different
from each other. (1) For the XBAYs, both the inductive effect and
conjugate effect of substituents are important, while the conju-
gate effect is very little and can be ignored for the XPEAYs. (2)
The δC(C = N) of XPEAYs is also affected by the excited-state
substituent effect of Y, however, that was not observed in XBAYs.
(3) The δC(C = N) of XPEAYs are not only affected by the
substituent-specific cross-interaction between X and Y but also
affected by the substituent-specific cross-interaction effect
between Me and Y. (4) Because there is a Me group attached
to the C = N bond, the substituents effects of substitutents X
and Y on the δC(C = N) are weakened. Thus, the gap between
the biggest value of δC(C = N) and the smallest one in XPEAYs
is less than the gap in corresponding XBAYs.
Effect of the Me attached to C = N bond on the δC(C = N)
As we know in previous research[18] that the main factors affecting
the δC(C= N) in XBAYs are inductive and conjugative effects of
substituents, the substituent specific cross-interaction between
substituents X and Y. Here, the same parameters were put into
an equation to quantify the δC(C= N) of XPEAYs; the obtained
results was not good. While the correlation of the quantitative equa-
tion has improved in case of adding the item χ2 (the substituent
specific cross-interaction effect between Me and Y). The coefficient
of χ2 is positive, it indicates that the substituent specific cross-
interaction effect between Me and Y can increase the δC(C = N).
It was observed that there are different gap of the δC(C = N)
between the biggest one and the smallest one for the two kinds
of compounds, some examples were listed in Table 5. For
instance, the biggest value of δC(C = N) in the series of molecules
p-MeOBAY is 161.54 ppm of p-MeOBACN-p, and the smallest one
is 155.69 ppm of p-MeOBANMe2-p; its gap is 5.85 ppm. While for
the corresponding series of molecules p-MeOPEAY, the biggest
one is 165.36 ppm of p-MeOPEAF-p, and the smallest one is
164.15 ppm of p-MeOPEANMe2-p; its gap is only 1.21 ppm. For
the p-O2NBAY, the gap is 8.24 ppm; while for p-O2NPEAY, the
gap is 2.30 ppm. In general, the gap in XBAYs is larger than that
Acknowledgements
The work was supported by the National Natural Science Foun-
dation of China (No. 21272063), Scientific Research Fund of
Hunan Provincial Education Department (No.14C0466) and the
Natural Science Foundation of Hunan (No. 14JJ3112).
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