Substituent effects on the stretching vibration of C═N in multi-substituted benzylideneanilines

Article abstract of DOI:10.1002/poc.3969

Forty-nine samples of 3,4′/4,3′/3,3′-disubstituted benzylideneanilines (XBAYs) and 52 samples of multi-substituted XBAYs were synthesized, and their infrared absorption spectra were recorded in this paper. On the basis of the stretching vibration frequencies ν_C═N of C═N bridging bond of 158 samples of substituted XBAYs (including 57 samples of 4,4′-disubstituted XBAYs from reference and 101 samples of substituted XBAYs synthesized in this paper), an extensional research of substituent effects on the ν_C═N values from 4,4′-disubstituted XBAYs to multi-substituted XBAYs was made. A modified equation for quantifying the ν_C═N values of multi-substituted XBAYs was obtained (shown as Equation (3)). Equation (3) indicates that the excited-state substituent constant of Y and the substituent specific cross-interaction effect between X and X cannot be ignored for the quantitative regression analysis of the ν_C═N values of multi-substituted XBAYs. Compared with Equation (1), Equation (3) has a wider application and more accuracy in quantifying the ν_C═N values of substituted XBAYs.

Full text of DOI:10.1002/poc.3969

Received: 22 November 2018
DOI: 10.1002/poc.3969
Revised: 30 March 2019
Accepted: 2 April 2019
R E S E A R C H A R T I C L E
Substituent effects on the stretching vibration of C═N in
multi‐substituted benzylideneanilines
Linyan Wang1,2
| Chaotun Cao3 | Chenzhong Cao3
1 School of Materials Science and
Engineering, Hunan University of Science
and Technology, Xiangtan, China
2 Hunan Provincial Key Laboratory of
Advanced Materials for New Energy
Storage and Conversion, Hunan
University of Science and Technology,
Xiangtan, China
3 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, School of
Chemistry and Chemical Engineering,
Hunan University of Science and
Technology, Xiangtan, China
Abstract
Forty‐nine samples of 3,4′/4,3′/3,3′‐disubstituted benzylideneanilines (XBAYs)
and 52 samples of multi‐substituted XBAYs were synthesized, and their infra-
red absorption spectra were recorded in this paper. On the basis of the
stretching vibration frequencies νC═N of C═N bridging bond of 158 samples
of substituted XBAYs (including 57 samples of 4,4′‐disubstituted XBAYs from
reference and 101 samples of substituted XBAYs synthesized in this paper),
an extensional research of substituent effects on the νC═N values from
4,4′‐disubstituted XBAYs to multi‐substituted XBAYs was made. A modified
equation for quantifying the νC═N values of multi‐substituted XBAYs was
obtained (shown as Equation (3)). Equation (3) indicates that the excited‐
state substituent constant of Y and the substituent specific cross‐interaction
effect between X and X cannot be ignored for the quantitative regression
analysis of the νC═N values of multi‐substituted XBAYs. Compared with
Equation (1), Equation (3) has a wider application and more accuracy in
quantifying the νC═N values of substituted XBAYs.
Correspondence
Chenzhong Cao, 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, School of
Chemistry and Chemical Engineering,
Hunan University of Science and
Technology, Xiangtan 411201, China.
Email: czcao@hnust.edu.cn
KEYWORDS
excited‐state substituent constant, multi‐substituted benzylideneanilines, stretching vibration
frequencies, substituent effects, substituent specific cross‐interaction effect
Funding information
National Natural Science Foundation of
China, Grant/Award Number: 21672058
1 | INTRODUCTION
identification and component analysis of compounds,
and it is always used to study the structure‐property
Benzylideneanilines (XBAYs) are a kind of typical com-
pounds with π conjugate system and have been applied
extensively in the fields of liquid crystal and nonlinear
optical material.[1–3] Their molecular structure‐property
relationships were explored widely in past years.[4–8]
Among the researches, infrared spectroscopy (IR) is a
very important method in the molecular structure
relationships.
In 1969, Molnar and Orchin[9] analyzed the infrared
spectra of some XBAY derivatives and related complexes.
The results showed the coordination of XBAYs to
palladium always resulted in a shift of the C═N to a
lower frequency. In 1991, Figueroa et al[10] found that a
donor group in para position of the benzylidene ring in
J Phys Org Chem. 2019;e3969.
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© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/poc.3969

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WANG ET AL.
molecule of XBAY had a significant effect on the skeletal
vibrations. And the interpretations for the vibrational
spectra of the XBAY and 4,4′‐disubstituted XBAY were
given. In 1993, Kozhevina et al[11] explored the vibra-
tional spectra of XBAY and its fluoroderivatives, and they
found that the fluorination of the aniline or benzylidene
rings did not exercise much influence on the ν(C═N) bond
position but caused a significant change in the intensity.
In 2002, Güner and Bayari[8] discussed the interpretation
of the substituent effect on the infrared data of XBAYs.
The correlation between Hammett constant σR and the
infrared data of XBAYs in which the para position of
the benzylidene ring was substituted by an electron‐
donating or electron‐withdrawing group was found, but
the Hammett relation was not obtained for the p‐aniline
ring substituent. In 2013, Sek et al[12] analyzed the influ-
ence of the chemical structure of azines and their
azomethine analogues on the IR spectra. In the IR spectra
of investigated compounds, the band characteristic for
the HC═N stretching vibration was detected in each case
in the spectral range of 1608 to 1633 cm−1. Compared
with the isolated C═N group, the band frequency is
strongly reduced by the conjugation of the C═N group
with phenyl ring because of the energy diminishing of
the C═N bond and the delocalization of nitrogen pair
into the imine double bond.
FIGURE 1 The possible modes of C═N stretching vibration
results showed that the largest contribution of the three
forms was the form (III); the next was the form (II).
In Cao et al,[13] the σp(X) and σp(Y) items were
considered to express the contribution of polar double
bond–form C═N to the change of νC═N; Δσ2 expressed
the contribution of single bond‐ion–form C+―N−; and
ex
σ
ðXÞ expressed the contribution of single bond‐
CC
diradical–form C•―N•.
Since the effects of substituents or three modes on the
νC═N of 4,4′‐disubstituted XBAYs has been studied, how
do they affect the νC═N values of 3,4′/4,3′/3,3′‐disubsti-
tuted and multi‐substituted XBAYs? To explore this
problem and study the substituent effects on the νC═N
values of substituted XBAYs more systematically, 49 sam-
ples of 3,4′/4,3′/3,3′‐disubstituted XBAYs and 52 samples
of multi‐substituted XBAYs shown in Scheme 1 were
synthesized, and the substituent effects on their νC═N
values were explored.
Given all that, the molecular structure makes a signif-
icant influence on the IR spectrum. In other words, the
change of substituents in the molecules can also affect
the IR spectra. But in previous researches, the substituent
effects on IR spectra have not been studied systematically.
Until recently, Cao et al[13] explored the substituent
effects on the stretching vibration frequencies of C═N
bridging bond (νC═N) of 4,4′‐disubstituted XBAYs system-
atically, and they obtained a quantitative equation shown
2 | RESULTS AND DISCUSSIONS
The νC═N values of 49 samples of 3,4′/4,3′/3,3′‐
disubstituted XBAYs and 52 samples of multi‐substituted
XBAYs measured in this work were collected and listed
in Table 1.
In Cao et al,[13] the parameters of σ(X), σ(Y), σ ðXÞ,
ex
CC
and Δσ2 were used to quantify the νC═N values of
as Equation (1). In Equation (1), σp(X), σp(Y), and Δσ2 are
Hammett polar constants.[14]
σ
ðXÞ is the excited‐state
4,4′‐disubstituted XBAYs (shown as Equation (1)). In
molecules of multi‐substituted XBAYs, the benzylidene
ring and/or the aniline ring can be substituted by more
than one group, so the respective parameters of the sum
ex
CC
substituent constant,[15,16] which has good applications
in the quantitative researches of the spectra and reduc-
tion potential properties of XBAY derivatives.[17–21]
Δσ2= (σ(X)−σ(Y))2.
ex
ex
of σ(X), σ(Y), σ ðXÞ, and σ ðYÞ (expressed by the
CC
CC
ex
CC
ex
CC
symbols Σσ(X), Σσ(Y), Σσ ðXÞ, and Σσ ðYÞ) were used
À
Á
2
in this paper. Δ(∑σ)2 and Δ ∑σ
were used to
ex
CC
νC═N ¼ 1624:78 þ 7:68840σpðXÞ þ 2:11844σpðYÞ
(1)
ex
þ 5:22127σ ðXÞ − 3:20243Δσ2
expressed the substituent specific cross‐interaction
CC
R = 0.9107, R2 = 0.8294, S = 3.13, n = 57, F = 63.18.
Through the analysis of the factors affecting νC═N, they
proposed three modes in the stretching vibration of C═N
bond: (I) polar double bond–form C═N, (II) single
bond‐ion–form C+―N−, and (III) single bond‐diradical
form–C•―N•. The three modes are shown as Figure 1.
In Cao et al,[13] the effects of the three modes on νC═N
of 4,4′‐disubstituted XBAYs were analyzed, and the
SCHEME 1 3,3′/4,3′/3,3′‐disubstituted and multi‐substituted
benzylideneanilines (XBAYs) synthesized in this paper

WANG ET AL.
3 of 7
TABLE 1 The νC═N values of model compounds and the correlative parameters for X and Y
b
b
c
Σσ(X)a
Σσ(Y)a
Σσ ðXÞ
CC
Σσ ðYÞ
CC
νC═N exp
.
νC═N cal
.
(1)d
νC═N.cal
(2)d
ex
ex
No.
X
Y
1
3‐F
4′‐Me2N
4′‐MeO
4′‐Me
4′‐Cl
0.34
0.34
−0.83
−0.27
−0.17
0.23
0.02
0.02
−1.81
−0.50
−0.17
−0.22
−1.81
−0.50
−0.17
0.06
1619
1621
1627
1628
1615
1621
1625
1626
1626
1619
1626
1622
1628
1629
1618
1607
1621
1629
1618
1625
1628
1618
1630
1627
1629
1627
1629
1602
1624
1620
1625
1625
1628
1605
1626
1628
1627
1624
1630
1629
1630
1620
1625
1626
1627
1619
1625
1626
1627
1627
1618
1625
1626
1627
1628
1620
1608
1622
1626
1626
1625
1623
1607
1622
1624
1627
1626
1625
1606
1622
1624
1627
1626
1625
1607
1626
1624
1628
1628
1628
1625
1627
1620
1625
1626
1627
1620
1625
1626
1627
1627
1619
1625
1626
1628
1628
1620
1608
1621
1626
1626
1624
1623
1607
1622
1624
1627
1626
1625
1607
1622
1624
1627
1626
1625
1608
1626
1624
1628
1628
1628
1625
1627
2
3‐F
3
3‐F
0.34
0.02
4
3‐F
0.34
0.02
5
3‐Br
4′‐Me2N
4′‐MeO
4′‐Me
4′‐F
0.39
−0.83
−0.27
−0.17
0.06
−0.03
−0.03
−0.03
−0.03
−0.03
0.56
6
3‐Br
0.39
7
3‐Br
0.39
8
3‐Br
0.39
9
3‐Br
4′‐Cl
0.39
0.23
−0.22
−1.81
−0.50
−0.17
−0.22
−0.70
−1.81
−0.03
−0.03
−0.03
−0.03
−0.03
−0.03
0.02
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
3‐CN
3‐CN
3‐CN
3‐CN
3‐CN
3‐MeO
4‐Me2N
4‐MeO
4‐Cl
4′‐NMe2
4′‐OMe
4′‐Me
4′‐Cl
0.56
−0.83
−0.27
−0.17
0.23
0.56
0.56
0.56
0.56
0.56
0.56
4′‐CN
4′‐Me2N
3′‐Me
3′‐Me
3′‐Me
3′‐Me
3′‐Me
3′‐Me
3′‐F
0.56
0.66
0.56
0.12
−0.83
−0.07
−0.07
−0.07
−0.07
−0.07
−0.07
0.34
0.10
−0.83
−0.27
0.23
−1.81
−0.50
−0.22
−0.12
−0.70
−1.17
−1.81
−0.50
−0.17
−0.22
−0.70
−1.17
−1.81
−0.50
−0.17
−0.22
−0.70
−1.17
−1.81
−0.70
−1.17
−0.22
−0.70
0.10
4‐CF3
4‐CN
4‐NO2
4‐Me2N
4‐MeO
4‐Me
4‐Cl
0.54
0.66
0.78
−0.83
−0.27
−0.17
0.23
3′‐F
0.34
0.02
3′‐F
0.34
0.02
3′‐F
0.34
0.02
4‐CN
4‐NO2
4‐Me2N
4‐MeO
4‐Me
4‐Cl
3′‐F
0.66
0.34
0.02
3′‐F
0.78
0.34
0.02
3′‐Br
−0.83
−0.27
−0.17
0.23
0.39
−0.03
−0.03
−0.03
−0.03
−0.03
−0.03
0.10
3′‐Br
0.39
3′‐Br
0.39
3′‐Br
0.39
4‐CN
4‐NO2
4‐Me2N
4‐CN
4‐NO2
4‐Cl
3′‐Br
0.66
0.39
3′‐Br
0.78
0.39
3′‐MeO
3′‐MeO
3′‐MeO
3′‐CN
3′‐CN
3′‐CN
3′‐Me
3′‐Me
−0.83
0.66
0.12
0.12
0.10
0.78
0.12
0.10
0.23
0.56
0.56
4‐CN
3‐MeO
3‐Me
3‐F
0.66
0.56
0.56
0.12
0.56
0.56
−0.07
0.34
−0.07
−0.07
−0.03
0.02
−0.03
−0.03
(Continues)

4 of 7
WANG ET AL.
TABLE 1 (Continued)
b
b
c
Σσ(X)a
0.34
Σσ(Y)a
0.34
Σσ ðXÞ
CC
Σσ ðYÞ
CC
νC═N exp
.
νC═N cal
.
(1)d
νC═N.cal
(2)d
ex
ex
No.
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
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
X
Y
3‐F
3′‐F
0.02
0.02
−0.03
−0.03
0.02
1632
1628
1633
1631
1630
1628
1633
1630
1627
1621
1627
1627
1628
1628
1618
1623
1620
1621
1629
1627
1625
1623
1630
1623
1617
1625
1625
1626
1626
1628
1625
1627
1621
1621
1627
1621
1623
1628
1629
1601
1627
1628
1628
1627
1628
1630
1627
1629
1628
1623
1622
1624
1625
1625
1623
1618
1623
1624
1623
1622
1627
1626
1627
1627
1626
1618
1625
1626
1627
1627
1626
1623
1626
1627
1628
1625
1616
1624
1626
1626
1605
1627
1628
1628
1627
1629
1630
1627
1629
1628
1622
1622
1624
1625
1625
1623
1618
1623
1623
1623
1622
1627
1626
1627
1627
1626
1618
1625
1626
1627
1627
1626
1623
1626
1627
1628
1625
1617
1624
1626
1626
1605
1627
3‐F
3′‐Br
3′‐Me
3′‐F
0.34
0.39
0.02
3‐CN
3‐CN
3‐CN
3‐Br
0.56
−0.07
0.34
0.56
0.56
0.56
3′‐CN
3′‐Me
3′‐CN
3′‐Br
H
0.56
0.56
0.56
0.56
0.39
−0.07
0.56
−0.03
−0.03
−0.03
−0.20
−0.20
−0.06
0.00
−0.03
0.56
3‐Br
0.39
3‐Br
0.39
0.39
−0.03
0.00
3,4‐Me
3,4‐Me
3,5‐Me
H
−0.24
−0.24
−0.14
0.00
0.00
4′‐Me
H
−0.17
0.00
−0.17
0.00
3′,4′‐Me
3′,5′‐Me
H
−0.24
−0.14
0.00
−0.20
−0.06
0.00
H
0.00
0.00
3,4‐MeO
3,4‐MeO
3,4‐MeO
3,4‐MeO
3,4‐MeO
3,4‐MeO
3,5‐MeO
3,5‐MeO
3,5‐MeO
3,5‐MeO
3,4‐Cl
3,4‐Cl
3,4‐Cl
3,4‐Cl
3,4‐Cl
3,4‐Cl
H
−0.15
−0.15
−0.15
−0.15
−0.15
−0.15
0.24
−0.40
−0.40
−0.40
−0.40
−0.40
−0.40
0.20
4′‐NMe2
4′‐Me
4′‐F
−0.83
−0.17
0.06
−1.81
−0.17
0.06
4′‐Cl
0.23
−0.22
−0.70
0.00
4′‐CN
H
0.66
0.00
4′‐Me
4′‐Cl
0.24
−0.17
0.23
0.20
−0.17
−0.22
−0.70
0.00
0.24
0.20
4′‐CN
H
0.24
0.66
0.20
0.60
0.00
−0.20
−0.20
−0.20
−0.20
−0.20
−0.20
0.00
4′‐NMe2
4′‐Me
4′‐F
0.60
−0.83
−0.17
0.06
−1.81
−0.17
0.06
0.60
0.60
4′‐Cl
0.60
0.23
−0.22
−0.70
−0.20
−0.20
−0.20
−0.20
−0.20
0.00
4′‐CN
3′,4′‐Cl
3′,4′‐Cl
3′,4′‐Cl
3′,4′‐Cl
3′,4′‐Cl
H
0.60
0.66
0.00
0.60
4‐Me
−0.17
0.06
0.60
−0.17
0.06
4‐F
0.60
4‐Cl
0.23
0.60
−0.22
0.02
3‐Cl
0.37
0.60
3,5‐Cl
3,5‐Cl
3,5‐Cl
3,5‐Cl
H
0.74
0.00
0.04
4′‐NMe2
4′‐Me
4′‐Cl
0.74
−0.83
−0.17
0.23
0.04
−1.81
−0.17
−0.22
0.04
0.74
0.04
0.74
0.04
3′,5′‐Cl
3′,5′‐Cl
3′,5′‐Cl
0.00
0.74
0.00
4‐NMe2
4‐F
−0.83
0.06
0.74
−1.81
0.06
0.04
0.74
0.04
(Continues)

WANG ET AL.
5 of 7
TABLE 1 (Continued)
b
b
c
Σσ(X)a
0.23
0.40
0.40
0.68
0.62
0.78
0.17
0.22
0.00
0.00
0.00
−0.15
0.60
0.60
0.60
0.17
0.17
0.78
0.78
Σσ(Y)a
0.74
−0.83
0.23
0.00
0.00
0.00
0.00
0.00
0.17
0.20
0.22
−0.14
0.60
0.20
0.74
0.60
0.20
0.20
0.74
Σσ ðXÞ
CC
Σσ ðYÞ
CC
νC═N exp
.
νC═N cal
.
(1)d
νC═N cal
.
(2)d
ex
ex
No.
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
X
Y
4‐Cl
3′,5′‐Cl
4′‐NMe2
4′‐Cl
−0.22
0.04
−1.81
−0.22
0.00
1625
1621
1630
1626
1626
1625
1620
1623
1633
1625
1620
1625
1622
1624
1626
1626
1623
1624
1626
1628
1619
1627
1626
1626
1625
1626
1627
1625
1625
1625
1623
1628
1627
1628
1627
1627
1625
1628
1628
1620
1627
1626
1626
1625
1626
1626
1626
1626
1625
1623
1628
1627
1628
1627
1627
1626
1628
3,4‐F
0.08
3,4‐F
0.08
3,5‐F
H
0.04
3,4‐Br
3,5‐Br
3‐F‐4‐Me
3‐Br‐4‐Me
H
H
−0.36
−0.06
−0.15
−0.20
0.00
0.00
H
0.00
H
0.00
H
0.00
3′‐F‐4′‐Me
3′‐Cl‐4′‐Me
3′‐Br‐4′‐Me
3′,5′‐Me
3′,4′‐Cl
3′‐Cl‐4′‐Me
3′,5′‐Cl
3′,4′‐Cl
3′‐Cl‐4′‐Me
3′‐Cl‐4′‐Me
3′,5′‐Cl
−0.15
−0.15
−0.20
−0.06
−0.20
−0.15
0.04
H
0.00
H
0.00
3,4‐MeO
3,4‐Cl
3,4‐Cl
3,4‐Cl
3‐F‐4‐Me
3‐F‐4‐Me
3,5‐Br
3,5‐Br
−0.40
−0.20
−0.20
−0.20
−0.15
−0.15
‐0.06
−0.06
−0.20
−0.15
−0.15
0.04
aΣσ(X/Y) = σ (Xm/Ym) + σ (Xp/Yp); the σ values of X and Y were taken from Hansch et al.[14]
À
Á
Σσ ðX=YÞ=σ ðXm=YmÞ+σeCxC Xp=Yp ; the σ values of X and Y were taken from previous studies.[15,16,22]
b
ex
CC
ex
CC
ex
CC
cExperimental values of this work.
dνC═N cal
(1) was calculated by Equation (2); νC═N.cal (2) was calculated by Equation (3).
.
effect between X and Y. Δ(∑σ)2 = (Σσ(X) − Σσ(Y))2;
As seen from Equation (2), the correlation coefficient R
À
Á
is good, and the standard deviation S is only 3.34 cm−1
.
2
= (Σσ ðXÞ − Σσ ðYÞ)2. In addition, there
ex
ex
ex
Δ ∑σ
CC
CC
CC
The vC═N values calculated by Equation (2) were listed in
would be the substituent specific cross‐interaction effect
between X (or Y) and X (or Y). Therefore, (∑σ(X))2
and (∑σ(Y))2 were tentatively used as the substituent
specific cross‐interaction effect between X (or Y) and
X (or Y) respectively in following research. (∑σ(X))2 =
∑ σ(X) × ∑ σ(X); (∑σ(Y))2 = ∑ σ(Y) × ∑ σ(Y).
Table 1. The average absolute error between the calcu-
lated values and the experimental ones is 2.50 cm−1 for
all the 158 samples of XBAYs. But we thought that the
Fischer ratio F could be improved. Moreover, the coeffi-
ex
ex
cients of ∑σ ðXÞ and ∑σ ðYÞ are close, that is to say
CC
CC
the two parameters can be merged. Besides, in the regres-
ex
On the basis of the above, Σσ(X), Σσ(Y), Σσ ðXÞ, Σ
CC
À
Á
sion process, we found that the statistics t values of
σ
ðYÞ, Δ(∑σ)2, Δ ∑σex 2, (∑σ(X))2, and (∑σ(Y))2 were
À
Á
ex
2
CC
CC
Δ ∑σ
and (∑σ(Y))2 were −0.67 and 0.32, respec-
ex
CC
first used to quantify the νC═N values of 158 samples of
substituted XBAYs, including 57 samples of 4,4′‐
disubstituted XBAYs from Cao et al,[13] 49 samples of
3,4′/4,3′/3,3′‐disubstituted XBAYs, and 52 samples of
multi‐substituted XBAYs. Then, Equation (2) was
obtained.
tively. It indicated that their contributions were relatively
unimportant, and they should be removed from the corre-
lation equation. It is worth noting that the statistics t value
of (∑σ(X))2 is −4.26, which indicates that it is especially
important for the regression analysis of the νC═N values
of multi‐substituted XBAYs. The t values of the parame-
ters used in Equation (2) were listed in Table 2.
νC═N ¼ 1625:46 þ 8:43339∑σðXÞ þ 1:68677∑σðYÞ
ex
ex
þ 1:15540∑σ ðXÞ þ 1:68330∑σ ðYÞ
À
Á
CC
CC
2
ex
CC
After removing Δ ∑σ
and (∑σ(Y))2 and merging
À
Á
(2)
2
2
ex
CC
− 2:11501Δð∑σÞ − 0:24799Δ ∑σ
ex
CC
ex
∑σ ðXÞ and ∑σ ðYÞ, the regression was made again.
CC
2
2
ex
− 9:68756ð∑σðXÞÞ þ 0:79001ð∑σðYÞÞ
And Equation (3) was obtained. In Equation (3), ∑σ
=
CC
R = 0.8680, R2 = 0.7535, S = 3.34, n = 158, F = 56.93.
ex
CC
ex
CC
∑σ ðXÞ + ∑σ ðYÞ.

6 of 7
WANG ET AL.
TABLE 2 The t values of the parameters used in Equation (2)
À
Á
2
ex
CC
Δ(∑σ)2
−2.96
Δ ∑σ
(∑σ(X))2
−4.26
(∑σ(Y))2
ex
ex
Param
∑σ(X)
∑σ(Y)
∑σ ðXÞ
∑σ ðYÞ
CC
CC
t
9.23
1.60
1.29
1.53
−0.67
0.32
XBAYs was made in this paper. And a modified equation
for quantifying the vC═N values of multi‐substituted
XBAYs was obtained (shown as Equation (3)). The results
show that the excited‐state substituent constant of Y
νC═N ¼ 1625:42 þ 8:45777∑σðXÞ þ 2:09814∑σðYÞ
2
þ 1:37082∑σeCxC − 2:26407Δð∑σÞ
(3)
2
− 9:61173ð∑σðXÞÞ
ex
∑σ ðYÞ and the substituent specific cross‐interaction
CC
R = 0.8675, R2 = 0.7525, S = 3.32, n = 158, F = 92.43.
Compared with Equation (2), Equation (3) also has
good correlation, and its Fischer ratio (F) is improved
from 56.93 to 92.43. So, Equation (3) is recommended to
express the change regularity of the C═N stretching
effect between X and X (∑σ(X))2 cannot be ignored for
the quantitative regression analysis of multi‐substituted
XBAYs, especially (∑σ(X))2. Compared with Equation (1),
Equation (3) has a wider application and more accuracy
in quantifying the vC═N values of substituted XBAYs.
Because of the addition of 3,4′/4,3′/3,3′‐disubstituted
XBAYs and multi‐substituted XBAYs (most of them are
trisubstituted XBAYs) to the research, the effects of
vibration frequencies (vC═N
)
for multi‐substituted
XBAYs. The vC═N values calculated by Equation (3) were
listed in Table 1. The average absolute error between the
calculated values and the experimental ones is 2.53 cm−1
for all the 158 samples of XBAYs.
∑σ ðYÞ and (∑σ(X))2 cannot be ignored for the quanti-
ex
CC
tative regression analysis of the vC═N values. If more
In Equation (3), the coefficients of ∑σ(X), ∑σ(Y), and
multi‐substituted XBAYs were added into the research,
there may be other parameters needed to be considered.
It is worthy of further research.
ex
∑σ
are positive, that is to say ∑σ(X), ∑σ(Y), and
CC
ex
∑σ present positive correlation with the vC═N value.
CC
The coefficients of Δ(∑σ)2 and (∑σ(X))2 are negative,
which demonstrates that Δ(∑σ)2 and (∑σ(X))2 present
negative correlation with the vC═N value. Because the
values of items Δ(∑σ)2 and (∑σ(X))2 are greater than or
equal to 0, the substituent specific cross‐interaction effects
always decrease the vC═N values of the XBAYs.
4 | DATASET
The substituted XBAYs were all synthesized by the
solvent‐free method according to Scheme 1.[23,24] They
were purified with anhydrous alcohol and confirmed
1
with H NMR and 13C NMR. The NMR spectra were
As seen from Equation (1) and Equation (3), their
results are consistent in some ways. When X and Y are
H, the vC═N values of HBAH obtained by Equation (1)
and Equation (3) are 1624.78 and 1625.42 cm−1, respec-
tively. Both of them are roughly 1625 cm‐1. It indicates
the two quantitative equations are reasonable. Moreover,
the coefficients of ∑σ(X), ∑σ(Y), ∑σeCxC, and Δ(∑σ)2 in
Equation (3) have the same positive or negative sign with
the corresponding parameters in Equation (1), that is to
say their influences on the vC═N values are also consis-
tent. The biggest difference between Equation (1) and
recorded by Bruker AV 500 MHz in CDCl3 at room
temperature at an approximate concentration. The NMR
chemical shifts were expressed in ppm relative to TMS
(0.00 ppm) used as an internal reference. The infrared
spectra of the model compounds were recorded by the
infrared spectrometer (Nicolet 6700) with potassium
bromide (KBr) disc. The detailed data of the synthesized
compounds are available in the Supporting Information.
ACKNOWLEDGMENTS
Equation (3) is the addition of ∑σ ðYÞ and (∑σ(X))2.
ex
CC
Because the benzylidene ring and/or the aniline ring in
The project was supported by the National Natural Sci-
ence Foundation of China (21672058).
molecules of multi‐substituted XBAYs can be substituted
by more than one group and the number of studied com-
pounds increases, the effects of ∑σ ðYÞ and (∑σ(X))2
ex
CC
ORCID
show out. And they cannot be ignored for the quantita-
Linyan Wang https://orcid.org/0000-0002-8080-7925
Chenzhong Cao https://orcid.org/0000-0001-5224-7716
tive regression analysis of multi‐substituted XBAYs.
3 | CONCLUSIONS
REFERENCES
An extensional research of substituent effects on the vC═N
values from 4,4′‐disubstituted XBAYs to multi‐substituted
[1] T. Donaldson, P. A. Henderson, M. F. Achard, C. T. Imrie, Liq.
Cryst. 2011, 38, 1331.

WANG ET AL.
7 of 7
[2] A. Karakas, H. Ünver, Spectrochim. Acta A Mol. Biomol.
Spectrosc. 2010, 75, 1492.
[18] C. Z. Cao, Z. J. Fang, Spectrochim. Acta A Mol. Biomol.
Spectrosc. 2013, 111, 62.
[3] J. P. Costes, J. F. Lamère, C. Lepetit, P. G. Lacroix, F. Dahan, K.
[19] L. Y. Wang, C. T. Cao, C. Z. Cao, J. Phys. Org. Chem. 2014, 27,
Nakatani, Inorg. Chem. 2005, 44, 1973.
818.
[4] S. Leela, K. Ramamurthi, G. Bhagavannarayana, Spectrochim.
Acta A Mol. Biomol. Spectrosc. 2009, 74, 78.
[20] L. Y. Wang, C. T. Cao, C. Z. Cao, Magn. Reson. Chem. 2015, 53,
520.
[5] A. Karakaş, A. Elmali, H. Ünver, I. Svoboda, Spectrochim. Acta
A Mol. Biomol. Spectrosc. 2005, 61, 2979.
[21] L. Y. Wang, C. T. Cao, C. Z. Cao, Chin. J. Chem. Phys. 2016, 29,
260.
[6] H. Neuvonen, K. Neuvonen, F. Fülöp, J. Org. Chem. 2006, 71,
[22] C. Z. Cao, Y. X. Wu, Sci. China Chem. 2013, 56, 883.
3141.
[23] J. Schmeyers, F. Toda, J. Boy, G. Kaupp, J. Chem. Soc., Perkin
Trans. 2. 1998, 4, 989.
[7] H. Celik, G. Ekmekci, J. Ludvík, J. Pícha, P. Zuman, J. Phys.
Chem. B 2006, 110, 6785.
[24] B. T. Lu, Master Dissertation, Hunan University of Science and
Technology, Hunan, 2013.
[8] V. Güner, S. Bayari, Spectrosc. Lett. 2002, 35, 83.
[9] S. P. Molnar, M. Orchin, J. Organomet. Chem. 1969, 16, 196.
[10] K. Figueroa, M. Campos‐Vallette, D. Venegas, A. Quiroz, E.
Quezada, Spectrosc. Lett. 1991, 24, 589.
SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of the
article.
[11] L. I. Kozhevina, E. B. Prokopenko, V. I. Rybachenko, E. V.
Titov, J. Mol. Struct. 1993, 295, 53.
[12] D. Sek, M. Siwy, K. Bijak, M. Grucela‐Zajac, G. Malecki, K.
Smolarek, L. Bujak, S. Mackowski, E. Schab‐Balcerzak,
J. Phys. Chem. A 2013, 117, 10320.
[13] C. T. Cao, Y. K. Bi, C. T. Cao, Spectrochim. Acta A Mol. Biomol.
Spectrosc. 2016, 163, 96.
How to cite this article: Wang L, Cao C, Cao C.
Substituent effects on the stretching vibration of
C═N in multi‐substituted benzylideneanilines. J
Phys Org Chem. 2019;e3969. https://doi.org/
10.1002/poc.3969
[14] C. Hansch, A. Leo, R. W. Taft, Chem. Rev. 1991, 91, 165.
[15] C. Z. Cao, G. F. Chen, Z. Q. Yin, J. Phys. Org. Chem. 2008, 21, 808.
[16] C. Z. Cao, B. Sheng, G. F. Chen, J. Phys. Org. Chem. 2012, 25,
1315.
[17] G. F. Chen, C. Z. Cao, B. T. Lu, B. Sheng, J. Phys. Org. Chem.
2012, 25, 327.