Synthesis, ir and nmr spectral correlations in some symmetrical diimines

Article abstract of DOI:10.4314/bcse.v28i1.9

A series of diimines have been synthesized by coupling of diamine with substituted benzaldehydes. The purities of these diimines were checked by their analytical and spectroscopic data. The spectral frequencies vCN (cm-1), NMR chemical shifts (v, ppm) of C-H and C=N of these diimines have been correlated with Hammett substituent constants, F and R parameters using single and multi-linear regression analysis. From the results of statistical analysis, the effect of substituents on the above spectral data has been studied.

Full text of DOI:10.4314/bcse.v28i1.9

Bull. Chem. Soc. Ethiop. 2014, 28(1), 73-79.
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v28i1.9
ISSN 1011-3924
 2014 Chemical Society of Ethiopia
SYNTHESIS, IR AND NMR SPECTRAL CORRELATIONS IN SOME
SYMMETRICAL DIIMINES
*
G. Thirunarayanan
Department of Chemistry, Annamalai University, Annamalainagar-608002, India
(
Received February 27, 2013; revised July 21, 2013)
ABSTRACT. A series of diimines have been synthesized by coupling of diamine with substituted
benzaldehydes. The purities of these diimines were checked by their analytical and spectroscopic data. The
-1
spectral frequencies νCN (cm ), NMR chemical shifts (δ, ppm) of C-H and C=N of these diimines have been
correlated with Hammett substituent constants, F and R parameters using single and multi-linear regression
analysis. From the results of statistical analysis, the effect of substituents on the above spectral data has been
studied.
KEY WORDS: Diimines, IR and NMR spectra, Spectral correlation, Hammett sigma constants
INTRODUCTION
In this decade synthesis of enantiometrically pure compounds from prochiral compounds using
chiral reagents have become topic of immense interest. Effective and enthusiastic efforts by
synthetic organic chemists in the last two decades are converting this difficult task to a
practically possible level. Many chiral molecules have been synthesized in excellent optical
purities through chemical process which reveal natural processes. Aldehydes and ketones react
with primary amines to give imines, in which the carbon-oxygen double bond is replaced by a
carbon-nitrogen double bond was discovered in 1864 by Hugo Schiff [1] and been always the
reaction of interest to chemists up to date in the fields of macrocyclic and supramolecular
chemistry. The diimines or bisimines or bis-Schiff’s bases also been synthesised by the reaction
of 1 mole diamine with 2 moles of aldehydes or ketones. Primary amine and β-diketones also
used for synthesis of cyclic diimines. Optically active amines and alkaloids, with a wide range
of molecular structures are used as chiral reagents. Numerous solvent assisted [2] or solvent free
greener [3] methods and reagents were available in the literature for synthesis of optically active
diimines. These diimines have been used as a precursor for synthesis of optically active cyclic
imines like piperazine derivatives [4], heterocycles such as imidazolines, pyrimidines,
carbapenem intermediates, bis-β-lactams, bisketenes [5, 6], polymers[7] and many metal
complexes[8]. Diimines possess important biological activities such as antioxidant [9], anti-
inflammatory and anti-analgesics [10]. Spectroscopic data were used for prediction of ground
state molecular equilibration of organic compounds such as, ketones, chalcones [11], imines
[
[
12], diimines [13], acyl chlorides [14], bromides and their esters [15]. Recently, Suresh et al.,
12] have studied the effects of substituent on infrared C=N, nuclear magnetic resonance
chemical shifts (ppm) δCH and CN. In this work they observed good, satisfactory and fair
degree of correlations for the above frequencies with Hammett substituent constants, F and R
parameters. In this view, there is no report available for the synthesis and spectral correlations
of diimines in literature in the past. Therefore the author has taken efforts to synthesis and
studied the effect of substituents on the spectral group frequencies of synthesized diimines.
_
*
_________
Corresponding author. E-mail: drgtnarayanan@gmail.com

74
G. Thirunarayanan
EXPERIMENTAL
General
All the chemicals involved in the present investigation were procured from Sigma-Aldrich and
E-Merck chemical companies. Melting points of all diimines were determined in open glass
capillaries on SUNTEX melting point apparatus and are uncorrected. Infrared spectra (KBr,
-
1
4
Bruker AV400 NMR spectrometer was used for recording NMR spectra operating 400 MHz for
000-400 cm ) were recorded on AVATAR-300 Fourier transform spectrophotometer. The
1
13
H and 100 MHz for C spectra in CDCl solvent using TMS as internal standard. Mass spectra
3
of diimines were recorded on SHIMADZU spectrometer using chemical ionization technique.
Synthesis of diimines
To a solution of aryl aldehydes (100 mmol) in methanol (80 mL) was added ethylenediamine
(
60 mmol) at 0 °C slowly in drops. Then the reaction mixture was stirred at room temperature
for 12 h (Scheme 1) [4]. The crude diimines were subjected to evacuate under vacuum. The
residue was treated with 100 mL of methylene chloride and dried over anhydrous potassium
carbonate. The diimines were obtained after evaporated the solvent under high vacuum. The
analytical, physical constants and mass fragments of these diimines are presented in Table 1.
The infrared and NMR spectroscopic data of these diimines are given in Table 2.
NH
2
N
R
X
CH OH
3
2OHC-R-X
0
°C, 12 h
NH
2
N
R
X
(
1-11)
Entry
R
X
1
2
3
4
5
6
7
8
9
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
H
2-Cl
4-Cl
4-N(CH
3
)
2
4-N(C
4-OH
2
H
5
)
2
2-OCH
4-OCH
3
3
4-CH
H
3
1
1
0
1
2-Pyridine
2-Thienyl
H
Scheme 1. Synthesis of diimines.
Bull. Chem. Soc. Ethiop. 2014, 28(1)

Synthesis, IR and NMR spectral correlations in some symmetrical diimines
75
Table 1. The analytical, physical constants and mass fragments (m/z) of diimines.
o
M.W. Yield (%) m.p. ( C)
Entry
X
H
M.F.
Mass (m/z)
+
236[M ]
1
C
16
C
16
C
16
C
20
C
24
C
16
C
18
C
18
C
18
C
14
C
12
H
H
H
H
H
H
H
H
H
H
H
16
N
2
236
304
304
322
378
268
296
296
264
238
248
94
89
89
85
86
87
93
94
90
85
86
39-49
8-40 [4]
87-88
4-88 [15]
140-141
40-142 [4]
174-175
73-174 [10]
115-116
14-116 [10]
121-122
20-122 [10]
113-114
12-114 [4]
108-109
06-108 [4]
152-154
52-154 [4]
138-140
39 [16]
83-84
2-84 [10]
3
+ +2
304 [M ], 306 [M ],
2
3
4
5
6
7
8
9
1
1
2Cl
14Cl
2
2
N
2
2
+
308 [M ]
4
8
+
304 [M ], 306 [M ],
+2
4-Cl
14Cl
N
+
308 [M ]
4
1
+
322 [M ]
4-N(CH
3
)
2
26
34
16
20
20
20
14
12
N
4
1
+
378 [M ]
4-N(C
2
H
5
)
2
N
4
1
+
268 [M ]
2-OH
N
N
N
N
2
2
2
2
O
2
1
+
296 [M ]
2-OCH
3
3
O
2
2
1
+
296 [M ]
4-OCH
O
1
+
264 [M ]
4-CH
3
1
+
238 [M ]
0
1
2-Pyridine
2-Thienyl
N
4
1
+
248 [M ]
N
2
S
2
8
-1
Table 2. The infrared νCN(cm ) frequencies, NMR δ(ppm) of C-H and C=N of diimines.
1
13
Entry
Substituent
IR
H NMR
C NMR
C=N
1649
1638
1645
1639
1642
1638
1633
1643
1633
1645
1632
CH=N
8.294
8.725
8.231
8.152
7.562
8.351
8.713
8.216
8.245
8.305
8.441
C=N
1
2
3
4
5
6
7
8
9
H
162.72
159.75
161.32
159.72
160.86
164.17
158.73
161.82
162.54
156.58
159.57
2-Cl
4-Cl
4-N(CH
3
)
2
4-N(C
2-OH
2
H
5
)
2
2-OCH
3
3
4-OCH
4-CH
3
1
1
0
1
2-Pyridine
2-Thienyl
RESULTS AND DISCUSSION
Infrared spectral study
In the present study, author has recorded the infrared spectrum of all synthesised diimines
-
1
containing single substituents in phenyl moieties with KBr disc. The C=N stretches (cm ) of all
-
1
diimines have been assigned and listed in Table 2. These stretches (cm ) were correlated with
Hammett substituent constants, F and R parameters. In this correlation, the Hammett equation is
employed as,
ν = ρσ + ν
o
(1)
Bull. Chem. Soc. Ethiop. 2014, 28(1)

76
G. Thirunarayanan
where ν
o
is the frequency for the parent member of the series. The assigned νC=N stretching
-
1
frequencies (cm ) were correlated with various Hammett substituent constants and F and R
parameters through single and multi-regression analyses [12, 17-19] including Swain-Lupton’s
parameters [20]. The results of statistical analysis of single parameter correlation are shown in
Table 3.
-1
1
13
Table 3. Results of statistical analysis of IR ν C=N (cm ), NMR δ H (ppm) CH=N and δ C (ppm) C= N of
+
N,N′-arylidineethane-1,2-diamines with Hammett substituent constants σ, σ , σ
parameters.
I R
, σ , F and R
Frequency
Constants
r
I
ρ
s
n Correlated derivatives
0.931 1640.91 7.029 5.61 8 H, 2-Cl, 4-Cl, 4-Me, 4-N(CH
OCH , 4-OCH
-1
ν C=N(cm )
σ
3
)
2
, 4-OH, 4-
, 4-OH, 4-
, 4-OH, 4-
3
3
+
σ
0.717 1640.33 1.506 5.98
0.803 1639.57 0.922 6.07
0.904 1643.50 11.050 5.37
0.804 1640.11 1.587 6.06
0.833 1642.30 6.021 5.68
8
8
8
8
8
σ
σ
F
I
R
R
δ CH=N(ppm) σ
0.902 8.396
0.184 0.23 8 H, 2-Cl, 4-Cl, 4-Me, 4-N(CH
3 2
)
OCH , 4-OCH
3
3
+
σ
σ
σ
F
0.907 8.431
0.875 8.231
0.857 8.307
0.841 8.227
0.811 8.704
0.196 0.21
0.586 0.28
0.170 0.23
0.579 0.22
0.908 0.24
8
8
8
8
8
I
R
R
δ C=N(ppm)
σ
0.900 161.56 1.321 1.93 8 H, 2-Cl, 4-Cl, 4-Me, 4-N(CH
3 2
)
OCH , 4-OCH
3
3
+
σ
σ
σ
F
0.817 161.53 0.482 1.95
0.835 162.06 3.425 1.85
0.827 162.00 1.932 1.91
0.828 162.07 3.067 1.90
0.800 161.89 1.291 1.92
8
8
8
8
8
I
R
R
r = correlation co-efficient; ρ = slope; I = intercept; s = standard deviation; n = number of substituents.
-
1
The correlation of νC=N (cm ) frequencies of diimines with Hammett σ constants and R
parameters were found to be satisfactory. All correlations gave positive ρ values. This implies
that the normal substituent effect operates in all systems. The remaining constants gave poor
-
1
correlations with νC=N (cm ) frequencies. This is due to the absence of polar, field and
inductive effects of the substituents were unable to predict the reactivity on C=N stretches. This
is associated with the conjugative structure shown in (Figure 1).
CH
3
O
N
N
O
CH
3
Figure. 1. The resonance conjugative structure.
Bull. Chem. Soc. Ethiop. 2014, 28(1)

Synthesis, IR and NMR spectral correlations in some symmetrical diimines
77
-
1
In short, some of the single parameter correlations of νC=N (cm ) frequencies with
Hammett substituent constants fail in correlation. So, the author think that it is worthwhile to
seek the multi regression analysis which may produce a satisfactory correlation with Resonance,
Field and Swain-Lupton’s [20] constants. This is shown in the multi-correlation equations 2 and
3
.
-
1
ν
ν
1
C=N (cm ) = 1642.87(±4.186) + 3.944 (± 1.144) σ
r = 0.948, n = 8, p > 90%)
I
+ 11.750 (± 9.491) σ
R
(2)
(3)
(
-
1
C=N(cm ) = 1642.18 (±4.721) + 0.602 (±0.142) F + 6.076(±0.729) R
(
r = 0.935, n = 8, p > 90%)
H NMR spectral study
1
The H NMR spectra of the diimine derivatives under the present investigation were recorded in
deuteriochloroform solution employing tetramethylsilane (TMS) as internal standard. The
signals of the imine protons have been assigned and are presented in Table 2.
1
13
In nuclear magnetic resonance spectra, the H or the C chemical shifts (δ) (ppm) depend on
the electronic environment of the nuclei concerned. These chemical shifts have been correlated
with reactivity parameters. Thus the Hammett equation has been used in the form as shown in
(
4).
= δ
where δ
∆
0
+ ρσ
is the chemical shift of the corresponding parent compound.
(4)
0
The assigned proton chemical shifts (ppm) of diimines have been correlated [12, 17-19]
with various Hammett sigma constants, F and R parameters. The results of statistical analysis
+
are presented in Table 3. Hammett σ and σ constants gave satisfactory correlation for these
proton chemical shifts (ppm). The remaining Hammett substituent constants, F and R
parameters were failed in correlation. All correlations give positive ρ values. This shows that the
normal substituent effect operates in all systems. The failure in correlation is attributed to the
conjugative structure shown in Figure. 1.
In view of the inability of the Hammett σ constants to produce individually satisfactory
correlations with the imine proton chemical shifts, the authors think that, it is worthwhile to
seek multiple correlations involving either σ
parameters. This is shown in the following equations 5 and 6 for protons:
I
R
and σ constants or Swain- Lupton’s [20] F and R
(
(
ppm)
ppm)
δ
CH
= 8.217(±1.641) + 0.568 (±0.044) σ
r = 0.951, n = 8, p > 95%)
I
- 0.070(±0.003) σ
R
(5)
(6)
(
δCH
= 8.281(±0.177) + 0.063 (±0.005) F + 0.156(±0.027) R
r = 0.957, n = 8, p > 95%)
(
1
3
C NMR spectra
1
3
C
Physical organic chemists and researchers [11, 17, 18, 19] have made extensive study of
NMR spectra for a large number of imines, ketones, styrenes, styryl ketones and keto-epoxides,
acyl chlorides, bromides and their esters. They have studied the linear correlation of the
α β
chemical shifts (ppm) of C , C and CO carbons with Hammett σ constants in alkenes, alkynes,
acid chlorides and styrenes. In the present study, the chemical shifts (ppm) of imine C=N
carbon, have been assigned and are presented in Table 3. Attempts have been made to correlate
the δC=N chemical shifts (ppm) with Hammett substituent constants, field and resonance
Bull. Chem. Soc. Ethiop. 2014, 28(1)

78
G. Thirunarayanan
parameters, with the help of single and multi-regression analyses to study the reactivity through
the effect of substituents.
The chemical shifts (ppm) observed for the δC=N have been correlated [12, 17-19] with
Hammett constants and the results of statistical analysis are presented in Table 3. The δC=N
chemical shifts (ppm) give satisfactory correlation with Hammett σ constants. The remaining
+
Hammett σ , σ
stated earlier with resonance conjugative structure as shown in Figure. 1.
I
R
, σ , F and R parameters are found to fail in correlation. This is due to the reason
In view of inability of some of the σ constants to produce individually satisfactory
correlation, the authors think that it is worthwhile to seek multiple correlation involving all σ
σR, F and R parameters [20]. This is given in the following correlation equations 7 and 8.
I
,
(
ppm)
δ
C=N
= 162.46(±1.434) + 2.908(±0.392) σ
r = 0.939, n = 8, p > 90%)
I
+ 1.417 (±0.325) σ
R
(7)
(
(
ppm)
δ
C=N
= 162.43(±1.549) + 2.700(±0.468) F + 1.043(±0.239) R
r = 0.933, n = 8, p > 90%)
(8)
(
CONCLUSIONS
A series of N,N′-arylidineethane-1,2-diamines have been synthesised by oxidative coupling
reaction of ethylene diamine and aryl aldehydes. The purities of these diimines were checked by
their analytical and spectroscopic data. The spectral frequencies of the functional groups of
diimines have been assigned and correlated with Hammett substituent constants, F and R
parameters. From the results of the statistical analysis, the effects of substituents on the
functional group of diimines have been discussed.
ACKNOWLEDGEMENTS
The author thank The UGC-Chemistry Network Resource Centre, School of Chemistry, Central
University, Hyderabad-500 040, for providing financial assistance through Summer Visiting
Fellowship-June 2006, under the guidance of Prof. Dr. Mariappan Periasamy for initiating this
diimines synthesizing work.
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