Vibrational, structural and electronic study of a pyridinium salt assisted by SXRD studies and DFT calculations

Article abstract of DOI:10.1016/j.molstruc.2016.11.033

The molecular structure of 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (C₁₂H₁₁IN₂O) is discussed using an experimental (FT-IR/ATR, NMR, SXRD) and theoretical (DFT, B3LYP/6-311G**) approach. Compound 2 crystallized in the monoclinic P2₁/c space group with 4 molecules per unit cell and unit cell dimensions a?=?7.5629?? (3), b?=?21.5694?? (7), c?=?7.8166?? (3). The crystal packing is governed by ion-dipole contacts and π-π stacking. High electrostatic potential at the ethanone hydrogens was derived from DFT calculations, further explaining the acidity and reactivity of the molecule as a Michael donor.

Full text of DOI:10.1016/j.molstruc.2016.11.033

Accepted Manuscript
Vibrational, structural and electronic study of a pyridinium salt assisted by SXRD
studies and DFT calculations
Pablo Labra-Vázquez, Miguel Palma-Contreras, Rosa Santillan, Norberto Farfán
PII:
S0022-2860(16)31196-6
10.1016/j.molstruc.2016.11.033
MOLSTR 23134
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 24 August 2016
Revised Date: 8 November 2016
Accepted Date: 10 November 2016
Please cite this article as: P. Labra-Vázquez, M. Palma-Contreras, R. Santillan, N. Farfán, Vibrational,
structural and electronic study of a pyridinium salt assisted by SXRD studies and DFT calculations,
Journal of Molecular Structure (2016), doi: 10.1016/j.molstruc.2016.11.033.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Vibrational, structural and electronic study of a pyridinium salt
assisted by SXRD studies and DFT calculations.
a
a
b
Pablo Labra-Vázquez, Miguel Palma-Contreras, Rosa Santillan, Norberto
a
Farfán. *
a
Facultad de Química, Departamento de Química Orgánica, Universidad Nacional
Autónoma de México, 04510 México D.F., México. e-mail: norberto.farfan@gmail.com,
Fax: +52 55 56223722; Tel: +52 55 56223899 ext. 44443
b
Departamento de Química, Centro de Investigación y de Estudios Avanzados del IPN,
México D.F. Apdo. Postal 14-740, 07000, México
Abstract
2
The molecular structure of 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (C12H11IN O)
is discussed using an experimental (FT-IR/ATR, NMR, SXRD) and theoretical (DFT,
B3LYP/6-311G**) approach. Compound 2 crystallized in the monoclinic P2 /c space
1
group with 4 molecules per unit cell and unit cell dimensions a = 7.5629 Å (3), b = 21.5694
Å (7), c = 7.8166 Å (3). The crystal packing is governed by ion-dipole contacts and π-π
stacking. High electrostatic potential at the ethanone hydrogens was derived from DFT
calculations, further explaining the acidity and reactivity of the molecule as a Michael
donor.
Keywords
Pyridinium salt; Polypyridyl compounds; Non-Linear Optics; DFT; X-Ray Diffraction.
1

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1
. Introduction
Pyridinium salts are heterocycles bearing a quaternary (usually alkylated or
acylated) annular nitrogen. The positive charge delocalized within the ring confers these
compounds unique chemical and physical properties that have been exploited in diverse
areas. Relevant applications include numerous synthetic strategies to obtain and modify a
myriad of heterocycles,[1-5] as well as improvements in the development of amphiphilic
polymers[6, 7] and advanced organoelectronic[8, 9] and photonic[10] materials.
The reactivity of pyridinium salts has been at the focus of intense research since the earlier
6
0’s. The first investigations by the group of F. Kröhnke, reported that these compounds
could be cleaved to yield aromatic amines or enamines, and that the pyridinium group
could also be used as a leaving group in S 2 reactions.[11] Such observations paved the
N
way to the report by Zecher and Kröhnke of their famous pyridine synthesis from
pyridinium salts and α,β-unsaturated ketones,[12] that has become one of the most used
synthetic methodologies for pyridine-containing organic compounds.
Particularly, 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide has been widely employed as
Michael donor in the synthesis of 2,2’-bipyridines (bpy) and 2,2’:6’,2’’-terpyridines (tpy),
among other polypyridyl ligands (Scheme 1).[13] However, a common issue in the
synthesis of these compounds is the concomitant formation of colored by-products that
significantly lower the yields, particularly when the α,β-unsaturated carbonyl counterpart is
poorly activated towards 1,4-addition, i.e. when electron donating groups are present. Only
few studies dealing with this issue have been published, with kinetic factors usually
invoked (stoichiometry or concentration) to explain the formation of such species.[14-16]
2

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Scheme 1. Use of 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (center) as Michael
donor in the synthesis of 2,2’-bipyridine (bpy) and 2,2’:6’,2’’-terpyridine (tpy) ligands.
As part of our ongoing program on devising efficient nitric oxide (NO) photo-releasing
Ru(II) tpy complexes,[17-19] we became interested in further unveiling the factors that
affect the overall synthetic yields of the tpy ligands via the Kröhnke route. To date, this
remains poorly described although the reactivity of the Michael donor is expected to play a
pivotal role. Thus, herein we report
a
structural study of 1-[2-oxo-2-(2-
pyridinyl)ethyl]pyridinium iodide comprising vibrational, spectral and theoretical
approaches.
2
. Results and Discussion
2
.1 Synthesis and NMR characterization.
Treatment of 2-acetylpyiridine (1) with a solution of iodine in pyridine followed by
heating to reflux, yielded the corresponding pyridinium salt (2) in moderate yields via an
Ortoleva-King reaction (Scheme 2). The identity of the compound was confirmed by high
+
resolution mass spectrometry, showing a peak at m/z 199.0869 for the [M-I] ion.
3

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Scheme 2. Synthesis and numbering of 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide
(2).
1
The H-NMR spectrum of 2 is characterized by the signal of the methylene hydrogens (H-
), appearing as a highly deshielded singlet at δ = 6.52 ppm due to negative inductive
effects from both the carbonyl group and the quaternary nitrogen of the pyridinium ring.
4
1
1
The COSY ( H- H) experiment allowed the distinction of two unique spin systems
corresponding to the pyridine (H-7 to H-10) and pyridinium (H-1 to H-3) rings. Given the
lack of overlap between the signals from these spin systems and the magnetic equivalence
of hydrogens within the pyridinium ring a straightforward and unequivocal assignment of
1
the H-NMR signals was achieved.
1
3
In a similar manner, the C-NMR spectrum of 2 showed characteristic signals at δ = 67.18
and δ = 192.05 ppm as expected for the methylene (C-4) and the carbonyl group (C-5)
resonances, correspondingly. Of particular relevance was the presence of through-bond spin
states transmission between hydrogens H-7/H-4 and the carbonyl group (C-5) and between
the methylene carbon (C-4) and the ortho hydrogens of the pyridinium ring (H-1), both
1
13
correlations derived from the HMBC ( H- C) experiment further confirmed the NMR
assignments.
1
13
Unambiguous assignment of the H and C chemical shifts of compound 2 was performed
1
1
with the aid of 2D-NMR techniques, including homonuclear ( H- H) COSY/NOESY and
4

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1
13
heteronuclear ( H- C) HSQC/HMBC experiments. Figure 1 summarizes the most relevant
interactions observed.
1
13
Figure 1. Relevant 2D-NMR interactions observed in the (a) HMBC ( H- C) and (b)
1
1
NOESY ( H- H) experiments for 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (2)
CDCl , 400 MHz).
(
3
2
.2. Structural analysis from X-Ray Diffraction and DFT studies.
Compound 2 crystallized in the monoclinic P2 /c space group with 4 molecules per
1
unit cell. As depicted in Figure 2, the acylpyridine fragment adopts a transoid
conformation, which may be attributed to electronic repulsion between the lone pairs of the
oxygen in the carbonyl group and those in the annular nitrogen of the pyridine ring. Crystal
data and structure refinement details are listed in Table 1.
5

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Figure 2. ORTEP drawing of 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (2) with the
thermal ellipsoids drawn at 50 % probability for every atom other than hydrogen.
It can be seen that in the solid state conformer of compound 2, the pyridine and ethanone
moieties are nearly coplanar, with a minimal torsion angle of 0.38 ° (C7-C6-C5-C4). The
most remarkable deviations from planarity arise from a 69.13 ° dihedral angle formed
between the planes containing the pyridinium (C-1 to C-3) and pyridine (C-6 to C-8) rings
(
Figure 3) and from a 13.73 ° torsion angle (C6-C5-C4-N).
The main intermolecular interactions occurring within the crystal lattice of compound 2 are
(a) π−π stacking between two adjacent pyridinium rings with anti-parallel arrangement
(3.718 Å inter-centroid distance) and (b) ion-dipole contacts between an iodine atom and
both H-4 (3.062 Å) and C-5 (3.635 Å). Due to these interactions, compound 2 exhibits a
centrosymmetric arrangement of infinite alternating pairs of pyridinium salts with face-to-
face orientation (Figure 4).
Table 1
Crystal structure and refinement.
Compound
Empirical formula
Formula weight
Temperature
Crystal system
Space group
a (Å)
2
C
12 2
H11IN O
326.13
293 K
Monoclinic
P2 /c
1
7.5629 (3)
6

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b (Å)
c (Å)
α (°)
21.5694 (7)
7.8166 (3)
90.0
β (°)
γ (°)
104.477 (1)
90.0
1234.61 (8)
4
1.755
0.1 x 0.1 x 0.1
2.938 to 27.497
3
Volume (Å)
Z
Density (g⋅cm )
Crystal size (mm)
θ Range (°)
-3
Index ranges
Nref
-9 ≤ h ≤ 9, -28 ≤ k ≤ 27, -10 ≤ l ≤ 9
2835
R (reflections)
0.0237 (2474)
0.0604 (2816)
wR (reflections)
2
Figure 4. Crystal structure of 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (2) viewed
along the crystallographic a axis.
The geometry of compound 2 was optimized at the B3LYP/6-311G(d,p) level of theory,
with the crystal structure geometry used as input. Main deviations from the solid state
conformation (Figure 5) were observed in (a) the interplanar angle between the planes
containing the pyridinium (C-1 to C-3) and pyridine (C-6 to C-8) rings (solid state: 69.13 °,
7

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DFT: 54.75 °) and (b) the distance between the pyridinium ring centroid and the iodide
counterion (solid state: 4.749 Å, DFT: 3.847 Å).
Figure 5. The solid state and equilibrium conformers of 1-[2-oxo-2-(2-
pyridinyl)ethyl]pyridinium iodide (2).
2
.3. Vibrational assignments
Vibrational modes of compound 2 were studied by solid-state FT-IR (ATR)
spectroscopy and analytical DFT computation of both the IR and RAMAN spectra at the
B3LYP/6-311G(d,p) level of theory from the equilibrium geometry. As expected for a
1
molecule with 27 atoms and C symmetry, 75 normal modes are predicted by the DFT
computation, all of which are expected to be IR and Raman active. A comparison between
the experimental and predicted IR spectra is shown in Figure 6.
8

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Figure 6. Experimental (FT-IR/ATR, top) and computed (B3LYP/6-311G**, bottom)
vibrational spectra for 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (2).
As depicted in Figure 7, although the DFT method employed overestimated the vibrational
frequencies, a good correlation between the experimental and theoretical values was found,
ensuring the reliability of the computed frequencies.
9

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Figure 7. Experimental FT-IR (ATR) vs computed (B3LYP/6-311G**) frequencies for 1-
[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (2).
Further improvement of the computed frequencies was achieved using an appropriate
scaling factor of 0.967.[20] Supplementary Table S1 shows the full final frequencies and
intensities of the vibrational modes of compound 2, along with their assignments aided by
the total energy distribution (TED) calculation as implemented in VEDA 4 computer
program.[21]
2
.3.1. C-H and C-C vibrations
The methylene –CH - fragment in the ethanone moiety of compound 2 gives rise to
2
six fundamental vibrations, exhibiting out of phase C-H stretching at ṽ = 3045 and ṽ = 2832
-1
-1
cm and HCH in phase bending at ṽ = 1404 cm . Lower frequency vibrations, namely the
1
0

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-1
wagging, twisting and rocking resonate at ṽ = 1332, ṽ = 1213 and ṽ = 952 cm ,
correspondingly.
Vibrational modes involving aromatic hydrogens from the pyridinium and pyridine rings
proved ubiquitous in the vibrational spectrum. Vibrations including changes in the C-H
-1
bond length lie at the 3262 to 2967 cm region as sharp and intense bands. On the other
-1
hand, in plane and out of plane HCC bending vibrations spanned from 1631 to 1027 cm
-1
and from 909 to 417 cm , respectively. These fundamental vibrations constitute mixed
normal modes in which the corresponding C=C stretches are constantly involved.
2
.3.2. C-N and C-O vibrations
The C=O stretch from compound 2 appears at ṽ = 1711 cm as a sharp and strong
-1
-1
band, while the C=N bond from the pyridinium ring resonates strongly at ṽ = 1332 cm .
Additional fundamental vibrations involving these groups occur at lower frequencies. The
carbonyl group participates in CCO in plane bending vibrations which originate low energy
-1
bands such as those observed at ṽ = 653 cm which include the C-6 atom from the pyridine
ring according to the DFT calculations, that also predicted OCCC out of plane bends
-1
experimentally observed at ṽ = 567 and ṽ = 417 cm .
2
.4. Non-linear optical analysis
Non-linear optics (NLO) is a research field of increasing interest with potential
applications in emerging technologies such as 3D data storage, microfabrication, photonic
devices and molecular machines, as well as biological uses, e.g. in two-photon fluorescence
imaging and photodynamic therapy.[22] The susceptibility of a material to produce a given
1
1

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NLO phenomenon is related to the macroscopic polarizability of its electron densities,
which relies on the local electronic delocalization within the molecule, the molecular dipole
moment and the symmetry elements of the bulk materials.[23, 24]
For second order nonlinear applications, such as second harmonic generation, molecules
should ideally possess intense dipole moments (
µ), low polarizability coefficients (α), high
first order hiperpolarizability coefficients ( ) and non-centrosymetric supramolecular
β
architectures, among other desired macroscopic features like high transparency in the
visible spectrum and thermal stability of the molecular materials.[23]
A
DFT study of these parameters was performed for 1-[2-oxo-2-(2-
pyridinyl)ethyl]pyridinium iodide (2) at the B3LYP/6-311G(d,p) level of theory from the
equilibrium geometry (Table 2). It was found that the molecule has an intense dipole
-30
moment and a moderate
β value, i.e. comparable with that of urea (β = 0.3728 x 10 esu).
Such characteristics, along with the potential of using the ethanone-pyridine submolecular
fragment as a bidentate ligand, render this compound as an interesting building block for
molecular materials with enhanced NLO properties.
Table 2
Electric dipole moment, linear polarizability and first order hyperpolarizability for
compound 2 (B3LYP/6-311G**).
Dipole moment,
µ
Polarizability,
α
First order
hyperpolarizability,
β
-
24
-33
Parameter
D
Parameter
esu (x10 )
-14.0224
4.3863
Parameter
esu (x10 )
-885.1476
114.4244
366.8940
-147.9256
-161.6970
62.5282
µx
µy
-7.6710
7.9674
1.3135
11.1377
α
α
α
α
xx
xy
yy
xz
β
β
β
β
xxx
xxy
xyy
yyy
µ
z
-17.4952
-0.2859
0.7187
-16.4646
24.4832
µ
αyz
αzz
βxxz
βxyz
α
tot
β
yyz
205.4760
1
2

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β
xzz
200.6097
-96.7801
24.3257
βyzz
βzzz
βtot
415.5692
2
.5. Electronic properties
The electronic absorption spectrum of 2 showed two intense bands at λ = 255 nm
and λ = 450 nm. Aiming to characterize the electronic transitions involved, the molecule
was fully optimized using the triple-ζ 6-311G(d,p) polarized basis set and several DFT
functionals; the resulting equilibrium geometries were used in the TD-DFT calculation of
the electronic transitions of 2. As shown in Table 3, none of the calculations with the iodide
counterion omitted in the starting geometry were able to reliably reproduce the
experimental electronic spectrum, indicating a relevant role of the iodine atom during
photoexcitation. Nonetheless, once the full molecule was taken into account, all of the DFT
methods predicted a redshift in the λmax of compound 2, with the B3LYP hybrid functional
yielding the most accurate prediction of the electronic transitions. It may therefore be
assumed that the presence of the iodide counterion produces charge stabilization in the
molecular ground and first excited states, acting as an electron donor towards the
pyridinium ring.
Table 3
Experimental and TD-DFT calculated absorption maxima for pyridinium salt 2 and the
+
cationic fragment [2-I] employing the 6-311G(d,p) basis set (DMSO, nm).
CAM-
B3LYP
236
LC-
BLYP
229
Experimental B3LYP PBE0
ωB97X-D
M06-2X
+
[
2-I]
2
−
450
288
414
271
242
238
379
316
316
329
258
It was also found that the first excited state of compound 2 is mainly populated by the
electronic transition between the frontier molecular orbitals (FMOs), namely the highest
1
3

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occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively). As
shown in Figure 8, the HOMO is mainly located at the iodide counterion, whereas the
LUMO shows a higher contribution of the pyridine (C-6 to C-10) and ethanone (C-4, C-5)
fragments.
Figure 8. Frontier orbitals plots for 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (2) at
the B3LYP/6-311G(d,p) level of theory.
The absence of covalent bonds between the submolecular fragments containing each of the
FMOs, suggests that the first excited state of 2 is reached via through-space electronic
polarization from the iodide counterion to the pyridinium ring, this is further confirmed by
Natural Bonding Orbital (NBO) analysis of the molecule, that provided a localized
description of the involved molecular orbitals and allowed us to characterize this process as
an electronic n-π* transition.
1
4

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The Molecular Electrostatic Potential Map (MEP) for compound 2 is presented in Figure 9
with the green and blue regions having the strongest repulsion and attraction to negative
potential, correspondingly. It can be seen that not only the pyridinium ring and the iodine
counterion have a predominant contribution to the HOMO, but also they hold most of the
electronic density in the molecule. Moreover, the methylene hydrogens show high
electrostatic potential, which helps explaining their remarkable acidity and thus the ability
of the molecule to yield the corresponding enolate upon deprotonation, which has been
widely used as a Michael donor in 1,4-additions.
Figure
9.
Molecular
Electrostatic
Potential
map
for
1-[2-oxo-2-(2-
pyridinyl)ethyl]pyridinium iodide (2) (B3LYP/6-311G**)
3
. Conclusions
The molecular structure of 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide was
studied using a combination of experimental and theoretical approaches. The positive
charge delocalized within the pyridinium ring dictates its crystal packing, which is
dominated by ion-dipole contacts and π-π stackings. Theoretical calculations show that the
molecule holds a moderate first order hyperpolarizability (β) and that its electronic density
is mainly located at the pyridinium ring, with high electrostatic potential at the ethanone
1
5

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hydrogens. This helped further understanding the acidity of these nuclei and the readiness
of the molecule to act as Michael donor. Further studies dealing with comparing the
stability of the enolate formed upon deprotonating this pyridinium salt with that of other
Michael donors commonly used in the synthesis of polypyridyl compounds are ongoing.
4
. Experimental
4
.1. General considerations
Reactions were performed under an atmosphere of nitrogen (chromatographic
grade) and monitored by TLC on pre-coated silica gel plates (ALUGRAM SIL G/UV )
2
54
and spots were visualized by exposure to a UV254 lamp. Melting points were measured in a
Barnstead Electrothermal 9300 apparatus and are uncorrected. IR experiments were
registered in a PerkinElmer Spectrum 400 spectrometer. NMR experiments were recorded
6
in DMSO-d solution using a Varian MR-400 instrument; chemical shifts are relative to the
1
13
residual DMSO-d signal, fixed on δ=2.50 ppm for H and δ= 39.52 ppm for C. HRMS
5
data was acquired in an Agilent Technologies MS TOF spectrometer. Starting materials
were purchased from commercial sources and used without further purification. Physical
and spectral data for compound 2 is in good agreement with that previously reported.[25]
1
-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (2). To a solution of iodine (6.0 g, 23.8
mmol) in pyridine (35 mL) was added 2-acetylpyridine (1) (2.7 mL, 23.8 mmol) and the
mixture was magnetically stirred under reflux for 2 hours. The brown solid thus formed
was collected, washed with methylene chloride (2x50 mL), coevaporated with toluene
(3x20 mL) to remove residual pyridine and dried in vacuo to yield 5.85 g (17.9 mmol, 75
%) of the title compound as a grayish crystalline solid. Melting point: 189-190 °C (Lit:
1
6

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1
1
88-189).[25] H-NMR (400 MHz, DMSO-d ) δ 9.03 (dd, J = 6.6, 1.3 Hz, 2H, H-1), 8.88
6
(ddd, J = 4.8, 1.6, 1.4 Hz, 1H, H-10), 8.74 (tt, J = 7.9, 1.3 Hz, 1H, H-3), 8.31 – 8.27 (m,
2
H, H-2), 8.14 (td, J = 7.6, 1.4 Hz, 1H, H-8), 8.07 (dt, J = 7.6, 1.3 Hz, 1H, H-7), 7.84 (ddd,
13
J = 7.6, 4.8, 1.3 Hz, 1H, H-9), 6.52 (s, 2H, H-4). C-NMR (100 MHz, DMSO-d ) δ 192.05
6
(C-5), 150.82 (C-6), 150.18 (C-10), 146.96 (C-3), 146.75 (C-1), 138.81 (C-8), 129.91 (C-
+
9
1
), 128.36 (C-2), 122.92 (C-7), 67.18 (C-4). HRMS (ESI-TOF ) m/z: [M-I] Observed:
12 2
99.0869, required for C12H N O: 199.0866, error: 1.48 ppm.
4
.2 X-Ray crystal structure determination
Crystals of 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (2) suitable for single-
crystal X-ray diffraction studies were obtained by room temperature evaporation of a
saturated solution of the analyte in dimethyl sulfoxide.
The intensity data were collected on an Enraf Nonius Kappa diffractometer with a CCD
area detector (λMoKα = 0.71073 A˚, monochromator: graphite) at 293 K. The crystals were
mounted on conventional MicroLoops.™ All heavier atoms were found by Fourier map
difference and refined anisotropically. All reflection data set were corrected for Lorentz and
polarization effects. The first structure solution was obtained using the SHELXS-97
program and the SHELXL-97 was applied for refinement and output data.[26] All software
manipulations were done under the WinGX environment program set.[27] The programs
Mercury 3.7 and ORTEP-3 were used to prepare artwork representations.[28, 29]
CCDC 1500500 contains the supplementary crystallographic data for this paper. These data
can be obtained free of charge via https://summary.ccdc.cam.ac.uk/structure-summary-form
1
7

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(or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2
1
EZ, UK; fax: +44 1223 336033).
4
.3. Computational details
Theoretical calculations were performed within the framework of the Density
Functional Theory using the Gaussian 09W software package.[30] The triple-ζ 6-
11G(d,p) polarized basis set was used for all atoms including iodine.[31, 32] Several
3
functionals were tested: B3LYP, PBE0, CAM-B3LYP and the long-range corrected
ωB97X-D, LC-BLYP and M06-2X. The popular B3LYP functional yielded the most
accurate prediction of the electronic and vibrational spectra and was consequently used to
perform the full set of computations from the optimized geometry. Single-Point energies
were computed at the same level of theory. TD-DFT computation of excitation energies
were achieved in dimethylsulfoxide under the Polarizable Continuum Model.
5
. Acknowledgements
Thanks are due to CONACYT for financial support and the scholarships granted to
P.L.-V. (337958) and M.P.-C. (730609) and to PAIP and PAPIIT 216616 for financial
support. Authors would like to express their gratitude to M. Romero-Ávila (FQ-UNAM)
and M. E. Ochoa (CINVESTAV-IPN) for technical assistance and to M. A. Leyva and G.
Cuellar (CINVESTAV-IPN) for X-Ray diffraction studies and HRMS analyses,
correspondingly.
6
. References
1
8

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acylpyridinium salts. A convenient method for the synthesis of 4-alkyl(aryl)pyridines, J.
Org. Chem., 47 (1982) 4315-4319.
[2] R. Yamaguchi, E. Hata, T. Matsuki, M. Kawanisi, An efficient regio- and
stereoselective synthesis of (.+-.)-monomorine I via the highly regioselective .alpha.-
alkynylation of a 1-acylpyridinium salt, J. Org. Chem., 52 (1987) 2094-2096.
[
3] T. Damiano, D. Morton, A. Nelson, Photochemical transformations of pyridinium salts:
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752.
4] I. Sasaki, J.-C. Daran, G. Commenges, The simple production of nonsymmetric
quaterpyridines through Kröhnke pyridine synthesis, Beilstein J.Org.Chem., 11 (2015),
781-1785.
5] M. Ziegler, V. Monney, H. Stoeckli-Evans, A. Von Zelewsky, I. Sasaki, G. Dupic, J.-C.
2
[
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Figure 3. Dihedral angle formed between the planes containing the pyridinium and
pyridine rings in compound 2.

ACCEPTED MANUSCRIPT
Highlights
•
The molecular structure of 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide has been
discussed based on Single Crystal X-Ray Diffraction Studies and DFT calculations.
1
13
•
•
A full assignment of the H and C NMR spectra was attained through 2D experiments.
A full vibrational and electronic study of the molecule was performed aided by DFT
computations, which further suggested a potential use of the molecule as building block
for enhanced Non-Linear Optical applications.
•
The reactivity of the molecule as Michael donor was discussed based on the computed
electrostatic potential map.