Vibrational, electronic, and structural properties of 6-nitro- and 6-amino-2-trifluoromethylchromone: An experimental and theoretical study

Article abstract of DOI:10.1021/jp312683s

Two 2-trifluoromethylchromones, 6-nitro-2-trifluoromethylchromone (1) and 6-amino-2-trifluoromethylchromone (2) were synthesized and characterized by NMR (¹H, ¹³C, and ¹⁹F), UV-vis, vibrational (IR and Raman) spectroscopy, MS spectrometry, and compound 1 also by single structural X-ray diffraction methods. This substance crystallizes in the monoclinic P2 ₁/c space group with Z = 4 molecules per unit cell. In the solid, the fused rings and the amino group of 1 are coplanar and the trifluoromethyl group adopts a nearly staggered conformation. The NMR, vibrational, and electronic spectra were discussed and assigned with the assistance of DFT calculations.

Full text of DOI:10.1021/jp312683s

Article
pubs.acs.org/JPCA
Vibrational, Electronic, and Structural Properties of 6‑Nitro- and
6‑Amino-2-Trifluoromethylchromone: An Experimental and
Theoretical Study
L. P. Avendano Jimenez,† G. A. Echeverría,‡ O. E. Piro,‡ S. E. Ulic,†,§,* and J. L. Jios⊥,*
́
̃
†CEQUINOR (CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 esq. 115, (1900) La Plata,
Republica Argentina
́
‡Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata e IFLP (CONICET, CCT-La Plata), C. C.
67, (1900) La Plata, Republica Argentina
́
§Departamento de Ciencias Bas
́ ́ ́
́
icas, Universidad Nacional de Lujan, Rutas 5 y 7, (6700) Lujan, Buenos Aires, Republica Argentina
⊥LASEISIC-PLAPIMU (UNLP-CIC), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata,
47 esq. 115, (1900) La Plata, Republica Argentina
́
S
* Supporting Information
ABSTRACT: Two 2-trifluoromethylchromones, 6-nitro-2-trifluorome-
thylchromone (1) and 6-amino-2-trifluoromethylchromone (2) were syn-
thesized and characterized by NMR (1H, 13C, and 19F), UV−vis, vibrational
(IR and Raman) spectroscopy, MS spectrometry, and compound 1 also by
single structural X-ray diffraction methods. This substance crystallizes in the
monoclinic P21/c space group with Z = 4 molecules per unit cell. In the solid,
the fused rings and the amino group of 1 are coplanar and the trifluoromethyl
group adopts a nearly staggered conformation. The NMR, vibrational,
and electronic spectra were discussed and assigned with the assistance
of DFT calculations.
the synthesis and reactivity of 2-polyfluoroalkylchromones.8−15
1. INTRODUCTION
Significant differences in the reactivity between 2-alkyl- and 2-
trifluoromethylchromones with respect to nucleophilic reagents
were observed.8 The introduction of the trifluoromethyl group
into the C2 position of chromone causes activation of the pyrone
ring due to the strong electron withdrawing capacity of the −CF3
group. Besides, this property has been found to enhance the
electrophilic character at cationic sites in superelectrophiles leading
to a higher positive charge delocalization.16 Recently, we reported
a simple one-pot synthesis procedure for 2-perfluoromethylchro-
mones, establishing a new synthetic route for molecules containing
the strong electron-withdrawing trifluoromethyl group.17 Until
now, to the best of our knowledge, the title compounds were not
thoroughly investigated. For 6-nitro-2-trifluoromethylchromone
Chromones, an important class of oxygen-containing hetero-
cyclic compounds, are widespread in nature.1 The existence of
chromones as parent compounds in a plant’s life-cycle is well-
known, mostly as dyes in plant leaves, fruits, and flowers.2−4 In
addition, 2-methylchromone derivatives are important in the
synthesis of other heterocycles, since they are usually readily
cleaved at the pyrone ring via nucleophilic attack at the C2
position.4 This property has been used to prepare a variety of
rearranged products and heterocyclic molecules.3
On the contrary, 2-perfluoroalkyl derivatives of chromones
have never been found in nature. The first 2-trifluoromethyl-
substituted chromones5 were prepared long time ago, but such
fluorinated molecules have been scarcely studied. The trifluo-
romethyl substituent is an important group, because its pres-
ence in organic molecules increases their applicability as
pharmaceuticals or agrochemicals. Pharmacological properties
such as fat solubility or metabolic stability are improved when
aromatic substrates are functionalized with this substituent.6
Despite its importance, there are no good general methods for
the introduction of the trifluoromethyl group into organic mol-
ecules. Recently, a catalytic reaction for the addition of this
useful group has been described.7 In the past decade, Sosnovskikh
and his group have devoted considerable attention to the study of
1
(1), the H NMR assignment and some bands of the FT-IR
spectrum were reported,18 while the 6-amino-2-trifluoromethyl-
chromone (2), is described for the first time in this paper. The
vibrational spectra of 7-amino-4-trifluoromethylcoumarin, an
isomer of 2, were assigned on the basis of normal coordinates
calculation.19 Vibrational spectra of related chromones were
Received: December 23, 2012
Revised: February 8, 2013
Published: February 11, 2013
© 2013 American Chemical Society
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analized both by computational and experimental methods.20,21
Moreover, UV absorption spectra of chromones were recently
subject of study, especially by the good agreement between
experimental spectra and those obtained by theoretical
calculations.22−24 This work presents the results of a complete
study of 6-nitro-2-trifluoromethylchromone (1) and 6-amino-2-
trifluoromethylchromone (2), depicted in Figure 1. The optimization
Table 1. Crystal Data and Structure Refinement Results for
6-Nitro-2-trifluoromethylchromone (1)
empirical formula
formula weight
temperature
C10H4F3NO4
259.14
295(2) K
wavelength
1.54184 Å
crystal system
space group
monoclinic
P21/c
unit cell dimensions
a = 6.1217(6) Å
b = 10.888(1) Å
c = 15.598(2) Å
β = 99.16(1)°
volume
1026.4(2) Å3
Z
4
density (calculated)
absorption coefficient
F(000)
1.677 Mg/m3
1.475 mm−1
520
crystal size
0.22 × 0.13 × 0.10 mm3
θ range for data collection
index ranges
4.97−70.98°
−7 ≤ h ≤ 5, −13 ≤ k ≤ 10, −18 ≤ l ≤ 19
reflections collected
independent reflections
3752
1983 [R(int) = 0.0221]
observed reflections
[I > 2σ(I)]
1370
completeness to θ = 70.98°
absorption correction
99.7%
semiempirical from equivalents
1.00000 and 0.833 75
full-matrix least-squares on F2
1983/0/179
max. and min transmission
refinement method
data/restraints/parameters
goodness-of-fit on F2
1.052
final R indices [I > 2σ(I)]
R indices (all data)
R1 = 0.0553, wR2 = 0.1483
R1 = 0.0746, wR2 = 0.1726
0.247 and −0.237 e·Å−3
Figure 1. Optimized structures (B3LYP/6-311++g(d,p)) of 6-nitro-2-tri-
fluoromethylchromone (1) and 6-amino-2-trifluoromethylchromone (2).
largest diff. peak and hole
MS: m/z (%) = 259 ([M]+, 100), 75 ([C6H3]+, 83), 213 ([M −
NO2]+, 43), 157 ([C8H4F3]+, 43), 137 ([C6H3NO3]+, 30), 107
([C6H3O2]+, 25), 74 (25), 229 ([M − NO]+, 21), 62 (21), 63
(20), 30 (15), 173 ([C8H4F3O]+, 12), 201 ([C9H4F3O2]+, 6),
240 (5); 214 (5); 212 (5); 185 ([C9H4F3O]+, 5). UV−vis
(methanol): λmax 240 and 287 nm.
of both geometries were performed using the DFT/B3LYP
method and different basis sets to assist the interpretation and the
1
assignment of experimental IR and Raman, UV−vis and H and
13C NMR spectra. Moreover, the crystal structure of 1 was de-
termined by X-ray diffraction methods, and their experimental
parameters were used to validate the theoretical results.
2.2. 6-Amino-2-trifluoromethylchromone (2). Synthe-
sis. 2 was obtained from 6-nitro-2-trifluoromethylchromone
(1) following the procedure reported by Merlic25 with slight
modifications. Iron powder (3.36 g, 60.16 mmol), water (5 mL),
and concentrated HCl (100 μL), were added sequentially to a
solution of 6-nitro-2-trifluoromethylchromone (1.1 g, 4.25 mmol)
in ethanol (22 mL). The reaction mixture was stirred at 90 °C for
1 h and then filtered out. The residue was washed twice with
10 mL of hot ethanol and the filtrates were collected with the first
portion. The resulting yellow solution was allowed to cool to
room temperature and then stored in a freezer overnight. After
filtration, the solid was recrystallized in ethanol. The yellow
crystalline solid (mp 186−188 °C) was suitable for spectroscopic
2. EXPERIMENTAL SECTION
2.1. 6-Nitro-2-trifluoromethylchromone (1). Synthesis.
1 was obtained, according to literature procedure, by the reaction
of 2-trifluoromethylchromone17 and HNO3/H2SO4 and then re-
crystallized from ethanol (mp 155−156 °C). Single crystals, ade-
quate for structural X-ray diffraction work, were obtained from slow
evaporation of initially unsaturated alcoholic solutions at controlled
1
temperatures. H NMR: δ = 9.06 (1H, d, J = 2.7 Hz, H-5); 8.60
(1H, dd, J = 9.1 and 2.7 Hz, H-7); 7.75 (1H, d, J = 9.1 Hz, H-8);
6.82 ppm (1H, s, H-3). 13C NMR: δ = 175.1 (C-4); 158.2 (C-8a);
152.8 (q, J = 40 Hz, C-2); 145.4 (C-6); 129.2 (C-7); 124.1 (C-5);
122.4 (C-4a); 120.3 (C-8); 118.2 (q, J = 275 Hz, CF3); 111.0 ppm
(C-3). 19F NMR: δ = −72.10 ppm. For atom numbering see Chart 1.
1
studies. H NMR: δ = 7.39 (1H, s, overlapped with H-5, H-8);
7.35 (1H, d, J = 2.9 Hz, H-5); 7.08 (1H, dd, J = 2.9 and 8.8 Hz,
H-7); 6.64 (1H, s, H-3); 3.97 ppm (2H, br·s, NH2). 13C NMR:
δ = 177.0 (C-4); 152.3 (q, J = 43 Hz, C-2); 149.2 (C-8a);
145.0 (C-6); 124.1 (C-4a); 123.1 (C-7); 119.3 (C-8); 118.7
(q, J = 274 Hz, CF3); 109.3 (C-3); 107.6 ppm (C-5). 19F
NMR: δ = −71.90 ppm. For atom numbering see Chart 1.
MS: m/z (%) = 229 ([M]+, 100), 201 ([M − CO], 12), 135
([C7H5NO2]+, 12), 107 ([C6H5NO]+, 14), 79 ([C5H5N]+, 30),
52 (29). UV−vis (methanol): λmax 205, 241, and 376 nm.
Chart 1. Structure and Atom Numbering for NMR Analysis
of 1 and 2
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2 cm−1 in the range from 4000 to 400 cm−1. Raman spectra of the
solid were measured in Pyrex standard capillaries (2.5-mm i.d.) on a
Bruker IFS 66 spectrometer (spectral resolution 4 cm−1), equipped
with a 1064 nm Nd:YAG laser, in the range from 3500 to 100 cm−1.
1
NMR Spectra. The H (200.0 MHz), 19F (188.7 MHz), and
13C (50.3 MHz) NMR spectra of the title compounds were re-
corded on a Varian Mercury Plus 200 spectrometer. The sample
was dissolved in CDCl3 in a 5 mm NMR tube. Chemical shifts,
δ, for 13C and 1H NMR spectra are given in ppm relative to TMS
(δ = 0 ppm) and are referenced by using the residual non
deuterated solvent signal. For 19F NMR spectrum, a 0.05%
trifluoroacetic acid (TFA) in CDCl3 solution was used as external
reference (δ = −71.00 ppm). Coupling constants, J, are reported
in Hz, being the singlet, doublet, double doublet, and quartet
marked as s, d, dd, and q, respectively.
UV−Visible Spectroscopy. The spectra of 1 and 2 in
methanol were recorded using a quartz cell (10 mm optical
path length) on a ChromTech CT-5700 UV/vis spectropho-
tometer, with 2.0 nm spectral bandwidth. Measurements were
carried out in the spectral region from 190 to 700 nm.
Figure 2. Plot of 6-nitro-2-trifluoromethylchromone (1) showing the
labeling of the non-H atoms and their displacement ellipsoids to the
30% probability level.
2.3. Instrumentation. Infrared and Raman Spectroscopy.
Infrared absorption spectra in KBr pellets were recorded on a
LUMEX Infra LUM FT-02 spectrometer with a resolution of
a b
,
Table 2. Selected Structural Parameters of 1 (Calculated and Experimental) and 2 (Calculated)
param
expt (1)
calcd (1)
calcd (2)
param
expt (1)
calcd (1)
calcd (2)
r(C1−C2)
r(C1−C6)
r(C2−C3)
r(C3−C4)
r(C3−N)
1.367(4)
1.386(4)
1.386(4)
1.366(3)
1.466(3)
1.395(4)
1.390(3)
1.468(3)
1.372(3)
1.320(4)
1.353(3)
1.499(4)
1.447(4)
1.227(3)
1.299(4)
1.306(4)
1.275(5)
1.217(3)
1.219(3)
−
1.382
1.398
1.401
1.381
1.481
1.400
1.401
1.484
1.368
1.341
1.352
1.515
1.468
1.219
1.346
1.341
1.346
1.222
1.224
−
1.382
1.395
1.414
1.393
1.391
1.399
1.398
1.481
1.379
1.345
1.343
1.513
1.465
1.224
1.348
1.348
1.343
−
∠(O1−N−O2)
∠(O1−N−C3)
∠(O2−N−C3)
∠(H1−N−H2)
∠(H1−N−C3)
∠(H2−N−C3)
∠(O3−C7−C10)
∠(O3−C6−C1)
∠(O3−C6−C5)
∠(O4−C9−C8)
∠(O4−C9−C5)
∠(F1−C10−F2)
∠(F1−C10−F3)
∠(F2−C10−F3)
∠(F1−C10−C7)
∠(F2−C10−C7)
∠(F3−C10−C7)
123.9(3)
118.3(2)
117.8(3)
−
−
−
110.0(3)
116.2(2)
121.5(2)
123.6(2)
122.4(2)
106.4(4)
106.4(4)
108.4(4)
112.3(3)
110.7(3)
112.4(3)
125.1
117.6
117.3
−
−
−
110.3
116.4
121.6
123.1
123.2
108.1
107.6
108.1
110.9
110.9
110.9
−
−
−
112.9
116.7
116.4
110.6
116.9
122.0
122.9
123.2
107.8
107.8
107.3
111.2
111.2
111.3
r(C4−C5)
r(C5−C6)
r(C5−C9)
r(C6−O3)
r(C7−C8)
r(C7−O3)
r(C7−C10)
r(C8−C9)
r(C9−O4)
r(C10−F1)
r(C10−F2)
r(C10−F3)
r(N−O1)
r(N−O2)
r(N−H1)
r(N−H2)
−
1.009
Φ(C3−C4−C5−C9)
Φ(C6−O3−C7−C10)
Φ(C6−O3−C7−C8)
Φ(O1−N−C3−C4)
Φ(O1−N−C3−C2)
Φ(O2−N−C3−C2)
Φ(O2−N−C3−C4)
Φ(H1−N−C3−C4)
Φ(H1−N−C3−C2)
Φ(H2−N−C3−C2)
Φ(H2−N−C3−C4)
Φ(O4−C9−C5−C4)
Φ(O4−C9−C8−C7)
Φ(F2−C10−C7−C8)
Φ(F2−C10−C7−O3)
Φ(F1−C10−C7−O3)
Φ(F1−C10−C7−C8)
Φ(N−C3−C4−C5)
Φ(F3−C10−C7−O3)
Φ(F3−C10−C7−C8)
−178.3
0.4
179.9
−179.9
0.0
−179.8
−179.9
0.1
−
−
1.009
179.2
1.7
0.0
−
−
−
−
∠(C1−C2−C3)
∠(C1−C6−C5)
∠(C2−C1−C6)
∠(C2−C3−N)
∠(C2−C3−C4)
∠(C3−C4−C5)
∠(C4−C3−N)
∠(C4−C5−C6)
∠(C4−C5−C9)
∠(C5−C9−C8)
∠(C6−C5−C9)
∠(C7−C8−C9)
∠(C7−O3−C6)
∠(C8−C7−O3)
∠(C8−C7−C10)
119.0(3)
122.3(2)
118.9(3)
118.4(2)
122.8(3)
118.8(2)
118.8(2)
118.2(2)
121.5(2)
114.0(2)
120.3(2)
120.8(3)
117.8(2)
125.5(3)
124.5(3)
119.3
122.0
118.9
118.7
119.1
122.2
119.2
118.6
121.1
113.7
120.2
120.6
118.8
125.0
124.7
121.3
120.9
119.2
120.1
118.5
120.9
121.4
119.1
121.0
113.9
119.9
120.7
118.4
125.1
124.3
−179.9
2.5
179.9
0.0
−175.9
−
−
−
−
−1.1
178.3
−7.3
173.8
55.1
−126.1
176.1
−64.8
114.0
179.9
−
−
−
−
−157.6
25.2
162.7
−20.1
0.1
179.9
−179.9
0.0
179.8
0.0
179.9
59.7
−120.2
−179.9
−59.8
120.2
−179.9
59.8
120.2
−177.2
−59.7
−120.2
a
b
Atom numbering taken from Figure 2. Experimental data from X-ray diffraction and computed parameters at B3LYP/6-311++g(d,p).
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Figure 3. Infrared spectrum of the solid (upper trace, KBr pellets) and
Raman spectrum (lower trace) of 6-nitro-2-trifluoromethylchromone
(1) at room temperature.
Mass spectrometry. The MS determinations were per-
formed by injection of methanol solutions (∼1 μL) in an HP
5890 Chromatograph coupled to an HP 5972 A mass selective
detector. An HP5-MS capillary column (30 m x 0.25 mm x
5 μm) has been used, with H2 as the carrier gas (0.6 mL/min).
The temperature set points were: 200 °C in the split injector,
300 °C in the interface, 185 °C in the ion source and the oven
ramp started at 80 °C and ended at 200 °C with a heat rate of
10 °C/min. The electron energy was 70 eV with a mass range
of 50−350 amu and a pressure in the mass spectrometer lower
than 10−5 Torr. The mass spectra of 1 and 2 are shown in
Figures S1 and S2 (Supporting Information).
X-ray diffraction data. A complete data set for 6-nitro-2-
trifluoromethylchromone (1) was collected on an Oxford Xcalibur,
Eos, Gemini CCD diffractometer with graphite-monochromated
CuKα (λ = 1.54184 Å) radiation. X-ray diffraction intensities were
collected (ω scans with ϑ and κ-offsets), integrated and scaled with
CrysAlisPro26 suite of programs. The unit cell parameters were
obtained by least-squares refinement (based on the angular settings
for all collected reflections with intensities larger than seven times
the standard deviation of measurement errors) using CrysAlisPro.
Data were corrected empirically for absorption employing the
multiscan method implemented in CrysAlisPro. The structure was
solved by direct methods with SHELXS-9727 and the molecular
model refined by full-matrix least-squares procedure on F2 with
SHELXL-97.28 All hydrogen atoms were located in a difference
Fourier map phased on the heavier atoms and refined at their
found positions with isotropic displacement parameters. Crystal
data and structure refinement results are summarized in Table 1.
2.4. Computational Methods. Theoretical calculations
were performed using the program package Gaussian 03.29
Preliminary geometry optimization for 1 and 2, was carried out
Figure 4. Infrared spectrum of the solid (upper trace, KBr pellets) and
Raman spectrum (lower trace) of 6-amino-2-trifluoromethylchromone (2).
with the density functional theory (B3LYP) method by using
the 6-31+g(d) basis set and scans of the potential energy
surface (in steps of 30°) by means of the 6-311+g(d) level of
theory. Final optimizations and vibration frequency calcula-
tions were implemented employing the 6-311++g(d,p) basis set.
The computed vibrational properties correspond, in all cases,
to potential energy minima with no imaginary values for the
frequencies. Electronic transitions were calculated within the
framework of the time-dependent density functional theory
(6-311+g(d)).30
1
The H and 13C chemical shifts were calculated with the
B3LYP/6-31+g(d) and 6-311+g(2d,p) optimized geometries
by GIAO method (gauge including atomic orbital),31 using the
corresponding TMS shielding, calculated at the same level of
theory, as the reference. This value was taken as a constant,
which is subtracted from the calculated isotropic chemical
shielding of a given nucleus to convert them in chemical shifts.
3. RESULTS AND DISCUSSION
3.1. Structure of 6-Nitro-2-trifluoromethylchromone 1
Determined by Single X-ray Diffraction. The solid state
molecular structure of 1 is shown in the ORTEP32 plot of
Figure 2. The corresponding interatomic bond distances and
angles are given in Table 2, where they are compared with the
corresponding computed geometrical parameters (B3LYP6-
311++g(d,p)).
Because of an extended π-bonding electronic structure, the
organic skeleton is planar (rms deviation of atoms from the best
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Table 3. Experimental and Calculated Frequencies (cm−1) and Tentative Assignment of Fundamental Vibration Modes in
6-Nitro-2-trifluoromethylchromone (1)
b
experimental
calculated
a
c
d
mode
IR
Raman
frequency
intensity
assignment
ν1
3236
3232
3231
3209
1737
1690
1660
1622
1588
1499
1469
1406
1372
1369
1292
1281
1251
1232
1184
1151
1140
1132
1078
1071
991
3 (112)
4 (93)
11 (34)
<1 (77)
372 (119)
30 (68)
136 (27)
32 (55)
149 (48)
77 (4)
100 (1)
43 (6)
71 (9)
285 (305)
225 (2)
152 (7)
168 (5)
44 (94)
259 (2)
81 (9)
293 (3)
94 (29)
20 (14)
78 (3)
<1 (<1)
13 (<1)
65 (2)
25 (12)
40 (<1)
31 (<1)
10 (2)
23 (3)
<1 (<1)
17 (2)
15 (17)
<1 (<1)
2 (<1)
4 (<1)
12 (2)
4 (2)
ν(C8−H)
ν(C2−H); ν(C1−H)
ν(C4−H)
ν(C1−H); ν(C2−H)
ν(C9−O4)
ν(C8−C7)
ν(C3−C4); ν(C1−C6); ν(C7−C8)
ν(C4−C5); ν(C1−C2); ν(C5−C6)
νas(NO2); ν(C2−C3); ν(C5−C6)
δ(C4−H); δ(C1−H); δ(C2−H)
ν(C5−C9); ν(C1−C2); ν(C4−C5)
ν(C7−O3); ν(C3−C4); ν(C1−C6); δ(C8−H)
ν(C1−C2); ν(C3−C4); ν(C5−C6)
νs(NO2); ν(N−C3); ν(C5−C6)
δ(C1−H); δ(C2−H); δ(C4−H); ν(C7−C10)
δ(C8−H); ν(C7−C10)
ν2
3098(w)
3094(6)
3085(9)
3055(4)
1662(62)
ν3
ν4
3056(w)
1678(vs)
ν5
ν6
ν7
1624(s)
1579(w)
1535(s)
1625(16)
1583(29)
1530(19)
ν8
ν9
ν10
ν11
ν12
ν13
ν14
ν15
ν16
ν17
ν18
ν19
ν20
ν21
ν22
ν23
ν24
ν25
ν26
ν27
ν28
ν29
ν30
ν31
ν32
ν33
ν34
ν35
ν36
ν37
ν38
ν39
ν40
ν41
ν42
ν43
ν44
ν45
ν46
ν47
ν48
ν49
ν50
ν51
ν52
ν53
ν54
ν55
ν56
ν57
ν58
1460(vs)
1404(m)
1402(5)
1355(vs)
1283(vs)
1230(s)
1198(s)
1351(100)
1286(9)
1237(21)
1226(15)
1210(15)
1167(5)
δ(C1−H); δ(C4−H)
ν(C6−O3); ν(C7−C10); ν(C5−C9)
νas(CF3)
1164(s)
δ(C1−H); δ(C2−H)
νas(CF3)
1131(vs)
1073(s)
1130(32)
1057(9)
ν(C3−N); δ(C8−H); δ(C4−H)
δ(C4−H); δ(C4−C5−C9)
νs(CF3); ν(C7−O3); δ(C8−H); δs(CF3)
γ(C1−H); γ(C2−H); γ(C4−H)
γ(C4−H)
δ(C8−C7−O3)
δ(C2−C3−C4); δ(C9−C8−C7)
γ(C8−H)
1056(m)
969
926(s)
909(s)
928(6)
934
913(17)
921
854(m)
827(w)
819(vw)
777(m)
900
847
γ(C1−H); γ(C2−H)
δ(NO2); δ(C2−C3−C4)
840
776(6)
784
δ(C5−C9−C8); δ(C5−C9−C4)
γ(C8−H); γ(C4−H); γ(C1−H); γ(C2−H); γ(C9−O4)
γ(NO2); γ(C2−H); γ(C4−H); γ(C1−C6−O3)
δs(CF3); δ(C6−C1−C2); δ(C4−C5−C3)
γ(O3−C7−C8)
γ(C1−H); γ(C5−C9−C8); γ(C8−H)
δ(C2−C3−C4); δ(C1−C6−C5)
δ(C5−C9−O4); δ(C1−C6−O3)
δas(CF3); δ(C5−C9−C8); δ(N−C3−C4)
δas(CF3); δ(O4−C9−C8)
γ(C2−C3−C4); γ(C5−C6−C1); γ(C6−O3−C7)
δ(O−N−C3); δ(C5−C9−C8); δ(C3−C4−C5)
δas(CF3); γ(C2−C3−C4); γ(C1−C6−C5)
δ(C6−O3−C7)
γ(C4−C5−C6); γ(C6−C1−C2)
τ(C8−C7−CF3)
γ(C2−C1−C6); γ(C7−O3−C6)
δ(C7−CF3)
δ(C9−C5−C4); δ(C2−C3−N)
γ(C9−C8−C7)
δ(C10−C7−C8); δ(N−C3−C2)
δ(N−C3−C4); δ(O3−C7−C10)
τ(C1−C6−O3−C7); τ(O4−C9−C8−C7)
τ(O4−C9−C5−C4)
τ(C8−C7−CF3);τ(O4−C9−C5−C4)
πip(CF3)
765
748(m)
720(m)
749(4)
733
723(26)
721
699
674(w)
650(w)
621(w)
678
657
622(6)
543(9)
624
548
541(w)
511(w)
515(14)
544
9 (4)
525
1 (1)
516
2 (7)
510
3 (1)
506
1 (2)
441
2 (<1)
6 (<1)
<1 (1)
<1 (1)
3 (4)
406
352
335
305
274
<1 (<1)
1 (4)
253
181
2 (1)
167
4 (<1)
5 (<1)
<1 (1)
2 (<1)
2 (1)
147
116
114
45
(C2−C3−NO2); (CF3−C7−O3)
2173
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Article
Table 3. continued
b
experimental
calculated
a
c
d
mode
IR
Raman
frequency
intensity
assignment
ν59
ν60
40
32
<1 (1)
<1 (2)
τ(C2−C3−NO2)
τ(C8−C7−CF3)
a
b
c
vs, very strong; s, strong; w, weak; vw, very week; sh, shoulder. 6-311++g(d,p). Calculated intensities: IR in km mol−1 and Raman
d
(in parentheses) in Å4 amu−1. ν, δ, γ and τ represent stretching, in-plane deformation, out-of-plane deformation and torsion modes.
least-squares plane of 0.065 Å). The observed covalent bond
structure confirms and quantifies what it is expected for this
molecule from organic chemistry’s rules. Particularly, the ob-
served aromatic ring C−C bond distances are in the 1.366(3)−
1.395(4) Å range as expected for a resonant structure. Within
the fused heterocycle C−O distances are 1.353(3) and
1.372(3) Å. C5−C9 and C8−C9 distances of 1.468(3) and
1.447(4) Å indicate the single character of these bonds while
the value d(C7−C8) = 1.320(4) Å agrees with the formally
double bond nature expected for this link. The trifluoromethyl
group adopts a nearly staggered conformation. The nitro group
shows N−O bond distances which are equal to within experi-
mental accuracy [1.217(3) and 1.219(3) Å] and a O−N−O
angle of 123.9(3)°.
3.2. Structural Properties. Potential energy curves
(B3LYP/6-311+g(d)) for internal rotations around the −CF3
and −NO2 or −NH2 groups for 1 and 2, respectively, were per-
formed to evaluate the minima energy structures adopted by
the title compounds. The molecules are mainly characterized by
a flat orientation throughout their structures (see Figure 2).
The −CF3 group has the same orientation in both compounds
with one fluorine atom in the plane of the molecule (syn respect
to the CC bond). This configuration is adopted probably to
minimize the interaction with the bridged oxygen atom.
The −NO2 group in compound 1 is in the same plane as the
molecular skeleton. Moreover, the −NH2 group in compound
2 has both hydrogen atoms slightly deviated above the molecular
plane, see Table 2.
Moreover, this mode is observed at 1652 (IR) and 1670 cm−1
(Raman) in chromone35 and at 1728 (IR) and 1739 cm−1
(Raman) in chromone-2-carboxylic acid.35
The assignment of the C−H and C−C stretching modes was
based on the results reported for chromone35 and phenol36 (see
Table 3).
6-Amino-2-trifluoromethylchromone. The prominent IR
bands at 3429 and 3345 cm−1 (see Figure 4) are assigned to the
νasNH2 and νsNH2 stretching modes (calculated: 3678 and
3578 cm−1), while only a very weak band is observed in the
Raman spectra at 3351 cm−1 corresponding to the νsNH2
stretching. The location of these bands is in good agreement
with those in some related aminochromones.37 The out-of-plane
bending of the NH2 group is predicted, by quantum chemical
calculations, as a strong band at 509 cm−1 but this vibration was
not detected in IR and Raman. This inconsistency could be
attributed to the fact that the −NH2 group is involved in inter-
molecular interactions.
The IR strong band at 1320 cm−1 can be attributed to the
C−N stretching mode (calculated at 1330 cm−1) which was not
detected in Raman.
The very intense band at 1641 (IR) and the one at 1635 cm−1
(Raman) are assigned to the ν(CO) stretching (calculated:
1713 cm−1). These values are in good agreement with those
reported for amino substituted chromones.37 The amino group
located on the aromatic ring shifts the frequency of the carbonyl
group down, when comparing with the nitro compound (see
Table 4) and other related 2-trifluoromethyl substituted
chromones.17
3.3. Vibrational Spectroscopy. The IR and Raman
spectra of solid 6-nitro-2-trifluoromethylchromone (1) and 6-
amino-2-trifluoromethylchromone (2) are shown in Figure 3 and
Figure 4, while the tentative assignment of the observed and
computed fundamental vibrational modes are presented in Table
3 and Table 4, respectively. Only the most relevant characteristic
functional groups of the molecules will be discussed.
Most of the observed spectral positions and intensities of the
bands for both compounds are in good agreement with the
corresponding values derived from quantum chemical calcu-
lations and with related compounds.
3.4. Electronic Spectroscopy. The electronic spectra in
methanol of 6-nitro-2-trifluoromethylchromone (1) (2.9 ×
10−5 M) and 6-amino-2-trifluoromethylchromone (2) (2.4 ×
10−5 M) are shown in Figures 5 and 7, together with simulated
spectra obtained from calculated electronic transitions. Absorp-
tion maxima of both compounds are compared with calculated
values in Tables 5 and 6, which also include tentative assign-
ments. For simplicity, only the dominant transitions (chosen
according to their oscillator strength) are used to assign the
observed bands. From these results, it can be concluded that the
calculated transitions closely reproduce the experimental elec-
tronic spectra.
6-Nitro-2-trifluoromethylchromone (1). Figure 6 shows the
MO’s (HOMO, highest occupied MO; LUMO, lowest
unoccupied MO) mainly involved in the electronic transitions
used to assign the experimental bands.
The observed bands (see Table 5) at 203 and 212 nm are
dominated by one-electron transitions, from the HOMO-4 to
the LUMO+1 and HOMO-1 to the LUMO+2, respectively,
despite minor contributions from other one-electron excitations.
They are assigned to transitions calculated at 219 and 224 nm,
6-Nitro-2-trifluoromethylchromone (1). Aromatic nitro
compounds have strong absorptions due to asymmetric and
symmetric stretching vibrations of the −NO2 group. Hydrogen
bonding has a little effect on the NO2 asymmetric stretching
vibrations.33,34 The asymmetric and symmetric NO2 stretching
bands of 1 have been assigned to the IR observed bands at 1535
(Raman: 1530 cm−1) and 1355 cm−1 (Raman: 1351 cm−1),
respectively, taking into account the predicted values (6-311+
+g(d,p)) and the assignment in 1-fluoro-3-nitrobenzene.34
The in- and out-of-plane deformations of the −NO2 group,
predicted as very weak absorbing modes, are attributed to
the weak and medium IR bands at 819 and 748 cm−1 bands,
respectively, and no counterparts were observed in the Raman
spectra. The C−N stretching mode can be assigned to the strong
IR band at 1073 cm−1 (calculated at 1132 cm−1), which was not
detected in Raman. The ν(CO) vibration is associated with the
very strong absorption band at 1678 cm−1 (IR) and to the medium
intense dispersion observed at 1662 cm−1 in Raman and it is
strongly coupled with the alkene ν(CC) predicted at 1690 cm−1.
2174
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Table 4. Experimental and Calculated Frequencies (cm−1) and Tentative Assignment of Fundamental Vibration Modes in
6-Amino-2-trifluoromethylchromone (2)
b
experimental
calculated
a
c
d
mode
IR
Raman
frequency
intensity
assignment
ν1
3429(s)
3345(s)
3234(m)
3678
3578
3231
3201
3184
3167
1713
1677
1666
1650
1614
1516
1488
1416
1375
1330
1294
1266
1251
1218
1176
1157
1131
1099
1087
1076
957
23 (60)
42 (279)
3 (108)
1 (135)
6 (50)
νas(NH2)
νs(NH2)
ν2
3351(5)
3240(6)
ν3
ν(C8−H)
ν(C1−H); ν(C2−H)
ν(C4−H)
ν(C2−H); ν(C1−H)
ν4
3096(10)
3081(15)
3039(9)
ν5
ν6
3056(vw)
1641(vs)
1611(m)
1579(m)
10 (109)
415 (188)
39 (61)
170 (105)
7 (40)
ν7
1635(100)
ν(C9−O4)
ν(C7−C8)
δ(NH2)
ν8
ν9
1581(73)
ν10
ν11
ν12
ν13
ν14
ν15
ν16
ν17
ν18
ν19
ν20
ν21
ν22
ν23
ν24
ν25
ν26
ν27
ν28
ν29
ν30
ν31
ν32
ν33
ν34
ν35
ν36
ν37
ν38
ν39
ν40
ν41
ν42
ν43
ν44
ν45
ν46
ν47
ν48
ν49
ν50
ν51
ν52
ν53
ν54
ν55
ν56
ν57
ν58
ν(C4−C5); ν(C1−C2); ν(C5−C6)
ν(C2−C3); ν(C5−C6); ν(C7−C8)
δ(C4−H); δ(C1−H); δ(C2−H)
ν(C5−C9); ν(C1−C2); ν(C4−C5)
ν(C7−O3); ν(C3−C4); ν(C1−C6); δ(C8−H)
ν(C5−C6); ν(C2−C3)
ν(N−C3); ν(C4−C5)
δ(C1−H); δ(C2−H); δ(C4−H); ν(C7−C10)
δ(C8−H); ν(C7−C10)
δ(C1−H); δ(C4−H); δ(C7−C10)
ν(C5−C9); ν(C7−C10); ν(C6−O3)
νas(CF3); δ(C1−H); δ(C2−H); δ(C4−H)
δ(C1−H); δ(C2−H)
1546(vw)
1492(vs)
18 (38)
204 (6)
54 (23)
77 (70)
21 (44)
87 (8)
1489(19)
1472(19)
1411(36)
1362(58)
1411(m)
1363(w)
1320(s)
1283(vs)
1255(w)
1243(s)
1210(m)
1184(vs)
1163(s)
1154(vs)
145 (12)
106 (76)
255 (1)
24 (17)
220 (2)
75 (15)
294 (3)
32 (8)
1257(75)
1211(23)
νas(CF3)
δ(N−C3−C4)
δ(C4−H); δ(C4−C5−C9)
νs(CF3), δ(C8−C7−O3)
29 (1)
1074(m)
1074(15)
924(65)
34 (3)
1 (<1)
45 (10)
28 (20)
6 (1)
γ(C1−H); γ(C2−H); γ(C4−H)
δ(C8−C7−O3); δ(C1−C2−C3)
δ(C1−C2−C3); δ(C9−C8−C7); νs(CF3)
γ(C4−H); γ(C8−H)
931(m)
923(m)
936
933
902
857(s)
820(m)
807(w)
887
48 (<1)
35 (<19)
18 (3)
γ(C8−H); γ(C4−H)
γ(C2−H); γ(C1−H)
828
816
δ(C6−C1−C2); δ(C4−C5−C3); δ(C−F3)
γ(C1−H); γ(C5−C9−C8); γ(C8−H); γ(C4−H)
δ(C6−C1−C2); δ(C5−C4−C3)
δs(CF3); δ(C6−C1−C2); δ(C3−C4−C5)
γ(O3−C7−C8)
763
<1 (<1)
2 (14)
732(56)
697(19)
620(21)
542(45)
527(31)
736
721(w)
716
7 (9)
698
<1 (<1)
1 (<1)
14 (2)
697
γ(C1−H); γ(C5−C9−C8); γ(C8−H); γ(C4−H); γ(C2−H)
δ(C5−C9−O4); δ(C1−C6−O3)
γ(C1−H); γ(C5−C9−C8); γ(C8−H); γ(C2−H)
δas(CF3); δ(O4−C9−C8)
δ(C5−C9−C8); δ(N−C3−C4)
δ(C5−C9−C8); δ(C6−O3−C7)
δas(CF3); γ(C1−C6−C5)
γ(NH2)
620(w)
553(vw)
547(vw)
622
563
18 (3)
557
9 (3)
539
1 (10)
532
5 (3)
518
14 (2)
509
315 (13)
20 (<1)
2 (<1)
1 (3)
473(vw)
474
δ(C6−O3−C7)
γ(C4−C5−C6); γ(C6−C1−C2)
δ(N−C3−C2)
γ(C2−C1−C6); γ(C7−O3−C6)
δ(C7−CF3)
441
393
389(23)
265
386
8 (2)
343
<1 (1)
18 (<1)
2 (<1)
2 (5)
302
ρ(NH2)
289
γ(C9−C8−C7); ρ(NH2)
δ(C10−C7−C8); (N−C3−C2)
δ(N−C3−C4); δ(O3−C7−C10)
τ(O4−C9−C5−C4)
τ(C7−C8−CF3); (O4−C9−C5−C4)
πip(CF3)
271
239
7 (2)
177
1 (<1)
3 (<1)
1 (1)
158
131
123
4 (1)
τ(C2−C3−NH2); (CF3−C7−O3)
2175
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Table 4. continued
b
experimental
calculated
a
c
d
mode
IR
Raman
frequency
intensity
assignment
ν59
ν60
53
31
<1 (3)
τ(C2−C3−NH2)
τ(C8−C7−CF3)
1 (2)
b
a
c
Key: vs, very strong; s, strong; w, weak; vw, very week; sh, shoulder. 6-311++g(d,p). Calculated intensities: IR in km mol−1 and Raman
d
(in parentheses) in Å4 amu−1. ν, δ, γ, and τ represent stretching, in-plane deformation, out-of-plane deformation and torsion modes.
Figure 7. Experimental (full trace, 2.4 × 10−5 M in methanol) and
calculated electronic spectra (B3LYP/6-311+g(d), dashed trace) of
6-amino-2-trifluoromethylchromone (2).
Figure 5. Experimental (full trace, 2.9 × 10−5 M in methanol) and
calculated electronic spectra (B3LYP/6-311+g(d), dashed trace) of
6-nitro-2-trifluoromethylchromone (1).
Table 5. Electronic Spectra of 2.9 × 10−5 M Methanolic
a
Solution of 6-Nitro-2-trifluoromethylchromone (1)
b
c
experimental
calculated
assignment
203
212
240
219 (0.057)
224 (0.037)
235 (0.184)
240 (0.189)
260 (0.085)
HOMO-4 → LUMO+1 (89%)
HOMO-1 → LUMO+2 (75%)
HOMO-4 → LUMO (92%)
HOMO-2 → LUMO+1 (87%)
HOMO-1 → LUMO+1(47%)
HOMO-2 → LUMO (36%)
HOMO-2 → LUMO (58%)
HOMO-1 → LUMO+1(33%)
HOMO-1 → LUMO (95%)
287
d
293
281 (0.012)
298 (0.135)
d
306
a
Calculated electronic transitions (B3LYP/6-311+g(d)) are also shown
b
and only those relevant for the assignments are listed. Absorption
maxima are given in nm. Oscillator strengths of calculated transitions,
shown in parentheses, are in atomic units. Shoulder.
c
d
the LUMO+1 orbital, both ruled by one-electron excitation.
The calculated wavelengths are 235 and 240 nm, respectively.
The observed absorption at 287 nm is assigned to a sole one-
electron excitation from the HOMO-1 to the LUMO+1 with an
important contribution from a HOMO-2 →LUMO excitation.
This band is attributed to a calculated transition at 260 nm.
The shoulders at 293 and 306 nm are due to singlet electron
excitations. The absorption at 293 nm corresponds to nearly
equal contribution from HOMO-2→LUMO and HOMO-1→
LUMO+1 transitions, whereas the one at 306 nm to a
dominant excitation from the HOMO-1 to the LUMO. The
calculated transitions are 281 and 298 nm, respectively.
The observed bands at 203, 212, and 287 nm correspond to
transitions involving both fused rings. Moreover, the bands at
240, 293, and 306 nm are mainly dominated by transitions from
both rings to the N−C bond with substantial contribution of
transitions that occur also in both rings (see Figure 6).
Figure 6. Molecular orbitals involved in the electronic transitions of
6-nitro-2-trifluoromethylchromone (1). The energy scale is only qualitative
and does not represent the actual energy of the molecular orbitals.
respectively. The absorption at 240 nm arises from the contribution
of transitions from HOMO-4 to the LUMO and HOMO-2 to
2176
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Table 6. Electronic Spectra of 2.4 × 10−5 M Methanolic
Table 7. Comparison between Experimental and Calculated
NMR Chemical Shifts in ppm for 1 and 2
a
ab
,
Solution of 6-Amino-2-trifluoromethylchromone (2)
b
c
experimental
203
calculated
assignment
1
2
196 (0.251)
201 (0.185)
HOMO-4 → LUMO (73%)
HOMO-2 → LUMO+1 (51%)
HOMO-3 → LUMO+1 (20%)
HOMO-4 → LUMO (17%)
HOMO-3 → LUMO+1 (71%)
HOMO-2 → LUMO+1 (16%)
HOMO-3 → LUMO (38%)
HOMO → LUMO+2 (32%)
HOMO-3 → LUMO+1 (11%)
HOMO-3 → LUMO (45%)
HOMO → LUMO+3 (24%)
HOMO → LUMO+2 (20%)
HOMO-2 → LUMO (83%)
HOMO → LUMO+1 (86%)
HOMO → LUMO (97%)
expt
6.80
6-311+g(2d,p)
exp.
6.64
6-311+g(2d,p)
3-H
5-H
7-H
8-H
2-C
3-C
4-C
5-C
6-C
7-C
8-C
4a-C
8a-C
CF3
6.87 (−0.07)
9.63 (−0.63)
8.96 (−0.38)
7.68 (+0.07)
160.1 (−7.3)
129.6 (−5.5)
179.3 (−4.2)
117.1 (−6.1)
151.4 (−6.0)
134.0 (−4.8)
122.9 (−2.6)
130.4 (−8.0)
165.5 (−7.3)
130.1 (−11.9)
6.71 (−0.07)
7.67 (−0.28)
7.13 (−0.05)
7.47 (−0.10)
158.6 (−5.9)
115.1 (−5.8)
180.0 (−3.0)
112.1 (−4.5)
151.4 (−6.4)
123.6 (−0.5)
123.5 (−4.2)
132.0 (−7.9)
155.4 (−6.2)
130.8 (−12.1)
9.00
8.58
7.75
7.39
7.08
7.37
d
207
205 (0.154)
229 (0.250)
152.8
152.7
241
124.1
175.1
111.0
145.4
129.2
120.3
122.4
158.2
118.2
109.3
177.0
107.6
145.0
123.1
119.3
124.1
149.2
118.7
242 (0.055)
253 (0.138)
280 (0.041)
356 (0.077)
294
377
a
a
Calculated electronic transitions (B3LYP/6-311+g(d)) are also
shown and only those relevant for the assignments are listed.
Absorption maxima are given in nm. Oscillator strengths of
Δ = δexp − δcalc in parentheses. For atom numbering, see Chart 1.
For comparison between experimental, B3LYP/6-31+g(d), and
B3LYP/6-311+g(2d,p) see Table S4 (Supporting Information).
b
b
c
calculated transitions, shown in parentheses, are in atomic units.
d
Shoulder.
attribute the observed bands of the UV−vis spectrum. All cases
correspond to one-electron excitations, see Table 6.
6-Amino-2-trifluoromethylchromone (2). Figure 8 shows
the MO’s that participate in electronic transitions used to
At low wavelengths, the experimental spectrum shows a band
at 203 nm and a shoulder at 207 nm. The band is dominated by
Figure 8. Molecular orbitals involved in the electronic transitions of 6-amino-2-trifluoromethylchromone (2). The energy scale is only qualitative
and does not represent the actual energy of the molecular orbitals.
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1
1
Figure 9. Comparison of experimental and theoretical chemical shifts of 1, (a) H, (b) 13C, and 2, (c) H, (d) 13C, calculated at the B3LYP/6-
31+g(d) and B3LYP/6-311+g(2d,p) levels of the theory.
a transition from HOMO-2 orbital to the LUMO+1 one, with
contributions from HOMO-3 → LUMO+1 and HOMO-4 →
LUMO excitations. The shoulder is mainly due to a transition
from HOMO-3 to the LUMO+1, besides other minor con-
tributions. They are assigned to transitions calculated at 201
and 205 nm, respectively.
The observed band at 241 nm is mainly generated by excita-
tions from HOMO-3 → LUMO and HOMO → LUMO+2
(calculated wavelength 230 nm); HOMO-3 → LUMO and
HOMO → LUMO+3 (calculated wavelength 242 nm) and
HOMO-2 → LUMO (calculated wavelength 253 nm).
The absorption at 294 and 377 nm are attributed to dominant
excitations from the HOMO to the LUMO+1 and from the
HOMO to the LUMO, respectively, whereas that the computed
transitions are 280 and 356 nm.
The observed bands at 203 and 207 nm correspond to
transitions within the aromatic ring. The band at 241 nm results
from transitions that involve both fused rings. The bands at 294
and 377 nm are basically dominated by excitations from the
aromatic fragment to orbitals that extend throughout the
molecule (see Figure 8).
A complete description of the electronic spectra and in-
volved orbitals of both compounds can be found in Supporting
Information.
The following correlations δcalc = a δexp + b given in Figure
9a−d were obtained. Part a: B3LYP/6-31+g(d) (R2 = 0.9855;
a = 1.2197; b = 1.4434), B3LYP/6-311+g(2d,p) (R2 = 0.979; a =
1.2652; b = 1.8781), Part b: B3LYP/6-31+g(d) (R2 = 0.9071;
a = 0.9357; b = 31.658), B3LYP/6-311+g(2d,p) (R2 = 0.9036;
a = 0.9364; b = 15.018), Part c: B3LYP/6-31+g(d) (R2 =
0.9897; a = 1.2565; b = 1.5616), B3LYP/6-311+g(2d,p) (R2 =
0.9562; a = 1.1782; b = 1.1432), Part d: B3LYP/6-31+g(d)
(R2 = 0.9838; a = 0.9762; b = 25.364), B3LYP/6-311+g(2d,p)
(R2 = 0.9812; a = 0.9755; b = 8.8912).
1
A good agreement between experimental and calculated H
NMR spectra is observed for 1 and 2 compounds employing
both basis sets, with values of Δ between +0.07 and −0.63 ppm.
However, the B3LYP/6-31+g(d) basis set proved to be not
suitable for predicting 13C NMR spectra and a better accuracy
was obtained using the triple-ζ basis set 6-311+g(2d,p). In this
case, the Δ-values found for the carbon atoms of the chromone
ring differ up to −8.0 ppm. The greatest discrepancy was found
in the prediction of the −CF3 chemical shift, with values of Δ =
−11.9 and −12.1 ppm for compounds 1 and 2, respectively
(see Table 7). This fact suggests that the isotropic shielding
of the fluorine atoms is underestimated by theoretical calcula-
tions. A more severe disagreement was observed in the calcu-
lated chemical shifts of this group in some trifluoromethyl
tetraisoquinolines.38
3.5. NMR Spectroscopy. After full geometry optimization
with the GAUSSIAN G03 program package (see computational
4. CONCLUSION
1
methods in Experimental Section) the H, and 13C chemical
Because of an extensive π-bonding electronic structure, both
compounds adopt an almost planar conformation. The quantum
chemical calculations reflects this behavior with the −CF3 group
staggered and one fluorine atom syn respect to the CC bond.
Besides, X-ray crystal structure of 1 shows also an atomic
arrangement similar to that predicted by calculations, but with the
trifluoromethyl group slightly off from the staggered conforma-
tion (ca. 7°), probably due to packing effects. The experimental
shifts were calculated with the GIAO method.31 Table 7 shows
the experimental and calculated chemical shifts (B3LYP/6-
311+g(2d, p)) for both compounds, while data obtained with
the low level of calculation (B3LYP/6-31+g(d)) were also
included in Table S4 (Supporting Information). The experimental
and calculated chemical shifts showed a linear relationship with
R-square values for each compound above 0.9036.
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and theoretical structural parameters of compound 1 are similar
to those obtained by theoretical calculations of compound 2,
suggesting that the change of a deactivating group in the aromatic
ring by an activating one, causes no appreciable effect on the
interatomic distances and bond angles. The NO2 moiety is in the
same plane as the rings, with the experimental torsion angle O1−
N−C3−C4 of 1.7°, while the predicted value results 0°. For 2,
the orientation of the NH2 group is slightly deviated from the
planarity (dihedral angle H1−N−C3−C2 = 25.2°), as expected
for the sp3 hybridization for the N atom. The GIAO method was
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1
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ASSOCIATED CONTENT
■
S
* Supporting Information
Complete description of the electronic spectra, complete ref 29,
mass spectrum of 6-nitro-2-trifluoromethylchromone (1)
(Figure S1), mass spectrum of 6-amino-2-trifluoromethylchro-
mone (2) (Figure S2), crystallographic information for 6-nitro-
2-trifluoromethyl chromone, including atomic coordinates and
equivalent isotropic displacement parameters (Table S1),
anisotropic displacement parameters (Table S2), and hydrogen
atoms positions (Table S3) and comparison between
experimental and B3LYP calculated NMR chemical shifts in
ppm for 1 and 2 (Table S4). This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Telephone: 0054 221 4714527. Fax: 0054 221 4714527.
E-mail: jljios@quimica.unlp.edu.ar (J.L.J); sonia@quimica.unlp.
edu.ar (S.E.U.).
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
this manuscript.
Notes
The authors declare no competing financial interest.
Crystal Data. A CIF file with details of the crystal structure
reported in the paper has been deposited with the Cambridge
Crystallographic Data Centre (12 Union Road, Cambridge
CB2 1EZ, U.K. Fax: +44−1223/336−033. E-mail: deposit@
ccdc.cam.ac.uk) and can be obtained free of charge at www.
ccdc.cam.ac.uk/conts/retrieving.html), reference number
CCDC 913967.
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ACKNOWLEDGMENTS
■
The authors thank Universidad Nacional de La Plata (UNLP),
CONICET, DAAD-Germany, and Departamento de Ciencias
Basicas de la Universidad Nacional de Lujan for financial
́ ́
support. S.E.U and J.L.J specially thanks the Deutscher
Akademischer Austauschdienst Germany (DAAD) for the
equipment grant and financial support. L.P.A.J. thanks
CONICET for a fellowship. The crystallographic work was
supported by CONICET (PIP 1529), and by ANPCyT
(PME06 2804 and PICT06 2315) of Argentina. S.E.U, G.A.E,
and O.E.P are research fellows of CONICET.
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