Investigation of the molecular dynamics of some phenols and their acetyl isomers in solutions by NMR relaxation

Article abstract of DOI:10.1134/S0036024410120307

The dynamics of relaxations and Fries rearrangements in phenol acetates and their acetyl isomers was studied by the NMR relaxation technique in acetone-d ₆. The results of ¹³C and ¹H spin-lattice nuclear relaxation measurements show that these experiments can be used for determining the mobility and activation energies of the molecular motions of compounds in different systems.

Full text of DOI:10.1134/S0036024410120307

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2010, Vol. 84, No. 12, pp. 2182–2186. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © I.G. Mamedov, A.M. Magerramov, M.R. Bairamov, E.V. Mamedova, 2010, published in Zhurnal Fizicheskoi Khimii, 2010, Vol. 84, No. 12, pp. 2382–2386.
SHORT
COMMUNICATIONS
Investigation of the Molecular Dynamics of Some Phenols
and Their Acetyl Isomers in Solutions by NMR Relaxation
I. G. Mamedov, A. M. Magerramov, M. R. Bairamov, and E. V. Mamedova
Baku State University, Baku, Azerbaijan
eꢀmail: ib.nmrlab@list.ru
Received May 25, 2009
Abstract—The dynamics of relaxations and Fries rearrangements in phenol acetates and their acetyl isomers
was studied by the NMR relaxation technique in acetoneꢀd6. The results of 13C and 1H spinꢀlattice nuclear
relaxation measurements show that these experiments can be used for determining the mobility and activaꢀ
tion energies of the molecular motions of compounds in different systems.
DOI: 10.1134/S0036024410120307
INTRODUCTION
The spinꢀlattice relaxation was evaluated by the
standard procedure using an inversion–reduction
Recent achievements in nuclear magnetic studies
are of great theoretical and practical value. In particuꢀ
lar, nuclear relaxation (theory and applications) was
discussed in numerous publications, the number of
which is constantly growing.
pulse sequence [Tꢀ180ꢀ ꢀ90°] (the measurement error
τ
was 0.01–0.10 s).
The activation parameters of molecular motions
were calculated by the equation [3]
Nuclear magnetic relaxation spectroscopy is a
convenient tool for comparing the theoretical models
of molecular structure and investigating the relaxꢀ
ation mechanisms in studies of the dynamics of variꢀ
ous solutions; it can also be used for determining the
activation energies of molecular motions, intraꢀ and
intermolecular interactions, complexations, associaꢀ
tions, etc. [1–12].
Е
= 19.13[Т(1) Т(2)/(Т(2)
– Т /
(1))]log(Т1(2) Т1(1)),
where Т(1) and Т(2) are the temperatures correspondꢀ
ing to the relaxation times Т1(1) and Т1(2). The calculaꢀ
tion error was 0.1–0.5 kJ/mol. The NOE factor was
calculated from the intensity ratio in the spectra
recorded with full suppression of spin–spin proton
coupling and decoupling only during spectrum meaꢀ
surements [14]. The samples were studied in aceꢀ
toneꢀd6 and CCl4 solutions (a few drops of acetoneꢀ
d6 were used for a lock signal for CCl4 solutions). The
Fries rearrangements of phenol esters were perꢀ
formed in the presence of AlCl3 or under UV irradiaꢀ
tion by known procedures [15–17].
As is known, carbonylꢀsubstituted alkenylphenols
are used as reagents in organic synthesis and stabilizer
monomers in polymerizations [13]. It is therefore
interesting to study various acetateꢀ and acetylꢀsubstiꢀ
tuted phenols by NMR relaxation spectroscopy and to
reveal a relationship between their structure and
behavior in the systems under study.
EXPERIMENTAL
RESULTS AND DISCUSSION
The samples were studied on an Avance 300 Bruker
pulse spectrometer at an operating frequency of
300 MHz for 1H and 75 MHz for 13C (TopSpin 3.1 softꢀ
ware) equipped with a BVT 3200 temperature sensor. The etophenone II and 2ꢀhydroxyꢀ5ꢀmethylacetophenone
error of the sensor was not more than
As model compounds, we used phenylacetate
ꢀtolyl acetate III, and their derivatives 2ꢀhydroxyacꢀ
I,
p
1
K.
IV obtained by the Fries rearrangement
2
1
2
1
OCOCH3
OH
3
OCOCH3
OH
3
2
1
2
1
3
3
COCH3
COCH3
8
7
4
8
7
8
7
4
8
7
4
5
4
5
5
5
6
6
6
6
CH3
CH3
(
I
)
(II)
9
9
(III
)
(IV)
2182

INVESTIGATION OF THE MOLECULAR DYNAMICS OF SOME PHENOLS
2183
Table 1. 1H and 13C spinꢀlattice nuclear relaxation times (
acetoneꢀd6 solutions at different temperatures (x is the concentration of a compound)
T1) and activation energies of the molecular motion in 5 and 10%
x, %
Fragment
–20
°
C
–5°
C
5°
C
22°
C
40°
C
50°
C
Е
, kJ/mol
I
5
10
COCH3 (1H)
COCH3 (13C)
2.43
2.35
3.68
3.27
4.51
4.45
4.73
4.55
5.25
5.13
5.81
5.75
8.45
8.68
5
10
–
7.28
–
8.53
–
10.27
12.37
11.49
12.60
11.65
–
12.04
–
4.88
II
5
10
COCH3 (1H)
COCH3 (13C)
1.94
1.85
2.15
2.03
2.33
2.22
3.27
2.98
3.68
3.33
3.89
3.78
6.75
6.93
5
10
–
7.23
–
8.18
–
10.23
11.61
10.48
11.93
10.77
–
11.35
–
4.37
III
5
10
COCH3 (1H)
COCH3 (13C)
ArCH3 (1H)
ArCH3 (13C)
2.38
2.19
2.91
2.69
3.43
3.05
3.77
3.70
4.61
4.52
5.64
5.22
8.37
8.42
5
10
–
5.87
–
7.47
–
8.05
9.29
9.40
–
11.43
12.31
12.03
–
6.96
5
10
1.83
1.83
2.17
2.14
3.38
2.97
3.75
3.29
4.57
4.12
4.74
4.68
9.23
9.11
5
10
–
5.86
–
7.28
–
8.10
8.58
9.05
–
9.19
9.55
9.32
–
4.50
IV
5
10
COCH3 (1H)
COCH3 (13C)
ArCH3 (1H)
ArCH3 (13C)
1.73
1.53
3.06
2.79
3.28
3.17
4.13
4.09
4.33
4.10
4.82
4.26
9.94
9.93
5
10
–
5.32
–
6.28
–
7.19
8.69
8.14
–
9.76
12.03
10.97
–
7.02
5
10
2.48
2.43
3.17
3.14
3.75
3.55
4.78
4.19
5.33
5.34
5.46
5.41
7.65
7.76
5
10
–
8.15
–
9.07
–
9.23
8.63
9.42
–
10.71
10.21
11.61
–
3.43
For the methyl groups of all the four compounds, dence of spinꢀlattice relaxation that is due to the
we calculated the 1H and 13C spinꢀlattice nuclear
dipole–dipole mechanism [3, 7] (Table 1). The activaꢀ
relaxation times (Т1) at different temperatures and
concentrations in deuteroacetone solutions. The
dipole–dipole C–H mechanism was found to prevail
for these fragments; this is typical of the dipole–dipole
mechanism of relaxation at elevated temperatures,
with spinꢀlattice relaxation times increasing concurꢀ
rently. The activation energies of the molecular
tion energies of the molecular motion for the methyl
1
13
groups on H and C nuclei are different, indicating
that anisotropic molecular reorientations occur in the
liquid [1].
Given below are the structural formulas of 2ꢀpropeꢀ
nylphenylacetate
V and the product of its Fries rearꢀ
motion were determined from the temperature depenꢀ rangement 2ꢀhydroxyꢀ3ꢀpropenylacetophenone VI
:
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MAMEDOV et al.
1) and activation energies of the molecular motion of comꢀ
Table 2. 1H and 13C spinꢀlattice nuclear relaxation times (
T
pounds in 5 and VI in 10% acetoneꢀ 6 solutions at different temperatures
V
d
Fragment
22
°
C
40°
C
Fragment x, % –20°C –5
°
C
5°
C
22°
C
40°
C
50°C Е, kJ/mol
V
VI
–
1.96
–
6.93
–
3.32
–
7.37
COCH3 (1H)
2.99
3.78 COCH3 (1H)
9.06
5
10
5
10
5
10
5
–
1.40
–
3.05
–
1.90
–
–
1.59
–
4.86
–
2.57
–
2.21
2.15
8.25
7.23
3.81
3.46
8.03
7.76
2.97
2.85
8.98
8.76
4.71
4.38
9.72
9.34
–
3.76
–
9.45
–
4.53
–
–
9.58
–
10.97
–
8.43
–
7.57
COCH3 (13C) 7.29
CH3 (1H)
CH3 (13C)
СH (13С)
CH (13C)
СH (13С)
CH (13C)
=СH (13С)
=СH (13С)
3.62
7.07
4.15
4.06
4.09
4.01
6.16
6.16
4.40 COCH3 (13C)
8.54
5.70 CH3 (1H)
5.63
5.23 CH3 (13C)
5.21
7.46
8.59
10
4.96
5.43
10.83
Table 3. Spinꢀlattice nuclear relaxation times (
T
1),
η
NOE factor, and DD and SR relaxation mechanisms for hydrogenꢀ
bearing 13C at 22
°
C
RS1R , s–1
TS1R , s
RD1 D , s–1
TD1 D , s
α
, %
α
, %
Atom
η
Т1, s
SR relaxation
DD relaxation
I
0.0218
С1
1.46
1.96
1.96
1.88
12.37
11.61
27
45.87
73
0.0590
0.0650
16.95
С4–С8
С5–С7
С6
II
0.0211
С1
С5
С6
С7
С8
1.51
1.87
1.92
1.94
1.81
24.5
47.39
75.5
15.38
III
0.0285
С1
1.47
1.90
1.88
1.27
9.29
26.5
35.09
73.5
0.0791
12.64
С4–С8
С5–С7
С9
8.58
8.69
36.5
22
0.0425
IV
0.0253
23.53
39.53
63.5
78
0.0740
0.0898
13.51
11.14
С1
С5
С7
С8
С9
1.56
1.88
1.82
1.80
1.13
8.63
43.5
0.0504
V
19.84
56.5
0.0655
15.27
С1
С5
С6
С7
С8
С9
С10
С11
1.88
1.92
1.82
1.88
1.88
1.94
1.88
1.75
7.29
4.15
4.06
4.09
4.01
6.16
6.16
7.07
6
4
9
6
6
3
6
12.5
0.0082
0.0096
0.0222
0.0147
0.0149
0.0049
0.0097
0.0177
VI
121.95
104.17
45.05
68.03
67.11
204.08
103.09
56.49
94
96
91
94
94
97
94
87.5
0.1289
0.2315
0.2241
0.2298
0.2344
0.1575
0.1526
0.1238
7.76
4.32
4.46
4.35
4.27
6.35
6.55
8.08
С1
С11
1.91
1.79
8.25
8.03
4.5
10.5
0.0055
0.0131
181.8
76.34
95.5
89.5
0.1158
0.1115
8.64
8.97
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INVESTIGATION OF THE MOLECULAR DYNAMICS OF SOME PHENOLS
2185
2
1
OCOCH3
OH
2
1
3
3
CH=CH−CH3
H3C−CH=CH
8
COCH3
4
8
7
9
10
11
11 10
9
4
5
5
7
6
6
(V
)
(VI)
Our studies showed that the dipole–dipole C–H bond energies varied from 5.2 to 6.3 kcal/mol, which
mechanism prevailed for all hydrogenꢀbearing carbon agrees well with the data of [6].
atoms. Using the temperature dependence for VI, we
According to Table 3, Т1 for acetyl methyl groups
decreased after the Fries rearrangement. This decrease
determined the activation energies of the molecular
motion that controlled this relaxation mechanism
in the mobility of methyl groups could be explained by
(Table 2).
the intramolecular hydrogen bonding.
According to Table 2, the spinꢀlattice relaxation
The copolymers obtained from 2ꢀhydroxyꢀ3ꢀproꢀ
penylacetophenone VI are proof against light and
other factors.
times Т1 are close for hydrogenꢀbearing aromatic carꢀ
bons in . This can be explained by the absence of the
V
dominant rotation axis for this molecule.
The results of our studies on 13C and 1H spinꢀlatꢀ
tice nuclear relaxation adequately reflect the
dynamics of the behavior of molecules in solution
and can be effectively used for determining the
compositions, mobility, and activation energies of
various systems.
A comparison of the relaxation times of two CH3
groups and CH groups in
V showed that for CH3 carꢀ
bons, Т1 exceeded that of CH carbon. On the basis of
these data, we can conclude that spinꢀrotational (SR)
relaxation occurs along with dipole–dipole (DD)
relaxation for these groups [4]. The calculated fracꢀ
tions of the DD and SR relaxations for the carbon of
the carbonyl and propenyl CH3 groups are 94 : 6 and
87.5 : 12.5%, respectively.
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propenylacetophenone VI in 5% acetoneꢀd6 and
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