I. G. Mamedov et al.
Table 8. SR and DD mechanisms of relaxation (13C) for II
Number of
carbon atom
Fragments
SR (%)
DD (%)
R1SR (s−1
)
T1SR (s)
R1DD (s−1
)
T1DD (s)
CH
3
5
6
7
9
17
4
83
96
84
57
56
0.0677
0.0151
0.0576
0.0662
0.0743
14.77
66.23
17.36
15.11
13.46
0.3307
0.3623
0.3022
0.0877
0.0946
3.02
2.76
CH
CH
16
43
44
3.31
CH3
CH3
11.40
10.57
R1SR, T1SR, R1DD and T1DD are respective relaxations rates and times, respectively.
The results can be explained by the existence two conformers
(a and b for the transoid or Z form) for the molecule N-(2-hydroxy-
4-methylphenyl)acetamide (II) for which the formation of two
H3C
H
O
.
.
.
O
CH3
O
· · ·
· · ·
intramolecular hydrogen bonds (O H–N, O H–O type) can be
confirmed (Scheme 4). For I and II, the intramolecular hydrogen
bond energy, the activation energies of intramolecular mobility,
and for II the free energy of activation (69.91 kJ/mol) and rate
constants were calculated.
N
O
N
.
H
.
H3C
H
.
H
H3C
a
b
NOE factors, relaxation times (T1), the contributions of SR and
DD mechanisms, the corresponding carbon relaxation rates (R1SR),
(R1DD)andrelaxationtimes(T1SR),(T1DD)forIandIIwerecalculated
in acetone-d6.
The methyl groups at unsaturated bond, the carbonyl and the
aromatic fragments are sterically strained allowing only partial
internal rotation (Tables 4 and 8).
II
N-(2-Hydroxy-4-methylphenyl)acetamide
Scheme 4. Two conformers in solution for the molecule II.
the conformers (a) and (b). The energy of intramolecular hydrogen
bonds at 22 ◦C and in 0.1% CCl4 solution is 5.13 0.2 kcal/mol (or
21.5 kJ/mol).
The NMR spectrum of the four exchange sites was calculated
by ‘WINDNMR’ (version 7.1.13), resu◦lting in the rate ◦constants
(k = 3.6 s−1 at −50 ◦C, 3.2 s−1 at −40 C, 2.8 s−1 at −30 C, 2.5 s−1
at−20 ◦C,1.9 s−1 at−5 ◦C,1.2 s−1 at+15 ◦C)inacetone-d6 solution
(Fig. 3). The free energy of activation has been calculated by the
formula[2]
References
[1] V. I. Bakhmutov, Practical NMR Relaxation for Chemists, Wiley:
England, 2004.
[2] J. B. Lambert, E. P. Mazzola, Nuclear Magnetic Resonance
Spectroscopy, Pearson Prentice Hall: New Jersey, 2003.
[3] L. M. Jackman, F. A. Cotton, Dynamic Nuclear Magnetic Resonance
Spectroscopy, Academic Press: New York, 1975.
[4] J. Sandstrom, Dynamic NMR Spectroscopy, Academic Press: New
York, 1982.
[5] A. E. Derome, Modern NMR Techniques for Chemistry Research,
ꢀGc = 2.3RTc[10.32 + log(Tc/kc)] = 69.91 kJ/mol
(4)
Pergamon Press: Oxford, UK, 1987.
[6] A. A. Vashman, I. S. Pronin, Nuclear Magnetic Relaxation
Spectroscopy, Nauka: Moscow, 1986.
[7] H. Gu¨nther, NMR Spectroscopy – An Introduction, Wiley: New York,
1980.
The calculated relaxation times (T1 for carbons, s, in 5% acetone-
d6 solution) for different CH3 and CH groups of II at various
temperatures are given in Table 6.
The spin–lattice relaxation time increases with rising temper-
ature. This is a typical feature of DD relaxation. The activation
energies of intramolecular mobility were calculated in the temper-
ature intervals −20 to +50 ◦C for the CH3 groups and 22–50 ◦C for
the CH groups (Table 6).
Further NOE factors, relaxation times (T1) and the contributions
of SR, DD mechanism for II were taken into account and the
corresponding carbon relaxation rates (R1SR), (R1DD) and relaxation
times (T1SR) and (T1DD) were calculated in acetone-d6. The results
are given in Tables 7 and 8.
[8] A. A. Vashman, I. S. Pronin, Nuclear Magnetic Relaxation and Its
Application in Chemical Physics, Nauka: Moscow, 1979.
[9] G. C. Levy, G. L. Nelson, Carbon-13 NMR for Organic Chemists, Wiley:
New York, 1972, (Russian translation, Mir, Moscow, 1975).
[10] E. Breitmeier,G. Bauer,13C-NMR-Spektroskopie,eineArbeitsanleitung
¨
mit Ubungen, Georg Thieme Verlag: Stuttgart, 1977.
[11] S. Braun, H. O. Kalinowski, S. Berger, 100 and More Basic NMR
Experiments, VCH: Weinheim (FRG), 1996.
[12] N. D. Sokolov, Hydrogen Bond, Nauka: Moscow, 1981.
[13] T. Yamaguchi, N. Matubayasi, M. Nakahara, J. Mol. Liquids 2005, 119,
119.
[14] S. Chelmieniecka, E. Grech, Z. Rozwadowski, T. Dziembowska,
W. Schilf, B. Kamienski, J. Mol. Struct. 2001, 565–566, 125.
[15] A. J. Horsewill, A. Aibout, J. Phys. Condens. Matter 1989, 1, 9609.
[16] A. Robert, H. Bernheim, H. Gutowsky, J. Lawrenson, J. Chem. Phys.
1961, 34, 565.
Conclusions
[17] I. G. Mamedov, A. M. Maharramov, M. R. Bairamov, Russ. J. Phys.
Our investigations confirm the formation of intramolecular
Chem. 2008, 7, 1382.
· · ·
hydrogen bonds between O–H N within the molecule and
[18] I. G. Mamedov, U. Eichhoff, A. M. Maharramov, M. R. Bayramov,
Y. V. Mamedova, Appl. Magn. Reson. 2010, 3, 257, DOI: 10.1007/
s00723-010-0117-0.
· · ·
N–OH O type intermolecular hydrogen bonds between oxime
molecules ( I).
c
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2010, 48, 671–677