GIAO, DFT, AIM and NBO analysis of the N-H...O intramolecular hydrogen-bond influence on the 1J(N,H) coupling constant in push-pull diaminoenones

Article abstract of DOI:10.1002/mrc.2643

In the series of diaminoenones, large high-frequency shifts of the ¹H NMR of the N-H group in the cis-position relative to the carbonyl group suggests strong N-H...O intramolecular hydrogen bonding comprising a six-membered chelate ring. The N-

Full text of DOI:10.1002/mrc.2643

Research Article
Received: 9 February 2010
Revised: 31 May 2010
Accepted: 2 June 2010
Published online in Wiley Interscience: 26 July 2010
(www.interscience.com) DOI 10.1002/mrc.2643
GIAO, DFT, AIM and NBO analysis of the
· · ·
N–H O intramolecular hydrogen-bond
influence on the 1J(N,H) coupling constant
in push–pull diaminoenones
Andrei V. Afonin,∗ Igor A. Ushakov, Alexander V. Vashchenko,
Evgeniy V. Kondrashov and Alexander Yu. Rulev
In the series of diaminoenones, large high-frequency shifts of the 1H NMR of the N–H group in the cis-position relative to
· · ·
the carbonyl group suggests strong N–H O intramolecular hydrogen bonding comprising a six-membered chelate ring.
1
· · ·
The N–H O hydrogen bond causes an increase of the J(N,H) coupling constant by 2–4 Hz and high-frequency shift of the
15N signal by 9–10 ppm despite of the lengthening of the relevant N–H bond. These experimental trends are substantiated
by gauge-independent atomic orbital and density functional theory calculations of the shielding and coupling constants in
the 3,3-bis(isopropylamino)-1-(aryl)prop-2-en-1-one (12) for conformations with the Z- and E-orientations of the carbonyl
· · ·
group relative to the N–H group. The effects of the N–H O hydrogen-bond on the NMR parameters are analyzed with the
· · ·
atoms-in-molecules (AIM) and natural bond orbital (NBO) methods. The AIM method indicates a weakening of the N–H
O
· · ·
hydrogen bond as compared with that of 1,1-di(pyrrol-2-yl)-2-formylethene (13) where N–H O hydrogen bridge establishes
a seven-membered chelate ring, and the corresponding 1J(N,H) coupling constant decreases. The NBO method reveals that the
LP(O)→ σ∗N–H hyperconjugativeinteractionisweakenedongoingfromthesix-memberedchelateringtotheseven-membered
one due to a more bent hydrogen bond in the former case. A dominating effect of the N–H bond rehybridization, owing to an
electrostatic term in the hydrogen bonding, seems to provide an increase of the J(N,H) value as a consequence of the N–H
hydrogen bonding in the studied diaminoenones. Copyright ꢀ 2010 John Wiley & Sons, Ltd.
1
· · ·
O
c
Keywords: NMR; 15N NMR; spin–spin coupling constants; N–H O intramolecular hydrogen bond; diaminoenones; MP2; DFT and GIAO
calculations; AIM and NBO analysis
· · ·
Introduction
R
One of the broadly used signs of hydrogen-bond formation is
a pronounced high-frequency shift of the H NMR signal of the
N
H
1
bridge hydrogen. Less attention was paid to how much the
hydrogen bonding influences the coupling constant across the
covalent bond engaged in hydrogen bonding. As the coupling
constants are a source of unique structural information, a
comprehensive study of this point appears to be worthwhile.
It was well documented that hydrogen bonding, where the N–H
covalent bond acts as a proton donor, causes a change in the
O
Ph
R = H, Ph
Scheme 1. Structure of the Z-isomer of 2-(2-acylethenyl)pyrroles.
1
relevant J(N,H) coupling constant. Strong linear intermolecular
revealed, and this experimental finding was supported by density
functionaltheory(DFT)calculations.[4] However,theincreaseofthe
1J(N,H) coupling constant by 2–3 Hz was observed in the series of
1
hydrogen bonding results in a decrease of the J(N,H) coupling
constant across corresponding N–H covalent bond.[1] This trend
was substantiated by ab initio calculations of the 1J(N,H) coupling
constant in hydrogen-bonded complexes.[2] The calculations also
show that the decrease of the 1J(N,H) coupling constant is
connected with the lengthening of the N–H covalent bond.[2]
The influence of intramolecular hydrogen bonding on the 1J(N,H)
coupling constant was less studied. The tautomeric and exchange
processes complicate reliable measurement of the 1J(N,H) values
in many molecules with the hydrogen bonding.[3] Nevertheless,
the decrease in the absolute size of the 1J(N,H) coupling constant
by 2–4 Hz in the Z-isomer of 2-(2-acylethenyl)pyrroles (Scheme 1)
· · ·
2-substituted pyrroles with the weak N–H N(O) intramolecular
hydrogen bonds.[5]
Very recently, the series of new 3,3-bis(alkylamino)-1-(aryl)prop-
2-en-1-ones was synthesized.[6] A peculiarity of the structure of
push–pulldiaminoenonesisthatanintramolecularsix-membered
∗
Correspondence to: Andrei V. Afonin, Institute of Chemistry, Favorski St. 1,
664033 Irkutsk, Russia. E-mail: sasha@irioch.irk.ru
· · ·
due to a strong N–H O intramolecular hydrogen bond was
Irkutsk Institute of Chemistry, 664033 Irkutsk, Russia
c
Magn. Reson. Chem. 2010, 48, 661–670
Copyright ꢀ 2010 John Wiley & Sons, Ltd.

A. V. Afonin et al.
[7]
· · ·
chelate ring with a strong N–H O hydrogen bond is formed.
than those of the trans-N–H covalent bond. On lowering the
temperature to −55 ◦C, the 1J(N,H) coupling constants for the
chelated N–H bond in 1–7 further increase by 1–2 Hz while those
of the free N–H bond change to a lesser extent (Table 1). This is a
To gain deeper insight into the factors that determine whether an
intramolecular hydrogen bond yields a decrease or increase of the
1J(N,H) coupling constant, NMR spectral parameters concerning
1
· · ·
· · ·
the N–H O hydrogen bridge in the diaminoenones [ J(N,H),
somewhatsurprisingfindingsincesimilarN–H Ointramolecular
δ(1H), δ(15N)] were measured. Throughout this paper, attention
is mainly focused on these hydrogen-bond spectral parameters,
although the complete 1H, 13C, 15N NMR data for the compounds
studied are also included. The NMR data for the series of 1,1-
di(pyrrol-2-yl)-2-acylethenesareincludedaswell,tocomparethem
with those of the diaminoenones, and most of them are being
published for the first time (Table 1). The experimental trends
are substantiated by quantum-chemical calculations. Also, with
analytical purpose, the theoretical methods of Bader atoms-in-
molecules(AIM)theory[8] andnaturalbondorbital(NBO)analysis[9]
are employed.
hydrogen bonds in a series of 2-(2-acylethenyl)pyrroles cause a
decrease of 2–4 Hz in the corresponding 1J(N,H) value.[4] Thus,
in 1,1-di(pyrrol-2-yl)-2-acylethenes 8–11, the 1J(N,H) coupling for
the N–H group involved in the hydrogen bonding (cis-position) is
smaller by 2–4 Hz than that of the free N–H group (trans-position;
Table 1). As a result, the difference between the cis-1J(N,H) and
trans-1J(N,H) absolute values, i.e. the parameter ꢀJ, has a positive
sign in the family 1–7, while in the family 8–11 it is negative
(Table 1).
InRef. [4]itwasshownthattheδ1H,δ15Nand1J(N,H)parameters
in the dipyrrolyl acylethenes depend on the solvent. Hence, the
solvent effect as well as the concentration effect on these values
was studied for the compound 2.
Results and Discussion
Solvent and concentration effects
Spectral data
As follows from the data in Table 2, the 1H signal of the trans-N–H
group in 2 shifts to the higher frequencies by 1.4 and 2.0 ppm
on going from CDCl3 to (CD3)2CO and (CD3)2SO, respectively,
although that of the cis-N–H group is shifted only slightly. The
cis- and trans-1J(N,H) couplings change in opposite directions.
While the former coupling decreases, the latter coupling increases
in (CD3)2CO and (CD3)2SO as compared to CDCl3 (Table 2). The
changes in the 15N chemical shifts are relatively small. It is worth
noting only the high-frequency shift of trans-δ15N in (CD3)2SO
with respect to CDCl3 by 4.6 ppm. The same regularity in change
The general formula of compounds studied in this work is shown
in Scheme 2. The 1H, 13C and 15N experimental data under
consideration for the diaminoenones 1–7 and 1,1-di(pyrrol-2-
yl)-2-acylethenes 8–11 are given in Table 1.
Enamino–imino tautomerism may be inherent to di-
aminoenones 1–7 (Scheme 3).[7] However, the values of the 13C1
chemical shift of the carbonyl group carbon, the 13C2 and 13C3
chemical shifts of the double bond carbons and the 15N chemical
shifts of the amino groups nitrogen (182–184, 75–80, 159–160,
−273 to −286 ppm, respectively; Table 1) unequivocally corre-
spond to the enamino form since typical values of δ(13C1), δ(13C2),
δ(13C3), δ(15N) in the diaminoenones range from 180, 90, 150,
−270 to 200, 100, 160, −300 ppm, respectively.[7a] Also, a large
low-frequency shift of the 13C2 chemical shift (∼20 ppm) in the
studied diaminoenones 1–7 is explained by an electron-donating
effect of second amino group at the C3 carbon. Therefore, no
transfer of the proton of the amino group to the oxygen of the
carbonyl group takes place in the compounds 1–7, which exist
largely in the tautomeric enamino form.
1
of δ1H, δ15N and J(N,H) in CDCl3 and (CD3)2SO was discovered
in dipyrrolyl acylethene 8,[4] and the relevant parameters of 8 are
also included in Table 2. It is rationalized as due to the formation of
the intermolecular hydrogen bond between the free N–H group
and a molecule of DMSO.[4] The same interaction with a molecule
of acetone or dimethylsulfoxide (DMSO) seems to be occurring in
case of molecule 2. Notably, the ꢀJ parameter in 2 demonstrates
a change in sign, from positive to negative, on going from CDCl3
to (CD3)2SO, although it becomes more negative in the case of 8
(Table 2). The interaction with DMSO molecule leads to a decrease
of the ꢀJ parameter in spite of its starting value (positive or
negative).
The concentration effect on δ1H and 1J(N,H) in 2 is rather
small. However, one can note some deshielding of trans-1H and
decrease of cis-1J(N,H) as well as the ꢀJ parameter with increase of
concentration (within 0.26 ppm and 0.7 Hz, respectively; Table 3).
The observed trend, being like the influence of (CD3)2CO and
(CD3)2SO, is probably connected with a self-association of solute
molecules on increase in concentration.
1
The δ(1H), δ(15N) and J(N,H) spectral parameters for the N–H
group in the cis-position relative to the carbonyl group in the
compounds 1–7 differ regularly from those of the N–H group
in the trans-position. The 1H signal of the cis-N–H group in
1–7 is dramatically shifted to higher frequencies as compared
to that of the trans-N–H group (11.3–11.5 vs 4.0–4.3 ppm;
· · ·
Table 1). This extraordinary shift occurs because of the N–H
O
strong intramolecular hydrogen bond which establishes the six-
membered chelate ring in the diaminoenones 1–7 (Scheme 3).
Since the diaminoenones 1–7 have both the chelated N–H group
in the cis-position to the carbonyl group and the free N–H group in
thetrans-position,theseareaveryconvenientmodeltoinvestigate
Quantum-chemical calculations
· · ·
the effects of N–H O intramolecular hydrogen bonding on the
· · ·
To see the effect of N–H O intramolecular hydrogen bonding
NMR spectral characteristics.
The 15Nnucleus of the cis-N–Hgroup in 1–7 resonates regularly
at a lower frequency with respect to that of the trans-N–H group
on the shielding and coupling constants, the conformations
with syn and anti orientations of the carbonyl group relative
the NH(i-Pr) moiety of model compound 12 were taken into
consideration (Scheme 4). Some geometrical parameters and
calculated chemical shifts for the syn and anti conformations
of 12 are shown in Table 4.
(−273 to −277 vs −283 to −287 ppm; Table 1). The deshielding of
15
· · ·
the N nitrogen mainly originates from the N–H O hydrogen
bonding,[4,10] although the electronic effect of the carbonyl group
may also contribute to the observed effect. One-bond 1J(N,H)
coupling constants across the cis-N–H covalent bond measured
at room temperature are also larger in absolute value by 2–3 Hz
· · ·
The optimized intramolecular distance r(NH O) in the syn
conformation of 12 at the MP2/6-311++G(d,p) level is only 1.77 Å
c
www.interscience.wiley.com/journal/mrc
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2010, 48, 661–670

· · ·
Analysis of the N–H O intramolecular hydrogen-bond influence
c
Magn. Reson. Chem. 2010, 48, 661–670
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/mrc

A. V. Afonin et al.
c
www.interscience.wiley.com/journal/mrc
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2010, 48, 661–670

· · ·
Analysis of the N–H O intramolecular hydrogen-bond influence
· · ·
indicating the strong N–H
O
intramolecular hydrogen anti conformation of 12. At the same time, change in the JPSO
bonding.[4,11] Stabilization of the syn conformer is evident, as term is of approximately 1 Hz only, and the change in the JDSO as
it is lower in energy by as much as 8.4 kcal/mol than the anti con- well as JSD terms is quite negligible (Table 5). Also, the modulus
former having no hydrogen bonding. The length of the cis-N–H of the JFC term of the cis-1J(N,H) coupling is larger by 4.1 Hz than
bond in the syn conformation of 12 is longer by 16 mÅ than that that of the trans-1J(N,H) coupling in the syn conformation of 12.
of the trans-N–H bond (Table 4). Such lengthening of the cis-N–H This is a main factor to rationalize why the measured values of
bondcanbeattributedtotheinfluenceoftheN–H Ointeraction the cis-1J(N,H) coupling are larger by 2–4 Hz than those of the
since the length of the cis- and trans-N–H bonds becomes equal
· · ·
trans-1J(N,H) coupling constant in the series of diaminoenones
in the anti conformation of 12 (Table 4).
The calculated H chemical shift of the cis-N–H group in the
1– 7.
1
However, the opposite trend was discovered in analyzing the
influence of N–H O hydrogen bonding on 1J(N,H) coupling
syn conformation of 12 by means of gauge-independent atomic
orbital (GIAO) is larger by 7 ppm than that of the trans-N–H group
· · ·
constants in the series of 2-(2-acylethenyl)pyrroles.[4] The values of
total 1J(N,H) coupling constants, together with their terms for the
model 1,1-di(pyrrol-2-yl)-2-formylethene 13 (Scheme 5), are also
included in Table 5.
· · ·
(10.92 vs 3.81 ppm; Table 4) reflecting the N–H O hydrogen
bonding. The difference between the calculated 1H chemical shifts
of the cis- and trans-N–H group matches well the experimental
difference of these chemical shifts. In the anti conformation of 12,
the 1H chemical shift of the cis-N–H group differs from that of the
trans-N–H group by only 0.4 ppm (Table 4). In accordance with the
computations, the 15N nitrogen of the cis-N–H group in the syn
conformation of 12 is deshielded by 20 ppm relative to that of the
trans-N–H group. However, the shielding of 6.5 ppm is predicted
bythecalculationsforthe cis-N–Hgroupascomparedtothe trans-
N–H group in the anti conformation of 12 (Table 4). It implies that
As is evident from the data of Table 5, the calculated cis-1J(N,H)
couplings in 13 are weaker by 1–2 Hz as compared to those of
trans-1J(N,H) depending on the conformation. Both Fermi-contact
andparamagneticspin-orbitalmechanismsbringaboutadecrease
of the cis-1J(N,H) absolute value in this case. A principal point in
the behavior of the 1J(N,H) coupling in 12 and 13 is that the JFC
and JPSO terms in the latter reveal a change in the same direction
providing a decrease of cis-JTOT, whereas a large increase of JFC for
cis-JTOT in the former cancels’ a small decrease of JPSO (Table 5).
Thus, the JFC term stipulates the different trends in the change
· · ·
the N–H O hydrogen bonding in the syn conformation of 12
causes the deshielding of the 15N nitrogen of the cis-N–H group
(vide supra), which is observed in the experiment.
1
of the measured J(N,H) values in the diaminoenones 1–7 and
A matter of special interest is the behavior of the 1J(N,H)
1,1-di(pyrrol-2-yl)-2-acylethenes 8– 11.
· · ·
coupling constants in 12 on breaking of the N–H O hydrogen
In order to elucidate the difference between the effects of the
bond. The 1J(N,H) coupling constants in 12 were computed at
the B3LYP/aug-cc-pVDZ level of DFT since this approach has
demonstrated the close correspondence between the calculated
and measured values of 1J(N,H).[4,5] As calculations yield negative
values of the one-bond 15N–1H spin–spin coupling constant
(Table 5) because of a negative value of the magnetogyric ratio
γ (15N), the changes in modulus of this coupling constant are
considered throughout the paper. The computed values of the
1J(N,H) coupling constants for the predominant syn conformation
of 12 are in the excellent agreement with the experimental values
of 1–7 obtained at low temperature [91.4 vs 91.2 ( 0.6) Hz for the
chelated N–H bond and 88.5 vs 87.9 ( 0.5) Hz for the free N–H
bond; Tables 1 and 5]. The calculations at the DFT level show that
the1J(N,H)couplingconstantacrossthecis-N–Hbonddecreasesin
absolute value by 8.3 Hz, whereas that across the trans-N–H bond
increases by 1.8 Hz on going from the syn to the anti conformation
of 12 (91.4 vs 82.9 Hz and 88.5 vs 90.1 Hz; Table 5). Therefore, the
· · ·
N–H Ointramolecularhydrogenbonding inthediaminoenones
and dipyrrolyl acylethene, the topological parameters for hy-
drogen bonds in the model diaminoenone 12 and dipyrrolyl
formylethene13 obtained from AIM calculations were considered.
AIM analysis
Calculations in accordance with AIM theory[8] reveal the formation
of a six-membered chelate ring built up by an intramolecular
· · ·
N–H O hydrogen bond in the diaminoenone 12 and a similar
seven-membered chelate ring in the dipyrrolyl formylethene 13.
Topological parameters of the hydrogen bonds and chelate rings
(electron density at critical points ρ; Laplacian of the electron
2
density at critical points ∇ ρ; and the λ1, λ2, λ3 eigenvalues of
the Hessian matrix) as well as the energetic properties of electron
density at critical points (the G local electron kinetic, V potential
and H total energy densities) are given in Table 6.
The electron density (ρBCP
parameters as well as energetic characteristics of hydrogen bond
N(O)) and other topological
· · ·
N–H O hydrogen bond in diaminoenones shows an increase
H· · ·
of the cis-1J(N,H) coupling constant, indeed, in the absolute size,
which is what is observed in the experiment. It should be stressed
that the strengthening of the cis-1J(N,H) coupling in 1–7 occurs
despite the lengthening of the cis-N–H bond (see above).
The total value of the coupling constants is known[12] to
be determined by the sum of the Fermi-contact (JFC), the
paramagnetic spin–orbital (JPSO), the diamagnetic spin–orbital
(DSO) (JDSO) and the spin–dipole (JSD) terms (Eqn (1)).
2
critical point (BCP) (∇ ρBCP
N(O), λ1, λ2, λ3, G, V, H) of two
H· · ·
hydrogen-bondedatomsmaybetreatedasmeasuresofhydrogen-
bond strength.[13,14] As is evident from the data of Table 6, the
ρBCP
N(O) and ∇ ρBCP
N(O) in the diaminoenone 12 are lower
H· · ·
2
H· · ·
than those of dipyrrolyl formylethene 13 (3.88 × 10−2 vs 4.30 ×
10−2 e/ao3 and14.66×10−2 vs15.75×10−2 e/ao5,respectively).All
three curvatures λ1, λ2, λ3 are also smaller in the former molecule
(Table 6). Finally, the G, V and H local energetic characteristics of
BCP in 12 reduce in the absolute value as compared to those of
JTOT = JFC + JPSO + JDSO + JSD
(1)
13 (3.69 × 10−2, −3.71 × 10−2 and −0.02 × 10−2 vs 4.12 × 10−2
,
The calculations of all contributions to the one-bond 1J(N,H) −4.31×10−2 and−0.19×10−2 kJ/mol×ao3,respectively;Table 6).
coupling constant reveal that the Fermi-contact contribution is
The listed topological parameters and energetic characteristics
have been shown[14] to be connected with the intermolecular
· · ·
the main factor that describes the influence of the N–H
hydrogen bonding on this coupling constant in 12. The modulus distances of the interacting atoms in the hydrogen-bonded
of the JFC term decreases by 9.3 Hz on going from the syn to the complexes, the parameters becoming smaller as the distance
O
c
Magn. Reson. Chem. 2010, 48, 661–670
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/mrc

A. V. Afonin et al.
o"
m"
4''
3''
2''
H
R1
5''
p"
"
3'
4'
R1
R2
O
N
o'
i"
m'
2'
2'
5'
N
1'
H
3'
3
3
1
N
R1'
i'
R1'
N
H
H
2
2
p'
6'
4'
R3
1
O
5'
R2
8
10
1
7
1: R1=R1' = cyclo-C6H11, R2 = R3 = H
3'"
2'"
2: R1=R1' = cyclo-C6H11, R2 = H, R3 = CH3
3: R1=R1' = cyclo-C6H11, R2 = H, R3 = OCH3
4: R1=R1' = cyclo-C6H11, R2 = H, R3 = Cl
5: R1=R1' = cyclo-C6H11, R2 = OCH3, R3 = H
6: R1=R1' = iso-Pr, R2 = H, R3 = CH3
4'"
8: R1' = R1" = H; R2 =
5'"
o'"
S
m'"
9: R1' = R1" = OCH3; R2 =
10: R1' = R1" = N(CH3)2; R2 =
i"'
p'"
7: R1=R1' = sec-Bu, R2 = H, R3 = CH3
5''
4''
6''
9''
4'
3''
5'
9'
3'
7''
H
8''
2''
3
6'
N
N
2'
O
N
N
H
8'
H
N
7'
H
H
2
N
H
13
1
O
O
2'"
3'"
12
4'"
S
11
5'"
Scheme 2. Compounds studied.
From a topological parameter viewpoint, one can see a
cis-
2
significant increase of both the ρRCP electron density and ∇ ρRCP
Laplacian of the electron density at the critical point of the chelate
ring on going from the seven-membered chelate ring in 13 to the
R
H
R
H
O
N
O
N
H
H
3
six-membered chelate ring in 12 (0.77×10−2 vs 1.65×10−2 e/ao
Ar
N
R
Ar
N
R
and 4.98 × 10−2 vs 11.29 × 10−2 e/ao5, respectively; Table 6),
showing the more linear character of the hydrogen bond in the
former molecule.
trans-
enamine
azomethine
Thus, an analysis of the topological and geometrical parameters
1
7
· · ·
of the N–H O hydrogen bond in the molecules 12 and 13
suggests that the more bent hydrogen bond in the case of the
Scheme 3. Possible enamine–imine tautomerism in diaminoenones 1–7.
six-membered chelate ring of 12 is weaker. As a result of this
· · ·
weakening, the effect of the N–H O hydrogen bond on the
1J(N,H) coupling constant changes the direction (increase in the
former molecules and decrease in the latter molecules). To gain
more unambiguous interpretation of the discussed phenomena,
the NBO method of Weinhold et al.[9] was employed.
increases. It allows one to suppose that a similar regularity
takes place in the case of intramolecular interactions, and the
· · ·
N–H O intramolecular hydrogen bond is weakened on going
from the dipyrrolyl formylethene 13 to the diaminoenone 12. The
· · ·
weakening of the N–H O hydrogen bond in 12 with respect
· · ·
to that in 13 reflects the elongation of the H O intramolecular
NBO analysis
distancefrom1.68 Å[4] inthelattermoleculeto1.78 Å intheformer
molecule. Besides, the ratios |λ1 + λ2|/λ3 and |V|/G in 13 show
some increase relative to those of 12 (0.476 vs 0.446 and 1.045 vs
1.007; Table 6) indicating an enhancement of the stabilizing effect
of the electric field over the repulsive, closed-shells interaction in
hydrogen bonding.[14]
TherelevantparameterstakenfromtheNBOanalysisarepresented
in Table 7. As shown by the NBO analysis, there are a strong
hyperconjugative interactions between both oxygen lone pairs
and the antibonding orbital of the N–H bond, LP1(O) → σ∗
N–H
and LP2(O) → σ∗N–H, in the molecules 12 and 13, providing
One of the essential reasons for the weakening of the hydrogen
bridge in diaminoenone 12 in comparison to that in dipyrrolyl
formylethene 13 is the more strained nature of the six-membered
chelate ring in the former with respect to the seven-membered
chelate ring in the latter. The bond angle θ at the bridge
hydrogen (Scheme 6) in the diaminoenone 12, corresponding
to the equilibrium geometry, is 142.5◦ (Table 4), while that of 13
increases to 152.7◦.[4]
a charge transfer from the former moieties to the latter moiety
· · ·
through the intramolecular N–H O hydrogen bond. The LP1(O)
interactions in the pyrrole
13 are noticeably stronger than those in diaminoenone 12
→ σ∗
and LP2(O) → σ∗
N–H
N–H
(7.46 vs 4.66 and 19.59 vs 16.06 kcal/mol; Table 7), yielding the
total intensification of the LP1,2(O) → σ∗
interaction in 13
N–H
by 6.3 kcal/mol. The reinforcement of the LP1,2(O) → σ∗
·N· –· H
interaction in 13 can be rationalized by the more linear N–H
O
c
www.interscience.wiley.com/journal/mrc
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2010, 48, 661–670

· · ·
Analysis of the N–H O intramolecular hydrogen-bond influence
Table 2. 1H, and 15N NMR data for compounds 2 and 8 in the different solvents
δ (ppm)
J (Hz)
trans-1J(N,H)
Compound
Solvent
cis-δ1H
cis-δ15N
trans-δ1H
trans-δ15N
cis-1J(N,H)
ꢀJ
2
CDCl3
(CD3)2CO
(CD3)2SO
CDCl3
11.49
11.78
−277.0
−277.4
4.08
5.45
−286.6
−285.3
89.9
89.2
87.3
88.8
2.6
0.4
11.46 (−0.03)a
−275.8 (1.2)
−220.3
6.10 (2.02)
8.84
−282.0 (4.6)
−234.6
87.8 (−2.1)
93.4
89.4 (2.1)
95.4
−1.6
−2.0
−4.5
8b
14.71
(CD3)2SO
14.46 (−0.25)a
−222.0 (−1.7)
11.86 (3.02)
−229.8 (5.8)
92.3 (−1.1)
96.8 (1.4)
a The differences between spectral prameters in (CD3)2SO and CDCl3 are given in parentheses.
b The data were taken from Ref. [4].
N
H
Table 3. Effect of solvent concentration on the 1H chemical
shift and 1J(N,H) coupling constant in 3,3-bis(cyclohexylamino)-1-(4-
methylphenyl)prop-2-en-1-one 2 in CDCl3
θ
Solvent
concentraion
δ (ppm)
J (Hz)
.
.
.
(M)
cis-δ1H trans-δ1H cis-1J(N,H) trans-1J(N,H) ꢀJ
O
0.013
0.026
0.052
0.105
0.210
0.420
11.49
11.53
11.53
11.53
11.51
11.50
4.08
4.11
4.13
4.16
4.22
4.34
89.9
89.7
89.5
89.3
89.3
89.2
87.3
87.4
87.4
87.3
87.3
87.3
2.6
2.3
2.1
2.0
2.0
1.9
Scheme 6. Hydrogen-bond angle.
a larger difference between the σ∗
occupation numbers for
N–H
the chelated and free N–H bonds in comparison with that of
12 (0.033 and 0.047 e, respectively; Table 7). An increase of the
σ∗
occupation numbers for the cis-N–H bond should result
N–H
in the lengthening of this bond as well as weakening of the
corresponding 1J(N,H) coupling.[15]
H
H
N
N
O
As hydrogen bonding involves electrostatic and charge transfer
interactions,[16] it is necessary to allow for a rehybridization of the
N–H bond, due to the electrostatic term, to lead to a change of
the bond length and one-bond coupling constant in a direction
oppositetothatofthechargetransferinteraction.[12b,17] Asevident
from data in Table 7, the percentage of nitrogen s-character of the
cis-N–H bond is higher in 12 and 13 than that of the trans-N–H
bond (28.1 vs 26.3 and 31.0 vs 27.5%). Obviously, the electrostatic
interaction in the seven-membered chelate ring in 13 is stronger
once again than that of the six-membered chelate ring in 12 since
the nitrogen s-character increases by ca 4% on going from the
cis-N–H bond to the trans-N–H bond in 13, while an increase
of only 2% is observed for the nitrogen s-character of the cis-
N–H bond as compared to that of the trans-N–H bond in 12. A
change in the s-character percentage of the N–H bond affects
the relevant shielding and coupling constants. From a theoretical
viewpoint, an increased s-character of a bond to nitrogen yields a
high-frequency shift of the corresponding 15N NMR signal owing
to an increase in the negative local paramagnetic term of the total
nuclear shielding.[18] The cis-15N nitrogen in the diaminoenones
1–7 shows a high-frequency shift of 10–11 ppm, indeed, and this
effect is substantiated by the GIAO calculations (see above). Also,
since there is a linear relationship between the one-bond 1J(N,H)
coupling constants and the nitrogen s-character percentage of the
N–H bond, the absolute value of 1J(N,H) increases as the percent
s-character of the N–H bond at the nitrogen atom increases.[12b,17]
It corresponds to the observed increase of the cis-1J(N,H) coupling
constant in 1–7 relative to that of the trans-1J(N,H) coupling
constant.
H
H
N
O
N
syn-
anti-
12
Scheme 4. The conformations studied for3,3-bis(isopropylamino)-1-prop-
2-en-1-one (12).
H
N
trans-
N
cis-
N
H
H
N
H
O
O
anti-
syn-
13
Scheme 5. The conformations studied for 1,1-di(pyrrole-2-yl)-2-
formylethene (13).
intramolecular hydrogen bonding in case of the seven-membered
chelate ring. As a consequence of the LP1,2(O) → σ∗
N–H
interaction, the σ∗
occupation number for the chelated N–H
N–H
bond in 12, 13 becomes greater than that of the free N–H bond.
A more intensive LP1,2(O) → σ∗
interaction in 13 ensures
N–H
c
Magn. Reson. Chem. 2010, 48, 661–670
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/mrc

A. V. Afonin et al.
Table 4. Selected geometrical parameters and calculated chemical shifts for the syn and anti conformers of 12
R (Å)
δ (ppm)
cis-15N–H
Hydrogen
cis-N–1H
trans-N–1H
trans-15N–H
· · ·
O
Conformer
bond angle (θ)
H
cis-N–H
trans-N–H
Syn
142.5
–
1.775
3.727
1.030
1.014
1.013
1.014
10.92
2.90
3.81
2.53
−279.2
−286.8
−299.2
−280.3
anti
Table 5. Calculated coupling constants for the syn and anti conformers of 12 and 13
Compound
J (Hz)
cis-1J(N,H)
trans-1J(N,H)
Conformer
JTOT
JFC
JPSO
JDSO
JSD
JTOT
JFC
JPSO
JDSO
JSD
12
Syn
anti
syn
−91.4
−82.9
−95.1
−94.9
−89.8
−80.4
−93.8
−93.7
−1.1
−2.1
−0.7
−0.7
−0.6
−0.5
−0.6
−0.6
0
0
0
0
−88.5
−90.1
−96.3
−96.9
−85.6
−87.3
−93.9
−94.6
−2.2
−2.2
−1.8
−1.7
−0.6
−0.5
−0.5
−0.6
−0.1
−0.1
−0.1
0
13a
anti
a Taken from Ref. [4]. As the 14N–1H coupling constants were erroneously reported in the previous paper,[4] they are converted to the corresponding
15N-based values using the equation J(15N, H) = −1.4027 J(14N, H) where the coefficient is the ratio of magnetogyric ratios γ (15N)/γ (14N). The syn
and anti conformations correspond the rotation of the trans pyrrole ring (Scheme 5).
The competition between the rehybridization and hypercon-
jugation effects on the 1J(N,H) coupling constant, operating in
opposite directions, may result in a decrease in the 1J(N,H) ab-
solute magnitude or an increase in the hydrogen bonding. Both
electrostatic and charge transfer interactions are stronger in the
case of the seven-membered chelate ring in comparison to the
six-membered chelate ring (compounds 12 and 13, respectively).
Nevertheless, based on the experimentally observed and theo-
the hydrogen bond. An increase of the absolute value of 1J(N,H)
should be expected for a bent hydrogen bond, while a decrease
of the 1J(N,H) coupling constant is expected on the formation
of a more linear hydrogen bond. The observed effect depends
on the solvent. In a basic solvent such as DMSO, a positive
effect of the intramolecular hydrogen bonding on the 1J(N,H)
coupling constant may be replaced by a negative effect since a
solvent molecule can form a competitive intermolecular hydrogen
bonding.
1
retically predicted trends in the change of the J(N,H) values for
the dipyrrolyl formy(acyl)ethenes and diaminoenones, one can
guess that the strong LP(O) → σ∗
interaction in 13 prevails
N–H
over the rehybridization effect and that the 1J(N,H) coupling con-
Experimental and Computational Details
· · ·
stant decreases as a result of the stronger N–H O intramolecular
Spectra
hydrogen bonding. However, a less important LP(O) → σ∗
N–H
NMR spectra were recorded in CDCl3 at 303 K on a Bruker
AVANCE 400 spectrometer (1H, 400.16 MHz; 13C, 101.61 MHz; 15N,
40.55 MHz)equippedwitha5-mmZ-gradientinversionprobehead
and XWIN-NMR 3.5 software package running on Windows XP. The
1H and 13C chemical shifts were referenced to internal TMS.
Theapplicationofthehomonucleartwo-dimensional(2D)COSY
and NOESY as well as heteronuclear 2D HSQC and HMBC methods
allowed the assignment of the 1H and 13C signals in compounds
1–11. To minimize the effect of the intermolecular hydrogen
bonding, the values of the one-bond 15N–1H coupling constants
were measured in a 2D [1H–15N] gHSQC experiment.[19] The
values of the 1J(N,H) coupling constant were determined from
the one-dimensional (1D) traces of the 2D [1H–15N] HSQC maps.
interaction in 12 is smaller compared to the rehybridization effect
and an increase of the 1J(N,H) coupling constant is exhibited as a
· · ·
consequence of the more bent N–H O intramolecular hydrogen
bond for the six-membered chelate ring. As expected, the term
mostsensitivetotherehybridizationandhyperconjugationeffects
turns out to be the Fermi-contact (JFC) term of the total J(N,H)
1
spin–spin coupling constant (see above).
Conclusion
An experimental and theoretical investigation of the influence
· · ·
of N–H O intramolecular hydrogen bonding on the one-bond
1J(N,H) spin–spin coupling constant in push–pull diaminoenones
finds no direct correlation between the N–H bond length and the
1J(N,H) value. Lengthening of the N–H covalent bond in hydrogen
bonding may be accompanied by an increase in the 1J(N,H)
coupling constant in absolute size rather than its decrease. This is
the case when the rehybridization effect of the N–H bond, due to
the electrostatic term of hydrogen bonding, predominates over
the hyperconjugation effect. The factor leading to a weakening of
the hyperconjugation between the oxygen atom lone pairs and
antibonding orbital of the N–H bond is the bent geometry of
1
The measurement of the J(N,H) values were carried out at +25
and −55 ◦C. A standard Bruker pulse program hsqcgpph without
GARP decoupling during acquisition was used. The acquisition
conditions consisted of 4 K × 256 datapoints without zero-filling
taken over sweep widths of 1.0 (1H, F2), 100 (15N, F1) ppm. The
digital resolution in the 1D traces from F2 projection was 0.1 Hz
1
per point, and the uncertainty in the J(N,H) coupling constants
was 0.1 Hz. The values of the δ(15N) were measured through a
2D [1H–15N] HMBC experiment.[20] The 15N chemical shifts were
referenced to CH3NO2 used as an external standard in a capillary.
c
www.interscience.wiley.com/journal/mrc
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2010, 48, 661–670

· · ·
Analysis of the N–H O intramolecular hydrogen-bond influence
Table 6. Topological parameters and energetic characteristics of the intramolecular hydrogen bonds and chelate rings in the compounds 12 and
13a
Energetic properties of
· · ·
NH O hydrogen BCP
Ring critical point
Eigenvalues of the Hessian matrix
electron density at BCP
ρBCP
∇ ρBCP
ρRCP
×102
∇ ρRCP
×102
λ1
×102
λ2
×102
λ3
×102
|λ1 + λ2|/
2
2
O· · ·H
O· · ·H
Compound
×102
×102
λ3
G × 102
V × 102
H × 102
|V|/G
12
13
3.88
4.30
14.66
15.75
1.65
0.77
11.29
4.98
−6.01 −5.81
−7.33 −6.99
26.49
30.08
0.446
0.476
3.69
4.12
−3.71
−4.31
−0.02
−0.19
1.007
1.045
a The ρ and ∇ ρ, λ1, λ2, λ3 values are given in e/ao3 and e/ao5, respectively; the G, V, H are given in kiloJoule per mol × ao
.
2
3
Table 7. Energy of the NBO hyperconjugative interactions, NBO nitrogen s-character percentage of the N–H bondsa and occupancy of the
antibonding σ∗N–H orbitals for the compounds 12 and 13
s-character of natural
Energy stabilization (kcal/mol)
Occupancy (e)
trans-σ∗
N–H
bond orbital (%)
Compound
LP1(O) → σ∗
LP2(O) → σ∗
cis-σ∗
cis-N–H
trans-N–H
N–H
N–H
N–H
12
13
4.66
7.46
16.06
19.59
0.03346
0.04668
0.01935
0.01521
28.07
30.95
26.25
27.53
a In all cases, the H s-character ranges from 99.93 to 99.96%.
The concentrations of solute molecules were within
0.01–0.05 M.
The three second-order terms (the Fermi-contact, paramagnetic
spin–orbital and spin–dipole) were calculated using the coupled-
perturbed Kohn–Sham (CP-KS) approach.[29] The first-order DSO
term was calculated as the mean value of the DSO operator in the
unperturbed reference state.[29]
Calculations
AIM calculations of topological parameters at the B3LYP/6-
311++G(d,p) level were performed as implemented in the
Gaussian 03 program. NBO characteristics (energy of the hy-
perconjugative interactions, nitrogen and hydrogen s-character
percentage of the N–H bonds, occupancy of lone pair and
Thegeometriesforallstructurespresentedherewerecalculatedat
the MP2 level of theory[21] without symmetry constraints by using
the Gaussian 03 W program package.[22] The triple split-valence
6-311G++(d,p) basis set of Pople, which included a set of diffuse
functions as well as d-type polarization functions on all non-
hydrogen atoms and p-type polarization functions on hydrogen
atoms, was adopted in the calculations.[23] The energy minima
with respect to the nuclear coordinates were obtained by the
simultaneous relaxation of all the geometrical parameters of the
molecules using the gradient method of Pulay.[24] Frequency
calculations at equilibrium geometries yielded no imaginary
values, indicating that the geometries obtained corresponded
to energy minima.
antibonding σ∗
orbitals) were obtained through the NBO
N–H
program[30] at MP2/6-311++G(d,p) level.
Synthesis of 1–7
Thesynthesesof3,3-bis(alkylamino)-1-(aryl)prop-2-en-1-ones1–6
have been previously described.[6] Diaminoenone 7 was synthe-
sized in the same way.
The proton and nitrogen magnetic shielding constants were
computed via the GIAO method[25] in the DFT framework. The
effect of electron correlation on DFT calculations was taken into
account by Becke’s three-parameter hybrid exchange function[26]
and correlation functional by Lee, Parr and Yang (B3LYP).[27] The
proton and nitrogen shielding constants calculations were carried
out for the MP2/6-311G++(d,p) optimized geometries using
Dunning’s correlation consistent basis set of double zeta quality
augmented with standard diffuse functions (aug-cc-pVDZ).[28]
Absolute isotropic shielding constants were also calculated for the
referencematerialsTMSandCH3NO2, andthevaluesofprotonand
nitrogen chemical shifts were obtained as the difference between
the proton and nitrogen shielding constants for the investigated
compounds and that for TMS and CH3NO2, respectively.
1-(4-Methylphenyl)-3,3-bis[(1-methylpropyl)amino]prop-2-
en-1-one (7)
A mixture of the corresponding bromostyrene (1 mmol) and sec-
butylamine (10 mmol) was refluxed in dioxane for 32 h. Then the
solvent was evaporated in vacuo, a solution of concentrated HCl
(5 ml) was added and the mixture was heated at 70 ◦C for 3 h
and then extracted by CHCl3. The target enone 7 was isolated by
column chromatography (silica gel, CHCl3: MeOH = 19 : 1). Yield:
228 mg (79%); yellow solid; m.p. 143–145 ◦C. 1H and 13C NMR
(Table 1). MS (EI) m/z (relative intensity): 288 (31) [M+], 231 (10),
160 (35), 147 (16), 119 (100), 91 (50), 72 (90). C18H28N2O (288.428):
calcd. C 74.96, H 9.78, N 9.71; found C 74.79, H 9.75, N 9.84.
The total value of the coupling constant was determined as the
sum of the Fermi-contact, paramagnetic spin–orbital, DSO and
spin–dipole contributions. They were computed for the MP2/6-
311G++(d,p) optimized geometries using the aug-cc-pVDZ basis
set with the B3LYP density functional for all types of coupling.
Acknowledgement
This study was supported by the Russian Foundation for Basic
Research (Grant Nos 08-03-00736-a, RFBR-DFG 07-03-91562-
NNO a and 08-03-00067-a).
c
Magn. Reson. Chem. 2010, 48, 661–670
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/mrc

A. V. Afonin et al.
References
Spectrosc. 2000, 41, 55; (d) E. M. B. Janke, A. Dunger, H.-H. Limbach,
K. Weisz, Magn. Reson. Chem. 2001, 39, s177; (e) G. L. Sosa,
N. M. Peruchena, R. H. Contreras, E. A. Castro, J. Mol. Struct. 2002,
577, 219.
[1] (a) A. J. Dingley, J. E. Masse, R. D. Peterson, M. Barfield, J. Feigon,
S. Grzesiek, J. Am. Chem. Soc. 1999, 121, 6019; (b) E. M. B. Janke,
A. Dunger, H.-H. Limbach, K. Weisz, Magn. Reson. Chem. 2001, 39,
S177; (c) R. Ishikawa, C. Kojima, A. Ono, M. Kainosho, Magn. Reson.
Chem. 2001, 39, S159.
[2] (a) J. E. Del Bene, J. Elguero, J. Phys. Chem. A 2006, 110, 7496;
(b) J. E. Del Bene, J. Elguero, J. Am. Chem. Soc. 2004, 126, 15624.
[3] I. Alkorta, J. Elguero, G. S. Denisov, Magn. Reson. Chem. 2008, 46,
599.
[16] (a) K. Kitaura, K. Morokuma, Int. J. Quantum Chem. 1976, 10, 325;
(b) K. Morokuma, K. Kitaura, Energy decomposition analysis of
molecular interactions. in Chemical Applications of Atomic and
Molecular Electrostatic Potentials, (Eds: P. Politzer, D. G. Truhlar),
Plenum: New York, 1981, p 215.
[17] R. H. Contreras, J. E. Peralta, C. G. Giribet, M. C. Ruiz de Azua,
J. C. Facelli, Ann. Rep. NMR Spectrosc. 2000, 41, 55.
[4] A. V. Afonin, I. A. Ushakov, L. N. Sobenina, Z. V. Stepanova,
O. V. Petrova, B. A. Trofimov, Magn. Reson. Chem. 2006, 44, 59.
[5] (a) A. V. Afonin, I. A. Ushakov, A. I. Mikhaleva, B. A. Trofimov, Magn.
Reson. Chem. 2007, 45, 220; (b) A. V. Afonin, A. V. Vashchenko,
I. A. Ushakov, N. V. Zorina, E. Yu. Schmidt, Magn. Reson. Chem. 2008,
46, 441.
[18] C. G. Levy, R. L. Lichter, Nitrogen-15 NMR Magnetic Resonance
Spectroscopy, Wiley-Interscience: New York, 1979.
[19] G. Bodenhausen, D. Ruben, J. Chem. Phys. Lett. 1980, 69, 185.
[20] A. Bax, M. F. Summers, J. Am. Chem. Soc. 1986, 108, 2093.
[21] C. Møller, M. S. Plesset, Phys. Rev. 1934, 46, 618.
[22] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
[6] A. Yu. Rulev, V. M. Muzalevskiy, E. V. Kondrashov, I. A. Ushakov,
A. V. Shastin, E. S. Balenkova, G. Haufe, V. G. Nenajdenko, Eur. J. Org.
Chem. 2010, 300.
[7] (a) J. L. Chiara, A. Gomez-Sanchez, in The Chemistry of Enamines,
(Eds: Z. Rappoport), Wiley & Sons: New York, 1994, Chapter 5,
p 279; (b) A. Perona, D. Sanz, R. M. Claramunt, J. Elguero, Magn.
Reson. Chem. 2008, 46, 930.
[8] R. F. W. Bader, Atoms in Molecules. A Quantum Theory, Oxford
University Press: New York, 1990.
[9] (a) A. E. Reed, L. A. Curtiss, F. Weinhold, Chem. Rev. 1988, 88, 899;
(b) F. Weinhold, in Encyclopedia of Computational Chemistry, vol. 3,
(Eds: Pv. R. Schleyer), Wiley: New York, 1998, p 1792.
J. R. Cheeseman, J. A. Montgomery,
T. Vreven, K. N. Kudin,
J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone,
B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson,
H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Nasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene,
X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth,
P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malik, A. D. Rabuk,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-
Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill,
B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian
2003, Gaussian, Inc.: Pittsburg, 2003.
[10] M. Weychert, J. Klimkiewicz, I. Wawer, B. Piekarska-Bartoszewicz,
A. Temeriucz, Magn. Reson. Chem. 1998, 36, 727.
[11] (a) N. N. Chipanina, V. K. Turchaninov, I. I. Vorontsov, M. Yu. Antipin,
Z. V. Stepanova, L. N. Sobenina, A. I. Mikhaleva, B. A. Trofimov, Russ.
Chem. Bull. 2002, 51, 107; (b) Z. V. Stepanova, L. N. Sobenina,
A. I. Mikhaleva, I. A. Ushakov, V. N. Elokhina, I. I. Vorontsov, M. Yu.
Antipin, B. A. Trofimov, Zh. Org. Khim. 2003, 39, 1705.
[23] (a) R. Krishnan, J. S. Binkley, S. Seeger, J. A. Pople, J. Chem. Phys.
1980, 72, 650; (b) T. Clark, J. Chandrasekhar, G. W. Spitznagel, Pv.
R. Schleyer, J. Comput. Chem. 1983, 42, 94.
[12] (a) N. F. Ramsey, Phys. Rev. 1953, 91, 303; (b) R. H. Contreras,
V. Barone, J. C. Facelli, J. E. Peralta, Annu. Rep. NMR Spectrosc. 2003,
51, 167.
[24] P. Pulay, Mol. Phys. 1969, 17, 197.
[25] (a) R. Ditchfield, Mol. Phys. 1974, 27, 789; (b) K. Wolinski, J. F. Hilton,
P. Pulay, J. Am. Chem. Soc. 1990, 112, 8251.
[13] (a) S. J. Grabowski, Chem. Phys. Lett. 2001, 338, 361; (b) S.
Wojtulewski, S. J. Grabowski, Chem. Phys. Lett. 2003, 378, 388;
(c) T.-H. Tang1, E. Deretey, S. J. Knak Jensen, G. Csizmadia, Eur. Phys.
J. D 2006, 37, 217.
[14] (a) E. Espinosa, I. Alkorta, J. Elguero, E. Molins, J. Chem. Phys. 2002,
117, 5529; (b) I. Mata, E. Molins, I. Alkorta, E. Espinosa, J. Phys. Chem.
A 2007, 111, 6425; (c) I. Mata, I. Alkorta, E. Molins, E. Espinosa, Chem.
Eur. J. 2010, 16, 2442.
[15] (a) C. Vizioli, M. C. Ruiz de Azua, C. G. Giribet, R. H. Contreras, L. Turi,
J. J. Dannenberg, I. D. Rae, J. A. Weingold, M. Malagoli, R. Zanasi,
P. Lazzeretti, J. Phys. Chem. 1994, 98, 8858; (b) A. J. Dingley,
J. E. Masse, R. D. Peterson, M. Barfield, J. Feigon, S. Grzesik, J. Am.
Chem. Soc. 1999, 121, 6019; (c) R. H. Contreras, J. E. Peralta,
C. G. Giribet, M. C. Ruiz de Azua, J. C. Facelli, Annu. Rep. NMR
[26] A. D. Becke, J. Chem. Phys. 1993, 98, 5648.
[27] C. Lee, W. Yang, R. P. Parr, Phys. Rev. 1988, B 38, 785.
[28] (a) D. E. Woon, T. H. Dunning, J. Chem. Phys. 1993, 98, 650;
(b) R. A. Kendall, T. H. Dunning, R. J. Harrison, J. Chem. Phys. 1992,
96, 6796.
[29] (a) J. E. Peralta, V. Barone, R. H. Contreras, D. G. Zaccari, J. P. Snyder,
J. Am. Chem. Soc. 2001, 23, 9162; (b) V. Barone, J. E. Peralta,
R. H. Contreras, D. G. Zaccari, J. P. Snyder J. Am. Chem. Soc. 2002,
106, 5607; (c) J. E. Peralta, G. E. Scuseria, J. R. Cheeseman, M. J. Frish,
Chem. Phys. Lett. 2003, 375, 452.
[30] E. D. Glendening, A. E. Reed, J. E. Carpenter, F. Weinhold, Program
as Implemented in the Gaussian 03, NBO version 3.1, Revision D.02,
Gaussian Inc.: Wallingford, 2004.
c
www.interscience.wiley.com/journal/mrc
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2010, 48, 661–670