Structure and proton donating ability of 2- and 2,5-bis(1- trifluoromethanesulfonylamido-2,2,2-trichloroethyl)pyrroles

Article abstract of DOI:10.1134/S107036320902025X

2-(1-Trifluoromethanesulfonylamido-2,2,2-trichloroethyl)pyrrole and 2,5-bis(1-trifluoromethanesulfonylamido-2,2,2-trichloroethyl)pyrrole according to quantum chemical calculations (B3LYP/6-311G**) exist in the isomeric forms whose structure determines the formation of intramolecular hydrogen bonds NH...Cl, NH...O=S and CH...O=S of different strength. Potentiometric and spectroscopic acidity of these compounds is determined. From the data of IR spectroscopy their proton donating ability upon interaction with Lewis bases is shown depending on the presence of intramolecular hydrogen bonds, mutual effects of intermolecular hydrogen bonds formed by the sulfonamide and pyrrole NH groups with the base, and electronic effects of the substituents.

Full text of DOI:10.1134/S107036320902025X

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 2, pp. 315–322. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © L.P. Oznobikhina, N.N. Chipanina, B.A. Shainyan, L.V. Sherstyannikova, V.A. Kukhareva, T.N. Aksamentova, E.V. Kondrashov,
G.G. Levkovskaya, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 2, pp. 326–333.
Structure and Proton Donating Ability
of 2- and 2,5-Bis(1-trifluoromethanesulfonylamido-2,2,2-
trichloroethyl)pyrroles
L. P. Oznobikhina, N. N. Chipanina, B. A. Shainyan, L. V. Sherstyannikova,
V. A. Kukhareva, T. N. Aksamentova, E. V. Kondrashov, and G. G. Levkovskaya
Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: nina_chipanina@irioch.irk.ru
Received June 15, 2008
Abstract―2-(1-Trifluoromethanesulfonylamido-2,2,2-trichloroethyl)pyrrole and 2,5-bis(1-trifluoromethane-
sulfonylamido-2,2,2-trichloroethyl)pyrrole according to quantum chemical calculations (B3LYP/6-311G**)
exist in the isomeric forms whose structure determines the formation of intramolecular hydrogen bonds NH…Cl,
NH…O=S and CH…O=S of different strength. Potentiometric and spectroscopic acidity of these compounds is
determined. From the data of IR spectroscopy their proton donating ability upon interaction with Lewis bases is
shown depending on the presence of intramolecular hydrogen bonds, mutual effects of intermolecular hydrogen
bonds formed by the sulfonamide and pyrrole NH groups with the base, and electronic effects of the substituents.
DOI: 10.1134/S107036320902025X
Perfluoroalkanesulfonamides and their derivatives
RFSO2NHR are characterized by high NH-acidity (pKa
for CF3SO2NHR (R = H, Me) 6.2–7.6 in water [1, 2]
and 11.1–12.7 in methanol [3]) that causes the
formation of strong intermolecular hydrogen bonds
NH…O=S in crystals, which are retained even in the
gas phase up to 440 K [4, 5]. In solution, the supra-
molecular structure of these compounds is determined
by the properties of the medium. Presence of two
trifluoromethanesulfonamide residues in the molecule
allows the formation of intramolecular hydrogen bonds
with various sulfonylimines, including chloral trifluoro-
methanesulfonylimine [7]. The presence in the mole-
cules of compounds II and III of acidic NH groups of
the two types: pyrrole and sulfonamide, as well as of
several centers of basicity (oxygen and halogen atoms)
makes them interesting as the objects for investigation
both from the viewpoint of NH-acidity and of homo-
and heteroassociation due to formation of intra- and
intermolecular hydrogen bonds in the presence of an
external base. In the present work using the methods of
IR spectroscopy and quantum chemical calculations
of various types as, for example, in bis(trifluoromethane- for compounds II and III as well as for the hitherto
sulfonylamino)methane CF3SO2NHCH2NHSO2CF3; the
compounds of this type exist in an inert medium as a
mixture of monomeric forms rather than associates, the
percentage of each form being dependent on the
polarity of the solvent [3].
unknown N-methylsubstituted analog of compound II,
2-(1-trifluoromethanesulfonylamido-2,2,2-trichloro-
ethyl)-1-methylpyrrole (I), we have studied their
structure in the isolated and crystalline state and in
inert media, the proton donating ability (spectroscopic
NH-acidity) upon intermolecular interaction with
Lewis bases, and determined the acidity of compounds
II and III in methanol by potentiometric titration.
Recently, we have prepared 2-(1-trifluoromethane-
sulfonylamido-2,2,2-trichloroethyl)pyrrole (II) and
2,5-bis(1-trifluoromethanesulfonylamido-2,2,2-trichloro-
ethyl)pyrrole (III) by the reaction of chloral trifluoro-
methanesulfonylimine CF3SO2N=CHCCl3 with pyrrole
[6] and performed theoretical analysis of regioselec-
tivity of the reactions of С-amidomethylation of pyrrole
Compounds II and III show high NH-acidity, their
pKa values in methanol are 9.32 and 9.68, respectively.
On the curve of potentiometric titration of amide II
with NaOH solution in methanol only one kink is
315

316
OZNOBIKHINA et al.
CH(CCl3)NHSO2CF3
CH(CCl3)NHSO2CF3
N
N
Me
H
I
II
CF3SO2NH(CCl3)CH
CH(CCl3)NHSO2CF3
N
H
III
observed, that is, under these conditions only the
sulfonamide group SO2NH is titrated and not the
pyrrole NH group. Amide III is titrated with two
equivalents of the base but on the potentiometric curve
also only one kink is observed that implies that the first
and the second constants of dissociation of this dibasic
NH-acid are similar. Probably, this is due to
remoteness of the NH groups separated by six bonds
from each other and low sensitivity of one acidic
center to emerging of the charge on the other center.
The acidity of compounds II and III is substantially
higher than for the earlier studied analogs CF3SO2·
NHR (R = H, Me, CH2NHCOMe, CH2NHSO2CF3) for
which the values of pKa in methanol lie in the range of
10.1 – 12.7 pKa units [3]. Apparently, this is first of all
due to strong electronoacceptor effect of trichloro-
methyl group (σ* = 2.48 [8]), as well as electrono-
acceptor effect of the 2-pyrrolyl residue. We failed to
find the value of σ* for the latter but the constants of
dissociation of benzoic and 2-pyrrolylcarboxylic acids
are close, 4.2 and 4.45 [9], that means that σ* for the
2-pyrrolyl group is equal to ~0.5.
compounds CF3SO2NHR in solution, as was shown in
[3], is nonvalent intramolecular interactions. To
establish the nature of such interactions we have
performed quantum chemical calculations of mole-
cules I–III at the B3LYP/6-311G** level of theory.
The isolated molecule I according to calculations
has the structure in which interatomic distances H…X
(X = Cl, O) (NH…Cl and CH…O=S) are less than the
sum of the van der Waals radii of the corresponding
atoms (2.95 and 2.72 Å) (Fig. 1). Here, the NH…Cl
fragment having the length of the nonvalent bond of
~2.9 Å (Table 1) should be considered as a reduced
interatomic contact rather than an intramolecular hydro-
gen bond (intra-HB). The value of ν(NH) of 3590 cm–1
in its calculated vibrational spectrum (Table 1)
somewhat exceeds the frequency of vibrations of the
free group ν(NH) 3580 cm–1 of N-methyltrifluoro-
methanesulfonamide CF3SO2NHMe (IV). This high-
frequency shift is explained by electronoacceptor
effect of the pyrrole ring and trichloromethyl group in
compound I.
In IR spectra of solutions of compound I in CCl4
(Table 2) the stretching vibrations of the NH group of
Apart from the electronic effects of substituents, an
important factor affecting the structure and acidity of
Cl
Cl
Cl
Cl
Cl
Cl
H
Cl
O
H2
H2
Cl
H2
Cl
N
S
N
S
C
N
C
C
O
O
O
N
H
F
S
H
N
H1
N
H1
F
O
F
F
O
F
F
F
F
F
I
IIa
IIb
Fig. 1. Molecular structure of 2-(1-trifluoromethanesulfonylamido-2,2,2-trichloroethyl)-1-methylpyrrole I and stereoisomers of 2-
(1-trifluoromethanesulfonylamido-2,2,2-trichloroethyl)pyrrole (IIа, IIb).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 2 2009

STRUCTURE AND PROTON DONATING ABILITY
317
Table 1. Calculated values of interatomic distances d(H…X)
X = Cl, O of intramolecular hydrogen bonds (intra-HB)
СН…O=S, NH…Cl and NH…O=S, Å, differences of energies
∆E, kcal mol–1, dipole moments μ, D, and frequencies ν(NH),
cm–1 of the studied compounds (B3LYP/6-311G**)
the sulfonamide fragment are characterized by bands at
3375 and 3280 cm–1. With decrease of concentration of
the solution the peak intensity of the high-frequency
band increases whereas that of the low-frequency
drops. Earlier it was shown that amide IV under
similar conditions represents an equilibrium mixture of
monomeric molecules and cyclic dimer characterized
by frequencies ν(NH) 3407 and 3316 cm–1, respect-
ively [5]. This gives grounds to assign the band at
3280 cm–1 in the spectrum of compound I to vibrations
of the NH group also participating in the formation of
the cyclic dimer by means of two intermolecular
hydrogen bonds NH…O=S (inter-HB). The high-
frequency band ν(NH) at 3375 cm–1 belongs to mono-
meric molecule I. Its low-frequency shift by 32 cm–1
with respect to the band of the free NH group of amide
IV is, apparently, due to sensitivity of ν(NH) vibra-
tions to effects of the medium. Indeed, in the solution
of compound I in polar CH2Cl2 the high-frequency
band ν(NH) of its monomeric molecule at 3336 cm–1 is
even more (by 44 cm–1) shifted to low frequencies as
compared to the band in the spectrum of amide IV. An
intense band ν(NH) at 3271 cm–1 in the IR spectrum of
crystalline compound I corresponds to its chain
polyassociates with NH2…O=S bonds which are also
present in pure amide IV [5]. Its low-frequency shift
by 30 cm–1 with respect to the IR spectrum of amide
IV in thin layer can be related with higher strength of
the inter-HB in compound I and/or different aggregate
Comp.
Intra-HB
d(H···X)
∆E
μ
ν(NH)
no.
NH···Cl
2.865
2.386
4.39
3590 (48)
I
CH···O=S
0
4.33
3660 (64)
3593 (49)
IIа
NH2···Cl
2.868
2.402
2.105
2.677
CH···O=S
NH1···O=S
NH2···Cl
1.5
0
2.73
1.82
3633 (133)
3571 (63)
IIb
NH1···Cl
CH···O=S
NH2···Cl1
CH···O=S
NH3···Cl2
2.574
2.331
2.946
2.368
2.830
3636 (85)
3559 (36)
3597 (56)
IIIа
NH1···O=S
NH2···Cl
2.085
2.687
2.331
2.944
1.6
2.88
3592 (134)
3569 (70)
IIIb
CH···O=S
NH3···Cl
3557 (37)
3580 (56)
3674 (61)
4.18
1.94
IV
V
Table 2. Frequencies of stretching vibrations (ν, cm–1) of N–H bonds and values of ∆ν(NH) as differences between the value
of ν(NH) of monomeric molecule in CCl4 (or СH2Cl2) solution and of its H-complex with the base
∆ν(NH)
ν(NH)
а
b
Comp. no.
solution in CCl4
dioxane DMF
296 315
solution in СH2Cl2
dioxane DMF
276 >290
CCl4
CH2Cl2
3336
KBr
3375
3280
3476
I
3271
3442
3380
3458
3335
160 (196)
260 (290)
110 (210)
260 (290)
150
230
115
II
3375
3280
>230
3274
3435
3288
3263
3437
3321
3255
3380
126 (130)
90 (100)
III
3407
3316
3496
243 (270)
113 (142)
272 (310)
140 (160)
232
126
288
166
IV
V
3300в
3403в
3476
a The values for solutions in pure bases are given in parentheses. b Thin layer.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 2 2009

318
OZNOBIKHINA et al.
states of amides I and IV, that is, with packing effects
in the crystal. Therefore, in nonpolar inert medium the
molecules of compound I exist in equilibrium with
cyclic dimers, whereas in the solid state they are
represented by chain polyassociates.
formation of chain associates with inter-HB NH2…
O=S. The pyrrole NH group of form IIа participates in
the formation of inter-HB NH1…O=S. In more curled
and, probably, stabilized by crystal packing effects
form IIb an intra-HB ВВС NH1…O=S with participa-
tion of the pyrrole NH group is realized that prevents
its participation in formation of intermolecular Н-
bonds.
For molecule II the calculations give two
conformers corresponding to minima on the potential
energy surface (Fig. 1, Table 1). Conformer IIа along
with the free NH1 group of the pyrrole fragment
contains the NH2 group of the sulfonamide fragment
having a reduced contact NH2…Cl (2.873 Å), and the
CH group forming a weak intra-HB CH…O (2.401 Å).
This conformer is 1.5 kcal mol–1 more stable than
conformer IIb with intra-HB NH1…O=S (2.105 Å) and
NH2…Cl (2.677 Å). The values of the dipole moments
4.33 D (IIа) and 2.73 D IIb make conformer IIа to be
better stabilized with increase of polarity of the
medium. The calculated values of ν(NH1) and ν(NH2)
reflect the structural peculiarities of conformers IIа
and IIb (Table 1). Thus, the frequency of stretching
vibrations of the free group NH1 of the pyrrole frag-
ment in IIа is by ~30 cm–1 higher than that of the same
group participating in intra-HB NH1…O=S in IIb and
by 14 cm–1 lower than that of pyrrole. More strong
intra-HB NH2…Cl in IIb as compared to IIа is
characterized by lower (by ~20 cm–1) value of ν(NH2).
2,5-Bis(1-trifluoromethanesulfonylamido-2,2,2-tri-
1
chloroethyl)pyrrole (III), as was shown earlier by H
NMR spectroscopy [7] in DMSO-d6 solution represents
the mixture (~6:1) of diastereomers. According to
calculations (B3LYP/6-311G**) [7] in the gas phase
the meso-form (R,S) is 1.6 kcal mol–1 more stable but
its dipole moment (1.82 D) is somewhat less than for
the (R,R)-diastereomer [or identical to it (S,S)-dia-
stereomer shown in Fig. 2] (2.88 D), so that the rela-
tive stability can depend on the nature of the solvent.
SCRF//B3LYP/6-311G** calculations of the structures
optimized at the same level of theory showed that in me-
thylene chloride the value of ΔE is equal to 2.5 kcal mol–1
in favor of the meso-form, as is the case in the gas
phase. This allowed us to assume that in solution the
(R,S)-diastereomer is the major one whereas the minor
component is a racemic mixture of enantiomers (R,R +
S,S).
In the IR spectra of solutions of compound II in
CCl4 the two vibration bands of the NH2 group of the
sulfonamide fragment (3375 and 3280 cm–1) have the
same frequencies and concentration dependence as in
the spectrum of compound I (Table 2). Hence, the
molecules of compound II in an inert nonpolar solvent
also exist in the equilibrium between their monomeric
form IIа and cyclic dimer closed by two inter-HB
NH2…O=S. In the IR spectrum of the crystalline com-
pound II an intense wide band at 3274 cm–1 corres-
ponds to chain associates formed by inter-HB NH2…O=S.
A narrow band of medium intensity at 3442 cm–1 in
this spectrum is caused by vibrations of the free group
NH1 of the pyrrole fragment whereas a wide intense
band at 3380 cm–1 belongs to vibrations of this group
participating in the formation of intra-HB NH1…O=S.
This conclusion is based of the values of ν(NH) in the
spectrum of solution of unsubstituted pyrrole V in
For both diastereomers the calculations give
intramolecular hydrogen bonds (Fig. 2). In the meso-
form (R,S) (IIIа) the H-bonds СН…O=S are formed in
both side chains. The pyrrole NH atom in IIIа forms
intra-HB NH1…Cl (2.574 Å) with one of the side
chains in which there is also a slightly reduced NH2…
Cl contact (2.946 Å) with the same chlorine atom. In
another side chain the contact NH3…Cl is somewhat
shorter (2.830 Å). The calculated value of ν(NH2) is by
40 cm–1 lower than ν(NH3).
Unlike in the meso-form (IIIа), in the (S,S)-
diastereomer (IIIb) the pyrrole NH atom forms intra-
HB NH…O=S (2.085 Å) with one of the side chains; in
the same chain an intra-HB NH2…Cl (2.687 Å) is
realized. In another side chain a slightly reduced
contact NH2…Cl (2.944 Å) and intra-HB СH…O=S
(2.331 Å) are realized.
In the IR spectrum of the solution of compound III
in CH2Cl2 (the compound in insoluble in CCl4) the
vibration frequency of the pyrrole NH group ν(NH1) is
by 20 cm–1 lower than that corresponding to vibrations
of the free group NH1 of compound II (Table 2). The
presence of the intra-HB NH1…Cl in form IIIа
N,N-dimethyltrifluoromethanesulfonamide
CF3SO2·
NMe2 VI, which correspond to the monomeric mole-
cule of pyrrole (3440 cm–1) and its solvate complex
with amide VI (3378 cm–1). Probably, molecular
crystals of compound II have two polymorphic forms.
Their sulfonamide groups NH participate in the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 2 2009

STRUCTURE AND PROTON DONATING ABILITY
F
319
O
F
F
O
S
O
Cl
H
O
F
H3
N
F
F
S
H
Cl
Cl2
H3
N
H2
H
Cl
Cl
C
C
N
Cl
C
Cl
Cl
N
H1
N
N
C
F
F
H2
H1
O
Cl
O
H
Cl
S
Cl
Cl1
O
F
S
F
O
F
F
IIIa
IIIb
Fig. 2. Molecular structure of stereoisomers of 2,5-bis(1-trifluoromethanesulfonylamido-2,2,2-trichloroethyl)pyrroles (IIIа, IIIb).
accounts for the observed low-frequency shift
corresponding to the calculated one. The equal and
rather high values of ν(NH1) in the spectra of the
crystalline disubstituted pyrrole III and its solution in
CH2Cl2 (~3435 cm–1) are indicative of the fact that the
pyrrole NH atom forming the intra-HB with the
chlorine atom does not contribute to the inter-HB with
the oxygen atom of the sulfonyl group. It should be
mentioned that the inter-HB NН1…O=S with partici-
pation of the pyrrole NH atom in compound II are
formed provided that the NН1 group is free and it
causes a decrease of its vibration frequency to 3380
cm–1. An intense doublet band with maxima at 3288
and 3263 cm–1 characterizes the two amide groups NH
of the solid compound III participating on the
formation of intermolecular associates. The band keeps
its doublet shape in the spectrum of the solution of this
compound in CH2Cl2. Its high-frequency component
(3321 cm–1) belongs to the NH3 group which is not
involved in the formation of inter-HB because of
formation of intra-HB NH3…Cl. The low-frequency
maximum at 3255 cm–1 belongs to the amide group
NН2 which shows only a reduced contact NH2…Cl
and, therefore, participates in the formation of inter-
HB NН2…O=S.
formed in solution upon addition of Lewis bases (di-
oxane, DMF) (Table 2).
According to the data obtained, the proton donating
ability of the sulfonamide group of compound I upon
its interaction with dioxane and DMF is substantially
higher that that of amide IV. This can be explained by
electronoacceptor effect of the 1-methylpyrrole and
trichloroethyl substituents. With this, N-methyltrifluoro-
methanesulfonamide IV itself, as we have shown
earlier [10], in the H-complexes with protophilic sol-
vents behaves as a strong hydrogen bond donor exceed-
ing 4-fluorophenol and being second only to 4-nitro-
phenol. An increase of the Δν(NH) value by 40–50 cm–1
in the H-complexes of compound I with respect to
similar complexes of amide IV takes place in both
inert solvents (CCl4 and CH2Cl2), the low-frequency
shift of the ν(NH) band for these compounds being
larger for DMF as a base.
Dioxane and DMF interact with the molecule of the
2-substituted pyrrole II at two proton donor centers as
witnessed by low-frequency shift of the vibrations
bands of both the amide and the pyrrole NH groups.
The values of Δν(NH) for the H-complexes with
participation of more acidic amide proton are by ~100
cm–1 larger than those of the pyrrole NH group. This is
in line with the fact that spectroscopic acidity of N-
methyltrifluoromethanesulfonamide IV upon its interact-
tion with the same bases also turns out to be almost
twice as large (by 110–130 cm–1) as for the unsub-
The proton donating ability of compounds I–III in
CCl4 and CH2Cl2 solutions was determined from the
values of spectroscopic acidity Δν(NH) as the dif-
ference between the values of ν(NH) for monomeric
molecules in an inert solvent and their Н-complexes
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 2 2009

320
OZNOBIKHINA et al.
150 cm–1 (CH2Cl2). Such a decrease of acidity of the
F
proton of the pyrrolyl group of compound II is most
probably due to variation of its conformational
structure upon interaction with strong base in the CCl4
solution. With this, the pyrrole and amide protons form
H-bonds with the two lone pairs of the oxygen atom of
one molecule of DMF thus closing the seven-
membered chelate ring (Fig. 3). Judged from the
calculations, the values of Δν(NH) for the pyrrole and
amide groups in such a complex of compound II with
DMF (80 and 230 cm–1) deviate from the experi-
mentally observed by only 30 cm–1 (110 and 260 cm–1),
and the difference between the values of Δν(NH1) and
Δν(NH2) both in calculations and in the experiment is
150 cm–1. At the same time, upon the formation of
complex of compound II with two molecules of DMF
these values amount to 230 and 460 cm–1 for the
pyrrole and amide group, respectively, being different
from the experiment. The length of the intermolecular
H-bonds NH1…О=С and NH2…О=С in this 1:2 com-
plex is 1.882 and 1.770 Å, respectively. It is note-
worthy that the value of Δν(NH2) equal to 460 cm–1 is
exaggerated owing to an additional H-bond closing the
seven-membered ring between the CH group of DMF
and the O=S group of molecule II with nonvalent
distance Н…О of 2.473 Å. Geometry optimization and
vibrational calculations of the chelate complex of
compound II with dioxane for slightly different
distances NH1…О (2.111 Å) and NH2…О (2.125 Å)
give close values of the spectroscopic acidity of the
pyrrole and amide protons: Δν(NH1) = 113, Δν(NH2) =
120 cm–1. These values are much less than the
substantially different experimental values of 160 and
260 cm–1, respectively.
F
F
S
Cl
O
H2
Cl
H
N
N
C
C
Cl
O
H1
N
Fig. 3. Molecular structure of chelate H-complex of 2,5-bis
(1-trifluoromethanesulfonylamido-2,2,2-trichloroethyl)-
pyrrole with DMF (NH1…O=C 2.177Å, NH2…O=C 1.947 Å).
stituted pyrrole V (Table 2). It must be noted that the
values of Δν(NH) characterizing the amide group of
compound II are by 40–50 cm–1 lower than those for
compound I and, as distinct from compounds I and IV
are practically equal for its complexes with dioxane
and DMF. Structurally, the amide NH groups of the
substituted pyrroles I and II are identical since both
show reduced contacts NH…Cl with similar nonvalent
distances. The calculated values of frequencies and
intensities of the ν(NH) vibrations of the SO2NH
groups in isolated molecules I and IIа are identical.
Also identical are the values of ν(NH) for these groups
in the IR spectra of the solutions of compounds I and
II in CCl4 and CH2Cl2 (Table 2). Consequently, the
observed decrease of the acidity of the amide hydrogen
atom in compound II as compared to I is due to the
effect of the Н-bond formed by the base with the
proton of its pyrrole group.
The suggested chelate structure of the complex of
II with DMF in which the oxygen atom of DMF
participates in the formation of H-bonds with two
hydrogen atoms is corroborated by comparing the
values of Δν(NH) obtained for the spectra of solutions
of compound II in pure bases. The difference between
the values of Δν(NH) related to the pyrrole and amide
groups in the dioxane solution remains unchanged as
compared to the solutions in inert media (~100 cm–1).
In DMF solution, the value of Δν(NH2) for the amide
hydrogen atom increases by 30 cm–1 with respect to
CCl4 solution, as is the case also for amide IV, and the
value of Δν(NH1) for the pyrrole hydrogen atom
increases from 110 to 210 cm–1. The observed effect is
consistent with the formation in pure DMF of the
solvate complexes with two-centered intermolecular
Spectroscopic acidity of the NH group of the
pyrrole fragment of compound II upon interaction with
dioxane is higher than that of pyrrole V: 160 and
113 cm–1 (CCl4), 150 and 126 cm–1 (CH2Cl2) respect-
ively, apparently, due to electronoacceptor effect of the
substituent in the 2 position. A different behavior is
observed in the case of more strong base, DMF. The
values of Δν(NH) for the pyrrole NH group in this
complex become lower than in the complex of pyrrole
V with DMF: 110 and 140 cm–1 (CCl4), 115 and
166 cm–1 (CH2Cl2), and also less than the values of Δν
(NH) in the complex of compound II with more weak
base, dioxane: 110 and 160 cm–1 (CCl4), 115 and
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 2 2009

STRUCTURE AND PROTON DONATING ABILITY
321
hydrogen bonds NH…O=C involving two molecules of
DMF which interact with the pyrrole and amide NH
groups.
DPX-400 spectrometer (400.13 and 100.62 MHz) in
DMSO-d6, chemical shifts are given with respect to
tetramethylsilane. The acidity of amides II and III in
methanol was determined by the method of poten-
tiometric titration on a EV 74 ionomer with glass working
electrode and chlorosilver electrode as a reference
electrode using 0.1 N solution of NaOH in methanol as
a titrant. Compounds II, III were prepared as
described in [6].
Proton donating ability of the pyrrole and amide
groups of compound III (Table 2) was determined
only with respect to dioxane in CH2Cl2 solution, since
addition of DMF caused formation of the precipitate.
The value of Δν(NH) for the pyrrole group NH1 is
126 cm–1, that is, much lower than for compound II,
and is comparable to the similar Н-complex of unsub-
stituted pyrrole V. A wide ν(NH) band of the amide
groups in the H-complex of compound III with di-
oxane has maximum at 3230 cm–1 and its spectro-
scopic acidity Δν(NH) is as low as 90 cm–1. This is
possible in the case of formation of bifurcate (three-
centered) hydrogen bonds when an intramolecularly H-
bonded complex rather than the free amide group NH
acts as an H-donor with respect to the external base
(dioxane) [11]. The decrease of the proton donating
ability of the pyrrole NH group of compound III with
Δν(NH) 126 cm–1 as compared to the monosubstituted
pyrrole II with Δν(NH) 150 cm–1 is apparently caused
by participation of the two amide hydrogen atoms in
the inter-HB with dioxane. The values of Δν(NH) for
solution of compound III in pure dioxane calculated as
the difference between ν(NH) of the monomeric
molecule in CH2Cl2 solution and its H-complex in
dioxane solution are only slightly different from those
in the inert medium and are equal to 100 and 130 cm–1.
It is not inconceivable that a low value of Δν(NH) for
the amide groups in compound III suggests the
structure of its H-complex in which both these groups
interact with the lone pair of one molecule of dioxane.
2-(1-Trifluoromethanesulfonylamido-2,2,2-tri-
chloroethyl)-1-methylpyrrole (I). To the solution of
0.01 mol of chloral trifluoromethanesulfonylimine
CF3SO2N=CHCCl3 prepared in situ [13] in 10 ml of
trichloroethylene the solution of 0.01 mol (0.81 g) of
1-methylpyrrole in 3 ml of CCl4 was added upon
cooling with cold water. The reaction mixture was kept
at room temperature for 6 h, solvent removed in
vacuum. From the NMR data, the residue represents
the mixture of product I and its isomer, 3-(1-trifluoro-
methanesulfonylamido-2,2,2-trichloroethyl)-1-methyl-
pyrrole in the ratio of 9:1. The total yield 3.06 g (85%).
Compound I. Yield 2.56 g (71%), m.p. 124–125°С
1
(from hexane). Н NMR, δ, ppm: 3.64 s (3Н, СН3),
5.22 s (1Н, СН), 6.03 m (1Н, Н4), 6.57 m (1Н, Н3),
6.81 m (1Н, Н5), 11.12 br. s (1Н, NH). 13С NMR, δ,
ppm: 33.78 (CH3), 64.56 (CH), 101.10 (CCl3), 107.19
1
(C4), 110.28 (C3), 119.16 q (CF3, JCF 322.4 Hz),
124.08 (C5), 124.56 (C2). Found, %: С 26.91; Н 2.27;
Cl 29.15; N 7.64; S 9.04. C8H8Cl3F3N2O2S. Calculated,
%: С 26.72; Н 2.24; Cl 29.58; N 7.79; S 8.92.
3-(1-Trifluoromethanesulfonylamido-2,2,2-tri-
chloroethyl)-1-methylpyrrole. 1Н NMR, δ, ppm: 3.60
3
s (3Н, СН3), 5.13 d (1Н, J 7.8 Hz, СН), 6.32 m (1Н,
Н4), 6.64 m (1Н, Н5), 6.99 m (1Н, Н2), 10.74 br. s (1Н,
NH). 13С NMR, δ, ppm: 35.87 (CH3), 67.68 (CH),
102.23 (CCl3), 108.77 (C4), 115.19 (C3), 119.16 q
(CF3, 1JC–F 322.4 Hz), 121.61 (C5), 122.72 (C2).
Therefore, the proton donating ability of the
sulfonamide and pyrrole NH groups of 2- and 2,5-
substituted pyrroles I–III is caused by electronic
effects of the substituents in the molecules, influence
of intermolecular H-bonds formed with Lewis bases,
and the presence of intramolecular H-bonds.
Pure compound I was prepared by carrying out the
reaction upon cooling to –15°С and crystallized from
hexane.
EXPERIMENTAL
N,N-Dimethyltrifluoromethanesulfonamide (VI).
Autoclave was charged with 70 ml of trifluoromethane-
sulfonylfluoride and 60 g of dimethylamine (frozen in
separate open vessels so that they were not mix before
the autoclave was sealed otherwise the exothermic re-
action with throwing out the reaction mixture occurs).
The autoclave was closed, kept at room temperature
for 1 day, cooled to 0°С, opened, the reaction mixture
treated with dry ether (3×50 ml) and filtered. The
Quantum chemical calculations including vibra-
tional calculations were performed at the B3LYP/6-
311G** level with full geometry optimization using
Gaussian 03 suit of programs [12].
IR spectra of pure compounds (in KBr or thin layer)
and of their solutions in CCl4 and CH2Cl2 were
recorded on a Varian 3100 FT–IR spectrophotometer.
1Н, 13С NMR spectra were registered on a Bruker
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 2 2009

322
OZNOBIKHINA et al.
8. Tables of Rate and Equilibrium Constants of Heterolytic
Organic Reactions, Palm, V.A., Ed., Moscow: VINITI,
1979, vol. 5(II), p. 162.
excess of dimethylamine was evaporated, the pre-
cipitate of dimethylamine hydrofluoride washed on
filter with ether, solvent removed from the combined
filtrate and the residue distilled in vacuum. Yield 67 g
(82%). bp 42°С (12 mm) Hg. nD20 1.3658. d420 1.374. 1Н
NMR, δ, ppm: 3.06 s (6Н, СН3). 13С NMR, δ, ppm:
37.94 (CH3), 120.42 q (CF3, 1JCF 320.5 Hz). 19F NMR,
δ, ppm: –75.95. Found, %: С, 20.99; Н, 3.74; N, 7.92;
S, 18.29; F, 32.36. C3H6F3NO2S. Calculated, %: С,
20.34; Н, 3.41; N, 7.91; S, 18.10; F, 32.17.
9. Tables of Rate and Equilibrium Constants of Heterolytic
Organic Reactions, Palm, V.A., Ed., Moscow: VINITI,
1979, vol. 1(I), pp. 239, 270.
10. Sterkhova, I.V., Chipanina, N.N., Shainyan, B.A., and
Turchaninov, V.K., Russ., J. Gen. Chem., 2007, vol. 77,
no. 1, p. 84.
11. Sidorkin, V.F., Doronina E.P., Chipanina, N.N.,
Aksamentova, T.N., and Shainyan, B.A., J. Phys.
Chem., A, 2008, vol. 112, no. 27, p. 6227.
REFERENCES
12. Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuse-
ria, G.R., Robb, M.A., Cheeseman, J.R., Montgomery, J.A.,
Jr., Vreven, T., Kudin, K.N., Burant, J.C., Millam, J.M.,
Iyengar, S.S., Tomasi, J., Barone, V., Mennucci, B.,
Cossi, M., Scalmani, G., Rega, N., Petersson, G.A.,
Nakatsuji, H., Hada, M., Ehara, M., Toyota, K., Fuku-
da, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y.,
Kitao, O., Nakai, H., Klene, M., Li, X., Knox, J.R.,
Hratchian H.P., Cross, J., B., Adamo, C., Jaramillo, J.,
Gomperts R., Stratmann R.R., Yazyev, O., Austin, A.J.,
Cammi R., Pomelli, C., Ochterski, J.W., Ayala, P.Y.,
Morokuma, K., Voth, G.A., Salvador, P., Dannen-
berg, J.J., Zakrzewski, V.G., Dapprich, S., Daniels, A.D.,
Strain, M., C., Farkas, O., Malick, D.K., Rabuck, A.D.,
Raghavachari, K., Foresman, J.B., Ortiz, J.V., Cui, Q.,
Baboul, A.G., Clifford, S., Cioslowski, J., Stefanov, B.B.,
Liu, G., Liashenko, A., Piskorz, P., Komaromi, I.,
Martin R.L., Fox, D.J., Keith, T., Al-Laham, M.A.,
Peng, C.Y., Nanayakkara, A., Challacombe, M.,
Gill, P.M.W., Johnson, B., Chen, W., Wong, M.W.,
Gonzalez, C., and Pople, J.A., Gausiian 03W, Gaussian
Inc., Pittsburgh, PA, 2003.
1. Koppel, I.A., Taft R.W., Anvia, F., Zhu, S.-Z., Hu, L.-Q.,
Sung, K., DesMarteau, D.D., Yagupolski, L.M., Yagu-
polski, Y.L., Ignat’ev, N.V., Kondratenko, N.V., Vol-
konskii, A.Y., Vlasov, V.M., Natario R., and Maria, P.-C.,
J. Am. Chem. Soc., 1994, vol. 116, no. 7, p. 3047.
2. Trepka R.D., Harrington, J.K., and Belisle, J.W., J. Org.
Chem., 1974, vol. 39, no. 8, p. 1094.
3. Sterkhova, I.V., Meshcheryakov, V.I., Chipanina, N.N.,
Kukhareva, V.A., Aksamentova, T.N., Turchaninov, V.K.,
and Shainyan, B.A., Russ. J. Gen. Chem., 2006, vol. 76,
no. 4, p. 583.
4. Chipanina, N.N., Sherstyannikova, L.V., Danilevich, Yu.S.,
Turchaninov, V.K., and Shainyan, B.A., Russ. J. Gen.
Chem., 2004, vol. 74, no. 4, p. 582.
5. Chipanina, N.N., Sherstyannikova, L.V., Turchaninov, V.K.,
and Shainyan, B.A., Russ. J. Gen. Chem., 2004, vol. 74,
no. 10, p. 1538.
6. Kondrashov, R.V., Rozentsveig, I.B., and Levkov-
skaya, G.G., Russ., J. Org. Chem., 2007, vol. 43, no. 11,
p. 1747.
7. Rozentsveig, I.B., Shainyan, B.A., Kondrashov, R.V.,
Rudyakova, R.V., Rozentsveig, G.N., Chernyshev, K.A,
and Levkovskaya, G.G., Zh. Org. Khim., 2008, vol. 44,
no. 9, p. 1348.
13. Rozentsveig, I.B., Levkovskaya, G.G., Kondrashov, R.V.,
Evstaf’eva, I.T., and Mirskova, A.N., Russ. J. Org.
Chem., 2001, vol. 37, no. 11, p. 1559.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 2 2009