IR spectra and structure of 2,5-pyrrolidinedione (succinimide) and of its nitranion: Experimental and ab initio MO studies

Article abstract of DOI:10.1016/S0022-2860(99)00200-8

The structures of 2,5-pyrrolidinedione (succinimide), its ¹⁵N labelled derivative, and of their nitranions have been studied on the basis of both quantitative IR spectra and ab initio RHF and MP2 calculations. The theory describes well the strong frequency decrease (down to 138 cm^-1) and the twofold increase in both the intensity and splitting of the carbonyl stretching bands, caused by the conversion of the succinimide molecule into the nitranion. According to the calculations, this conversion leads to essential changes in all the bond lengths and angles in the ring, but it remains planar. The anionic charge is localized mainly within the carbonyl groups. The alkali-metal derivatives of succinimide exist in DMSO as free solvated ions mainly.

Full text of DOI:10.1016/S0022-2860(99)00200-8

Journal of Molecular Structure 516 (2000) 237–245
www.elsevier.nl/locate/molstruc
IR spectra and structure of 2,5-pyrrolidinedione (succinimide) and
of its nitranion: experimental and ab initio MO studies
*
B.A. Stamboliyska , Y.I. Binev, V.B. Radomirska, J.A. Tsenov, I.N. Juchnovski
Institute of Organic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Received 28 January 1999; received in revised form 12 April 1999; accepted 22 April 1999
Abstract
15
The structures of 2,5-pyrrolidinedione (succinimide), its N labelled derivative, and of their nitranions have been studied on
the basis of both quantitative IR spectra and ab initio RHF and MP2 calculations. The theory describes well the strong frequency
Ϫ1
decrease (down to 138 cm ) and the twofold increase in both the intensity and splitting of the carbonyl stretching bands,
caused by the conversion of the succinimide molecule into the nitranion. According to the calculations, this conversion leads to
essential changes in all the bond lengths and angles in the ring, but it remains planar. The anionic charge is localized mainly
within the carbonyl groups. The alkali–metal derivatives of succinimide exist in DMSO as free solvated ions mainly. ᭧ 2000
Elsevier Science B.V. All rights reserved.
Keywords: 2,5-Pyrrolidinedione (succinimide); Nitranion; IR; Ab initio MO; Force field; Fermi-resonance
1
. Introduction
of the IR [4–7,10] and Raman [7,10] bands of succi-
nimide, based on polarized IR [5,7,10] and Raman
[7,10] measurements, normal coordinate analysis
[7,10] and N-deuterio [4,7] and N [6] isotopic
effects.
2,5-Pyrrolidinedione (succinimide) was first
1
5
prepared by Fehling in 1844 [1]. Succinimide and
other cyclic carboximides are starting materials for
various organic syntheses, and their nitranions are
intermediates in many of the corresponding chemical
reactions. Succinimide itself is used now in medicine
as a hypooxaluric agent [1], so the structure of both its
molecule and nitranion could be of special interest.
Starting by the work of Kahovec et al. [2] we found
in the literature over 25 studies on the vibrational
spectra of succinimide. Most of them deal with its
carbonyl stretching bands nCO, e.g. [2–11], including
their splittings, and aggregate state and solvent effects
on them [6–8,11]. There are also detailed assignments
The IR spectra of nitranions of cyclic imides, viz
those of phthalimide and saccharin have been studied
repeatedly [12–14] (and references therein); Ognya-
nova et al. have recently reported IR data for a large
series of amide nitranions [15]. Only the nCO frequen-
cies of the succinimide nitranion itself have been
reported [16]. All the authors [12–16] have stated
that the conversion of amides and imides into nitra-
nions results in strong decreases in the nCO
frequencies.
Olsson and Cremer [17] have recently calculated
both the NMR chemical shifts and the dipole moments
of a series of molecules, including succinimide. In the
literature we have found neither quantitative IR data,
nor ab initio force field calculations for the title
*
Corresponding author. Tel.: ϩ 359-2-7299-20; fax: ϩ 359-2-
7
002-25.
E-mail address: soa@orgchm.acad.bg (B.A. Stamboliyska).
0
022-2860/00/$ - see front matter ᭧ 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(99)00200-8

2
38
B.A. Stamboliyska et al. / Journal of Molecular Structure 516 (2000) 237–245
15
Scheme 1. Preparation of succinimide- N and of its alkali–metal derivatives.
species, so the purpose of the present study is to
follow the spectral and structural changes, which
take place in the course of the conversion of the succi-
nimide molecule into the nitranion, by means of both
quantitative IR spectra and ab initio force field calcu-
lations.
of 0.13 mm path length (for DMSO and DMSO-d6
solutions), a KBr cell of 1 mm path length (for
CDCl solutions) and in KBr, discs at a resolution of
3
Ϫ1
1 cm and 50 scans. The spectra of the alkali–metal
derivatives of succinimide in DMSO are identical, so
these derivatives exist in this solvent as kinetically
free solvated ions mainly, like those of o-sulfobenzi-
mide [14], acetylsalicylic acid [19], the isomeric
(cyanophenyl)acetonitriles [20] etc.
2. Experimental
Commercial succinimide (Fluka) was recrystallized
1
5
from dry ethanol. Succinimide- N was prepared by
3. Computations
1
5
reacting succinic acid with aqueous NH (Isocom-
3
merz, 95% at. enrichment), followed by an evaporiza-
tion of the water and an atmospheric distillation of the
The ab initio force field computations have been
performed using the gamess software [21] (version
1
5
ء
ء
residue. The distillate (succinimide- N, I in Scheme
) was recrystallized from dry ethanol to show a m.p.
of 125ЊC, in agreement with [1]. Succinimide nitra-
1998) at the HF/6-31G and 6-31 ϩ G and MP2/6-
ء
1
31G levels. No scaling in the ab initio force field has
been done.
1
4
15
ϩ
ϩ
ϩ
nions (II, N and N, counter ions Li , Na and K )
were prepared by adding DMSO and DMSO-d solu-
6
3.1. Energies
1
4
15
tions of the parent succinimides N and N to excess
of dry alkali–metal methoxides and methoxides -d3
The total energies Etot of the succinimide molecule
and of its nitranion respectively, calculated within the
basis sets used, are as follows:
(Scheme 1); the reaction mixtures were stirred for
half a minute and filtered under argon. The conversion
was practically complete (no bands of the parent
succinimide were seen in the spectra after metalation,
cf. Figs.1 and 3), as succinimide is a moderately weak
acid: its pK in H O is 9.5 [1]. The metalation with
•
•
•
Etot ˆ Ϫ358.603313 and Ϫ358.023340 (HF/6-
ء
3
1G );
E ˆ Ϫ358.613510 and Ϫ358.046960 (HF/6-31 ϩ
tot
ء
a
2
G ); and
K CO gave almost the same result, but the spectrum
2
3
Etot ˆ Ϫ358.598283 and Ϫ358.019028 (MP2/6-
Ϫ1
showed an additional sharp band at 2337 cm (CO2
in DMSO [18]).
ء
3
1G ).
The IR spectra were measured on Bruker IFS 113 V
The following deprotonation energies E of succini-
D
and Vector 22 FTIR spectrophotometers in a CaF cell
mide corresponds to the above values:
2

B.A. Stamboliyska et al. / Journal of Molecular Structure 516 (2000) 237–245
239
ء
Ϫ1
Fig. 1. Theoretical (ab initio MP2/6-31G , low) and experimental (up) IR spectra of succinimide. Curve a: 0.025 mol l in CDCl
0
3
; curve b:
Ϫ1
Ϫ1
.020 mol l in DMSO; curve c: 0.205 mol l in DMSO-d
6
; curve d: 2/200 mg KBr disk, threefold enhanced. For cell path lengths see
Experimental.
•
E ˆ E (nitranion)ϪE (molecule) ˆ 1522, 1487
saccharin, compared to those of 1,2-dicarboxamides
D
tot
tot
Ϫ1
and 1520 kJ mol respectively, depending on the
basis set.
(pK ’s near 14, solvent DMSO [22]).
a
These values are not away from E ’s of 1533 and
539 kJ mol , calculated for phthalimide and hexa-
D
4. Results and discussion
Ϫ1
1
hydrophthalimide respectively, but essentially higher
4.1. Infrared spectra
Ϫ1
than E of 1470 kJ mol , calculated for o-sulfoben-
D
zimide (saccharin) [14]. These results agree with the
Let us consider first the IR spectra of the species
studied, which will make it possible to follow the
considerably higher acidity (pK ˆ 4.0 [22]) of
a

2
40
B.A. Stamboliyska et al. / Journal of Molecular Structure 516 (2000) 237–245
Table 1
ء
Theoretical (ab initio MP2/6-31G ) and experimental (solvent DMSO-d
6
) IR data for the succinimide molecule
Experimental
a
Ab initio force field
Ϫ1
b
Ϫ1
Ϫ1
c
Ϫ1
Ϫ1
No.
n (cm
)
n
(cm
)
A (km.mol
)
Approximate description
n (cm
)
A (km.mol )
d
1
.
3660
3449
78.3
100 nNH
3410
49.9
110.8
d,e
3223
as
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
.
.
.
.
.
.
.
.
3203
3189
3142
3137
1875
1841
1542
1519
1389
1384
1353
1307
1280
1220
1199
1053
1051
927
868
856
673
643
633
563
542
538
3019
3006
2962
2956
1767
1735
1453
1432
1309
1305
1275
1232
1207
1150
1130
993
991
874
817
807
636
607
597
530
2.2
0.3
0.4
100 n
100 n
100 n
CH2
as
CH2
s
d
d
2964
2945
1771
1713
1431
1400
1349
1334
1294
1265
1241
1186
1175
0.6
3.2
37.0
284.0
6.2
11.2
34.1
4.3
14.1
9.5
CH2
s
8.8
100 n
CH2
s
ip
36.9
675.5
14.1
0.1
118.4
101.3
25.7
45.9
0.0
167.2
0.4
0.0
3.9
17.9
4.1
85 n , 10 d
CO
as
HNC
ip
85 n , 14 d
CO
HNC
(scissoring)
s
100 d
100 d
CH2
as
(scissoring)
CH2
as
ip
0.
1.
2.
3.
4.
5.
6.
7.
8.
9.
0.
1.
2.
3.
4.
5.
6.
7.
8.
9.
0.
36 n , 20 d
CNC
HNC
ip
s
as
54 d
, 30 n , 10 n
CO
HNC
CNC
ip
69 dCH2 , 25 d
66 dCH2 , 22 nCC
ring
94 d
14.9
71.4
27.3
CH2
as
ip
HNC
42 n , 30 d
CNC
97 dCH2
50 dCH2 , 39 d
ring
oop
d
f
83 n
90 d
4
5
, 14 dCH2
998
901
849
817
632
2.3
weak
9.9
1.9
strong
C ϪC
ip
ring
s
d
d
g
67 nCC, 15 n
53 dCH2 , 41 d
CNC
oop
5.9
ring
asoop
OCN
147.7
27.7
0.0
3.9
3.9
8.1
21.6
6.3
100 d
89 d
59 d
79 d
ip
ring
ip
s
s
CO
, 31 n , 10 n
HNC
CNC
soop
d
d
, 10 dCH2
543
528
4.5
2.2
OCN
oop
511
507
365
122
70 d , 17 d
ring
CH2
ip
ip
78 d
66 d
100 d
, 16 d
OCN
ring
ip
ip
HNC
d
h
388
131
56
, 26 d
400
160
19.1
strong
OCN
oop
ring
oop
OCN
53
0.0
62 d
, 30 dCH2
a
Measured after having decomposed the complex bands into components.
Scaled by 0.9427 [25].
Vibrational modes: n, stretching; d, deformation (all kinds of); t, torsion; superscripts: s, symmetrical; as, asymmetrical; ip, in-plane; oop,
b
c
out-of-plane. The numbers before the mode symbols indicate percent contribution (10 or more) of a given mode to the corresponding normal
vibration, according to the energy distribution matrix [21].
d
3
Solvent CDCl .
e
f
A broad band corresponding to H-bonded nNH vibrations.
Solvent CHCl [6].
3
g
h
Solvent CCl
Solvent C H
6
4
[7].
[7].
6
spectral changes, caused by the conversion of the
succinimide molecule into the nitranion.
good agreement between measured and scaled theore-
tical frequencies can be seen there. The mean devia-
Ϫ1
tion between them is 24 cm . This value lies within
Ϫ1
4.1.1. The succinimide molecule
the interval of 14–30 cm , typical for molecules
The theoretical and experimental IR spectra for
succinimide are compared in Fig. 1 and Table 1. A
containing carbonyl groups [14,19,23,24,26–29].
The approximate description of the normal vibrations

B.A. Stamboliyska et al. / Journal of Molecular Structure 516 (2000) 237–245
241
Fermi-resonance. Our experiments have confirmed
Ϫ1
that the nCO spectrum of 0.01–0.08 mol l chloro-
form solutions of succinimide does not depend prac-
tically on the concentration, but it does depend
1
5
essentially on the N isotope labelling (Fig. 2 (A)
and (B)). So, the bands in the spectrum of succini-
1
4
Ϫ1
mide- N (Fig. 2(A)) are, as follows (n in cm , A
Ϫ1
in km mol ): 1720.7, 296.2; 1753.5, 76.0; 1781.6,
8.2. Those of succinimide- N (Fig. 2(B)) are:
714.5, 219.7; 1743.8, 99.1; 1783.4, 58.5. The
1
5
4
1
presence of these quantitative IR data now makes it
possible to check the assumptions [6–8] of Fermi-
splittings. Having accepted the assumptions that the
Ϫ1
weak bands (1781.6 cm in Fig. 2(A) and 1783.4 in
s
Fig. 2(B)) correspond to n and the other bands are
CO
as
CO
Fermi-splitts of n , as well as using Eq. (1) [30] for
calculating the unperturbed frequency n of a Fermi-
doublet, we found the values of 1727.4 and
Ϫ1
as
14
1
723.6 cm for unperturbed n of succinimide- N
CO
1
5
and N, respectively in chloroform.
1
5
n A ϩ n A
Fig. 2. IR spectra (nCO region) of succinimide. (A) N,
1
1
2 2
n ˆ
ꢀ1†
Ϫ1
15
Ϫ1
0
.025 mol l in CDCl
3 3
; (B) N, 0.025 mol l in CDCl . For cell
A1 ϩ A2
path lengths see Experimental.
4
.1.2. The succinimide nitranion
The theoretical and experimental IR data for this
(
Table 1) corresponds to the empirical assignments of
Parellada et al. [6] and Woldbaek et al. [7] rather than
to those of Uno and Mashida [4] or Shimada and
Ozono [10]. There is a fairly good agreement
nitranion are compared in Fig. 3 and Table 2. The
agreement between measured and scaled theoretical
frequencies is somewhat worse than in the preceding
case (Section 4.1.1). The mean deviation between
1
5
between calculated and measured N isotopic shifts
D ˆ nlabelledϪnnon-labelled, e.g. (No., Dcalculated, Dmeasured):
Ϫ1
Ϫ1
them is 28 cm , within the interval 16–38 cm
typical for anions containing carbonyl groups
14,19,23,24,26,28,29]. The agreement between
calculated and measured isotopic shifts D (4.1.1) is
again fairly good, e.g. (No. from Table 2, Dcalculated
1
, Ϫ8, Ϫ8; 6, 0, 0; 7, Ϫ1,Ϫ 1; 10, Ϫ9, Ϫ10; 12, Ϫ2,
Ϫ3; 13, Ϫ3, ; 14, 0, Ϫ2; 15, Ϫ3, Ϫ5; 19, Ϫ8, Ϫ8; 20,
Ϫ10, Ϫ9; 21,Ϫ 2, Ϫ1.
[
A special attention should be paid to the bands in
the nCO region. The IR spectra of chloroform [6] and
carbon tetrachloride [6,7] solutions, as well as of
oriented crystals [7] of succinimide show three
bands each. Parellada et al. [6] have found that the
spectrum in the nCO region does not depend on the
concentration (0.1 mol.l or lower), so they have
rejected the early assumption [4] (etc.) for the
presence of a band, corresponding to nCO of
hydrogen-bonded molecules. The authors [6,7] have
,
Dmeasured): 5, 0, Ϫ1; 6, Ϫ1, Ϫ1; 9, Ϫ8, Ϫ6; 10, Ϫ15,
Ϫ10; 11, Ϫ3,Ϫ 3 (the others are close to zero).
In general, the theoretical method used describes
adequately the essential spectral changes, which
take place in the course of the conversion of the succi-
nimide molecule into the nitranion, e.g.:
Ϫ1
s
as
1. strong decreases in the n and n frequencies:
CO CO
Ϫ1
Ϫ1
predicted 64 cm and 115 cm , measured 74 and
s
Ϫ1
assigned the weak high-frequency band as n , the
strong low-frequency one as n , and have supposed
138 cm , respectively;
CO
as
CO
s
CO
2. a decrease in the A integrated intensity: calcu-
that the moderate middle band corresponds to an
overtone or a combination tone, enhanced by
lated 1.2 fold, found 1.6 fold;
3. an essential increase in the A
as
CO
integrated

2
42
B.A. Stamboliyska et al. / Journal of Molecular Structure 516 (2000) 237–245
ء
ϩ
Fig. 3. Theoretical (ab initio MP2/6-31G , low) and experimental (counter ion Na , up) IR spectra of the succinimide nitranion. Curve a:
0
Ϫ1
Ϫ1
6
.205 mol l in DMSO-d ; curve b: 0.024 mol l in DMSO.
Ϫ1
intensity: calculated 1.8 fold, found 2.3 fold; the
increase in the summary ACO is: calculated 1.5
fold, measured 2.1 fold;
nCN(down to 147 cm ) accompanied by dramatic
,
increases in ACN (up to 70 fold) [20];
2. the nCN splitting in the spectra of geminal dinitriles
Ϫ1
4
. a more than twofold enlargement of the n split-
enlarges from 4 cm (calculated but not measur-
CO
s
as
CO
ting (Dn ˆ n Ϫn ): predicted 2.6 fold,
able) for benzylidenemalononitrile [31] and its 4-
hydroxy derivative [32] or 12–19 cm , measured
for enaminodinitriles [33,34], to 49–54 cm ,
measured in cases of anions [31,32], zwitterions
[31,35] and a dianion [32], containing dicyano-
methide group.
CO
Ϫ1
measured 2.1 fold, etc.
Ϫ1
For comparison:
1
. the conversion of the isomeric (cyanophenyl)ace-
tonitriles into anions results in strong decreases in

B.A. Stamboliyska et al. / Journal of Molecular Structure 516 (2000) 237–245
243
Table 2
Theoretical (ab initio MP2/6-31G ) and experimental (solvent DMSO-d
ء
ϩ
6
, counter ion Na ) IR data for the succinimide nitranion
a
Ab initio force field
Experimental
Ϫ1
b
Ϫ1
Ϫ1
c
Ϫ1
Ϫ1
No.
n (cm
)
n
(cm
)
A (km.mol
)
Approximative description
n (cm
)
A (km.mol
)
as
1.
2.
3.
4.
5.
6.
7.
8.
3163
3144
3106
3094
1806
1718
1551
1524
2982
2964
2928
2917
1703
1620
1462
1437
61.0
2.7
100 n
100 n
100 n
2960
2942
2927
2837
1697
1574
1439
1389
14.5
1.7
12.7
3.1
23.7
656.9
3.7
CH2
as
CH2
s
33.7
53.4
44.2
1186.2
3.2
CH2
s
100 n
CH2
s
s
80 n , 14 n
CO
CNC
as
ip
ring
80 n , 10 d
CO
s
94 d
94 d
(scissoring)
(scissoring)
CH2
as
CH2
0.2
4.7
1
1
333
318
54.6
13.6
131.8
46.6
7.9
s
ip
OCN
9
1
1
1
1
.
1343
1338
1281
1268
1253
1266
1261
1208
1195
1181
163.3
183.5
14.4
0.0
30 n , 28 d
, 20 dCH2
1282
1246
1219
CNC
as
CNC
0.
1.
2.
3.
62 n , 20 nCC
78 dCH2 , 10 nCC
oop
ring
85 d , 13 d
CH2
d
oop
ring
90.2
48 d
1129
19.4
a
Measured after having decomposed the complex bands into components.
Scaled by 0.9427 [25].
Vibrational modes: n, stretching; d, deformation (all kinds of); t, torsion; superscripts: s, symmetrical; as, asymmetrical; ip, in-plane; oop,
b
c
out-of-plane. The numbers before the mode symbols indicate percent contribution (10 or more) of a given mode to the corresponding normal
vibration, according to the energy distribution matrix [21].
d
Followed by 14 lower-frequency normal vibrations.
4
.2. Structure
of the succinimide molecule into the nitranion results
in essential variations in all the bond lengths in the
ring. Of course the most strong is the shortening of the
C–N bonds (they are at the nitranionic center), less
essential is the lengthening of the next CyO and C–
CO bonds (Table 3). This result is qualitatively
The structures of the succinimide molecule and of
its nitranion are shown in Scheme 2, and the numer-
ical data for the geometry parameters are listed in
Table 3. According to the calculations the conversion
ء
ء
Scheme 2. Ab initio MP2/6-31G (HF/6-31 ϩ G in brackets) structures of succinimide and of its nitranion. Bond orders (in italics) and net
electric charges of the fragments (in bold) are indicated at the Formulae.

2
44
B.A. Stamboliyska et al. / Journal of Molecular Structure 516 (2000) 237–245
Table 3
˚
Bond lengths (A) and angles (deg.) of the succinimide molecule and its nitranion
Molecule
Nitranion
Ab initio
HF/6-31G
Experimental [36,37] Ab initio
a
ء
ء
ء
ء
ء
ء
Geometry prameters
HF/6-31G
HF/6-31 ϩ G
MP2/6-31G
HF/6-31 ϩ G
MP2/6-31G
a
a
a
r(C–N)
r(CyO)
r(C–CO)
r(C–CC)
r(N–H)
1.385
1.225
1.505
1.50
–
1.376
1.187
1.519
1.535
0.998
0.0240
115.4
107.2
105.1
127.6
125.2
122.3
1.02
1.376
1.189
1.519
1.535
0.999
0.0235
115.2
107.4
105.0
127.5
125.1
122.4
0.88
1.392
1.219
1.523
1.533
1.016
0.016
115.2
106.8
105.6
127.8
125.4
122.4
1.20
1.343
1.214
1.542
1.520
–
1.343
1.217
1.539
1.521
–
1.464
1.234
1.553
1.517
–
b
m.d.
0.0000
–
–
–
Ͻ (CNC)
Ͻ (CCN)
Ͻ (CCC)
Ͻ (CCO)
Ͻ (OCN)
Ͻ (CNH)
113
110.4
111.9
102.8
120.5
127.6
–
110.3
112.0
102.8
120.6
127.4
–
109.2
112.2
1032
120.6
127.2
–
a
a
a
a
108.5
105.0
127.5
124.0
–
b
m.d.
0.00
–
–
–
a
Mean values of two non-equivalent positions in the monocrystal.
Mean absolute deviations (A, deg.) between theoretical and experimental values.
b
˚
similar to those found in cases of the nitranions of
saccharin [14] and paracetamol [28], and of carba-
nions of carbonyl compounds [24,26,29] and nitriles
succinimide molecule into the corresponding nitra-
nion results in strong spectral and structural changes.
Both these changes can be predicted and described by
the ab initio MO theory.
[20,24,26,29,31,32]. All the angels in the ring undergo
changes, mostly the Ͻ CNC one (at the nitranionic
center), but according to the calculations, the ring
remains planar.
Acknowledgements
The increase in the P(C–N) bond order by 0.3 units
and the decrease in the P(CyO) one by 0.2 units,
which accompany the conversion of the succinimide
molecule into nitranion, is in a good agreement with
the respective changes in the lengths of the same
bonds (cf. Scheme 2 and Table 3).
This work has been supported financially by the
Bulgarian National Fund of Scientific Research,
Contract X-801.
The changes in the fragment net charges Dq ˆ q
(
oxia-
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