IR spectra and structure of 1-H-isoindole-1,3(2H)-dione (phthalimide), cis-hexahydro-1-H-isoindole-1,3(2H)-dione (hexahydrophthalimide) and of their nitranions

Article abstract of DOI:10.1016/S0022-2860(99)00123-4

The spectral and structural changes, accompanying the conversions of 1- H-isoindole-1,3(2H)-dione (phthalimide) and its cis-hexahydro derivative into the corresponding nitranions have been observed through IR spectra. These conversions lead to a strong decrease in carbonyl stretching frequencies v(s)(CO) by 74 cm^-1 and v(as)(CO) by 134 cm^-1 (mean values), a two-fold increase in the v(CO) spliting, etc. According to ab initio MO calculations, greater parts of anionic charges are delocalized within carbonyl groups. The alkali-metal derivatives of the imides studied mainly exist in the dimethyl sulphoxide as free solvated ions.

Full text of DOI:10.1016/S0022-2860(99)00123-4

MOLSTR 10936
Journal of Molecular Structure 513 (1999) 231–243
www.elsevier.nl/locate/molstruc
IR spectra and structure of 1-H-isoindole-1,3(2H)-dione
(phthalimide), cis-hexahydro-1-H-isoindole-1,3(2H)-dione
(hexahydrophthalimide) and of their nitranions
*
I.G. Binev , B.A. Stamboliyska, Y.I. Binev, E.A. Velcheva, J.A. Tsenov
Institute of Organic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Received 28 January 1999; received in revised form 22 March 1999; accepted 22 March 1999
Abstract
The spectral and structural changes, accompanying the conversions of 1-H-isoindole-1,3(2H)-dione (phthalimide) and its cis-
hexahydro derivative into the corresponding nitranions have been observed through IR spectra. These conversions lead to a
as
strong decrease in carbonyl stretching frequencies nsCO by 74 cmϪ1 and n by 134 cmϪ1 (mean values), a two-fold increase in
CO
the nCO spliting, etc. According to ab initio MO calculations, greater parts of anionic charges are delocalized within carbonyl
groups. The alkali–metal derivatives of the imides studied mainly exist in the dimethyl sulphoxide as free solvated ions. ᭧ 1999
Elsevier Science B.V. All rights reserved.
Keywords: Infrared; 1,2-Dicarboximides; Anions; Ab initio force field; 15N labelling
1. Introduction
phthalimide [12–15], based on the normal coordinate
analysis [12,14,15]. The spectra of phthalimide
nitranion (counter ions Kϩ and Naϩ) have also been
studied repeatedly [12,16–18]; all the authors have
found that the nCO frequencies of the anion are essen-
tially lower than those of the parent phthalimide mole-
cule [12,16–18]. Qualitatively similar strong nCO
decreases have recently been found to accompany
the conversions of other carboximides, viz. succini-
mide [19] and o-sulfobenzimide (saccharin) [20,21]
into nitranions and of carboxamides into anions
[22–25] and dianions [23,24]. The IR spectrum of
cis-hexahydrophthalimide has not been studied in
detail [26] and its nitranion has not been measured.
The structures of the phthalimide molecule
[15,17,18,27] and of its nitranion [18,28] have been
studied by Hu¨ckel’s and semiempirical methods. The
crystal and molecular structures of phthalimide and
potassium phthalimide have been determined by
Phthalimide (1 in Scheme 1) is a starting material
for numerous organic syntheses. As early as 1887
potassium phthalimide (1A, M ˆ K) was used for
the preparation of primary amines via alkylphthali-
mides (Gabriel’s reaction) [1,2]. To begin with the
pioneering work by Chouteau [3], we found in the
literature 33 studies on the vibrational spectra of
phthalimide. Most of these deal with the carbonyl
nCO and/or imido nNH stretching bands, as well as
the formation of hydrogen bonds between these
groups and with the solvent, e.g. Refs. [4–11] (and
the references therein). There are also present detailed
assignments of the IR and Raman bands of
* Corresponding author. Tel.: ϩ 359-2-729920; fax: ϩ 359-2-
700225.
E-mail address: binev@orgchm.bas.bg (I.G. Binev)
0022-2860/99/$ - see front matter ᭧ 1999 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(99)00123-4

232
I.G. Binev et al. / Journal of Molecular Structure 513 (1999) 231–243
Scheme 1. Preparation of phthalimide-15N (1) and of its alkali–metal derivatives (1A).
Matzat [29] and Nagel et al. [30], respectively, on the
basis of X-ray diffraction, and the dipole moments of
phthalimide [31] and hexahydrophthalimide [26]
were determined in dioxan by Lee and Kumler quite
a long time ago.
residue. The sublimate (phthalimide–15N, 1 in
Scheme 1) was recrystallized from dry ethanol to
show a m.p. of 238ЊC, in agreement with Ref. [32].
Cis–hexahydrophthalimide was prepared in a similar
way from the corresponding anhydride (Fluka) and
14NH4 aq.; m.p.136ЊC in agreement with Ref. [32].
Dry sodium and potassium methoxides-d3 were
prepared by reacting the metals with methanol-d4
(Merck), followed by removing the excess of alcohol
in vacuo. The nitranions (counter ions Naϩ and Kϩ) of
the phthalimide, phthalimide–15N (1A in Scheme 1)
and cis-hexahydrophthalimide were prepared by
adding DMSO and DMSO-d6 solutions of the parent
imides to an excess of dry alkali metal methoxides-
d3. The metallation was practically complete: no
bands of the parent imides were seen in the spectra
after metalation, as 1,2-dicarboximides are moder-
ately weak acids, e.g. pKa of phthalimide and succini-
mide are 13.4 and 14.6 (solvent DMSO), respectively
[34].
In the literature we have found neither the qualita-
tive IR data, nor ab initio force-field calculations of
the title species. Combined IR/ab initio studies in a
series of imides [19,21], amides [23–25] and their
nitranions [19,21,24], carbanions [23,25] and dianions
[23,24] have proved to be useful in studying the
changes in the parent molecules, caused by their
conversions into anions. Hence, the purpose of the
present study is to follow the spectral and structural
changes, which take place during the course of the
conversions of phthalimide and its hexahydro deriva-
tive into the corresponding nitranions on the basis of
both, quantitative IR spectra and ab initio force-field
calculations.
The IR spectra were recorded on Bruker IFS 113v
and Vector 22 FTIR spectrometers in a CaF2 cell of
0.13 mm path length (for DMSO and DMSO-d6 solu-
tions, concentrations 0.02–0.16 mol lϪ1), a KBr cell
of 1 mm path length (for the CDCl3 solutions, concen-
tration 0.02–0.07 mol lϪ1), and KBr and CsI discs, at
a resolution of 1 cmϪ1 and 50 scans. The integrated
intensities were measured after having decomposed
2. Experimental
Commercial phthalimide (Fluka) was recrystallized
from dry ethanol. Phthalimide–15N was prepared by
reacting phthalic anthydride with aqueons 15NH3
(Isocomerz, 95% at. enrichment), followed by the
evaporation of the water and sublimation of the

I.G. Binev et al. / Journal of Molecular Structure 513 (1999) 231–243
233
Table 1
Theoretical (HF/6-31G) and experimental (DMSO/DMSO-d6 solutions) infrared data for the phthalimide molecule
No.
Ab Initio force field
Experimentala
n (cmϪ1
)
nb (cmϪ1
)
Dc
Ϫ8.2
A (km molϪ1
)
Approximate descriptiond
n (cmϪ1
)
Dc
A (km molϪ1
)
1
2
3
4
5
6
7
8
3937
3388
3380
3368
3355
1983
1937
1822
1797
1646
1642
1526
1489
1459
1404
3516
3025
3018
3009
2996
1771
1729
1627
1604
1469
1466
1363
1330
1303
1254
127.8
13.0
4.4
5.8
1.7
164.5
905.9
13.9
2.2
13.0
4.8
4.6
204.9
1.3
100 nCH
99 nPhH
99 nPhH
99 nPhH
99 nPhH
3429e
3088e
3061e
2977e
Ϫ7.4
1.2
Ϫ1.5
1.5
81.6
1.0
8.2
0.8
0.0
0.0
0.0
0.0
Ϫ0.1
Ϫ1.7
0.0
0.0
0.0
80 nsCO, 13 dHNC
1769
1727
1607
Ϫ0.5
Ϫ0.9
Ϫ0.4
35.3
368.5
7.8
as
74 n , 12 dNCC
CO
63 nCC, 25 dCCC
9
97 nCC
ip
10
11
12
13
14
15
52 d , 42 nCC
1467
1424
0.0
Ϫ1.1
6.0
0.9
PhH
ip
0.0
57 d , 30 dCCC, 11 nCC
PhH
Ϫ12.8
Ϫ3.2
0.0
71 dHNC, 16 nCO
36 nCC, 20 dHNC, 14dNCO
1376
1341
1304
1206
1181
1142
Ϫ1.3
Ϫ0.7
Ϫ6.5
Ϫ1.0
Ϫ2.0
Ϫ4.1
57.4
2.9
37.0
4.7
12.8
3.3
ip
68 d , 20 dCCC
PhH
ip
Ϫ6.8
151.3
30 d , 30 nCC, 22 nCN
PhH
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
1321
1291
1262
1213
1200
1181
1154
1112
1064
927
1179
1153
1127
1083
1027
1055
1030
993
950
827
814
797
Ϫ1.8
Ϫ0.8
Ϫ3.4
Ϫ1.2
0.0
Ϫ7.3
0.0
Ϫ0.3
0.0
Ϫ1.6
0.0
Ϫ1.9
Ϫ3.7
Ϫ3.3
0.0
40.2
5.0
0.0
29.0
0.0
79.6
1.2
0.3
0.0
0.4
0.0
27 dCCC, 23 nCN, 21 nCC, 18 dip
PhH
ip
50 d , 36 nCC, 13 nCN
PhH
42 dCCC, 39 nCC
50 dCCC, 20 nCC, 13 nCN
1089e
1069e
1036e
1010e
977f
Ϫ0.5
Ϫ0.5
Ϫ6.1
Ϫ0.6
Ϫ0.4
8.4
2.7
45.2
0.3
80doPohpH, 14tCCCC
46 nCN, 32 dCCC, 15 dCNC
oop
PhH
90 d
60 dCCC, 16 nCC
vw
oop
100 d
95 d
PhH
oop
818f
804f
794f
745f
714f
Ϫ3.0
0.0
Ϫ0.7
Ϫ4.3
Ϫ2.3
vw
vw
w
w
m
PhH
912
893
844
820
100 tNCCC
32 dNCC, 32 dCCC, 12 nCC
82 tHNCO
69 nCC, 28 dNCC
60 tCCCC, 32 tHNCO
3.6
329.8
3.5
754
732
668
748
0.0
729
719
710
651
642
634
Ϫ3.3
Ϫ0.4
Ϫ3.6
1.8
65.7
19.3
61 dNCO, 30 dCCC
100 tHNCC
50 dHNC, 14 dCCC
,
668f
649f
559
0.0
Ϫ6.0
Ϫ1.0
Ϫ3.1
Ϫ0.4
m
m
64.2
4.5
6.4
34
35
36
37
38
39
40
41
42
605
597
525
476
370
267
218
192
150
540
533
469
425
330
238
195
172
139
Ϫ3.7
Ϫ0.4
0.0
Ϫ0.2
Ϫ0.2
0.0
Ϫ0.7
Ϫ1.0
0.0
11.3
11.8
0.0
3.5
26.0
0.5
6.8
5.5
0.0
41 dCCC, 26 nCN
50 dCCC, 26 dNCC
60 tCCCC, 26 tHNCO
90 tCCCC
56 dNCO, 24 dHNC
68 dCCC, 22 dNCO
52 tCCCC, 35tHNCC
60 tHNCC, 22tCCCC
64 tNCCC, 20 tHNCO
546e
529e
408f
359f
270g
210g
175g
–
0.3
Ϫ0.3
Ϫ0.8
Ϫ2.2
Ϫ2.3
vw
m
m
m
s
a Measured after having decomposed the complex bands into components. Relative intensities: s, strong; m, medium; w, weak; vw, very weak.
b Scaled by 0.8929 [36].
c Calculated and meashured 15N isotopic shifts D ˆ nlabelledϪnnon-labelled
:
d Vibrational modes: n, stretching; d, deformation (all kinds of); t, torsion; superscripts: s, symmetrical; as, asymmetrical; ip, in-plane; oop,
out-of-plane; subscript sk, skeletal. The numbers before the mode symbols indicate % contribution (10 or more) of a given mode to the
corresponding normal vibration, according to the energy distribution matrix [33].
e Solvent CDCl3.
f Solid, in KBr disc.
g Raman data, solvent DMSO [15].

234
I.G. Binev et al. / Journal of Molecular Structure 513 (1999) 231–243
Table 2
Theoretical (HF/6-31G) and experimental (DMSO/DMSO-d6 solutions) infrared data for the cis-hexahydrophthalimide molecule
No
Ab initio force field
Experimentala
n (cmϪ1
)
n b (cmϪ1
)
A (km molϪ1
)
Approximate descriptionc
n (cmϪ1
)
A (km molϪ1
)
1
2
3
4
5
6
7
8
3873
3278
3260
3254
3243
3237
3200
3196
3184
3167
3161
1960
1914
1664
1657
1652
1646
1548
1539
1535
1528
1521
1498
1478
1465
1454
1427
1396
1391
1346
1322
1272
1234
1218
1164
1155
1119
1045
1030
978
3458
2927
2911
2905
2896
2890
2857
2854
2843
2828
2822
1750
1709
1486
1479
1475
1470
1382
1374
1371
1365
1358
1338
1320
1308
1299
1274
1246
1242
1202
1180
1136
1102
1088
1039
1032
999
97.5
31.7
7.3
57.6
51.9
22.6
37.0
8.0
31.7
25.6
10.7
86.9
851.2
6.6
12.8
3.8
6.9
3.9
14.6
0.3
1.7
3.2
29.3
5.3
6.7
150.1
9.2
2.1
12.9
88.4
71.2
8.2
0.3
29.9
8.3
1.7
4.9
11.1
19.8
3.9
0.9
2.7
133.5
1.8
67.8
12.6
32.8
2.4
100nNH
3407d
2947d
2927d
2914d
2877d
54.9
57.2
5.8
14.4
4.1
as
74n
25nNH
CH2
73nCH, 25ns
CH2
as
94n
CH2
as
74n , 12nsCH
CH2
2
as
76n , 22nsCH
CH2
2
88nsCH
2862d
2
96nsCH
2
9
80nsCH ,14nCH
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
95nsCH
2
84nsCH nsCO,n
as
CO
2
82nsCO, 16dCNC
1772
1712
35.3
341.0
as
CO
73 n , 10dHNC
97dCH (scissoring)
2
99dCH (scissoring)
1451
10.0
2
91dCH (scissoring)
2
94dCH (scissoring)
2
70dCH , 17dHCC
2
64dHNC, 18nCO
1393
2.1
92dCH
2
93dCH
1365
1354
1339
1333
10.1
1.4
14.8
5.5
2
88dCH
2
44dHCC, 31d
53dHCC, 33d
CH2
CH2
53dCH , 35dHCC
2
70dCNC, 19dOCC
1317
1263
1249
1233
1190
1173
1136
1114
1074
1047
1034
1000
937e
893e
881e
841e
820e
797e
784e
743e
716e
643e
605d
586d
564d
23.2
1.7
6.0
4.0
26.1
26.5
7.2
1.4
12.2
5.8
1.0
4.2
m
vw
vw
m
w
vw
w
48dCH , 20dHCC, 10nCC
2
71dCH , 21dHCC,
2
55dHCC, 20dCH ,10nCC
2
33dCH , 30nCN,19dHCC
2
32dCH , 30nCN, 20dCCC
2
63dCH , 21tCCCC
2
45nCC, 27dHCC, 19d
41nCC, 22nCN,18d
CH2
CH2
42dCH , 37nCC
2
66nCC, 22d
38dCCC, 33dCH ,15 nCN
CH2
2
933
920
873
865
824
801
782
740
716
673
623
593
45dCH , 27dCCC, 19nCC
2
75nCC, 22nCN
47nCC, 28d
51dCCC, 25nCC, 23d
49nCC, 24dCCC, 15d
CH2
968
923
897
876
829
802
753
698
CH2
CH2
25tNCCC, 21tHNCC, 24dOCC
51dCH , 41nCC,
2
40tHNCC, 23nCC, 19dCCC
56 nCC, 16dOCC
45tOCCC
45dCCC, 40nCC
73dNCC, 20dOCC
53dNCC, 23nCC
w
w
vw
8.7
2.4
11.5
665
622
6.4
15.3
555

I.G. Binev et al. / Journal of Molecular Structure 513 (1999) 231–243
235
Table 2 (continued)
No
Ab initio force field
Experimentala
n (cmϪ1
)
nb (cmϪ1
)
A (km molϪ1
)
Approximate descriptionc
n (cmϪ1
)
A (km molϪ1
)
550d
532d
449d
428d
421e
375f
344f
270f
238f
179e
1.7
2.6
1.1
2.0
3.2
51
578
516
4.7
36tCCCC, 30dOCC
52
53
54
55
56
57
58
59
60
490
455
392
353
283
238
181
141
85
438
406
350
315
253
216
162
126
76
1.3
14.4
19.6
1.3
3.2
0.5
15.4
0.9
0.3
76dCCC
33 dCNC, 32dCCO, dCCC
40dCCC, 33dCCO, 18dCNC
46tCCCC, 25tCCCH
64tCCCC, 14tCCCH
72tCCCC, 15tCCCO
59tCCCO, 38tCCCN
86tCCCC
w
vw
vw
vw
w
76tCCCC, 21tCCCO
a Measured after having decomposed the complex bands into components. Relative intensities: s, strong; m, medium; w, weak; vw, very
weak.
b Scaled by 0.8929 [36].
c Vibrational modes: n, stretching; d, deformation (all kinds of); t, torsion; superscripts: s, symmetrical; as, asymmetrical; ip, in-plane; oop,
out-of-plane; subscript sk, skeletal. The numbers before the mode symbols indicate % contribution (10 or more) of a given mode to the
corresponding normal vibration, according to the energy distribution matrix [33].
d Solvent CDCl3.
e Solid, in KBr.
f Solid, in CsI.
the complex bands into components by using the opus
2.0 program, which is a part of the Bruker’s software.
The fitting procedure was carried out for all the bands,
in order to account for their baselines and real widths.
The spectra of the nitranions studied do not depend on
the counterion (Naϩ or Kϩ) thus these derivatives
exist in DMSO as kinetically free solvated ions
mainly, like those of succinimide [19] and o-sulfoben-
zimide [21] etc.
4. Results and discussion
4.1. Infrared spectra
Considering first the IR spectra of the species
studied will make it possible to follow the spectral
changes caused by the conversion of the molecules
studied into the corresponding nitranions.
4.1.1. Molecules
The IR spectra of the molecules studied are quite
similar, but the obvious difference between them is in
the nCH region: the presence of four methylene groups
3. Computations
in the hexahydrophthalimide molecule gives rise to
as
and nsCH bands, whereas the nPhH
The ab initio force-field computations have been
performed using the gamess software [35] (AIX
version, 1995) at the RHF 3-21 and 6-31G levels.
As we have recently found in the case of succinimide
[19], the enlargement of the latter basis set by
including polarisation and diffuse functions leads to
some deterioration rather than improvement of the
results. No scaling in the ab initio force field has
been done.
moderate n
CH2
2
bands of phthalimide are much weaker. There is a
good agreement between experimental and scaled
theoretical frequencies of the molecules studied
(Tables 1 and 2). The mean deviation between them
is 21 cmϪ1 for phthalimide and 14 cmϪ1 for its hexa-
hydro derivative. These values lie within the interval
of 14–30 cmϪ1 of mean deviations, typical for mole-
cules containing carbonyl groups [19,21,23–25].

Table 3
Theoretical (HF/6-31G) and experimental (DMSO/DMSO-d6 solutions, counter ion Naϩ) infrared data for the phthalimide nitranion
No
Ab initio force field
Experimentala
n (cmϪ1
)
nb
Dc
A (km molϪ1
)
Approximate descriptiond
n (cmϪ1
)
Dc
A (km molϪ1
)
e
e
e
e
e
1
2
3
3361
3355
3333
3001
2996
2976
0.0
0.0
0.0
28.3
35.1
46.0
99nPhH
99nPhH
99nPhH
3076
3045
3028
3013
2958
1699
1612
1569
1591
1493
1457
1369
1348
1275
1236
1206
1188
1178
1127
1094
1051f
1040g
1006f
974f
3.7
3.1
1.7
0.9
6.3
56.0
259.9
76.4
246.4
5.1
4
5
6
7
8
9
10
3311
1916
1823
1797
1772
1632
1631
2956
1711
1628
1605
1582
1457
1456
0.0
0.0
Ϫ0.2
0.0
Ϫ0.7
0.0
0.0
9.1
93.2
242.7
15.1
1163.2
9.0
99nPhH
72nsCO, 16nCN
54nCC, 23dCCC
Ϫ0.2
Ϫ0.9
0.0
90nCC
as
66n , 11dNCC
Ϫ0.7
CO
ip
e
56d , 30nCC
PhH
ip
e
8.8
58d , 34dCCC
4.9
PhH
Ϫ2.0
0.0
15.3
35.0
100.4
9.2
51.1
31.5
7.7
65.4
4.0
w
vw
vw
vw
w
m
vw
vw
11
12
13
14
15
16
17
18
19
20
21
22
23
1449
1434
1361
1322
1278
1249
1245
1200
1164
1124
1105
1038
908
1294
1280
1215
1180
1141
1115
1112
1071
1039
1004
987
Ϫ0.9
Ϫ0.5
Ϫ9.2
Ϫ12.2
Ϫ0.5
Ϫ7.9
Ϫ5.8
Ϫ0.2
0.0
128.2
1.5
263.3
205.7
1.9
64.1
20.3
5.1
0.0
3.5
7.1
0.0
50nCC, 23dip
Ϫ9.5
Ϫ1.4
Ϫ6.2
Ϫ2.4
Ϫ4.2
PhH
ip
67d , 15 dccc
PhH
29nsNC, 28dip , 18 dCNC
PhH
69n , 17dip
as
NC
PhH
ip
46d , 46nCC
PhH
ip
26d , 23nCC, 21nNC
Ϫ9.1
PhH
42nCC, 20dip
e
PhH
82dccc
oop
PhH
82d
oop
PhH
0.0
Ϫ0.2
0.0
92d
62dCCC, 17dip
PhH
oop
PhH
927
811
93d
951f
Ϫ2.8
19.6
30dOCC, 24dNCC, 22dCCC
840f
820f
oop
PhH
24
25
894
875
798
781
Ϫ0.7
0.0
24.6
0.0
89d
799f
89tCCCC
769f
756f
743f
717f
688f
664f
629f
573f
559
vw
vw
vw
s
vw
vw
w
vw
vw
m
26
27
28
29
30
31
815
784
757
751
716
612
728
700
676
671
639
546
Ϫ3.0
Ϫ3.6
Ϫ2.4
0.0
Ϫ3.8
Ϫ4.6
0.8
128.5
1.4
0.0
1.0
65nCC, 21dNCO
79tCCCC, 14doop
PhH
54docc, 34dCCC
68tCCCC, 37tOCCC
55dCNC, 13dNCC, 15nNC
38dCCC, 20nNC, 20nCC
10.9
32
592
529
Ϫ0.6
29.4
56dCCC, 29dNCC
538f

Table 3 (continued)
No
Ab initio force field
Experimentala
n (cmϪ1
)
nb
Dc
A (km molϪ1
)
Approximate descriptiond
n (cmϪ1
)
Dc
A (km molϪ1
)
416
vw
33
34
528
483
471
431
0.0
Ϫ0.3
0.0
0.1
64tCCCC, 24tNCCO
98tNCCC
408f
399
vw
vw
m
vw
vw
vw
m
35
375
335
Ϫ0.1
16.3
48dNCO, 26 dCNC
364f
340
269
36
37
38
39
254
223
201
148
227
199
179
132
0.0
Ϫ3.9
Ϫ0.4
0.0
0.7
0.2
9.5
0.0
68dCCC
208f
190f
164f
156g
40tCCCC, 30tNCCO
60tNCCO, 36tCCCC
68tNCCC
m
vw
a Measured after having decomposed the complex bands into components. Relative intensities: s, strong; m, medium; w, weak; vw, very weak.
b Scaled by 0.8929 [36].
c Solvent CDCl3.
d Vibrational modes: n, stretching; d, deformation (all kinds of); t, torsion; superscripts: s, symmetrical; as, asymmetrical; ip, in-plane; oop, out-of-plane; subscript sk, skeletal.
The numbers before the mode symbols indicate % contribution (10 or more) of a given mode to the corresponding normal vibration, according to the energy distribution matrix [33].
e No reliable data.
f Hase’s solid state IR data [12].
g Hase’s solid state Raman data [12].

238
I.G. Binev et al. / Journal of Molecular Structure 513 (1999) 231–243
Table 4
Theoretical (HF/6-31G) and experimental (solvent DMSO/DMSO-d6, counter ion Naϩ) infrad data for the cis-hexahydrophthalimide nitranion
No
Ab initio force field
Experimentala
n (cmϪ1
)
nb
A (km molϪ1
)
Approximate descriptionc
n (cmϪ1
)
A (km molϪ1
)
as
1
2
3
4
5
6
7
8
3254
3230
3221
3213
3207
3190
3176
3150
3138
3125
1883
1746
1665
1655
1651
1644
1541
1527
1522
1510
1491
1477
1463
1419
1403
1387
1386
1358
1311
1264
2906
2884
2876
2869
2864
2848
2836
2813
2802
2790
1682
1559
1486
1478
1474
1468
1376
1364
1359
1348
1331
1318
1306
1267
1253
1238
1237
1212
1171
1129
73.2
38.6
83.6
46.6
58.8
84.2
24.0
67.4
57.0
30.5
68.2
1381.3
14.7
11.7
1.9
16.2
2.6
2.5
1.8
0.7
13.7
1.6
21.1
3.7
231.4
152.6
74.8
53.4
19.6
9.4
90n
2937
2923
2898
2867
83.1
26.5
13.9
4.3
CH2
as
96n
CH2
as
92n
CH2
85nsCH
2
58nsCH , 36n
as
CH2
2
63nsCH , 29n
2854
20.8
as
CH2
2
52nsCH , 41n
as
CH2
2
as
74n , 22nsCH
CH2
2
9
94nsCH
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30d
75nsCH , 22nsCH
2
2
74nsCO, 18dCCC
1690
1580
1460
1449
18.4
549.7
2.5
as
76n , 11dNCC
CO
94dCH (scissoring)
97dCH (scissoring)
94dCH (scissoring)
95dCH (scissoring)
65dCH , 23dHCC
72dCH
90dCH
85dCH
58dHCC, 23d
45dHCC, 30d
48dCH , 22dHCC
62dCH , 15tHCCC
69dCNC, 16dOCC
50nCN, 24tHCCC
43dCH , 17nCN, 10tHCCC
37tHCCC, 20d ,14nCC
39dCH , 33tHCCC
2
5.2
2
2
1435
1363
3.1
8.0
2
2
2
2
1348
1326
5.3
43.3
2
CH2
CH2
1306
68.5
2
2
1247
1224
115.5
11.6
2
1211
1171
1129
12.7
2.5
17.5
CH2
2
56dCH , 21nCC
2
a Measured after having decomposed the complex bands into components. Relative intensities: s, strong; m, medium; w, weak; vw, very
weak.
b Scaled by 0.8929 [36].
c Vibrational modes: n, stretching; d, deformation (all kinds of); t, torsion; superscripts: s, symmetrical; as, asymmetrical; ip, in-plane; oop,
out-of-plane; subscript sk, skeletal. The numbers before the mode symbols indicate % contribution (10 or more) of a given mode to the
corresponding normal vibration, according to the energy distribution matrix [33].
d Followed by 27 low-frequency normal vibrations.
There is a fairly good agreement between calculated
and measured 15N isotopic shifts D (Table 1, cf.
columns 4 and 8). The approximate description of
the normal vibrations of phthalimide (Table 1) is not
dissimilar from the band assignments of Hase [12] and
Arenas et al. [15]; there are some differences in the
case of certain low-frequency bands. In the literature
we did not find any detailed band assignment of the IR
spectrum of hexahydrophthalimide.
4.1.2. Nitranions
The IR spectra of the nitranions studied are not so
similar than those of the corresponding molecules:
essential differences are seen near 3000 and
1600 cmϪ1. The theoretical and experimental IR
data for the nitranions studied are compared in Tables
3 and 4. The mean deviation between experimental
and scaled theoretical frequencies is 20 cmϪ1 for the
phthalimide nitranion and 13 cmϪ1 for its hexadeutero

I.G. Binev et al. / Journal of Molecular Structure 513 (1999) 231–243
239
derivative. So, the agreement between these values
can be considered as very good, having in mind the
interval of 16–49 cmϪ1 of mean deviations, found for
anions and dianions containing carbonyl groups
[19,21,23–25,34]. However the agreement between
the calculated and measured 15N isotopic shifts D
for the phthalimide nitranion (Table 3, columns 4
and 8) is somewhat worse than in the previous case
(cf. Table 1). The approximate description of most
normal vibrations of the same anion (Table 3) agrees
with Hase’s assignments of vibrational bands of
potassium phthalimide [12].
weaker than expected on the basis of both theoretical
data (Table 3, No. 8) and experimental results for cis-
hexahydrophthalimide nitranion (Formula 4, see
Table 4, No.12) and succinimide nitranion (5).
Hence, we think that in the case of the phthalimide
as
CO
nitranion there is an intensity borrowing from n to
the n9a band.
Special attention should be paid to the spectrum near
1600 cmϪ1. As early as 1964 Matsuo [16] reported three
almost equi-intense bands near 1600 cmϪ1 in the spec-
In good agreement between the theory and the
experiment, the conversion of both phthalimide and
hexahydrophthalimide molecules into corresponding
nitranion leads to strong spectral changes (cf. Tables
1–4), for example:
trum of the solid potassium phthalimide. The author
as
CO
assumed that n
“is split into a triplet for some
unknown reasons” [16]. Twenty-four years later Hase
[12] confirmed the presence of these three bands, strong
in the IR and medium in the Raman spectra. However,
as
1. Strong decreases in nsCO by 74 cmϪ1 and inn by
CO
134 cmϪ1 (mean values for the two imides studied).
We have recently found the corresponding values of
74 and 139 cmϪ1 in the case of succinimide [19].
Strong nCO decreases have been found to accompany
the conversions of other imides [18,20,21], many
amides [22–25] and many other carbonyl
the author [16] assigned them, as follows: 1587 cmϪ1,
as
CO
n
; 1596 cmϪ1, ring stretch; 1610 cmϪ1, ring stretch.
We found that both potassium and sodium phthalimide
show in DMSO only two equi-intense very strong
as
bands, described in Table 3 as: 1591 cmϪ1, n and
CO
1612 cmϪ1, ring vibration type 9a (Wilson’s nota-
tion). Hence, Hase’s assignment is confirmed unam-
biguously. However, the intensity of the 1612 cmϪ1
band is surprisingly high.
compounds [18,34,40,41] into anions and dianions.
as
2. Enlargement of nCO splittings DnCO ˆ nsCO Ϫ n
CO
from 51 to 109 cmϪ1 (mean values). The corre-
sponding DnCO increase in the succinimide case is
from 58 to 123 cmϪ1 [19]. For comparison the
conversion of the malononitrile (Formula 6) and its
ylidene derivatives (7) into anions (8) leads to a 12-
to 13-fold enlargement of the nCN splitting, from
4 cmϪ1 (calculated, but not measurable) to 49–
54 cmϪ1 [41,42].
1. According to the theory the n8a band should be
as
five-fold weaker than n (Table 3).
CO
2. The fully analogous n8a band of the o-sulfobenzi-
mide (saccharin) nitranion (Formula 2) has only
moderate intensity, 41.6 km molϪ1, and is four-
fold weaker than nCO [21].
3. Very strong n8a,b bands are typical only for anions
where the anionic center is directly bonded to the
phenyl (phenylene) ring (Formula 3) [24,35–41].
as
CO
However, the n band of phthalimide nitranion is

240
I.G. Binev et al. / Journal of Molecular Structure 513 (1999) 231–243
Table 5
˚
Bond lengths (A) and bond angles (deg.) of the phthalimide molecule and of its nitranion
Geometry parametersa
Molecule
X-rayb
Nitranion
X-rayd
MINDO/3c
3-21G
1.357
6-31G
1.388
3-21G
1.357
6-31G
1.360
r(N1–C2)
r(N1–H12)
r(C2–C4)
1.387e
0.93
1.395
1.025
1.510
1.205
1.464
1.403
1.417
1.397
0.0204
121.4
103.7
125.9
117.2
107.6
132.9
119.8
120.7
2.19
1.367
–
1.498
1.236
0.956
1.471
1.207
1.391
1.392
1.406
1.402
0.0161
0.992
1.485
1.213
1.388
1.375
1.394
1.390
0.0094
–
–
1.439e
1.214e
1.383
1.384e
1.391e
1.389
0.0000
119
1.536
1.225
1.372
1.370
1.394
1.387
0.0197
–
1.518
1.235
1.381
1.376
1.397
1.390
0.0093
–
r(C2yO10)
r(C4–C5)
r(C4–C6)
r(C6–C8)
r(C8–C9)
m.d.f
0.0000
–
110.6
124.8
107.1
Ͻ (H12N1C2)
Ͻ (N1C2C4)
Ͻ (N1C2O10)
Ͻ (C2N1C3)
Ͻ (C2C4C5)
Ͻ (C2C4C6)
Ͻ (C4C6C8)
Ͻ (C6C8C9)
m.d.f
122.6
123.4
105.6
125.1e
112.5
108.2
130.2e
116.6
121.6
0.00
104.8
125.6
114.9
107.7
130.4
116.9
121.3
105.1
125.8
113.3
108.3
130.2
117.4
121.0
108.2
108.9
129.5
110.9
106.3
132.1
117.7
120.6
128.6
109.9
106.2
132.3
117.7
120.8
0.79
0.57
0.00
3.63
2.77
a For atom numbering see Scheme 2.
b Ref. [29].
c Ref. [15].
d Ref. [30].
e Mean values of two non-equivalent positions in the monocrystal.
f Mean absolute deviations (r(N1–H12) and Ͻ (H12N1C2) are excluded).
Both the above results for the imides studied can be
explained by the conjugation of the nitranionic charge
with the carbonyl groups: decrease in CyO bond
orders and increase in the C–C ones (Section 4.2),
accompanied by an enhancement of the nCO
couplings.
Etot(nitranion) Ϫ Etot(molecule) correspond to the
above values:
ED ˆ 1533.9 kJ molϪ1 for phthalimide; and
ED ˆ 1539.5 kJ molϪ1 for cis-hexahydrophthali-
mide.
We calculated that both trans-hexahydrophthali-
mide molecule and nitranion are less stable (by 14.4
and 20.1 kJ molϪ1, respectively) than the corre-
sponding cis-isomers, so the corresponding ED is
1545.2 kJ molϪ1. All these values are close to ED of
succinimide, i.e. 1536.3 kJ molϪ1 [19], and hence
correspond to the close acidities of these compounds:
pKas of phthalimide and succinimide are 13.4 and 14.6
(solvent DMSO) [43]. For comparison: ED of o-sulfo-
benzimide (saccharin) has been calculated to be
essentially lower, 1469.5 kJ molϪ1 (3-21Gء) [21] or
1415.7 kJ molϪ1 (6-31Gء) [42], as saccharin is a
4.2. Energies
The HF 6-31G total energies of the species studied
are, as follows:
Etot
Etot
ˆ
ˆ
Ϫ509.861590h and Ϫ509.277209h for the
phthalimide molecule and its nitranion, and
Ϫ513.345467h and Ϫ512.758965h for cis-
hexahydrophthalimide molecule and its
nitranion, respectively.
The following deprotonation energies ED
ˆ

I.G. Binev et al. / Journal of Molecular Structure 513 (1999) 231–243
241
Scheme 2. Ab initio RHF/6-31G structure of phthalimide (A1), hexahydrophthalimide (B1) and of their nitranions (A2, B2). The bond orders (in
italics) and net electric charges on the fragments (in bold) are indicated in the Formulae.
much stronger acid (pKa ˆ 4.0) [43] than the above
(Table 5) are essentially larger than the experi-
mental errors, which are 0.002–0.005 A for
˚
1,2 dicarboxamides.
distances between heavy (non-hydrogen) atoms
4.3. Structure
and 0.2–0.4Њ for the corresponding angles
˚
[29,30], 0.06 A and 4Њ for parameters with the
The structure of the species studied are shown in
Scheme 2; the numerical data for their geometry para-
meters are listed in Tables 5 and 6. At least the
following considerations should be mentioned:
1. The 6-31Gء geometry parameters correspond best
to the X-ray data, however the mean deviations
participation of hydrogen atoms [29].
2. We have recently found in the case of 2,5-pyrroli-
dinedione (succinimide) that extensions of the
basis set by adding polarization and diffuse func-
tions within the RHF theory results in deterioration
in both vibrational and structural parameters.

242
I.G. Binev et al. / Journal of Molecular Structure 513 (1999) 231–243
Table 6
Scheme 2 and Tables 5 and 6). However, a slight
decrease, by 0.07 units only, in P(C2–C4) correspond
to the strongest bond length change in the phthalimide
˚
Bond lengths (A) and bond angles (Њ) of the hexahydrophthalimide
molecule and of its nitranion
Geometry parametersa Molecule
3-21G
Nitranion
3-21G
˚
case, i.e. enlargement: calculated by 0.033 A, deter-
˚
mined experimentally by 0.059 A (Table 5 and A1, A2
6-31G
1.381
6-31G
1.354
in Scheme 2). In the case of hexahydro-phthalimide
case (B1, B2 in Scheme 2) the calculated P(C2–C4)
decrease is 0.02 units only; the corresponding
enlargement of the C2–C4 bond is calculated to be
r(N1–C2)
1.384
0.999
1.522
1.205
1.504
1.529
1.537
1.538
1.348
–
r (N1–H12)
r (C2–C4)
0.994
1.518
1.214
1.549
1.531
1.531
1.532
–
1.560
1.229
1.528
1.529
1.537
1.539
–
110.2
128.9
110.9
101.1
113.0
112.5
110.3
1.544
1.239
1.535
1.529
1.532
1.533
–
r (C2yO10)
r (C4–C5)
˚
0.026 A (Table 6).
The net electric charges on the fragments are shown
in Scheme 2. They seem to be overestimated, as the
dipole moments of 3.92 and 3.17 Debye, calculated
for phthalimide and hexahydrophthalimide respec-
tively, are larger than the experimental ones of
2.91 Debye [30] and 2.24 Debye [26] (solvent
dioxane). We have recently found that in the case of
succinimide both RHF and DEPT theories give quite
larger dipole moment values, 2.00–2.86 Debye, than
the experimental value of 1.47 Debye [19] and refer-
ences therein.
r (C4–C6)
r (C6 C8)
r (C8–C9)
Ͻ (H12N1C2)
Ͻ (N1C2C4)
Ͻ (N1C2O10)
Ͻ (C2N1C3)
Ͻ (C2C4C5)
Ͻ (C2C4C6)
Ͻ (C4C6C8)
Ͻ (C6C8C9)
122.9
122.9
106.0
125.9
114.4
102.6
113.8
112.5
110.2
106.9
125.2
114.1
103.1
115.4
113.5
110.8
110.9
127.8
110.2
101.4
115.4
113.5
110.7
a For atom numbering see Scheme 2.
The net charge changes, Dq ˆ q(nitranion) Ϫ
q(molecule), resulting from the conversion of the
1,2-dicarboximide molecules studied into the
corresponding nitranions, are very informative for
showing the distribution of the nitranionic changes.
We can calculate on the basis of the data from Scheme
2, that the greater parts of the nitranionic charges,
nearly 0.6 eϪ, are localized within the carbonyl
groups, and the rest of them, ca. 0.1 and 0.3 eϪ, are
held by the nitranionic centers and hydrocarbon
moieties.
3. Nobody could expect complete coincidences
between X-ray experimental data for single crys-
tals and theoretical data for isolated molecules or
ions.
The essential changes in the C–N and CyO bond
lengths (and in the corresponding bond orders,
Scheme 2), which accompany the conversion of the
phthalimide molecule into the nitranion, have
obviously been expected. However, an enlargement
in r(C2–C4) is almost twice greater than expected
(Table 5). There are essential changes in all the pyrro-
lidine ring angles (Table 5), although it remains
planar.
We found no experimental structural data for either
hexahydrophthalimide or its nitranion, but on the
basis of the above results we assume that calculations
(Table 6) will give an adequate description of the
structure of these species.
5. Conclusion
As can be seen from this work, conversion of the
1,2-dicarboxamides into the corresponding nitranions
results in strong spectral and structural changes. Both
these changes can be predicted and described at
moderate levels of the ab initio MO theory.
The increase in the P(C–N) bond order by 0.35
units and the decrease in the P(CyO) one by 0.20
units, accompanying the conversion of the 1,2-dicar-
boximides studied into nitranions, are in a good agree-
ment with the respective changes, both calculated and
measured, in the lengths of the same bonds (cf.
Acknowledgements
The financial support by the Bulgarian National
Science Fund of Contract X-801 is politely acknowl-
edged.

I.G. Binev et al. / Journal of Molecular Structure 513 (1999) 231–243
243
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