AM1 and electron impact mass spectrometry study of the fragmentation of 4-acyl isochroman-1,3-diones

Article abstract of DOI:10.4314/bcse.v26i2.15

Recently, in electron impact mass spectrometry (EIMS), it has been found a good correlation between the fragmentation processes of coumarins and the electronic charges of the atoms of their skeleton. In this paper, the same analytical method has been applied to 4-acyl isochroman-1,3-diones, whose mass spectra had been studied earlier and described for the very first time from our laboratory. Results obtained are in good agreement with the last study.

Full text of DOI:10.4314/bcse.v26i2.15

Bull. Chem. Soc. Ethiop. 2012, 26(2), 311-318.
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v26i2.15
ISSN 1011-3924
 2012 Chemical Society of Ethiopia
SHORT COMMUNICATION
AM1 AND ELECTRON IMPACT MASS SPECTROMETRY STUDY OF THE
FRAGMENTATION OF 4-ACYL ISOCHROMAN-1,3-DIONES
Abdoulaye Djandé1, Bintou Sessouma2, Félix B. Kini3, Leopold Kaboré1, Bayo Karifa2, Pierre I.
Guissou3 and Adama Saba1*
1Laboratoire de Chimie Bio Organique et Phytochimie, UFR-SEA, Université de Ouagadougou,
03 BP 7021 Ouagadougou, Burkina Faso
2Laboratoire de Chimie de Coordination, UFR-SEA, Université de Ouagadougou, 03 BP 7021
Ouagadougou, Burkina Faso
3Institut de Recherche en Sciences de la Santé (IRSS/CNRST), 03 BP 7029 Ouagadougou,
Burkina Faso
(Received April 19, 2010; revised October 14, 2011)
ABSTRACT. Recently, in electron impact mass spectrometry (EIMS), it has been found a good correlation
between the fragmentation processes of coumarins and the electronic charges of the atoms of their skeleton. In
this paper, the same analytical method has been applied to 4-acyl isochroman-1,3-diones, whose mass spectra had
been studied earlier and described for the very first time from our laboratory. Results obtained are in good
agreement with the last study.
KEY WORDS: 4-Acyl isochroman-1,3-dione, Electron impact mass spectrumetry, AM1, Electronic charges,
Fragmentation
INTRODUCTION
4-Acyl isochroman-1,3-diones 1 are very interesting compounds studied in our laboratories. It
has been found to have several properties for these compounds. They exhibit fluorescence [1-2],
anti-oxidant [3] and anti-bacterial properties [4], among others. Some of their spectral
properties, nuclear magnetic resonance (NMR) [5], mass [6], UV-Visible [3], and their
reactivity [3, 7-9], have been described. Their crystal structures have also been investigated [10-
12]. Recently a new approach of analysis of fragmentation processes of coumarins in electron
impact mass spectrometry has been described to give a good correlation with the electronic
charges of their atoms [13-15]. It has been found that fragmentation processes in electron
impact mass spectrometry (EIMS) takes place mainly at the level of atoms bearing high negative
charge. It seems to be possible to predict and explain most of their fragmentations, using
electronic charges of atoms. So, as a part of our continuing investigations about 4-acyl
isochroman-1,3-diones 1, the fragmentation processes of these compounds in electron impact
mass spectrometry (EIMS) was successfully analyzed by the calculated AM1 electronic charges
of atoms. It has been found that the method presents a good reliability. The electronic charges of
atoms become a valuable instrument for understanding the fragmentation processes of organic
compounds in MS. This study is the second investigation about mass spectra of these
compounds but the very first one with both experimental and theoretical investigations.
__________
*Corresponding author. E-mail: nabaogos@yahoo.fr

312
Abdoulaye Djandé et al.
EXPERIMENTAL
The title compounds 1 have been obtained as described in the literature [1], by action of acid
chlorides or acid anhydrides on homophthalic anhydride in the presence of a base, as shown
below:
R
O
O
C
H
O
O
R
X
O
O
B
O
O
1
X = Cl or OCOR; B = pyridine or triethylamine.
1a: R = CH3 ; 1b: R = C2H5; 1c: R = C6H5; 1d: R = p-ClC6H4; 1e: R = p-NO2C6H4.
Scheme 1. Synthesis of 4-acyl isochroman-1,3-diones 1.
RESULTS AND DISCUSSION
The acylated isochroman-1,3-diones 1 have been obtained with more than 70% yield [1]. They
have been identified by their melting points and by their 1H, 13C and 17O NMR spectra [3, 5].
14
x
15
13
4
O
4
O
12
13
5
16
11
11
H
H
17
5
O3
O3
10
9
10
4
1
4
1
6
7
6
7
3
3
O
2
O
2
9
8
8
O
1
O
1
Scheme 2. Structure of 4-acyl isochroman-1,3-diones 1.
Mass spectra. All the mass spectra were obtained by electron impact mass spectrometry (EIMS)
on a CPG-JSM AX505 apparatus at 70 eV and the data are given in Table 1.
AM1 calculation of electronic charges of atoms. The electronic charges of atoms were
performed by Austin Model 1 (AM1) semi empirical method [16] using “Chem3D Ultra8”
software on a Pentium 4 Computer. Results are given in Table 2.
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Short Communication
Table 1. Mass spectra (EIMS) of compounds 1.
R = CH3 (1a) R = C2H5 (1b) R = C6H5 (1c) R = p-ClC6H4 (1d) R = p-NO2C6H4 (1e)
313
m/z
204
186
176
162
145
134
118
105
89
%
45
100
17
50
4
m/z
218
200
189
162
145
135
134
118
105
89
%
4
m/z
266
249
238
222
194
165
144
118
105
89
%
35
1
m/z
302
300
287
285
272
256
228
209
195
158
156
141
139
118
111
37
%
10
14
9
m/z
311
294
283
267
238
237
221
209
165
150
133
118
104
76
%
75
4
15
6
8
8
8
10
9
6
27
14
13
2
5
5
90
18
34
19
15
10
6
27
14
100
6
10
0.8
14
100
4
22
16
2
6
1.8
28
70
32
100
2
12
77
12
12
48
1
100
6
63
77
77
32
5
51
57
51
12
25
11
4
43
33
3
51
-
-
39
39
2
-
-
28
2
29
8
-
-
38
1
63
-
-
-
-
-
-
39
1
Table 2. Electronic charges of atoms of compounds 1.
Atoms R = CH3 (1a) R = C2H5 (1b) R = C6H5 (1c) R = p-ClC6H4 (1d) R = p-NO2C6H4 (1e)
C1
C3
0.414
0.426
-0.321
-0.207
-0.149
-0.209
-0.109
-0.175
0.050
0.215
-0.351
-
0.414
0.425
-0.319
-0.206
-0.145
-0.211
-0.110
-0.175
0.045
0.211
-0.254
-0.349
-
0.402
0.417
0.413
0.424
0.395
0.410
C4
-0.309
-0.200
-0.154
-0.216
-0.107
-0.175
0.035
-0.299
-0.200
-0.149
-0.209
-0.113
-0.177
0.045
-0.231
-0.138
-0.183
-0.183
-0.118
-0.126
-0.034
0.346
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
O1
O2
O3
O4
0.269
0.254
-0.113
-0.136
-0.206
-0.162
-0.215
-0.139
-0.313
-0.249
-0.365
-0.323
-0.109
-0135
-0.185
-0.065
-0.184
-0.138
-0.300
-0.249
-0.355
-0.298
-0.157
-0.080
-0.149
-0.103
-0.150
-0.148
-0.208
-0.247
-0.292
-0.248
-
-
-
-
-
-
-
-0.301
-0.285
-0.355
-0.307
-0.300
-0.286
-0.354
-0.307
Cl
-0.0036
N: 0.522
O: -0.302
O: -0.294
NO2
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Abdoulaye Djandé et al.
Tautomery of compounds 1. The three tautomeric forms A, B, C (Scheme 3) had been suspected
and described as possible structures for these compounds [8, 9] but the only one form C has
been really observed both in solution [5] and in crystalline form [10-12].
R
O
R
O
R
O
H
C
H
O
H
O
C
O
O
O
O
O
O
O
C
B
A
Scheme 3. Tautomeric forms of 1.
Formation of molecular ion. In all the precedents descriptions of the structure of compounds 1
using NMR [5] or crystallographic methods [10-12], only the tautomeric form C had been
found, whatever the nature of R (aliphatic or aromatic). AM1 calculation of heat of formation
(∆H) of 1 gave positive values also the same results [5]. The behaviour of these compounds in
mass spectrometry has been reported for the very first time since a few years [6]. It had been
observed only the two enolic forms, B and C, of this tautomery. Nevertheless, this tautomery
takes place only after formation of molecular ion. According to the above theory, the molecular
ion must take place at the level of O4 and/or O3, as oxygen bearing the highest negative charges.
Fragmentations must then take place at the level of C4, C5, C6, C7, C8, C9, C12 and oxygen atoms
(O1, O2, O3 and O4). So, formation of the resulting molecular ion, its tautomery and the
subsequent fragmentations shown below, were induced by O3, O4 and C4 atoms. These atoms
are bearer of the highest negative charges. The tautomery can take place after ionisation because
the values of the charges of C4, O3 and O4 are very close to themselves. The formation of R-CO
or Ar-CO fragments take place for every molecule with a significant percentage (32 ≤ % ≤ 100).
Only this tautomery can explain the formation of the R-CO or Ar-CO fragments, observed in all
the spectra.
R
O
O
O
R
C
H
O
H
O
C
H
O
+
R
C
O
O
O
O
O
O
B
C
R = CH3, m/z = 43 (33%); R = C2H5, m/z = 57; R = C6H5, m/z = 105; R = p-ClC6H4, m/z = 139
and 141; R = p-NO2C6H4, m/z = 150.
Scheme 4. Formation of molecular ion and of fragments R-CO+ or Ar-CO+.
Other fragmentations processes of 4-acyl isochroman-1,3-diones 1.
Formation of M-18 and M-17 fragments. It has been observed that compounds 1, with an
aliphatic R, loose one molecule of water (M-18) while the compounds with arylic R loose
Bull. Chem. Soc. Ethiop. 2012, 26(2)

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315
simply the OH radical, as shown in the below Scheme 5. This fragmentation is initiated and
guided by the two atoms, O4 and C12.
H
H
O
O
R'
C
H
O
R'
C
R'
C
H
O
O
H2O
+
O
O
O
O
O
O
M - 18
R’ = H : 1a m/z 186; R’ = CH3 : 1b m/z = 200.
Ar
O
Ar
C
H
O
C
O
+
HO
O
O
O
O
M - 17
Ar = C6H5 : 1c, m/z = 249; Ar = pClC6H4 : 1d, m/z = 285 and 287; Ar = pNO2C6H4 : 1e m/z = 294.
Scheme 5. Formation of M-18 and M-17 fragments.
The M-18 fragmentation takes place after transposition of aliphatic hydrogen from C12 onto
O4 atom, to produce water. The M-17 fragmentation takes place by direct lost of the hydroxyl
group, when R is an aromatic moiety. In this case, there is no hydrogen on C12 to remove from
this aromatic group. It must be noticed that for compounds 1a and 1b, atoms C12 and O4 exhibit
high negative charges.
Formation of the fragments m/z = 162, 145 and 134. Due to the proximity of the charges values
of C4 and O4, the transposition of aliphatic hydrogen described above in the formation of water,
can also take place onto C4, leading to another type of fragmentation shown below. It is then
obtained the fragments m/z = 162 (Scheme 6), 145 and 134 (Scheme 7). The following
mechanism had been described to explain the formation of these fragments, obtained
exclusively when R is an aliphatic moiety (R = CH3 or C2H5). However, the difference of
stability of this fragment m/z = 162, 50% for 1a and only 8% for 1b, can be explained by the
difference between the charges value of their C12 atom: -0.351 for 1a and -0.254 for 1b. So, the
transfer of the aliphatic hydrogen from this C12 onto C4 is less favoured for 1b than for 1a.
H
H
O
O
O
O
O
O
R
H
O
R
H
O
H
H
O
R
H
O
H
H
R
+
C C O
O
O
O
O
O
m/z=162
R = CH3 or C2H5.
Scheme 6. Formation of fragment m/z = 162.
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Abdoulaye Djandé et al.
This fragment presents several mesomeric forms as shown below and lead to the fragments
m/z =145 and 134.
H
H
O
H
H
O
H
H
O
O
O
O
O
O
O
H
H
H
C
H
H
O
O
C
+
OH
O
O
O
O
C
O
O
m/z = 145
H
H
O
CO
+
O
m/z = 134
Scheme 7. Formation of fragments m/z = 145 and 134.
In all these last fragmentations, atoms which put a lot into the fragmentations processes are
C9, C4, C12, O1, O2 and O3. On the other hand, it is then possible to understand why the
compound 1b, (R = CH3-CH2), has its base peak at m/z = 118. Its formation take place from the
fragment m/z = 162 by the follow mechanism, after losing CO2 (Scheme 8). It is, once,
noticeable that these atoms exhibit high negative electronic charge.
H
H
H
H
O
H
C
- CO2
H
C
H
O
O
O
O
H
O
m/z = 162
Scheme 8. Formation of base peak of 1b.
m/z = 118.
Formation of fragments m/z = 105, 77 and 51. An original behaviour has been signalled the
presence of three unusual fragments m/z = 105, 77 and 51 in the spectrum of fused bicyclic
heterocyclic compounds. These fragments had been observed both for 1a and 1b (R aliphatic)
[6]. Usually, these fragments are characteristic of mono substituted phenones and mono
substituted derivatives of benzoic acid. If the presence of these fragments has been naturally
obtained and described above for the compound 1c (Ar = C6H5), in the present case, this
phenomenon has been explained after considering the fragment m/z = 145, as their parent peak
because only these two compounds can form these fragments. In this case, the follow process
had been described.
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H
C
H
C
C
O
C2O +
O
C
O
m/z=105
- C2H2
m/z =145
H
H
- CO
C
O
m/z=51
m/z=77
m/z=105
Scheme 9. Formation of fragments m/z = 105, 77 and 51.
After a transfer of hydrogen atom from the fragment m/z = 145, the ion with the m/z = 105
is obtained, which leads to other fragments 77 and 51 by the usual process of fragmentation
(Scheme 9) [6]. This process is driven by C4, C7 and C9 which are bearers of high negative
electronic charges.
CONCLUSIONS
After the application of analysis of fragmentations of three series of coumarins through the
electronic charges of their atoms, title compounds had also been investigated by electron impact
mass spectrometry, using the electronic charges of atoms obtained by AM1 semi empirical
method. The method appeared as a useful one for understanding and explaining the processes of
the fragmentations. In this study, it has been found logic and good explanations of most of
fragmentations obtained: formation of molecular ions of the compounds and most of their
fragments take place mainly at the level of atoms bearing high positive charge. So loss of water
(H2O) or hydroxyl (OH.) group and formation of fragments m/z = 162, 145, 134, 105, 77 and 51
can be justified by exploiting electronic charges of atoms. The correlation between charges of
atoms and fragmentations processes of these compounds had been found to be very suitable. So,
the method seemed to be applicable to every family of organic compounds.
REFERENCES
1. Djandé, A.; Cissé, L.; Kaboré, L.; Saba, A.; Tine, A.; Aycard, J.P. Heterocyclic Comm.
2008, 24, 237.
2. Djandé, A.; Cissé, L.; Kaboré, L.; Saba, A.; Tine, A.; Aycard, J.P. Bull. Chem. Soc. Ethiop.
2009, 23, 105.
3. Djandé, A. Thèse Unique, Université de Ouagadougou, Burkina Faso, 2008.
4. Bationo-Napon, B. Thèse de Pharmacie, Université de Ouagadougou, Burkina Faso, 2009.
5. Saba, A.; Sib, F.S.; Faure, R.; Aycard, J.P. Spectrosc. Lett. 1996, 29, 1649.
6. Djandé, A.; Kaboré, L.; Saba, A.; Aycard, J.P. Phys. Chem. News 2006, 31, 125.
7. Saba, A.; Sib, F.S.; Aycard, J.P. Spectrosc. Lett. 1995, 28, 1053.
8. Schnekenburger, J. Arch. Pharm. 1964, 298Bd, 4.
9. Nadkarni, D.R.; Usgahonkar, R.N. Indian J. Chem. 1978, 16B, 320.
10. Kakou-Yao, R.; Saba, A.; Ebby, N.; Pierrot, M.; Aycard, J. P. Acta Cryst. 1999, C55, 1591.
11. Kakou-Yao, R.; Djandé, A.; Kaboré, L.; Saba, A.; Aycard, J.P. Acta Cryst. 2008, E63,
o4275.
Bull. Chem. Soc. Ethiop. 2012, 26(2)

318
Abdoulaye Djandé et al.
12. Abou, A.; Goulizan Bi, S.D.; Kaboré, L.; Djandé, A.; Saba, A.; Kakou-Yao, R. Z.
Naturforschung 2009, 64b, 328.
13. Cissé, L.; Tine, A.; Kaboré, L.; Saba, A. Spectrosc. Lett. 2009, 42, 95.
14. Cissé, L.; Kaboré, L.; Tine, A.; Saba, A. Bull. Chem. Soc. Ethiop. 2010, 24, 305.
15. Cissé, L.; Kaboré, L.; Saba, A.; Tine, A. Phys. Chem. News 2010, 53, 101.
16. Dewar, M.J.S.; Zoebish, E.G.; Healy, E.F.; Steward, J.J.P. J. Am. Chem. Soc. 1985, 107,
3902.
Bull. Chem. Soc. Ethiop. 2012, 26(2)