Effect of hydration and structure on the fragmentation of 2,2-(propane-1,3-diyl)bis(isoindoline-1,3-dione) and 2,2-(ethane-1,2-diyl)bis(isoindoline-1,3-dione) in electron impact ionization-mass spectrometry: A theoretical and experimental study

Article abstract of DOI:10.1016/j.molstruc.2019.127105

Two bis-phthalimide derivatives, 2,2-(ethane-1,2-diyl)bis(isoindoline-1,3-dione) (3) and 2,2-(propane-1,3-diyl)bis(isoindoline-1,3-dione) (4) were synthesized and characterized by ¹H NMR, ¹³C NMR and electron impact ionization-mass spectrometry (EI-MS). Effect of the alkyl length on the fragmentation of the compounds 3 and 4 was investigated and it was found that molecular ion of 3 with a CH₂–CH₂ group is almost completely decomposed, so that a small peak was observed for its molecular ion at m/z of 320. On the other hand, an intense peak with m/z of 334 was observed for the molecular ion of 4 indicating the stability of 4⁺ ion. The results were interpreted using computational method at B3LYP/6-31 + G(d) level of theory. Also, comparison of the mass spectra showed that the cation 4⁺ is tri-hydrated while 3⁺ is not hydrated. From the optimized structures of 4⁺(H₂O)_1-3 clusters, it was found that the extra stability of 4⁺(H₂O)₃ is due to formation of hydronium ion (H₂O)₂H₃O⁺.

Full text of DOI:10.1016/j.molstruc.2019.127105

Journal of Molecular Structure 1200 (2020) 127105
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Effect of hydration and structure on the fragmentation of 2,2-
(propane-1,3-diyl)bis(isoindoline-1,3-dione) and 2,2-(ethane-1,2-diyl)
bis(isoindoline-1,3-dione) in electron impact ionization-mass
spectrometry: A theoretical and experimental study
Samiyeh Yosefdad, Younes Valadbeigi*, Mohammad Bayat
Department of Chemistry, Faculty of Science, Imam Khomeini International University, Qazvin, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 July 2019
Received in revised form
1 September 2019
Accepted 20 September 2019
Available online 23 September 2019
Two bis-phthalimide derivatives, 2,2-(ethane-1,2-diyl)bis(isoindoline-1,3-dione) (3) and 2,2-(propane-
1,3-diyl)bis(isoindoline-1,3-dione) (4) were synthesized and characterized by 1H NMR, 13C NMR and
electron impact ionization-mass spectrometry (EI-MS). Effect of the alkyl length on the fragmentation of
the compounds 3 and 4 was investigated and it was found that molecular ion of 3 with a CH2eCH2 group
is almost completely decomposed, so that a small peak was observed for its molecular ion at m/z of 320.
On the other hand, an intense peak with m/z of 334 was observed for the molecular ion of 4 indicating
the stability of 4þ ion. The results were interpreted using computational method at B3LYP/6-31 þ G(d)
level of theory. Also, comparison of the mass spectra showed that the cation 4þ is tri-hydrated while 3þ is
not hydrated. From the optimized structures of 4þ(H2O)1-3 clusters, it was found that the extra stability of
4þ(H2O)3 is due to formation of hydronium ion (H2O)2H3Oþ.
Keywords:
Phthalimide derivatives
Fragmentation
Mass spectrometry
Hydration
© 2019 Elsevier B.V. All rights reserved.
1. Introduction
ion sources including electron impact (EI) ionization, electrospray
ionization (ESI), photoionization, matrix-assisted laser desorption/
Phthalimide derivatives are important organic compounds
having wide applications as precursors in synthesis of many classes
of compounds including anthranilic acid, azo dyes, amines, pep-
tides, and saccharin [1e3]. Also, some phthalimide derivative have
pharmaceutical application and are used as drugs such as talme-
toprim, thalidomide, taltrimide, and amphotalide [4e6]. Also, fol-
pet and captan are two fungicides with phthalimide scaffold.
Recently, phthalimide derivatives have been introduced as anti-
cancer and antitumor drugs [7,8]. Hence, considerable efforts have
been made to synthesize and characterize the phthalimide de-
rivatives [9e12]. Several techniques including mass spectrometry
(MS), nuclear magnetic resonance (NMR), X-ray diffraction, FT-IR
and UVeVis spectroscopy have been used for characterization of
phthalimide derivatives [13e16].
ionization (MALDI), plasma ionization, and atmospheric pressure
chemical ionization (APCI) [17e20]. EI is a hard ionization tech-
nique so that it leads to fragmentation of the parent molecule,
hence, EI-MS is a useful technique for characterization of organic
compounds via identification of the fragments [21,22]. The EI-MS
determines the fragments of a molecule, however, combination of
quantum computational methods with the experimental data
provides detailed information on the structures of the studied
molecules [23,24]. Also, the theoretical methods have been used for
interpretation of effects of different parameters such as hydration
and substitution on the strength of the bonds and their cleavage in
the EI ionization source [25,26]. These studies show that hydration
changes the fragmentation patterns and can protect the clusters
from hard fragmentation.
Mass spectrometry is a useful technique for determination and
characterization of compounds which has been used with different
In this work, two symmetric bis-phthalimide derivatives are
synthesized and characterized by 1H NMR, 13C NMR and EI-MS.
Effects of hydration and structure of the fragmentation these
compounds are investigated experimentally and theoretically by
density functional theory (DFT).
* Corresponding author.
E-mail
addresses:
valadbeigi@sci.ikiu.ac.ir,
y.valadbeigi@yahoo.com
(Y. Valadbeigi).
https://doi.org/10.1016/j.molstruc.2019.127105
0022-2860/© 2019 Elsevier B.V. All rights reserved.

2
S. Yosefdad et al. / Journal of Molecular Structure 1200 (2020) 127105
Scheme 1.
White powder; yield: 0.43 g (82%); m.p. 245e247 ꢀC. 1H NMR
2. Experimental
(300 MHz, DMSO): 4.10 (2H, d, CH2), 7.71 (2H, m, ArH), 7.80 (2H, m,
ArH). 13C NMR (75.4 MHz, DMSO): 38.8, 123.3, 131.9, 134.0, 168.3. IR
(KBr) (ymax/cmꢁ1): 3274, 2062, 1631, 1200, 650. Anal. Calcd for
2.1. General
C
18H12N2O4 (320.30): C, 67.50; H, 3.78; N, 8.75. Found: C, 67.8; H,
The 1,n-diamine (GC grade: > 99%), phthalic anhydride (ACS
reagent grade: > 99%), pentane-2,4-dione (GC grade: > 99%), acetic
anhydride, triethylamine, ethanol (GC grade: > 99.5%), diethyl
ether, hexane were obtained from Merck and Aldrich and were
used without further purification. NMR spectra were recorded with
a Bruker DRX-300 Avance instrument (300 MHz for 1H and
75.4 MHz for 13C) with DMSO as solvent. Chemical shifts are given
3.5, N, 8.6.
in ppm (d) relative to internal TMS and coupling constant (J) are
reported in hertz (Hz). Melting points were measured with an
electrotherma1 9100 apparatus. Mass spectra were recorded with
an Agilent 5975C VL MSD with Triple-Axis Detector operating at an
ionization potential of 70 eV. The samples were introduced directly
to the ionization chamber. The ion source, and quadrupole tem-
peratures were set to 230 ꢀC, 150 ꢀC, respectively. The probe tem-
perature is variable depending on the melting point of samples. IR
spectra were measured with a Bruker Tensor 27 spectrometer
(Fig. S1 in Supplementary Materials). Elemental analyses for C, H
and N were performed using a PerkinElmer 2004 series [II] CHN
elemental analyzer.
(4) : 1.2.1. 2,2-(propane-1,3-diyl)bis(isoindoline-1,3-dione)
White powder; yield: 0.36 g (70%); m.p. 204e206 ꢀC. 1H NMR
3
(300 MHz, DMSO): 2.10 (2H, p, JHH ¼ 7.4 Hz, CH2), 3.78 (2H, t,
3JHH ¼ 7.4 Hz, CH2), 7.71 (2H, m, ArH), 7.80 (2H, m, ArH). 13C NMR
(75.4 MHz, DMSO): 27.6, 35.7, 123.3, 132.1, 134.0, 168.2. IR (KBr)
(
C
ymax/cmꢁ1): 2946, 1710, 1390, 1173, 1019, 720. Anal. Calcd for
19H14N2O4 (334.33): C, 68.26; H, 4.22; N, 8.38. Found: C, 68.6; H,
4.4, N, 8.2.
2.2. General procedure for the synthesis of 3
2.3. Computational details
To a solution of phthalic anhydride (1 mmol) and pentane-2,4-
dione or diethyl malonate (1 mmol) in acetic anhydride (0.56 ml)
at 25 ꢀC, triethylamine (2 mmol) was added dropwise and the
mixture stirred for 30 min. The reaction was quenched by the
addition of aqueous hydrochloric acid (2.3 ml of 1 M solution). The
resulting solid was collected by filtration, and washed with diethyl
ether (1.5 ml) and then with hexane (1.5 ml) to give 1 as colorless
crystals (Scheme 1). A mixture of diethyl-2-(3-oxo-2-isoindoline-1-
ylidene)malonate 1 (0.30 g, 1 mmol), 2-(nitromethylene)imidazo-
line 2 (1 mmol) and EtOH (5 ml) in a 50 mL flask was heated at
reflux for 3 h. After completion of the reaction [monitored by TLC
(Thin-Layer Chromatography), ethyl acetate/n-hexane, 1:1], the
reaction mixture was cooled to room temperature and the formed
solid filtered. The solid was washed with ethanol or recrystallized
from ethanol to give pure product 3 in high yield.
Structures of the neutral and cationic molecules as well as the
hydrated species were fully optimized by density functional theory
employing B3LYP functional. The basis set 6-31 þ G(d) including
diffuse and polarization functions were used for the calculations.
Also, the larger basis set 6e31þþG(d,p) was used for computing
thermodynamic data of the hydration reactions. The frequency
calculations were performed at the smae level to calculate the
thermodynamic quantities such as enthalpy (
DH) and Gibbs free
energy ( G) values of hydration. Both the vertical (VIE) and adia-
D
batic ionization energies (AIE) for the compounds 3 and 4 were
calculated at the same level of theory. In the case of VIE, the
structure of the neutral compound (M) was optimized and the
same geometry was used for its corresponding cation (Mþ). For the
AIE, the structures of both M and Mþ were optimized. The calcu-
lations in solvent (chloroform) were performed by Tomasi’s Polar-
ized Continuum Model (PCM) [27] at the same level of theory. All
calculations were carried out using Gaussian 09 software [28].
3. Result and discussion
3.1. Effect of structure on the fragmentation of 3 and 4
Fig. 1 shows the structures of the compounds 3 and 4, optimized
in gas phases. Two isomers, a and b, for each compounds were
considered. The isomers 3b and 4b are more stable in gas phase,
while the stability of the isomers 3a and 4a increases in CHCl3
(3) : 1.2.2. 2,2-(ethane-1,2-diyl)bis(isoindoline-1,3-dione)

S. Yosefdad et al. / Journal of Molecular Structure 1200 (2020) 127105
3
solvent. However, the energy difference of the isomers in both gas
phase and CHCl3 solvent is not considerable and their stabilities are
comparable.
their lone pair and accommodate the positive charge fades. We
investigated the effect of alkyl chain length on the CeC and NeC
bond lengths in different cations of phthalimide derivatives
(Fig. S7). The optimized structures of these cations show that as the
length of the alkyl chain increases the CeC bond length shortens
and the NeC bond length is elongated. From these theoretical re-
sults it is concluded that as the alkyl chain lengthens, the CeC bond
strengthen and the NeC bond is weakened. The HeCeH angles of
the middle and lateral CH2 groups of 4þ are 109.5 and 110.7ꢀ,
respectively, indicating the least changes in the nature of the bonds.
Hence, the probability of 4þ fragmentation is smaller than that of
3þ and an intense peak is observed for the intact ion of 4þ in m/z of
334. Also, the peak appeared at m/z of 335 may be attributed to the
protonated form of 4, (4 þ H)þ.
Figs. S2eS5 (Supplementary Materials) show the 1H NMR and
13C NMR spectra of the compounds 3 and 4. For comparison, the
computationally obtained NMR spectra of these compounds have
been shown in Figs. S2eS5. The experimental and theoretical NMR
spectra are in good agreement with each other.
Fig. 2 shows the EI-MS spectra of the compounds 3 and 4. The
fragmentation patterns for the compounds 3 and 4 are almost the
same, however, for the compounds 3, the molecular ion (parent
ion) peak with m/z of 320 is very small. In contrast, the MS spectra
of 4 shows a sharp peak for the parent ion, Mþ, with m/z of 334. The
calculated ionization energies for these compounds (Table S1) are
approximately equal. It seems, the number of CH2 groups between
the phthalimide moieties is responsible for different fragmentation
of the compounds 3 and 4.
Figs. 4 and 5 show the suggested paths for fragmentation of 3
and 4, respectively. The possible structural isomers of the frag-
ments have been considered and their relative stabilities have been
compared. The peaks with m/z of 146 and 147 are due to phthali-
mide fragments, C8H4NO2 and C8H5NO2, (fragments 6 and 15)
[29,30] which can be produced directly from the 4þ and 3þ,
respectively.
Beside the common fragments of 3 and 4, generally, fragmen-
tation of 4 results in fragments having an extra hydrogen atoms:
fragments with m/z of 147, 161, and 174 in the 4 spectrum versus
those with m/z of 146, 160, and 173 in the 3 spectrum. The differ-
ence is due to tautomersim or intramolecular proton transfer in the
parent cations 3þ and 4þ. Figs. 4 and 5 show that beside keto forms,
3þ and 4þ have also enolic tautomers, 3þb, 4þb, and 4þc. In the
enolic tautomers 3þb and 4þc, the NeCH bond is stronger than
NeCH2 bonds in the keto tautomers, 3þa and 4þa (the NeC bond
lengths in the keto and enol isomers have been compared Fig. S8).
Hence, the NeCH2 bond is broken more easily than NeCH bond in
all tautomers. The NeCH2 cleavage in compound 3 leads in frag-
ments 5, 6, and 7 the peaks with m/z of 173, 146, and 160 (Fig. 4)
while NeCH2 cleavage in compound 4 produces fragments 12, 15,
and 14 with m/z of 174, 147, and 161, respectively. For example, the
Fig. 3 compares the CeC and NeC bond lengths in the neutral 3
and 4 and their cationic forms, 3þ and 4þ. Ionization of 4 does not
lead in considerable change in the CeC and NeC bond lengths so
that the changes in the CeC and NeC upon ionization are 0.024 and
0.023 Å, respectively. On the other hands, ionization of 3 leads to
larger change in the CeC and NeC bond lengths, 0.091 and 0.047 Å,
respectively. The larger bond change in 3 after ionization increases
the possibility of fragmentation, hence, its parent ion peak is not
observed. In the 3þ, with two CH2 groups, the N atom donates its
lone pair to the carbons of the CH2 groups to relieve and accom-
modate some of the positive charge of C atoms. Hence, the NeC
bond become shorter and obtains a nature between single, NeC,
and double bonds, N]C. Alsoþ, the HeCeH angle change from
109.5ꢀ in neutral 3 to 113.1ꢀ in 3 . This weakens the H2CeCH2 bond
and induces its fragmentation so that an intense peak is observed in
m/z of 160 for symmetric cleavage of 3þ.
In the case of 4þ, the positive charge is distributed on the larger
number of atoms, especially on the middle CH2 group (Fig. S6 in
Supplementary Materials) and the role of N atoms for donating
Fig. 1. Optimized structures of two isomers of compounds 3 and 4 and comparison of the relative energies of the isomers in gas phase and in CHCl3 solvent. The data in parenthesis
are relative energies in CHCl3 solvent. The energies are in kJ molꢁ1
.

4
S. Yosefdad et al. / Journal of Molecular Structure 1200 (2020) 127105
Fig. 2. The MS spectra for compounds 3 and 4 recorded with EI-MS.
calculated
D
H values for formation of 5a (173) and 12a (174) form
thermodynamically more feasible.
3þb are
Both the MS spectra of 3 and 4 show a peak at m/z of 133. This
peak has been observed by other authors working on the frag-
mentation of phthalimide derivatives [30] and attributed to
methoxybenzonitrile, fragment 17e. However, we consider six
possible isomers for fragment 17 (Fig. 5) and the calculations show
that the structure 17d is the most stable isomer. Another possible
fragment with m/z of 133 is fragment 9 with two possible isomers
(Fig. 4). The fragments 9 and 17 can be produced from both the
larger fragments 7 (m/z ¼ 160) and fragment 14 (m/z ¼ 161) by loss
of HCN and CO, respectively, hence, a common peak with m/z of 133
is observed in both the spectra of 3 and 4. Although the peak with
m/z of 130 is observed in both spectra, its intensity is considerably
more in the spectrum of 4. This peak may be assigned to fragments
8 (C8H4NO) and 16 (C9H8N).
3þb / C8O2NH5 þ 5a (m/z ¼ 173),
D
H ¼ 79.0 kJ molꢁ1
(1)
(2)
3þb / C8O2NH4 þ 12a (m/z ¼ 174),
D
H ¼ 250.6 kJ molꢁ1
Comparison of the DH values reveals that formation of 5a from
3þb is thermodynamically more favored.
In the case of cation 4þ, the enolic tautomer 4þb has no strong
NeCH bond because the oxygen atom has captured the H atom of
the middle CH2. Hence, the NeC cleavage can occur simply leading
in fragments 11, 12, 13, 14, and 15 with m/z of 188, 174, 187, 161, and
147, respectively (Fig. 5). The fragment 12 can be also formed from
the fragmentation of the tautomer 4þc:
The peak with m/z of 187 is observed only in the spectrum of 4
because it is due to a phthalimide moiety bearing a C3H5 group
(fragment 13). Four possible structural isomers were considered for
fragment 13, however, the isomer with the eCH]CHeCH3 group,
13b, was more stable (Fig. 5). The peak with m/z of 104 is present in
4þc / 12a (m/z ¼ 174) þ C9O2NH6,
D
H ¼ 142.0 kJ molꢁ1
(3)
Comparison of the DH values of reactions (2) and (3) shows that,
formation of the fragment 12 (m/z ¼ 174) from 4þc is

S. Yosefdad et al. / Journal of Molecular Structure 1200 (2020) 127105
5
3.2. Effect of hydration on the fragmentation of 3 and 4
The ethanol used as solvent for synthesis of the compounds 3
and 4 contained some water impurity and also during the synthesis
some water was produced because of condensation. Fig. 6 com-
pares the MS spectra of 4 before and after drying by oven. Before
drying, the sample contains some water content and hydrated ions
can be produced.
Fig. 6 shows a peak with m/z of 388 for wet 4 which is attributed
to 4þ(H2O)3. We did not observe the mono- and di-hydrated cat-
ions, 4þ(H2O) and 4þ(H2O)2, that was strange at first. Also, the same
experiment was repeated for 3, and interestingly, the MS spectra of
the dry and wet 3 were the same so that no hydrated cation was
observed indicating that the 3þ cation is fragmented before hy-
dration or 3þ is not hydrated.
To explore these results in details, hydrations of cations 3þ and
4þ with up to 3 water molecules were studied, theoretically. Fig. 7
shows the hydrated forms of the cations 3þ and 4þ, 3þ(H2O)1-3 and
4þ(H2O)1-3, respectively, optimized by B3LYP/6-31 þ G(d) method.
The cations 3þ and 4þ are hydrated via hydrogen bonding in-
teractions between the hydrogen atoms of H2O and carbonyl oxy-
gen of 3þ and 4þ and hydrogen atoms of CH2 groups and oxygen
atom of H2O. However, the tri-hydration of 4þ is different because
the water molecules capture a hydrogen atom from a lateral CH2
group and form a hydronium ion (H2O)H3Oþ. If fact, the tri-
hydrated form of 4þ is as [(4-H)(H2O)2H3O]þ. The calculated
values of
summarized in Table 1. Although the
values show that hydration of 3þ is not thermodynamically favored
and 3þ is not hydrated. Also, comparison of the
G values for hy-
DH and
D
G for hydration of the 3þ and 4þ cations are
H values are negative, the
D
DG
D
dration of 4þ shows that mono- and di-hydration of 4þ is not
thermodynamically possible while 4þ(H2O)3 is easily produced.
The more stability of 4þ(H2O)3 cluster can be attributed to stronger
hydrogen bonding interactions in the hydronium ion, (H2O)2H3Oþ
what is absent in 4þ(H2O)1 and 4þ(H2O)2. The calculated thermo-
dynamic results are in excellent agreement with the MS spectrum
of wet 4 so that we observed only one peak with m/z of 388 for
4þ(H2O)3 and the peaks of 4þ(H2O)1 and 4þ(H2O)2 with m/z of 352
and 370, respectively, did not appear. Also, the data in Table 1 show
that 3þ is not hydrated and we observed the same spectrum pat-
terns for the wet and dry 3 (not shown).
Another structural feature of the hydrated cations is change in
the H2CeCH2 bond length of 3þ upon hydration. The CeC bond
length is elongated due to ionization from 1.54 in 3 to 1.63 Å in 3þ
(Fig. 3) and hydration elongates more the CeC bond to 1.65 Å
(Fig. 7). The effect of hydration on the CeC bond length in the 4þ
cation is negligible. Hence, hydration does not increase the frag-
mentation of 4þ. However, new peaks between the peaks 187 and
334 appear for the wet 4 indicating that hydration influences the
mechanism of fragmentation. Fig. 8 shows the proposed paths for
formation of fragments 18 and 19 with m/z of 315 and 287,
respectively, from 4þ(H2O)3. According to this suggested mecha-
nism, 4þ is tri-hydrated, 4þ(H2O)3, then the water molecules cap-
ture an H atom from 4þ to form [(4-H)(H2O)H3O]þ (Fig. 7) with m/z
of 388. During the dehydration, the complex [(4-H)(H2O)2H3O]þ
loses four water molecules instead of three water molecules to
produce fragment 18 with m/z of 315. In other words, the 4þ obtains
three H2O and loses four H2O molecules so that the primary three
water molecules can catalyze loss of an extra water molecule.
Another straightforward path is dehydration of (4-H)þ and for-
mation of (4-H3O)þ, 20, without assistance of the hydrating water
molecules. However, in both paths, presence of the hydrating water
molecules for formation of 20 with m/z of 315 is necessary. The
fragment 21 with m/z of 287 is produced from fragment 20 by loss
of a CO group. Other fragments with m/z of 268 (22) and 241 (23)
Fig. 3. Change in the CeC and NeC bond lengths in 3 and 4 compounds upon ioni-
zation. The bond lengths are in Å.
both spectra of Fig. 2 and has been reported previously for the
phthalimide derivatives [30]. This peak may due to fragment 10,
C7H4O, with two possible isomers (Fig. 4) or fragment 19, C7H6N
(Fig. 5), [31]. The optimized structures of all fragments of the
compounds 3 and 4 have been provided in Fig. S9 (Supplementary
Materials).

6
S. Yosefdad et al. / Journal of Molecular Structure 1200 (2020) 127105
Fig. 4. The proposed paths for fragmentation of 3þ in EI-MS. The bold numbers are relative energies in kJ molꢁ1
.
are formed from 21 by consecutive loss of H2O and CO. Also, the
observed peak at m/z of 342 may be due to [M-COþ2H2O]þ. The
optimized structures of the fragments 20e23 have been shown in
Fig. S10 (Supplementary Materials).
that we observed only a small peak for its molecular ion, Mþ, with
m/z of 320. In contrast, for the 4 with a longer alkyl chain,
Ne(CH2)3eN, an intense peak was observed for the molecular ion
peak at m/z of 334. These results were interpreted theoretically
using charge distribution analysis and change in the bond
strengths. Effect of hydration on the ionization and fragmentation
of 3þ and 4þ was studied and it was found that 3þ is not hydrated
and consequently hydration does not influence its fragmentation
mechanism. The MS spectra showed that 4þ is tri-hydrated,
4þ(H2O)3, and theoretical results confirmed that only tri-
hydration of 4þ is thermodynamically possible while 4þ(H2O)1
and 4þ(H2O)2 were not stable. Also, hydration of 4þ leaded to
appearance of some new peaks, hence, it was concluded that hy-
dration influences the fragmentation mechanism of 4þ. The opti-
mized structure of tri-hydrated form of 4þ revealed that the water
molecules capture one of the hydrogen atoms of CH2 group so that
4. Conclusion
The phthalimide derivatives 3 and 4 were synthesized and their
structures were characterized by 1H NMR, 13C NMR and EI-MS.
Ionization and fragmentation of 3 and 4 in electron impact ioni-
zation source were studied both experimentally by mass spec-
trometry and theoretically using DFT calculations. It was found that
fragmentation of the compounds 3 and 4 and consequently their
MS spectra patterns depend on both structure and hydration while
hydration itself depends on the structure. The molecular ion of 3
with an Ne(CH2)2eN group was almost completely decomposed so

S. Yosefdad et al. / Journal of Molecular Structure 1200 (2020) 127105
7
Fig. 5. The proposed paths for fragmentation of 4þ in EI-MS. The bold numbers are relative energies in kJ molꢁ1
.

8
S. Yosefdad et al. / Journal of Molecular Structure 1200 (2020) 127105
Fig. 6. Effect of hydration of the spectrum pattern: Comparison of the MS spectra of dry and wet 4.
Fig. 7. The optimized structures of the hydrated forms of the 3þ and 4þ cations. The bond lengths are in Å.
the final complex is as [(4-H)(H2O)2H3O]þ. The appearance of the
new peaks in MS spectrum of wet 4 was attributed to hydrogen
abstraction from 4þ by the water molecules.

S. Yosefdad et al. / Journal of Molecular Structure 1200 (2020) 127105
9
Table 1
The H and D
G values for hydration of the 3þ and 4þ cations in gas phase at 298 K,
Appendix A. Supplementary data
D
calculated at B3LYP/6-31 þ G(d) level. The data in parenthesis have been calculated
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molstruc.2019.127105.
using 6e31þþG(d,p) basis set.
Hydration
D
H (kJ molꢁ1
)
D )
G (kJ molꢁ1
3þ þ H2O / 3þ(H2O)
ꢁ32.9 (ꢁ31.3)
ꢁ36.2 (ꢁ30.7)
ꢁ30.1 (ꢁ31.8)
ꢁ29.3 (ꢁ28.6)
ꢁ37.6 (ꢁ35.9)
ꢁ106.0 (ꢁ119.1)
6.4 (8.5)
5.2 (5.2)
7.7 (8.7)
8.5 (9.0)
ꢁ0.9 (ꢁ0.2)
References
3þ(H2O) þ H2O / 3þ(H2O)2
3þ(H2O)2 þ H2O / 3þ(H2O)3
4þ þ H2O / 4þ(H2O)
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4þ(H2O) þ H2O / 4(H2O)2
4þ(H2O)2 þ H2O / 4þ(H2O)3
ꢁ49.5 (ꢁ62.6)
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