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Jelena-Hadži-Đorđević 1 Isidora Cekić-Lasković 1, 3 Rade Marković 2, 3 Aleksandar Rašović 3 Dragica Minić 1, 3 1 Faculty of Physical Chemistry, University.

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Presentation on theme: "Jelena-Hadži-Đorđević 1 Isidora Cekić-Lasković 1, 3 Rade Marković 2, 3 Aleksandar Rašović 3 Dragica Minić 1, 3 1 Faculty of Physical Chemistry, University."— Presentation transcript:

1 Jelena-Hadži-Đorđević 1 Isidora Cekić-Lasković 1, 3 Rade Marković 2, 3 Aleksandar Rašović 3 Dragica Minić 1, 3 1 Faculty of Physical Chemistry, University of Belgrade, Serbia 2 Faculty of Chemistry, University of Belgrade, Serbia, 3 Institute of Chemistry, Technology and Metallurgy, Belgrade, Serbia References 1. A. Rašović, P. J. Steel, E. Kleinpeter, R. Marković, Tetrahedron, 63, (2007), R. Marković, A. Shirazi, Z. Džambaski, M. Baranac, D. Minić, J. Phys. Org. Chem., 17, (2004), R. Marković, M. Baranac, Z. Džambaski, M. Stojanović, P. J. Steel, Tetrahedron, 59, (2003), E. Kleinpeter, K. Rasch, W.- D.Ridolf, J. Schmidt, Journal f. Prakt. Chemie,333, (1991), O. Martiskainen, K. Sztanke, D.Matosiuk, K. Pihlaja, Rapid Commun. Mass Spectrom., 20, (2006), V. V. Ovcharenko, R. A. Shaikhutdinov, K. Pihlaja, G. Stájer, J Am Soc Mass Spectrum, 12, (2001), 1011 Acknowledgment Jelena Hadži-Đorđević would like to acknowledge the support and friendship of Professor Einar Uggerud and Mass Spectrometry Group, University of Oslo during her stay in their Institute where MS measurements were done. MASS-SPECTROMETRIC DIFFERENTATION OF SULFUR CONTAINING, ELECTRON-RICH HETEROCYCLES Selected, highly delocalized 2-alkylidene-4-oxothiazolidines, 1,2-trithiaazapentalenes and 1,3-thiazines, exemplified by general structures 1, 2 and 3, respectively, have received considerable synthetic attention as model compounds for studying electronic materials based on organic matter. The mass spectrometry behavior of these compounds, which exhibit in most cases a high-intensity molecular ion peak, depends on the nature of the heterocyclic ring, and position of the substituents within specific ring system. In terms of the characterization, a good correlation between the structure and the fragmentation pathways investigated under EI and CI conditions, was established for all three classes of heterocyclic compounds. The mass spectrometry results will be presented with respect to the spectroscopic and electronic properties of the materials 1-3 which were studied previously via UV-Visible spectroscopy and cyclic voltammetry. Over the last few years we have reported that push-pull 2-alkydene-4-oxothiayolidines of the general structure 1, containing the cisconfigured –S-C=C-C=O moiety, participate in a number of reactions through activation of the nucleophilic α-carbon atom of the exocylcic C=C bond. We anticipated that the 1,5-type SO close contact, in combination with rigid and flat 4-oxothiazolidine ring conjugated with the C side chain, can be electronically tuned to induce specific chemical transformation of substrates 1. It has been confirmed experimentally by a ring-opening-closing transformation of selected 4-oxothiazolidine enaminoketones 1 in the presence of Lawessons reagent (LR), to produce functionalized 1,2-dithiole-3-ylidene thiones. The mass spectra were recorded on a VG ProSpec Q mass spectrometar (Manchester, UK) equipped with OPUS data acquisition software. In the EI mode the samples were introduced using direct inlet probe at ambient temperatures. The ionization energy of 70 eV and trap current of 200 μA were used for producing positive ions. Basic spectra were obtained at a resolving power of Accurate mass measurements were determined at a resolving power at (10% valley definition) using perfluorkerosen (PFK) as a reference compound. CI spectra were recorded on the same instrument under the following operating conditions: Methane was used as reagent gas and its pressure in the inner source was maintained at mbar. Samples were introduced with a direct inlet probe. The elemental compositions and routes of the fragmentation processes were confirmed by accurate mass measurements and metastable ion spectra. Accurate mass measurement. Measured accurate masses agree well with the accurate mass of elemental compositions, determined within an average accuracy of 0,5 ppm. Fig.1 EI mass spectra of compounds 1, 4 and 6 Fig.2 CI mass specrta of compounds 1, 4 and 6 Fig 3. Cyclic voltammograms of compounds 1a, 1b and 1c in 0.1 M TBAHF 6 + CH 3 CN, sweep rate 100mV/s, concentration 4 mM. Insert cyclovoltammogram of Pt working electrode in basic electrolyte, same sweep rate In the EI spectrum, we observed the molecular ions as a most abundant ions. The appearance of the strong molecular ions and the most significant peaks at m/z 232, 128, 105, 77 and 55 in all the spectra can be rationalized by the most analogous fragmentation processes for compounds 1 an 2. The examination of the mass spectra of all the samples shows presence of a peak at m/z 87, corresponding to the fragment with the composition C4H7O2. This fragment is obviously formed by the loss of CH 2 COOC 2 H 5 from the molecular ion of the 4-oxothiazolidine. The fragmentation in compound 1 is observed at m/z 305, and this is the base peak. We observed some isotopic peaks at m/z 306, 307, 308. The observed ratio agrees well with calculated ratio. Peak at m/z 260 is due to the loss of C 2 H 5 O, and resulting ion is a acylium ion. This ion is produced by an α-cleavage at the ester-carbonyl group. Peak at m/z 232 is due to the loss of C 2 H 5 OCO from the molecular ion by an α-cleavage. Peak at 105 is widely observed in compounds which have carbonyl group, and peak at m/z 77 is phenyl cation. In the CI spectrum, reagent gas CH 4, an intense peak due to MH + at m/z 306 was observed. The isotopic distribution is nearly the same as the calculated ratio. The ion at 305 is produced by electron ionization. Observed fragment ions would mainly come from 305. The internal energy of m/z 305 ions is lower than that in EI conditions because of collisions with CH 4. Thus the intensity distribution of fragment ions would be different from those in the EI spectrum, even if all the fragment ions come from m/z 305. Ions at m/z 320 and m/z 334 indicate that these ions are produced by some ion-molecule reactions. Cyclic voltammetry (CV) was performed on a CHI760b Electrochemistry workstation (CHI Instrument CO., USA) using one-compartment electrolytic cell (volumetric capacity 10 ml) with a three- electrode configuration. A platinum disc (2.0 mm diameter, CH Instruments, Inc.) and a platinum flag wire were used as the working and the counter electrode, respectively. The working electrode was mechanically refreshed with emery paper of decreasing grain size, polished with alumina (0.5 particle size) and cleaned in 18 M water in an ultrasonic bath. For each experiment, the electrode prepared was first examined in basic electrolyte by CV before the substance was added in the solution A silver wire in 0.01M AgNO 3 solution of TBAHF 6 in acetonitrile (anhydrous) served as a non- aqueous reference electrode which was separated from the rest solution by a fine glass frit. Measurements were performed in predried solution of 4mM selected 2-alkylidene-4-oxothiazolidines, 1,2- trithiaazapentalenes and 1,3-thiazines in 0.1 M TBAHF 6 in acetonitrile at a sweep rate of 100 mV/s in the potential range from -2 to 2 V. As shown on Figure 3, the different electrochemical processes were identified on the basis of the cyclic voltammograms, recorded by changing the direction of the polarisation potential. All three compounds undergo irreversible reduction and oxidation processes involving chemical step. M+M+ M C 2 H 5 -C 2 H 5 O M M M M H M CO -C 2 H 5 O CO+O+ + M M M C 2 H 5 -HS C 2 H 5 O+CO HCS M M M M+M+ M M CH 3 -C 2 H 5 -CH 3 CH 2 CH - CH 3 CH 2 CHNH - CH 3 CH 2 CHN MH + M+M+ M + +C 2 H 5 M + +CH 3 M C 2 H 5 O -CO -C 2 H 5 O M M CO+O+ M+M+ MH + M + +C 2 H 5 M + -C 2 H 5 M + -HS C 2 H 5 O+CO M+M+ MH + M + -C 2 H 5 M + -CH 3 M + +C 2 H 5 M + -CH 3 CH 2 CH M + -CH 3 CH 2 CHN M M + -90


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