Study of selected benzyl azides by UV photoelectron spectroscopy and mass spectrometry R.M. Pinto a , R.I. Olariu b , J. Lameiras c , F.T. Martins c,1 , A.A. Dias a , G.J. Langley d , P. Rodrigues e , C.D. Maycock e,f , J.P. Santos a , M.F. Duarte c , M.T. Fernandez c , M.L. Costa a, * a CFA, Centro de Física Atómica, Departamento de Física, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal b Department of Analytical Chemistry, ‘‘Al. I. Cuza” University of Iasi, 11 Carol I Bd., 700506 Iasi, Romania c CQB, Centro de Química e Bioquímica, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal d School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK e ITQB, Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apartado 127, 2780-901 Oeiras, Portugal f Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal article info Article history: Received 30 April 2010 Received in revised form 7 July 2010 Accepted 8 July 2010 Available online 14 July 2010 Keywords: Benzyl azides UVPES EIMS IRC calculations abstract Benzyl azide and the three methylbenzyl azides were synthesized and characterized by mass spectrom- etry (MS) and ultraviolet photoelectron spectroscopy (UVPES). The electron ionization fragmentation mechanisms for benzyl azide and their methyl derivatives were studied by accurate mass measurements and linked scans at constant B/E. For benzyl azide, in order to clarify the fragmentation mechanism, label- ling experiments were performed. From the mass analysis of methylbenzyl azides isomers it was possible to differentiate the isomers ortho, meta and para. The abundance and nature of the ions resulting from the molecular ion fragmentation, for the three distinct isomers of substituted benzyl azides, were rational- ized in terms of the electronic properties of the substituent. Concerning the para-isomer, IRC calculations were performed at UHF/6-31G(d) level. The photoionization study of benzyl azide, with He(I) radiation, revealed five bands in the 8–21 eV ionization energies region. From every photoelectron spectrum of methylbenzyl azides isomers it has been identified seven bands, on the same range as the benzyl azide. Interpretation of the photoelectron spectra was accomplished applying Koopmans’ theorem to the SCF orbital energies obtained at HF/6-311++G(d, p) level. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Phenyl azide prepared in the nineteenth century was the first synthetic organic azide [1]. Since then the application of organic azides, in science and technology, has grown dramatically [1–3]. Organic azides have been largely used as precursors for synthesis [1–3], for amines and recently in ‘‘click” chemistry [4–7]. This concept has, recently, emerged [4] exploiting rapid, modular reac- tions developing under a large thermodynamic driving force. The resulting synthetic products have been applied in areas such as supramolecular chemistry [5], biochemistry [6] and in developing compounds relevant for antiviral and anticancer treatment [7]. On the other hand, azidonucleosides showed to be of primordial interest in AIDS treatment [2,8], azido sugars in biological label- ling [9] and in tumor-growth inhibition [10]. Moreover, azides are potential high-energy density materials (HEDMs) [11] and are also used in the generation of electrically conducting poly- mers [12] and in the covalent modification of polymer surfaces [13]. Due to their thermodynamic instability, explosive nature and shock sensitivity [11], their structural characterization is experi- mentally challenging. However, the physico-chemical properties of some aliphatic azides have been investigated spectroscopically by ultraviolet photoelectron spectroscopy (UVPES) and matrix isolation infrared spectroscopy (MIIS) [14–16]. Electron ioniza- tion mass spectrometry (EIMS) has been successfully applied to the study of phenyl azides and its derivatives [17]. Some azides, already studied by UVPES and MIIS were also investigated by EIMS [18,19] and chemical ionization mass spectrometry (CIMS) [20]. At present very little is known about the fate of organic azides involving an aromatic ring such as benzyl azide. Thus, benzyl azide and three methylated isomers were synthesized and characterized in terms of electronic configuration and ionization energies, using mass spectrometry and UV photoelectron spectroscopy. 0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2010.07.009 * Corresponding author. E-mail address: mllc@fct.unl.pt (M.L. Costa). 1 Present address: Wellcome Trust Clinical Research Facility, C Level West Wing, Southampton General Hospital, Tremona Road, SO16 6YD Southampton, UK. Journal of Molecular Structure 980 (2010) 163–171 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc