Journal of Molecular Structure, 82 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGF (1982) 277-282 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands ELECTRONIC STRUCTURE OF IMDES BY UV PHOTOELECTRON SPECTROSCOPY AND INDO/S CALCULATIONS: HYDANTOIN AND URAZOLE DAVID AJG and MAURIZIO CASARIN Istituto di Chimica e Tecnologia dei Radioelementi dcl C.N.R.. Corso Stati Uniti, 36100 Padoua (Italy) GAETANO GRANOZZI, ALBINO POLI and EUGENIO TONDELLO Istituto di Chimica Generale ed Inorganica dell’l/niuersilti, Via Loredan 4, 35100 Padoua (Italy) (Received 18 January 1982) ABSTRACT He(I) excited photoelectron spectra of hydantoin, l-methylhydantoin and urazole are presented and discussed. The spectra are assigned by comparison with the spectrum of succinimide and by INDO/S calculations. The electronic structure of the imido group of succinimide is not substantially perturbed by the replacement of one or two CH, groups by NH groups. The HOMO is mainly localized on the additional nitrogen atoms in both the title compounds. INTRODUCTION A deeper understanding of the chemical and biological properties zyxwvutsrqponmlkjihg of organic molecules can be gained by studying their electronic structure. For this purpose, quantum mechanical calculations have been widely used in the past, while more recently gas-phase UV photoelectron (PE) spectroscopy has been applied to biological molecules and related organic systems. Hydantoin (2,4-imidazolidinedione) and its derivatives are of biological interest because of their pharmacological activity [ 11 and their structural analogy with nucleic acid bases and peptide units. Urazole (1,2,4-triazolidine- 3,5dione) and its derivatives, besides their biological uses [2, 31 , are impor- tant intermediates in the reactions of the extremely reactive dienophiles [ 41 . The PE and quantum mechanical results reported in this paper form part of a systematic investigation [ 5-91 into the electronic structure of the N- substituted amides and, in particular, imidic systems. The simplest compound in the series of five-membered cyclic imides, succinimide, was previously studied by several authors [g-11] _ Assignment of the ionization events peculiar to the imide group was supported by analysis of the spectrum of the N-methyl derivative [ 91. N-Methyl substitution pro- duces different effects on the nitrogen 71 and n, oxygen lone-pair MOs, thus 0022-2860/82/0000-0000/$02.75 o 1982 Elsevier Scientific Publishing Company