Infrared absorption spectra of 2-oxo-1,3-bis-(phenylhydrazono) derivatives and related bis- and tris-phenylhydrazones

Abstract

The infrared absorpti on spectra of six 2-oxo-l ,3-bis(ph e nylh ydrazon es), four tris(ph e nylhydra-zon es), and six related mon o-a nd bis-(phe nylhydra zo no) de rivativ es are prese nted_ ror compa ri son , partia l spec tra of te n selec ted a romati c azo co mpound s a re al so give n a nd di sc ussed_ The importa nt feature s of the absorption bands ari sin g from th e N = N (1579 to 1558 em-I and 1447 to 1408 e m-I), N-H (bending) (1557 to 1515 e m-I) , and Ph-N (1163 to 1123 em-I) groups are presented and discussed_ Key Words: Absorption spectra, infrared spec tra , mono-, bis-, and tris-(phenylhydrazones), phe nylazo compounds 1. Purpose and Scope of the Study The main objective of the present study was to , record the infrared absorption spectra of selected, characteristic members of a group of 2-oxo-l ,3-bis(phenylhydrazono) derivatives. These compounds have attracted interest because of their unique structure, in which an electrophilic oxo group is in proximity to two phenylhydrazono groups_ Interaction of these groups can give rise to tautomeric phenylhydrazono-phenylazo structures, and the expected N = N vibration frequencies in the compound formed are of particular interest. As is known [1,2],1 the N = N vibration frequencies of aromatic and aliphatic azo compounds are difficult to recognize , and therefore they have been the least studied. In this report, complete spectra are recorded for six 2-oxo-l , 3-bis(phenylhydrazono) derivatives ; also spectra of ten selected aromatic azo compounds are presented. 2. Compounds Investigated Table 1 lists the compounds studied, their melting points , pertinent references, and an index to the spectrograms; the serial number of a compound is the same as the number of its spectrogram. I Fi gures in brac ke ts indicat e th e lit e rature re fe re nces at th e e nd of this paper. The ref-e re nces for tabl e I are give n at th e e nd of th e table. Spectra were measured in the region of 4000 to 667 cm-I for compounds I-XVI , and in the region of 400 to 1300 cm-t for compounds XVII-XXVI. The spectrograms of compounds I-XVI, XVIII, and XXI are given in figures 1 and 2, respectively. 3. Structure of 2-0xo-l,3-bis(phenylhydra-zono) Derivatives and Related Mono-, Bis-, and Tris-(phenylhydrazones) The structures of the 2-oxo-l,3-bis(phenylhydra-zono) derivatives , compounds I to VI , have recently been established [3] [4]. A typical new representation of the str~cture of compound I, as shown elsewhere [3], is depicted in formula Ia. The conventional structure I , having a free C = 0 group, has been found to exist as the resonance-stabilized, enolic phenylhydrazono-phenylazo structure Ia. Although, for simplicity of representation, conventional car-boxyl structures are shown with spectrograms 1-6, ~ OH N_N~Ph H H H r/