Proximate,syn-Periplanar Bisdiazene Skeletons: Syntheses, Structures, Homoconjugate Reactivity and Photochemistry

Abstract

Rigid NN/NN (diazene/diazene) systems (F) consisting of more or less alkylated DBH and DBO chromophoric units (1, 2, X‐ray structures), with very short π,π distances [d = 2.849 (1a, av.), 2.822 Å (2)] and almost perfect syn‐periplanar π,π alignments [ω = 168.6 (1a), 174.2° (2)] as well as the more flexible, less “proximate” metathesis isomers (3a,c, 27a,c, d >4.6 Å, ω = 90‐100°) have been synthesized. Homoconjugate π,π interaction (in 1, 2, not in 3, 27) is deduced from UV spectroscopic measurements [π → π* maxima at 239 (234) nm (sh, 260)], while PE analyses furnished only small interaction parameters (1a: <0.3 eV). The potential of the novel syn‐periplanar NN/NN motif in 1 and 2 for the synthesis of somewhat exotic polyheterocycles has been explored by calculation (B3LYP) as well as experimentally: i.a. kinetically stabilized, all‐cis‐peralkylated tetrazolidines (38, 44) and perhydro‐1,2,4,5‐tetrazines (41, 47) have become accessible (i.a. via novel azomethine/diazene and azomethine/azomethine cycloadditions). In 1a with its unreactive DBO chromophoric subunits, in the “buttressed” derivatives 1b‐d, as well as in the DBH/DBO combination 2, and likewise in more ‘distant’ 27 (differently from the analogous CC/CC and NN/CC systems), irrespective of the excitation conditions employed (light of λ ≥≥ 280, 254 nm, low temperature matrix irradiation, acetone sensitization) no [2+2]photocycloaddition was observed. Instead exclusively N2‐elimination took place. It is argued that unproductive NN/NN photocycloaddition would have become observable through metathesis isomerization of the respective tetrazetidines.

Theoretical and Experimental Vibrational Characterization of Biologically Active Nd(III) Complex

“…In our IR spectra ( Figure 2 ), one very strong band can be observed in this region (at 1712 cm −1 for orotic acid), which was assigned to the C=O stretching modes. In the same region we observed one medium band at 1713 cm −1 in the Raman spectrum of the free ligand, and two shoulders at 1743 and 1728 cm −1 in the Raman spectrum of the complex ( Figure 3 ) [ 27 , 30 , 31 , 32 , 33 ]. According to theoretical data shown in Table 2 , these vibrations can safely be assigned to the C=O stretching modes of carbonyl groups.…”

New samarium(III) complex of 5‐aminoorotic acid with antioxidant activity

“…The vibrational fundamentals of the FT‐IR and Raman spectra, presented in Figs. and , were analysed by comparing these modes with those from the literature and in combination with the results of our DFT calculations (i.e. harmonic vibrational wavenumbers and their Raman scattering activities) .…”

“…In contrast, the C4O4 moiety is nearer to the NH 2 group, and due to intramolecular contact between both, the NH and C4O4 bonds appear slightly lengthened . The dimer form is best characterized by the Raman bands in the 1640–1680 cm −1 range and by FT‐IR bands around 1290 cm −1 and between 1440 and 1395 cm −1 (CO stretching mode) (Figs. and ; Table ) .…”

Theoretical and spectroscopic studies of new lanthanum(III) complex of orotic acid

“…3). The dimer form is best characterized by the Raman band in the 1680-1640 cm À1 range [84][85][86] and by two IR bands: at about 1290 cm À1 (in plane C-O-H bending mode) and somewhat weaker band, which is seen at 1440-1395 cm À1 (C-O stretching mode) (Figs. 3 and 4; Table 3) [87,88].…”