Photochemistry and Vibrational Spectra of Matrix-Isolated 5-Ethoxy-1-Phenyl-1H-Tetrazole

Abstract

A combined matrix isolation FT-IR and theoretical DFT(B3LYP)/6-311++G(d,p) study of the molecular structure and photochemistry of 5-ethoxy-1-phenyl-1H-tetrazole (5EPT) was performed. A new method of synthesis of the compound is described. Calculations show three minima, very close in energy and separated by low-energy barriers (less than 4 kJ mol -1 ), in the ground-state potential energy profile of the molecule. The method of matrix isolation enabled the reduction of the number of populated conformational states in the experiment at low temperature due to the effect known as conformational cooling. As a result, the spectrum of the as-deposited matrix of 5EPT closely matches that of the most stable conformer predicted theoretically, pointing to the existence of only this conformer in the low-temperature matrixes. In this structure, the dihedral angle between the two rings, phenyl and tetrazole, is ca. 30°, whereas the ethyl group stays nearly in the plane of the tetrazole ring and is as far as possible from the phenyl group. In situ UV irradiation (λ > 235 nm) of the matrix-isolated 5EPT induced unimolecular decomposition, which led mainly to production of ethylcyanate and phenylazide, this later compound further reacting to yield, as final product, 1-aza-1,2,4,6-cycloheptatetraene. Anti-aromatic 3-ethoxy-1-phenyl-1H-diazirene was also observed experimentally as minor photoproduct, resulting from direct extrusion of molecular nitrogen from 5EPT. This species has not been described before and is now characterized by infrared spectroscopy for the first time.

Structure, vibrational spectroscopy, and photochemistry of 5-phenoxy-1-phenyltetrazole in argon and nitrogen cryomatrices

“…In agreement with the spectral data previously obtained for 5MPT and 5EPT, 39,40 the IR spectrum of 5PPT may be considered as formed by three groups of bands associated respectively with the vibrational modes of the phenyl group, tetrazolyl ring, and phenoxyl substituent. The bands comprised in the first group appear in the spectrum of 5PPT at nearly the same frequencies observed for 5MPT 39 and 5EPT.…”

“…The calculated bond lengths and angles around the central ether linkage in 5PPT are compared with corresponding data previously obtained by our groups for 5-methoxy-1-phenyltetrazole (5MPT) 39 and 5-ethoxy-1-phenyltetrazole (5EPT) 40 (Table 1). In all of these compounds, the tetrazole ring and the heavy atom skeleton of the second ether substituent are preferentially oriented in a near coplanar fashion, with the latter pointing in the opposite direction relatively to the phenyl substituent of the tetrazole (C a -O-C-N(Ph)).…”

Tautomer Selective Photochemistry in 1-(Tetrazol-5-yl)ethanol

“…Under identical experimental conditions to those used in the present study, all tetrazole derivatives we studied previously were found to react extensively in a few minutes. [22][23][24][25] In this regard, the observed ring-opening reaction in 1-TE is slower, with only about 50% of the reactive tautomer initially present being consumed after 8 h of irradiation. The reasons for the relatively inefficiency of the photochemical process as well as its tautomer selectivity must then be related with the characteristics of the substituent present in the tetrazole ring.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] From a fundamental point of view, tetrazoles are also particularly interesting systems, especially because of the tautomerism they may exhibit and their diversified photochemistry. 1,[21][22][23][24][25][26][27][28][29] Unsubstituted tetrazole, for example, was found to exist exclusively in the crystalline phases as the 1H-tautomer, [30][31][32] whereas in solution and gas phase 1H-and 2H-tautomers coexist, the population of the most polar 1H form increasing with the polarity of the solvent. 21,[33][34][35][36][37] According to the experimental findings, 2H-tetrazole was found to be the lowest energy tautomer in media with a dielectric constant smaller than about 7, while in media with a larger dielectric constant, a reversal of energy takes place and 1H-tetrazole becomes the tautomeric ground state.…”

Photochemistry of 1-allyl-4-aryltetrazolones in solution; structural effects on photoproduct selectivity

“…Azides, isocyanates or aziridines are generally obtained, but the presence of labile hydrogen atoms, either directly linked to the tetrazole ring or in substituent groups, may open additional photocleavage pathways or allow for secondary photochemical reactions to take place concomitantly with the main primary photoprocesses. [4][5][6][7][8][20][21][22][23][24][25][26] The photochemistry of tetrazoles is also influenced by the chemical nature and conformational flexibility of substituents linked to the heterocycle, which may favor or exclude certain reaction channels, [9][10][11][12][13][14] determining the nature and relative amount of the final photoproducts.…”