A correlation of substituent effects with the acidity of aromatic tetrazolic acids

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

“…Considering the minimum energy structure of 5EPT (conformer T in Figure 1), it can be easily verified that the molecule assumes a geometry in which the ethyl group stays nearly in the plane of the tetrazole ring and is situated as far as possible from the phenyl group (C (5) …”

“…29,32,[51][52][53][54][55][56][57][58] For instance, it is known that the chlorine substituent in 5-chloro-1-phenyl-1H-tetrazole (5CPT) is responsible for the large inter-ring angle (54°) observed for this tetrazole derivative. 31 Hence, the steric effect due to the presence of the chloro substituent at C (5) in the 5CPT molecule is clearly more important than the corresponding effect caused by the ethoxy group attached to the same position in 5EPT (inter-ring angle; 30°). In addition, the inter-ring dihedral angle in 5-methoxy-1-phenyl-1H-tetrazole was found to be 29°, 29 i.e., smaller than in 5CPT and similar to that found for all 5EPT low energy conformers (see Table S1), indicating that in the experimentally relevant conformers of these molecules (all exhibiting the trans arrangement around the -C (5) -O (17) -axis) the orientation of the ethyl substituent does not influence the interaction between the two rings.…”

“…23 The proposed reaction pathways resulting from irradiation of 5EPT are schematically shown in Scheme 1, and the complete list of bands due to the products of photolysis is presented in Tables 2 and 3. The observed photochemistry of 5EPT shows two major reaction pathways: (1) cleavage of the tetrazole ring through the C (5) -N (1) and N (3) -N (4) bonds, with production of phenylazide and ethylcyanate as primary photoproducts (phenylazide can then undergo further reactions to give 1-aza-1,2,4,6-cycloheptatetraene, ACHT), and (2) cleavage of the N (1) -N (2) and N (3) -N (4) bonds, with molecular nitrogen elimination, leading to formation of the antiaromatic 3-ethoxy-1-phenyl-1H-diazirene (EPD). Both observed photoprocesses imply cleavage of the N (3) -N (4) bond.…”

“…Both observed photoprocesses imply cleavage of the N (3) -N (4) bond. The first one also implies disruption of the C (5) -N (1) bond, while the second one requires cleavage of the N (1) -N (2) bond. These are the three formally single bonds in the tetrazole ring, with calculated lengths longer than 135.7 pm (Table S1, Supporting Information).…”

“…These are the three formally single bonds in the tetrazole ring, with calculated lengths longer than 135.7 pm (Table S1, Supporting Information). The N (2) -N (3) and C (5) -N (4) bonds are considerably shorter (128.0 and 131.4 pm, respectively, as calculated at the DFT(B3LYP)/6-311++G(d,p) level of theory), and represent the two double bonds of the tetrazolic system. Thus, the bonds that undergo cleavage in the photoreactions correspond to the tetrazole ring's weakest bonds.…”