Quantum chemical studies of azoles: 11. Transition states in the routes of electrophilic substitution in 2H-tetrazole via the elimination—addition mechanism without preliminary formation of N-protonated azolium salts

• Published in: Russian chemical bulletin 2017-06, Vol.66 (6), p.941-945
• Main Authors: Chuvylkin, N. D., Subbotin, A. N., Belov, S. A., Belen´kii, L. I.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Full Articles; Inorganic Chemistry; Organic Chemistry
• ISSN: 1066-5285; 1573-9171
• DOI: 10.1007/s11172-017-1835-3

The results of theoretical search for model transition states of the electrophilic substitution reaction in 2 H -tetrazole ( 1 ) without the preliminary formation of N -protonated azolium salts are presented for two routes that were previously suggested by the authors and thermodynamically investigated: A , the attack of molecule 1 by the nucleophile (HO – (aq)) to form the anion to which the electrophile H 3 O + (aq)) is added and B , the attack of molecule 1 by the same electrophile followed by the addition of the same nucleophile to the specifically solvated protonated species formed in the preceding reaction step. The calculations were performed using the DFT/B3LYP/6-31G(d) method and the scanning procedure of the potential energy surface (PES). Both steps of route A turned out to be nearly barrierless, while in route B only its first step is barrierless and the second one is conjugated with passing an activation barrier of ∼45 kcal mol –1 between non-interacting or weakly interacting reactants and electrophilic substitution products. Unlike the specifically solvated protonated species of 1 H -tetrazole in an aqueous solution, a similar species of 2 H -tetrazole does not form a prereaction complex with the attacking nucleophile (HO – (aq)) and the five-membered ring is destroyed in fact in the nitrogen-containing reaction product formed after passing the activation barrier. The optimized structure of the transition state differs strongly from the nitrogen-containing structure of the reaction product with the destroyed ring, which was found by scanning of the PES.