Conformational properties and photochemistry of new allyl tetrazoles: Matrix isolation FTIR and computational approach

The photochemistry and molecular structure of 1-allyltetrazole (1-ALT) and 2-allyltetrazole (2-ALT) were studied in argon matrices by infrared spectroscopy and B3LYP/6-311++G(2d,2p) calculations. Both allyltetrazoles were found to possess three stable conformers (1-ALT1, 1-ALT2, 1-ALT3 and 2-ALT1, 2-ALT2, 2-ALT3) differing in the orientation of the allyl group relative to the ring. Matrix isolation technique together with the annealing experiments allowed for detection of all 1-ALT and 2-ALT conformers. A conformational cooling phenomenon was observed for the 1-ALT3 → 1-ALT1 process in agreement with the predicted low energy barrier of 4.84 kJ mol−1 for this reaction. The broad-band UV irradiation of 1-ALT/Ar and 2-ALT/Ar matrices led to the same photoproducts. The main product N-allylcarbodiimide (P1) and two minor photoproducts allylcyanamide (P2) and C-allylnitrilimine (P3) are formed through the tetrazole ring cleavage and N2 elimination. None of these molecules have been described before.

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► Theoretical and spectroscopic characterization of allyl tetrazoles.
► Three conformers of 1-ALT and 2-ALT trapped in solid argon environment.
► Conformational cooling phenomenon for 1-ALT3 → 1-ALT1.
► N-allylcarbodiimide molecule as the main product of allyl tetrazoles photolysis.