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organic compounds
The crystal structures of 4-methyl-4H-1,2,4-triazole, C3H5N3, and 1-methyl1H-tetrazole, C2H4N4, are composed of layers of planar molecules with partially delocalized π systems. Differences in the bond lengths in these two closely related ring systems are ascribed to differing π-electron polarization effects, which are analysed with reference to ab initio calculations performed using a triple zeta + polarization basis set at both the SCF and MP2 levels of theory.