The crystal and molecular structures of 4,6‐diethoxy‐1‐ethylpyrimidinium tetrafluoroborate and 6‐ethoxy‐1,3‐diethyl‐1,4(3,4)‐dihydro‐4‐oxopyrimidinium tetrafluoroborate, two isomeric reaction products of 4,6‐diethoxypyrimidine with Meerwein reagent

The crystal and molecular structures of two isomeric compounds, 4,6-diethoxy-1-ethylpyrimidinium tetrafluoroborate and 6-ethoxy-1,3-diethyl-1,4(3,4)-dihydro-4-oxopyrimidinium tetrafluoroborate, reaction products of 4,6-diethoxypyrimidine with Meerwein reagent [O(C2H5)+3 BF−4], have been determined by means of X-ray diffraction. 4,6-Diethoxy-1-ethylpyrimidinium tetrafluoroborate is monoclinic a = 10.794, b = 13.361, c = 10.892 A, β = 112.6°, space group P21/n, four molecules per unit cell. 6-Ethoxy-1,3-diethyl-1,4(3,4)-dihydro-4-oxopyrimidinium tetrafluoroborate is monoclinic, a = 17.637, b = 14.054, c = 11.501 A, β = 101.7°, space group C2/c, eight molecules per unit cell. In both structures the fluoroborate ions are disordered. The bond distances in the π-electron systems are reasonably well described in terms of a small number of resonance structures.