The molecular structure of pyrazine as determined from gas-phase electron diffraction data

The structure of pyrazine (1,4 diazabenzene, C4H4N4) has been determined at 333 K by means of gas-phase electron diffraction. The r g parameters are as follows: r(C-C) = 1.339 ± 0.002 Å. r(C-N) = 1.403 ± 0.004 Å, r(C-H) = 1.115 ± 0.004 Å. C-C-N = 115.6 ± 0.4°, and C-C-H = 123.9 ± 0.6° (error limits are 2.5σ). At a 10% level the rα structure does not differ significantly from the structure in the solid state, so long as high order X-ray, results corrected for librational motion are used; otherwise significantly different results are found even at the 1% level. Calculated and observed mean square amplitudes compare favourably.