The molecular structure and barrier to internal rotation of p-bromonitrobenzene, determined by gas-phase electron diffraction

Abstract

The molecular structure of gaseous p-bromonitrobenzene has been studied by the electron diffraction method. The torsion of the nitro group has been treated as a large-amplitude motion, and the barrier to internal rotation was found to be 4.2(8) kcal mol −1. The angular distortion of the benzene ring mainly affects the internal angles ∠ αCC BrC = 122.6(2)° and ∠ αCC NO2 C = 121.6(2)° which, as expected for electronegative substituents, are significantly larger than 120°. The other geometrical parameters are: r a(NO) = 1.239(2) Å, r a(CN) = 1.454(4) Å, r a(CBr) = 1.896(2) Å, r a(C 1C 2) = 1.393(4) Å, r a(C 2C 3) = 1.402(4) Å, r a(C 3C 4) = 1.395(3) Å, r a(CH) = 1.095(7) Å, ∠ αCNO = 117.5(2)°. Values in parentheses are one standard deviation from the least-squares refinement using a diagonal weight matrix.