Internal rotation and equilibrium structure of 2-chloro-3-nitrothiophene from gas electron diffraction and quantum chemistry

Abstract

The equilibrium structure of the 2-chloro-3-nitrothiophene molecule and the internal rotation of the nitro group have been studied in gas phase using electron diffraction data and quantum chemical calculations in the framework of the large-amplitude motion model for internal rotation.Quantum chemical calculations at the MP2 and B3LYP levels of theory with various Pople and Dunning basis sets predict the planar minimum energy molecular conformation, with the internal rotation barrier height in the interval 1140–1560 cm−1.The experimental GED data are consistent with the dynamic model governed by the twofold cosine potential energy function with the barrier height in the range from 600 to 1400 cm−1.The main equilibrium structure parameters are as follows (values in parentheses correspond to 3 times standard deviations): re (NO) = 1.225/1.227(3) Å, re(C − C)/re(C − N) = 1.362/1.376/1.403/1.438(3) Å, re(C − Cl)/re (C − S) = 1.700/1.712/1.715(2) Å, ∠e C2SC5 = 92.2 (5)°, ∠e C3C2S = 110.8 (6)°, ∠e C4C5S = 111.3 (5)°, ∠e C3C4C5 = 113.0 (7)°, ∠e C2C3C4 = 112.7 (8)°, ∠e C3NO11 = 116.9(6)°, ∠eC3NO10 = 118.5 (6)°, ∠e SCCl = 118.6 (5)°, ∠e C4C3N = 121.8 (7)°, ∠e ONO = 124.6(6)°, ∠e C2C3N = 125.1 (6)°, ∠e C3C2Cl = 130.7 (6)°.Thermally averaged parameters are provided for comparison with the results of traditional studies.