Conformations of n-butyl imidazole: Matrix isolation infrared and DFT studies

Conformations of n-butyl imidazole (B-IMID) were studied using matrix isolation infrared spectroscopy by trapping in argon, xenon and nitrogen matrixes using an effusive nozzle source. The experimental studies were supported by DFT computations performed at the B3LYP/6-311++G(d,p) level. Computations identified nine unique minima for B-IMID, corresponding to conformers with tg(+/-)tt, tg(+/-)g(-/+)t, tg(+/-)g(-/+)t, tg(+/-)tg(+/-), tg(+/-)tg(-/+), tg(+/-)g(-/+)g(-/+), tg(+/-)g(+/-)g(+/-), tg(+/-)g(-/+)g(+/-) and tg(+/-)g(+/-)g(-/+) structures, given in order of increasing energy. Computations of the transition state structures connecting the higher energy conformers to the global minimum, tg(+/-)tt structure were carried out. The barriers for the conformer inter-conversion were found to be similar to 2 kcal/mol. Natural Bond Orbital (NBO) analysis was performed to understand the reasons for conformational preferences in B-IMID. (C) 2014 Elsevier B.V. All rights reserved.