Abstract
The Raman (3500 cm(-1)-100 cm(-1)) and IR spectra (4000 cm(-1)-400 cm(-1)) of liquid trimethylacetonitrile (C5H9N, TMA) have been obtained. In addition, the H-1 and C-13 NMR spectra of TMA were obtained in DMSO-d(6) and CDCl3. The staggered conformer (C-3v) was favored using MP2 and DFT(B3LYP/omega B97XD) quantum mechanical calculations utilizing a 6-311+G(d,p) basis set. High energy difference estimates of 4534 cm(-1) -5338 cm(-1) (12.96 kcal/mol-15.26 k-cal/mol) were predicted, along with three imaginary torsion frequencies for the eclipsed conformer, therefore considered a transition state. The H-1 and C-13 NMR chemical shifts were predicted with B3LYP and omega B97XD methods using the GIAO approximation and 6-311+G(d,p) basis set. B3LYP frequencies calculation is favored herein owing to the relatively good compilation with the experimental measurements. The computed structural parameters are well correlated to those reported from electron diffraction and microwave studies. Moreover, the C-13-H-1 coupling constant was estimated and found consistent with that observed for the sample dissolved in DMSO-d(6)/CDCl3 solvents. Using the observed methyl torsion at 266 cm(-1) in gas phase and the kinetic parameter F number, a potential function (V-3) of 1578 +/- 30 cm(-1) (4.51 +/- .09 kcal/mol) was obtained, this barrier to internal rotation is well correlated to 1527 cm(-1) (4.37 kcal/mol) predicted from MP2/6-311+G(d,p) potential surface scan. Aided by the predicted wavenumbers and their IR intensity/Raman activity, the observed IR/Raman bands were intensively discussed and therefore assigned to their corresponding fundamentals, in agreement with novel normal coordinate analysis and potential energy distributions (PEDs).