Table 3.

$V_3$ and $V_6$ barriers for 2- and 3- methylfuran (MF), methylthiophene (MT) and methylpyrrole (MP) calculated with B3LYP/aug-cc-pVTZ as the function of the methyl groups torsional angle $\alpha$. Uncertainties are the standard error given by Gnuplot [24] for the fit of the DFT potential based on Equation (5). The experimental values determined in this work for MF or in the literature for MT and MP are mentioned in square brackets.

Molecule	${\mathit{V}}_3$ /cm${}^{-1}$	${\mathit{V}}_6$ /cm${}^{-1}$	100 ${\mathit{V}}_6/{\mathit{V}}_3$
2-MF	376.12 (22) [420.3157 (35)] ${}^a$	−1.49 (22) [−9.010 (11)] ${}^a$	−0.40 [−2.143]
2-MT	198.08 (33) [194.1] ${}^b$	1.71 (33)	0.86
2-MP	263.62 (67) [279.7183 (26)] ${}^c$	1.96 (67)	0.74
3-MF	348.92 (50) [357.77 (22)] ${}^a$	−10.81 (50) [−2.481 (13)] ${}^a$	−3.10 [−0.693]
3-MT	254.47 (20) [259] ${}^d$	−8.27 (20)	−3.25
3-MP	223.55 (34) [245.14101 (89)] e	−7.71 (34)	−3.45

^a Experimental value obtained from BELGI-C_s. ^b Experimental value taken from [31]. ^c Experimental value taken from [32]. ^d Experimental value taken from [33]. ^e Experimental value taken from [34].