Origins of the rotational barriers of TG(-) form of ethyl propionate molecule have been investigated. The barrier heights, as determined from the Raman spectrum, are estimated to be 2.88 and 3.17 kcal/mol for the -CH3 (I) and -CH3 (II) methyl groups of the molecule respectively. The detail analyses suggest that the combined relaxations of the C-2-C-3, C-2-C-4 bond lengths and H-10-C-3-H-11, C-2-C-4-H-13 angles together play a significant role to control the barrier heights of methyl CH3 (I), CH3 (II) groups of the molecule. (C) 2014 Elsevier B.V. All rights reserved.