Ethyl group

Abstract: Raman spectra of liquid 1-ethyl-3-methylimidazolium (EMI+) salts, EMI+BF4-, EMI+PF6-, EMI+CF3SO3-, and EMI+N(CF3SO2)2-, were measured over the frequency range 200−1600 cm-1. In the range 200−500 cm-1, we found five bands originating from the EMI+ ion at 241, 297, 387, 430, and 448 cm-1. However, the 448 cm-1 band could hardly be reproduced by theoretical calculations in terms of a given EMI+ conformer, implying that the band originates from another conformer. This is expected because the EMI+ involves an ethyl group bound to the N atom of the imidazolium ring, and the ethyl group can rotate along the C−N bond to yield conformers. The torsion energy for the rotation was then theoretically calculated. Two local minima with an energy difference of ca. 2 kJ mol-1 were found, suggesting that two conformers are present in equilibrium. Full geometry optimizations followed by normal frequency analyses indicate that the two conformers are those with planar and nonplanar ethyl groups against the imidazolium ring pl...

Abstract: The complete basis set method CBS-QB3 has been used to study the thermochemistry and kinetics of the esters ethyl propanoate (EP) and methyl butanoate (MB) to evaluate initiation reactions and intermediate products from unimolecular decomposition reactions. Using isodesmic and isogeitonic equations and atomization energies, we have estimated chemically accurate enthalpies of formation and bond dissociation energies for the esters and species derived from them. In addition it is shown that controversial literature values may be resolved by adopting, for the acetate radical, CH3C(O)Ȯ, (298.15K) = −197.8 kJ mol-1 and for the trans-hydrocarboxyl radical, Ċ(O)OH, −181.6 ± 2.9 kJ mol-1. For EP, the lowest energy decomposition path encounters an energy barrier of ∼210 kJ mol-1 (∼50 kcal mol-1), which proceeds through a six-membered ring transition state (retro-ene reaction) via transfer of the primary methyl H atom from the ethyl group to the carbonyl oxygen, while cleaving the carbon−ether oxygen to form ethene...