CH center dot center dot center dot O intramolecular interactions determining conformational stabilities in 2-propoxyethanol

Conformational energies and structural parameters for relevant conformers of methyl propyl ether (MPE = CH3CH2CH2OCH3), 1,2-dimethoxyethane (DME = CH3OCH2CH2OCH3), 2-methoxyethanol (ME = CH3OCH2CH2OH) and 2-propoxyethanol (PE = CH3CH2CH2OCH2CH2OH) have been determined at the MP2/6-31G*parallel to 3-21G* level. Three interesting structural features due to the presence of intramolecular CH ... O contacts stand out of these results. In the first, the gt conformer of MPE and the gttgg' and g'ttgg' conformers of PE are stabilized by about 2 kJ mol(-1) relative to the tt and tttgg' conformers, respectively. In the second, the gg arrangement of the propoxy fragment is stabilized when this fragment is ''linked'' to the tgg' fragment of ME giving rise to the ggtgg' and g'g'tgg' conformers of PE, In turn, the gt fragment of MPE is not much affected in relative conformational energy by merging with the tgg' fragment of ME to give rise to the more stable gttgg' conformer of PE. In the third important structural feature, substitution of the hydroxyl H atom in ME by a methyl group leads to stabilization of those conformers which do not have any intramolecular OH ... O contact, namely, the ttt and ttg conformers. In spite of this relative stabilization, the tgg' conformer is the second more stable conformer of DME very close in energy to the more stable all-trans conformer. In addition, tgg' and ggg' keep approximately the same energy difference they had in ME.