The Raman and infrared spectra of 2,5-dioxahexane CH3OCH2CH2OCH3, 2,5-dithiahexane CH3SCH2CH2SCH3 and 2-oxa-5-thiahexane CH3OCH2CH2SCH3 were measured for the gaseous, liquid, glassy and crystalline states and were correlated with the normal-vibration calculations. The rotational isomerism was studied and the following conclusions were obtained. (1) The molecular form existing in the crystalline state is a non-extended form, in contrast with the cases of the unbranched ethers or sulfides containing one oxygen or sulfur atom which take the extended all-trans form. (2) Many forms coexist in the gaseous, liquid and glassy states. (3) The form existing in the crystalline state is the most stable in the liquid state. It was found that the repulsive force between non-bonded hydrogen atoms is one of the important factors influencing the conformational stabilities and for 2,5-dioxahexane the dipole-dipole interaction is another important factor. The stable conformations of these molecules were correlated with those of the polyether and polythioether chains. The stable isomers of 2-oxa-5-thiahexane could be explained on the basis of the knowledge of the conformational stabilities of the unbranched ethers and sulfides. The force constants of the ethers and sulfides were satisfactorily transferred to 2-oxa-5-thiahexane.
The Raman spectra of butane, pentane, hexane, pentane-d12, and hexane-d14 and infrared spectra of pentane-d12 and hexane-d14 were measured for the liquid and solid states. The rotational isomerism of normal paraffins was studied on the basis of the spectral observations and the normal coordinate calculations. The spectra of the deuterated compounds were useful in the confirmation of the less stable isomers and the establishment of the local symmetry force field of normal paraffins. The enthalpy differences among the rotational isomers were studied on pentane and hexane, which yielded some important data for the study of the conformations and properties of longer hydrocarbons.
The Raman spectra of ethyl methyl sulfide and its three deuterated compounds CD3SC2H5, CH3SCH2CD3, and CH3SC2D5 were measured for the liquid and crystalline states. The Raman spectra of the undeuterated species in the gaseous state were measured at different temperatures. The normal vibration frequencies were calculated by using a consistent set of force constants for aliphatic sulfides. The combination of the spectral observations of the deuterated compounds and the normal vibration calculations showed that only the gauche form exists in the crystalline state and the trans and gauche forms coexist in the liquid and gaseous states. The enthalpy difference between the gauche and trans forms in the gaseous state, ΔHG–T, was obtained as −30±50 cal/mol.
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