The conformation of the alkyl chain in α-dodecyl-ω-hydroxytris(oxyethylene) (C12E3) in water has been studied by C−D stretching infrared spectroscopy. This conformational analysis is based on the fact that the wavenumbers of the isolated C−D stretching vibrations are sensitive to the conformation in the vicinity of the C−D bond. Infrared spectra were measured for five selectively monodeuterated species of C12E3, namely CH3(CH2)11-k CHD(CH2) k -1(OCH2CH2)3OH, where k = 1, 2, 4, 6, and 8, in the lamellar (Lα) and isotropic solution (L2) phases. The C−D stretching bands for each of the monodeuterated species were assigned to particular conformations of the specifically deuterated part of the chain. From the observed intensities of the C−D stretching bands, the fractions of the trans conformation around the dodecyl C−C bonds and the oxyethylene-adjoining O−C bond and the fractions of the consecutive trans conformations around the two adjoining bonds were evaluated. The conformational change at the phase transition from L2 to Lα is not significant and only a small increase in the trans fraction is observed for the C−C bonds close to the alkyl/oxyethylene interface. This implies that the conformational states in the L2 and Lα phases in the vicinity of their boundary are substantially not different. In the Lα phase, when the composition or the temperature approaches the region of the phase separation or transition, the trans fractions for the C−C bonds closer to the alkyl/oxyethylene interface and those closer to the chain terminal decrease significantly. These observations indicate that the conformational transformation from trans to gauche at these chain positions makes the lamellar structure less stable and leads eventually to the structural destruction. The fraction of the consecutive trans conformations may be used as a measure of the conformational order at particular positions of the chain. The present results show that the ordering is the highest in the middle of the chain in the Lα and L2 phases. This vibrational spectroscopic observation, together with the previous NMR observations, indicates that the alkyl/oxyethylene interface is flexible with respect to the conformation and the orientation of the chain.

The Raman spectra of aqueous solutions of CH3(OCH2CH2)mOCH3 (m = 1−4) were measured for mole fractions down to 0.005. The spectral observation for the compounds with m ≥ 2 indicates that, on addition of water, the POE chain progressively prefers the gauche conformation for the OCH2–CH2O segment at the first stage, but this direction of the conformational preference is reversed for concentrations lower than a particular solution composition. This anomalous conformational behavior is suggestive of a new structural aspect of the POE–water system.

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The isolated C-D stretching vibrations have been studied for a number of selectively monodeuterated species of tetrahydropyran, methyl ethyl ether, methyl propyl ether, methyl butyl ether, methyl hexyl ether, and cyclohexane, and the dependence of the C-D stretching wavenumbers on the conformation of the CO-C(D)-CC, OC-C(D)-CC, and CC-C(D)-CC structures of the alkoxyl chain has been examined. The infrared spectra of three monodeuterated species of tetrahydropyran with a chair form gave definitive evidence for the conformational dependence of the C-D stretching wavenumbers. The observed wavenumbers of the C-D stretching vibrations for the monodeuterated compounds studied are correlated linearly to the C-D bond lengths calculated by the ab initio MO method using the basis set with polarization functions. The dependence of the C-D stretching wavenumbers on the conformational disposition of the C-D bond in the CO-C(D)-CC structure is more significant than that of the C-D bond in the OC-C(D)-CC or CC-C(D)-CC structure. For the CO-C(D)-CC structure, the stretching wavenumbers of the C-D bond trans to the DC-OC and DC-CC bonds are higher by about 90 cm -1 than those of the C-D bond gauche to the same bonds. C-D stretching vibrational spectroscopy has been shown to be one of the advantageous methods for determining the conformation of alkyl chains, which may contain any heterogenous atoms.

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