Conformation of polymer analogs in solution. X‐ray scattering from ethylene oxide oligomers carrying iodine atoms at the chain ends

Abstract

AbstractThe angular dependence of X‐ray scattering intensities of solutions of diiodobenzenes was compared with that of iodobenzene solutions containing the same concentration of iodine atoms. The data yielded interiodine distances of 3.6, 5.9, and 6.9 Å for the ortho, meta, and para isomers, respectively, in good agreement with the known values of 3.52, 5.92, and 6.84 Å. The same method was applied to a study of inter‐iodine separations in ICH2CH2(OCH2CH2)nI (n = 1, 2, 3) using CH3CH2OCH2CH2I as the monoiodo analog. Experimental limitations preclude detailed interpretation of the data in terms of a probability distribution of the end‐to‐end distances of these model compounds. The intramolecular inter‐iodine distances were characterized by the first minimum and the first maximum of the scattering function i(s) = ΔĪcorr/f, where ΔĪ is the difference in the scattering intensity from solutions of the diiodo and monoiodo compounds corrected for polarization, fI is the form factor of iodine and s = 4π sin Θ/λ, 2Θ is the scattering angle and λ the wavelength of the X‐rays. The molecular chains of all three oligomers were significantly more expanded in m‐xylene than in ethanol, the difference increasing with increasing chain length. A conformational analysis was carried out for ICH2CH2OCH2CH2I choosing the energies for conformational transition so as to yield a conformational distribution with the observed average square dipole moment and scattering function in non‐polar media. The contraction of the molecule in ethanol is much larger than can be accounted for by the reduction in the COULOMBic energy of dipole interaction in a medium of higher dielectric constant.