Experimental spectroscopic and theoretical studies of organic compounds and polymeric structures
Ryall, John P.
Solid state IR and Raman as well as aqueous solution state Raman spectra are reported for urazole, 4-methylurazole and their deuterated derivatives. DFT calculations, at the B3-LYP/cc-pVDZ level, established that the structures and vibrational spectra of the molecules can be interpreted using a model with hydrogen-bonded water molecules, in conjunction with the conductor-like polarizable continuum solvation method. The vibrational spectra were computed at the optimised molecular geometry, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments. Solid-state pseudopotential-plane-wave DFT calculations, using the PW91 functional, were also carried out reflecting the importance of intermolecular hydrogen bonding in the solid state.\ud \ud Solid state IR and Raman as well as aqueous solution state Raman spectra are reported for the anions of urazole and 4-methylurazole, and their N-deuterated derivatives. DFT calculations, at the B3-LYP/cc-pVTZ level, established that the structures and vibrational spectra of both anions can be interpreted using a model that incorporates hydrogen-bonded water molecules, in conjunction with the polarizable continuum solvation method. In the case of the urazole anion it is shown that deprotonation occurs primarily at N1 rather than N4, but there is also evidence for the second tautomeric structure in both in the solid state and in aqueous solution. The vibrational spectra were computed at the optimised molecular geometry in each case, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments.\ud \ud IR and Raman spectra have been obtained for N, N'–dicyclohexylcarbodiimide (DCC) in the solid state and in CHCl3 solution. Structures and vibrational spectra of isolated gas phase DCC molecules with C2 and Ci symmetries, computed at the B3-LYP/cc-pVTZ level, show that the IR and Raman spectra provide convincing evidence for a C2 structure in both the solid and CHCl3 solution states. Using a scaled quantum-chemical force field these DFT calculations have provided detailed assignments of the observed IR and Raman bands in terms of potential energy distributions. Comparison of solid state and solution spectra, together with a Raman study of the melting behaviour of DCC, revealed that no solid state effects were evident in the spectra.\ud \ud Homopolymeric poly(N-isopropylacrylamide) and poly(4-vinylpyridine) as well as copolymer poly(N-isopropylacrylamide/4-vinylpyridine) [poly(NIPAM/4-VP)] microgels (the latter synthesized using percentage composition of 4-VP in the range of 7.5 – 90 %, w/w in the original reaction mixture) were prepared by surfactant-free emulsion polymerization. Freeze-dried samples of the microgels were subjected to analysis by Raman spectroscopy using 632.8 nm exciting radiation from a helium-neon laser. The Raman spectral profiles of the different microgels are compared and contrasted in the 600-1100 cm-1 wavenumber region. In the case of the poly(NIPAM/4-VP) copolymer microgels, differing in monomer composition, Raman spectroscopy can be employed as a quick/easy method to ensure that co-polymerization has occurred and also to determine, semi-quantitatively, the percentage incorporation of the 4-VP monomer.
views in local repository
downloads in local repository
The information is available from the following content providers: