Koji Ohta

Generalized Hartree-Fock natural-orbital configuration-interaction (GHF NO CI) approach to unstable molecules: trimethylene

Abstract A configuration interaction (CI) method by use of natural orbitals (NO) derived from the generalized Hartree-Fock (GHF) solutions is proposed and applied to trimethylene as an example. It is found that the GHF NO CI method is equivalent to the traditional restricted HF (RHF) CI approach in the domain of weak correlation, and is similar to the generalized VB (GVB) CI method in the strong-correlation region. The GHF NO CI method thus seems to be promising for the study of the electronic structure of unstable molecules which are characterized by orbital and spin degeneracies.

Localized natural orbitals of unstable molecules: ozone

Abstract Use of localized natural orbitals (LNOs) is proposed for the elucidation of chemical valence of unstable ground-state molecules. The LNOs of ozone as an example have been derived from its generalized Hartree-Fock (GHF) solutions. It is shown that the LNO descriptions of ozone are much in line with the results which Goddard et al. have obtained using the generalized valence bond (GVB) method.

Stereospecific anionic polymerization and copolymerization of 1,1-diphenylethyl methacrylate

Abstract 1,1-Diphenylethyl methacrylate (DPEMA), which is a new methacrylic ester, was synthesized and polymerized by n-butyllithium (n-BuLi) in toluene and THF. The triad tacticity of the polymers was determined from the n.m.r. spectrum of poly(methyl methacrylate) (PMMA) which was derived from them. A highly stereoregular polymer was not formed either in toluene or in THF by n-BuLi between −78° and 30°C. In toluene, the tacticity depended very much on the polymerization temperature, and unexpectedly, the polymer obtained at −78°C was rich in syndiotacticity. The polymers obtained in THF were atactic regardless of the temperature. A highly isotactic polymer was formed with Grignard reagents. DPEMA (M 1 ) was also copolymerized with methyl methacrylate (MMA), diphenylmethyl methacrylate (DPMMA), and trityl methacrylate (TrMA) (M 2 ) in toluene and THF with n-BuLi; the tacticity of the copolymers was determined. Generally, the stereoregularity of the copolymers was lower than those of the M 2 homopolymers. In the copolymerization with MMA monomer reactivity ratios were also determined.

Anionic Polymerizations and Copolymerizations of Methacrylates-Reactivity of Monomer and Tacticity of Polymer

Abstract The anionic polymerizations and copolymerizations of methacrylates were investigated. The studies were focused on the stereoregularity of the polymers and the relative reactivity of the monomers in relation to the stereospecificity of polymerization.

Determination of assigned configurational parameters for cross propagation in radical copolymerization of methyl methacrylate and trityl methacrylate

SummaryCopolymer of methyl methacrylate-d8(M1) with a small amount of trityl methacrylate(M2) was radically prepared in tetrahydrofuran and converted into the copolymer of methyl methacrylate-d8 with a small amount of undeuterated methyl methacrylate by the selective hydrolysis of the trityl group and subsequent methylation with diazomethane. From the 1H NMR spectrum of the derived copolymer the assigned coisotactic parameters σ12 and σ21 were determined to be 0.14 and 0.61, respectively. This may be the first example of the unequivocal determination of assigned configurational parameters in cross propagation for copolymerization.

Studies on the anionic polymerization of methyl methacrylate with butyllithium by using perdeuterated monomer

SummaryMethyl methacrylate-d8 was polymerized by C4H9Li in toluene at −78°C and the resultant polymer and oligomer were studied for butyl group by 1H NMR spectroscopy according to the precision coaxial tubing method (HATADA 1977a). A polymer and an oligomer molecule was found to have about one butyl group incorporated through the attack of C4H9Li on the carbonyl group as well as one terminal butyl group. The total amount of the C4H9Li residue introduced in both the polymer and oligomer molecules was measured to be 0.45mmol and almost corresponded to the amount of the C4H9Li used (0.50mmol).