• Bulletin of the Korean Chemical Society
• /
• 제24권11호
• /
• pp.1649-1654
• /
• 2003

We have investigated substituent effect on the stabilization energies, and nucleus-independent chemical shifts of pentafulvalenes and on the electronic structures of the corresponding polypentafulvalenes to design environmentally stable semiconductive or conductive polymers. Geometrical optimizations of the molecules were carried out at the density functional level of theory with B3LYP hybrid functional and 6-311+G(d) basis set. Stabilization energies were estimated using isodesmic and homodesmotic reactions. As a criterion of aromaticity nucleus-independent chemical shifts of the molecules were computed using GIAO approach. For the polymers the geometrical parameters were optimized through AM1 band calculations and the electronic structures were obtained through modified extended Huckel band calculations. It is found that strong electronwithdrawing substituents increase isodesmic and homodesmotic stabilization energies of pentafulvalene, though it does not increase the aromaticity. Nitro-substituted pentafulvalene is estimated to have stabilization energy as much as azulene. However, substitution either with electron-donating groups or with electronwithdrawing groups does not significantly affect the electronic structures of polypentafulvalene and poly (vinylenedioxypentafulvalene).

• Bulletin of the Korean Chemical Society
• /
• 제26권11호
• /
• pp.1717-1722
• /
• 2005

The analytical transfer matrix method suggests a new quantization condition for calculating bound state eigenenergies exactly. In the quantization condition, the phase shifts of bound state wave functions scattered at classical turning points are explicitly introduced. We calculate the phase shifts of eigenfunctions of the Morse potential with various boundary conditions in order to understand the physical meaning of phase shifts. The Morse potential is known to adequately describe the interaction energy between two atoms and, therefore, it is frequently used to determine the vibrational energy levels of diatomic molecules. The variation of Morse potential eigenenergies influenced upon by changing boundary conditions is also investigated.

• 생약학회지
• /
• 제8권1호
• /
• pp.17-21
• /
• 1977

$^{13}C-NMR$ behaviors of phenolic compounds such as phenol, catechol, pyrogallol, resorcine, phoroglucine and hydroquinone were studied. From the study on the effects of OH-substitution on benzene and its dervatives it was found that the additivity rule can be applied to the ortho-and para-effect but not to the meta-effect for the OH-function. The empirically calculated chemical shifts regarding the o-and p-effects coincide very well with the results of measurement. The chemical shifts of the phenolic compounds can be classified into three types. 1) Catechol-type C-1 and C-2 145 ppm C-3 and C-6 116-107 ppm 2) Pyrogallol-type C-1 132ppm C-2 and C-6 146ppm C-3 and C-5 106ppm 3) Resorcin-type C-1 and C-3 159ppm C-2 103-95ppm C-4 and C-6 107ppm

• 생약학회지
• /
• 제11권3_4호통권43호
• /
• pp.153-162
• /
• 1980

1) The hydroxy-substitution in the simple phenolic compounds follows an additivity rule in the chemical shifts of their aromatic carbon atoms. In para-and ortho-effects is a good agreement between calculated and measured values, but the meta-effect is not certain. 2) The additivity rule was applied to assign the chemical shifts of catechins. 3) The nuclear overhauser effect was applied to assign the chemical shifts of C-8 and C-6 atoms of catechins and their polymer. The signal of C-8 is lower in intensity and appear in lower field than C-6. 4) The results of the NOE were applied to determine the bonding positions of catechin units in the catechin dimer and trimer. The bonding positions are C-8a and C-8b atoms of the second and third catechin units. 5) It was tried to determine the conformation of the catechin dimer and trimer by analysing the signal shapes of C-3' and C-4' atoms in the catechol moieties. The catechol moieties lie in opposite side in the dimer and trimer structure. A combined analysis of $^{13}C-and\;^1H-NMR$ results lead to the suggestion that such a catechin polymer is a zigzag planar form.

• Bulletin of the Korean Chemical Society
• /
• 제18권9호
• /
• pp.1002-1006
• /
• 1997

1H NMR spectra of D2O solutions containing 2,2-dimethylaziridine (1) or 2-methylaziridine (2) and [SiW11COⅡO39]6- (SiW11Co) or [SiW11NiⅡO39]6- (SiW11Ni) exhibit separate signals for the free ligand and the complex, indicating that the ligand exchange is slow on the NMR time scale. Identified are two linkage isomers with the methyl group of 2 at trans or cis position with respect to the metal. The isotropic shifts of 1 and 2 coordinated to SiW11Ni originate mainly from the contact shifts, and they agree reasonably with the relative values reported for similar ligands coordinated to bis(2,4-pentanedionato)nickel(Ⅱ). The isotropic shifts for the SiW11Co complexes were separated into contact and pseudocontact contributions. The pseudocontact shifts show that (χ∥-χ⊥) is positive, while that for the SiW11Co complexes of pyridine derivatives is negative. This result indicates that the ordering of dxy and dxz, dyz orbitals in SiW11Co complexes can be reversed by ligands.

• Bulletin of the Korean Chemical Society
• /
• 제18권4호
• /
• pp.369-373
• /
• 1997

When 1H NMR spectra of pyridine, 4-amino-, 4-methyl-, and 4-cyanopyridine coordinated to the paramagnetic polyoxometalate, [SiW11CoⅡO39]6- in D2O are compared, both α- and β-proton peaks are shifted upfield as the basicity of the ligand decreases. The isotropic shifts are separated into contact and pseudocontact contributions by assuming that the contact shifts are proportional to the isotropic shifts of the same ligands coordinated to [SiW11NiⅡO39]6-. This separation reveals that the shift variations with the axial ligand basicity are dominated by changes in the magnetic anisotropy (pseudocontact shift) of [SiW11CoⅡ(ptl)O39]6- (ptl=pyridine-type ligand). The magnitude of the magnetic anisotropy in a series of pyridine-type ligands increases linearly as the pKa of their conjugate acids decreases.

• 생약학회지
• /
• 제8권1호
• /
• pp.23-29
• /
• 1977

The $^{13}C-chemical\;shifts$ of the phenolic coumarine derivatives, aesculetin, daphnetin and herniarin were studied on the basis of my previous report. All spectral data found in this report could be utilized to the structure elucidation of the unknown phenolic coumarine derivatives and other phenolic compounds. In addition, it is suggested that a long range coupling may occur in the following structure as represented by arrow.

• 대한화학회지
• /
• 제34권6호
• /
• pp.509-516
• /
• 1990

n-알코올 용매에서 아세트아미드(AA)의 아미노 양성자의 nmr 화학적 이동과 선모양을 온도의 함수로 조사 연구하였다. 아미노 양성자의 화학적 이동 변화를 용매의 극성 파라미터 중에서 Reichardt의 $E_{T}$(30)으로 고찰하여 그들 사이에 다음과 같은 관계가 존재함을 밝혔다. ${\delta}_{obs}$ = ${\delta}_{o}$ ＋ aE$_{T} (30) ＋ b[E_{T}(30)]^2$ 여기서 ${\delta}_{o}$는 용질의 기체 상태 또는 $E_{T}$(30)가 0인 상태에서의 용질의 화학적 이동이며, a는 알코올 용액에서 용질이 갖는 고유한 특성이며, b는 용질-용매의 상호작용을 나타내는 상수이다. 또한, 선모양의 분석에서 얻은 N-C(O) 결합 주위로의 부자유회전 장애도 아미노 양성자에 대한 화학적 이동의 행동과 유사하게 용매의 $E_{T}$(30)과 밀접한 관계가 있음을 알아 내었다.

• Bulletin of the Korean Chemical Society
• /
• 제21권1호
• /
• pp.148-150
• /
• 2000

• Bulletin of the Korean Chemical Society
• /
• 제11권6호
• /
• pp.570-572
• /
• 1990