• Bulletin of the Korean Chemical Society
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• 제6권5호
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• pp.277-279
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• 1985

Orbital interactions of the types, ${\sigma}-{\pi},\;{\sigma}^*-{\pi},\;{\sigma}-{\pi}^*\;and\;{\sigma}^*-{\pi}^*$ are investigated for the rotamers of ${\alpha}$-X-acetones (X = F and Cl) using STO-3G method of calculation. It was found that the interactions are possible only in gauche forms, and the ${\sigma}^*-{\pi}^*$ interactions are in general greater than the $\sigma-\pi$ interactions due to the greater overlap, in spite of the greater energy gap involved; the greater ${\sigma}^*-{\pi}^*$ interaction causes greater lowering of ${\pi}^*$ level relative to the lowering of ${\sigma}$ in the ${\sigma}-{\pi}$ interaction so that both ${\sigma}-{\pi}^*$ and $n-{\pi}^*$ interactions are enhanced in the gauche forms. The extra stability of the gauche form and the red shift in the $n-{\pi}^*$ transition are thus found to be natural corollaries of the greater ${\sigma}^*-{\pi}^*$ interaction in the gauche forms.

• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4195-4198
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• 2011

Intramolecular ${\pi}-{\pi}$ and ${\sigma}-{\pi}$ interactions are omnipresent for numerous energetic and structural phenomena in nature, and the exact description of these nonbonding interactions plays an important role in the accurate prediction of the three-dimensional structures for numerous interesting molecular systems such as protein folding and polymer shaping. We have selected two prototype molecular systems for benchmarking calculations of intramolecular ${\pi}-{\pi}$ and ${\sigma}-{\pi}$ interactions. Accurately describing conformational energy of such systems requires highly elaborate but very expensive ab initio methods such as coupled cluster singles, doubles, and (triples) (CCSD(T)). Our calculations reveal a double hybrid density functional incorporating dispersion correction (B2PLYP-D) that agrees excellently with the CCSD(T) results, indicating that B2PLYP-D can serve as a practical method of choice.

• 대한화학회지
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• 제29권1호
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• pp.23-30
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• 1985

${\pi}^{\ast}$-${\pi}^{\ast}$ 궤도간 상호작용에 관한 섭동식을 유도하였다. 섭동식으로부터 예측되는 ${\pi}$-${\pi}$와 ${\pi}^{\ast}$-${\pi}^{\ast}$ 상호작용간의 중요한 두가지 차이점은 : (ⅰ)에너지분리정도가 ${\pi}$-${\pi}$ 상호작용의 경우보다 ${\pi}^{\ast}$-${\pi}^{\ast}$의 경우가 더 컸으며, ( ii ) 상호작용에 의한 에너지 변화량은 ${\pi}$-${\pi}$ 상호작용의 경우보다 ${\pi}^{\ast}$-${\pi}^{\ast}$의 경우가 더 불안정화 되었다. 이러한 예측들은 실험결과들과 MO이론적 계산에 의하여 잘 밝혀졌다. 한편 STO-3G 및 INDO-LCBO 계산방법은 ${\pi}^{\ast}$-${\pi}^{\ast}$ 상호작용을 과소평가하고 있음을 알았으며 MO이론적 계산을 이용하여 이러한 ${\pi}^{\ast}$-${\pi}^{\ast}$상호작용을 적절히 표현하는 데는 split valence 기초함수를 사용하여야 함을 밝혔다.

• 한국염색가공학회지
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• 제22권2호
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• pp.83-87
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• 2010

Crystal structure of coumarin 6 has been solved by X-ray diffraction. The crystals are triclinic, space group P-1, with a=8.823(2) ${\AA}$, b=8.898(2) ${\AA}$, c=11.025(9) ${\AA}$, ${\alpha}$=86.41(3)$^{\circ}$, ${\beta}$=85.39(3)$^{\circ}$, ${\gamma}$=76.23(3)$^{\circ}$, Mr=350.42, V=837.1(3) ${\AA}^3$, Z=2 and R=0.0516. The molecules are packed parallel to each other by weaker ${\pi}{\cdots}{\pi}$ and C-H${\cdots}{\pi}$ interactions. The detailed geometry of C-H${\cdots}{\pi}$ interactions were discussed. The hydrogen bonds and non-traditional C-H${\cdots}O$ interactions join the no-parallel molecules together. All the molecules packed wall-like with the molecular brick.

• Bulletin of the Korean Chemical Society
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• 제34권6호
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• pp.1913-1916
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• 2013

• Bulletin of the Korean Chemical Society
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• 제34권6호
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• pp.1814-1822
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• 2013

By using density functional theory calculations, we have performed a systemic study on the electronic structures and topological properties of interactions between N-butylpyridinium nitrate ($[BPY]^+[NO_3]^-$) and thiophene (TS), benzothiophene (BT), dibenzothiophene (DBT), naphthalene (NAP). The most stable structure of $[BPY]^+[NO_3]^-$ ion pair indicates that hydrogen bonding interactions between oxygen atoms on $[NO_3]^-$ anion and C2-H2 on pyridinium ring play a dominating role in the formation of ion pair. The occurrence of hydrogen bonding, ${\pi}{\cdots}$H-C, and ${\pi}{\cdots}{\pi}$ interactions between $[BPY]^+[NO_3]^-$ and TS, BT, DBT, NAP has been corroborated at the molecular level. But hydrogen bonding and ${\pi}{\cdots}{\pi}$ interactions between $[BPY]^+[NO_3]^-$ and NAP are weak in terms of structural properties and NBO, AIM analyses. DBT is prior to adsorption on N-butylpyridinium nitrate ionic liquid.

• Bulletin of the Korean Chemical Society
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• 제3권1호
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• pp.1-4
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• 1982

A quantitative treatment of ${\pi}$-nonbonded and $n-{\sigma}^{\ast}$ interactions and through-bond coupling effect was attempted using n-butane, n-butyl radical, and tetramethylene diradical. Results of STO-3G level calculations showed that: (1) conformational preferences can be predicted quantitatively based solely on the additive effect of ${\pi}$-nonbonded and $n-{\sigma}^{\ast}$ interactions, the predominant effect being the ${\pi}$-nonbonded interactions, (2) $(n-{\sigma}^{\ast})_{anti}$ is destabilizing whereas $(n-{\sigma}^{\ast})_{syn}$ is weakly stabilizing, which are contrary to what we expect from the normal $n-{\sigma}^{\ast}$ interaction, (3) througb-bond coupling of the two radical lobes is destabilizing for the triplet but stabilizing for the singlet tetramethylene diradical.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.205-205
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• 2011

The self-assembly of ${\gamma}$-phenylalanine on Au(111) at 150 K was investigated using scanning tunneling microscopy (STM). Phenylalanine can potentially form two-dimensional (2D) molecular networks through hydrogen bonding (through the carboxyl and amino groups) and ${\pi}-{\pi}$ stacking interactions (via aromatic rings). We found that ${\gamma}$-phenylalanine molecules self-assembled on Au(111) surfaces into well-ordered structures such as ring-shaped clusters (at low and intermediate coverages) and 2D molecular domains (intermediate and monolayer coverages), whereas ${\alpha}$-phenylalanine molecules formed less-ordered structure on Au(111). The self-assembly of ${\gamma}$- but not ${\alpha}$-phenylalanine may be related to the flexibility of the carboxyl and amino groups in the molecule. Moreover, as expected, the 2D molecular network of ${\gamma}$-phenylalanine on Au(111) was mediated by a combination of hydrogen bonding and ${\pi}-{\pi}$ stacking interactions.

• 한국전기전자재료학회논문지
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• 제24권6호
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• pp.510-514
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• 2011

Based on first-principles LCAO method, we study the electronic and atomic structures of DNA nucleobases adenine (A), thymine (T), guanine (G), and cytosine (C) adsorbed on graphene surfaces. The ${\pi}-{\pi}$ stacking interactions between graphene and nucleobases lead to the bilayer geometries similar to the Bernal stacked graphite. Through the density of states and charge density analyses, it is found that nucleobases are physisorbed on graphene by dispersive interactions with negligible charge exchange. Our calculations reproduce the atomic structures obtained in previous plane wave calculations accurately with much less computation, and well describe the delocalized ${\pi}-{\pi}$ interactions in graphene-nucleobases system, indicating that the LCAO method is very efficient for investigating graphene-bio systems.

• Bulletin of the Korean Chemical Society
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• 제4권4호
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• pp.157-161
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• 1983

Ab initio calculations were performed on systems containing various basic ${\pi}$ fragments and glycines to generalize the ${\pi}$-nonbonded interaction (${\pi}$-NBI) method of determining relative conformational and configurational stability of organic molecules. It was found that the relative stability of conformational isomers can be determined in general by the simple application of the ${\pi}$-NBI method, but the method is not applicable to the geometrical isomerism in which stronger structural factors are involved. The ${\pi}$-NBI effect of a crowded ${\pi}$-structure ($n{\pi}/m$) is maximum for the system in which n is equal to m. In crowded structures containing heteroatoms, ${P^{\pi}}_{ij}$ values of 4N+1 system may become negative, but this sign reversal does not invalidate the predictions based on the ${\pi}$-NBI method.