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Conformational behaviors of trans-2,3- and trans-2,5-dihalo-1,4-diselenanes. A complete basis set, hybrid-density functional theory study and natural bond orbital interpretations

Diğer Başlık: Conformational behaviors of trans-2,3- and trans-2,5-dihalo-1,4-diselenanes. A complete basis set, hybrid-density functional theory study and natural bond orbital interpretations

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Tür: Makale

Yayınlanma Durumu: Yayınlanmış

Dosya Biçimi: Dosya Yok

Dil: İngilizce

Hakemli mi?: Evet

Uluslararası indekslerde yer alıyor mu?: Evet

Yazar(lar): Nori-Shargh, Davood (Yazar), Mousavi, Seiedeh Negar (Yazar), KAYI, Hakan (Yazar),

Emeği Geçen(ler):

DOI: 10.1007/s00894-014-2249-x

URL: http://link.springer.com/article/10.1007%2Fs00894-014-2249-x

Kaynak: http://link.springer.com/article/10.1007%2Fs00894-014-2249-x


Yayınlayan: Journal of Molecular Modeling Yayın Adı: Conformational behaviors of trans-2,3- and trans-2,5-dihalo-1,4-diselenanes. A complete basis set, hybrid-density functional theory study and natural bond orbital interpretations Yayın Yeri: Journal of Molecular Modeling Yayın Tarihi: 10-05-2014 Cilt: 20 Yayınlandığı Sayfalar: 2249


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Özet

Complete basis set CBS-4, hybrid-density functional theory (hybrid-DFT: B3LYP/6-311+G**) based methods and natural bond orbital (NBO) interpretations have been used to examine the contributions of the hyperconjugative, electrostatic, and steric effects on the conformational behaviors of trans-2,3-dihalo-1,4-diselenane [halo = F (1), Cl (2), Br (3)] and trans-2,5-dihalo-1,4-diselenane [halo = F (4), Cl (5), Br (6)]. Both levels of theory showed that the axial conformation stability, compared to its corresponding equatorial conformation, decreases from compounds 1 → 3 and 4 → 6. Based on the results obtained from the NBO analysis, there are significant anomeric effects for compounds 1-6. The anomeric effect associated with the electron delocalization is in favor of the axial conformation and increases from compounds 1 → 3 and 4 → 6. On the other hand, dipole moment differences between the axial and equatorial conformations [Δ(μ eq - μ ax)] decrease from compounds 1 → 3. Although Δ(μ eq-μ ax) parameter decreases from compound 1 to compound 3, the dipole moment values of the axial conformations are smaller than those of their corresponding equatorial conformations. Therefore, the anomeric effect associated with the electron delocalizations (for halogen-C-Se segments) and the electrostatic model associated with the dipole-dipole interactions fail to account for the increase of the equatorial conformations stability on going from compound 1to compound 3. Since there is no dipole moment for the axial and equatorial conformations of compounds 4-6, consequently, the conformational preferences in compounds 1-6 is in general dictated by the steric hindrance factor associated with the 1,3-syn-axial repulsions. Importantly, the CBS-4 results show that the entropy difference (∆S) between the equatorial axial conformations increases from compounds 1 → 3 and 4 → 6. This fact can be explained by the anomeric effectassociated with the electron delocalization which affects the C2-Se bond orders and increase the rigidity of the corresponding rings. The Gibbs free energy difference values between the axial and equatorial conformations (i.e. ΔG ax-ax and ΔG eq-eq) of compounds 1 and 42 and 5 and also 3 and6 have been calculated. The correlations between the anomeric effectelectrostatic model, ΔG eq-ax, ΔG ax-ax, ΔG eq-eq, bond orders, dipole-dipole interactions, structural parameters and conformational behaviors of compounds 1-6 have been investigated.


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