Conformational behaviors of 2-halo-1,2,4,5-tetrahydrobenzo[d]oxepines. A hybrid-density functional theory study and natural bond orbital interpretations

  • سال انتشار: 1391
  • محل انتشار: همایش ملی نانو فناوری و شیمی سبز
  • کد COI اختصاصی: IAUET01_152
  • زبان مقاله: انگلیسی
  • تعداد مشاهده: 950
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نویسندگان

Sahar Saadetfard

Department of Chemistry,Azad University of Tehran, Tehran, Iran

Seiedeh Megar Mousavi

Department of Chemistry,Azad University of Tehran, Tehran, Iran

Vavood Nari Shargh

Department of Chemistry, Arak Branch, Islamic Azad University, Arak, Iran

چکیده

Hybrid-density functional theory (hybrid-DFT: B3LYP/6-311+G**) based methods and natural bond orbital (NBO) interpretation have been used to examine the impacts of the hyperconjugative, electrostatic and steric effects on the conformational behaviors of 2-fluoro-1,2,4,5-tetrahydrobenzo[d]oxepine (1), 2-chloro-1,2,4,5-tetrahydrobenzo[d]oxepine (2) and 2-bromo-1,2,4,5-tetrahydrobenzo[d]oxepine (3). B3LYP/6-311+G** results showed that the axial conformations of compounds 1-3 are more stable than their corresponding equatorial conformations and the axial conformation stability, compared to its corresponding equatorial conformation, increases from compounds 1→3. Based on the results obtained from the NBO analysis, there are significant anomeric effects associated with the electron delocalization for compounds 1-3. The endo-anomeric effect associated with LP(1)O(3)→σ*(C2-X) and LP(2)O(3)→σ*(C2-X) electron delocalizations increases from the axial conformation of compound 1 to compound 2 but decreases from compound 2 to compound 3. The exo-anomeric effect decreases from compounds 1→3. The anomeric effect [i.e. ∑(endo-anomeric effect+exo-anomeric effect)(eq)-∑(endo-anomeric effect+exo-anomeric effect)ax] increases from compounds 1→3. Dipole moments of the equatorial conformations of compounds 1-3 are greater than those of their corresponding axial conformations and dipole moment difference between the axial and equatorial conformations [Δ(μeq - μax)] decreases from compounds 1→3. Therefore, the anomeric effect associated with the electron delocalizations explain the conformational preferences in compounds 1-3 but the electrostatic model associated with the dipole-dipole interactions fails to account the conformational preferences in compounds 1-3. The correlations between the anomeric effect, electrostatic model, ΔGeq-ax, bond orders, dipole-dipole interactions, structural parameters and conformational behaviors of compounds 1-3 have been investigated.

کلیدواژه ها

Anomeric effects; Stereoelectronic interactions; molecular modeling; Ab initio; 2-Halo-1,2,4,5-tetrahydrobenzo[d]oxepines

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