Transition structures, energetics, and nucleus-independent chemical shifts for divinylcyclobutene-to-cyclooctatriene rearrangement: A DFT study

The minimum energy reaction paths and nucleus-independent chemical shifts (NICS) for the Cope rearrangement of cis-3,4-divinylcyclobutene, obtained by (U)B3LYP/6-31G* calculations, are reported. Three transition structures (endo-boatlike, chairlike, and exo-boatlike) have been located, giving rise to formation of cis,cis,cis-, cis,cis,trans-, and trans,cis, trans- 1, 3,5-cyclooctatrienes, respectively. The minimum energy path proceeds through an endo-boatlike, aromatic transition structure. The reaction path of the rearrangement is intervened by enantiomerization saddle point of the product. NICS values calculated for transition structures agree qualitatively with their activation energy and reaction exothermicity orders. Cope rearrangement and electrocyclic ring-opening processes of cis-3,4-divinylcyclobutene are competitive, but the former is relatively more favored and exothermic than the latter.


Transition structures, energetics, and nucleus-independent chemical shifts for 6 pi electrocyclizations of dienylketenes to cyclohexadienones: A DFT study
Zora, Metin (American Chemical Society (ACS), 2004-03-19)
6pi electrocyclizations of dienylketenes to 2,4-cyclohexadienones have been investigated at the (U)B3LYP/6-31G* level and found to be a favored and exothermic process for most dienylketenes. As evidenced by calculations, dienylketene cyclizations proceed via a pseudopericyclic process. If the terminal double bond of dienylketenes is embedded into a benzenoid-type aryl moiety, the partial or complete loss of aromaticity, as indicated by NICS values, increases the activation barrier and makes the reaction les...
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Atalar, Taner; Algi, Fatih; Balcı, Metin (ARKAT USA, Inc., 2008-01-01)
To reveal the stability and the aromatic character of pentalenoquinones (PQs) 1-4 and the corresponding bromo derivatives (Br-PQs) 6-9, DFT calculations (B3LYP/6-311+G(d,p)) concerning the geometry optimization, total energy and nucleus independent chemical shift (NICS) values were performed. It was found that all of the compounds have planar geometry. As the energy difference between HOMO-LUMO energy levels (Delta epsilon=epsilon(LUMO) - epsilon(HOMO)) and total energies were considered for the pentalene f...
Synthesis of 1,2,3,5- tetrasubstituted pyrrole derivatives via 5-exo-dig type cyclization and stereoselective functionalisation of ferrocene derivatives
Kayalar, Metin; Demir, Ayhan Sıtkı; Department of Chemistry (2005)
A convenient and new method for the synthesis of 1,2,3,5-tetrasubstituted pyrrole derivatives starting from 1,3,-dicarbonyl compounds through acid catalyzed cyclization reaction is described. Alkylation of 1,3-dicarbonyl compound with propargyl bromide followed by one step cyclization with the introduction of primary amines in the presence of catalytic amount of triflouroacetic acid (TFA) affords the corresponding pyrrole derivatives in high yields. The investigations on the studies of developing a new meth...
Substituent Effects on the Ring-Opening Mechanism of Lithium Bromocyclopropylidenoids to Allenes
AZİZOĞLU, AKIN; Balcı, Metin; Mieusset, Jean-Luc; Brinker, Udo H. (American Chemical Society (ACS), 2008-11-07)
The ring-opening reactions of lithium bromocyclopropylidenoids to allenes have been investigated computationally at the B3LYP/6-31 G(d) level of theory. Formally, two pathways can be considered: the reaction may either proceed in a concerted fashion or stepwise with the intermediacy of a free cyclopropylidene. In both cases, the loss of the bromide ion determines the kinetic of the reaction. The stability of the reactive intermediate, i.e., the carbene, is dependent on the substituent. Cyclopropylidenes bea...
Cettaertalyst-Free Hydrogenation of Alkenes and Alkynes with Hydrazine in the Presence of Oxygen
Menges, Nurettin; Balcı, Metin (Georg Thieme Verlag KG, 2014-03-17)
A series of alkenes and alkynes was subjected to reduction with hydrazine hydrate in ethanol in the presence of oxygen. An efficient method was developed for the reduction of C-C double bonds and C-C triple bonds with diimide, generated in situ from hydrazine hydrate by oxidation with oxygen. The reduction process proceeded for 24-48 hours with high chemoselectivity and excellent yields. This reduction procedure offers synthetic advantages over metal-catalyzed hydrogenation as well as other systems.
Citation Formats
M. Zora, “Transition structures, energetics, and nucleus-independent chemical shifts for divinylcyclobutene-to-cyclooctatriene rearrangement: A DFT study,” JOURNAL OF ORGANIC CHEMISTRY, pp. 857–862, 2004, Accessed: 00, 2020. [Online]. Available: