New Findings on the Diels-Alder Reactions. An Analysis Based on the Bonding Evolution Theory
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- 作者：Slawomir Berski ; Juan André ; s ; Bernard Silvi ; Luis R. Domingo
- 刊名：Journal of Physical Chemistry A
- 出版年：2006
- 出版时间：December 28, 2006
- 年：2006
- 卷：110
- 期：51
- 页码：13939 - 13947
- 全文大小：247K
- 年卷期：v.110,no.51(December 28, 2006)
- ISSN：1520-5215
文摘
Two Diels-Alder type reactions, i.e., normal electron demand (NED) between 1,3-butadiene (BD) and acrolein(Acr) and inverse electron demand (IED) between 2,4-pentadienal (PDA) and methyl vinyl ether (MVE),have been investigated using the bonding evolution theory (BET). BET combines topological analysis of theelectron localization function (ELF) and catastrophe theory. Catalyst effect has been incorporated throughLewis acid BH3. The B3LYP hybrid HF/DFT method along with 6-31G(d), 6-311++G(d,p) basis sets havebeen used. All reactions yield two-stage mechanism and there is no topological evidence that they might beconcerted with two bonds partially formed during transition structure. A formation of six-membered ringrequires 10 (or 11) steps separated by two types of catastrophes: fold and cusp. The first "intermolecular"bond (C1-C6) is formed at 1.93, 1.92 Å (NED) and 1.92, 1.97 Å (IED). The six-membered ring is "closed"at 2.11, 2.13 Å (NED) and 2.5, 2.6 Å (IED) via formation of the second bond C4-C5. All reactions beginwith "reduction" of C=C bonds to single C-C (cusp catastrophes). Subsequently, the nonbonding electrondensity is concentrated (fold catastrophes) on terminal C atoms. Finally the new bonds, C1-C6 and C4-C5,are established (cusp catastrophes). Both magnitude and regularity of the electron redistribution, happeningduring reactions enable us to distinguish two effects: (1) the "ring effect", where a large amount of electrondensity is regularly transferred from double C=C bonds to intermolecular regions and single C-C bonds, (2)the "side chain effect"-usually weaker and irregular-involving substituents' bonds. In the transition structure,well formed bonding basin V(C1,C6), is observed only for the PDA···BH3/MVE reaction. For other reactionsonly the nonbonding basins: V(C1) and V(C6), are found in the interaction region C1···C6.