Bond exchange reaction

Heitler-London type VB theory uses only "perfect-pairing" type "structures. (The effects of ionic structures are included via the delocalization of the atomic orbitals). Thus for a model two-bond exchange reaction there are only two structures that need to be considered. 

JI 14] Ji S., Cao W., Yu Y. et al., Dynamic diselenide bonds exchange reaction induced by visible fight without catalysis , Angewandte Chemie International Edition, vol. 53, no. 26, pp. 6781-6785,2014. 

Figure B2.4.5. Simulated lineshapes for an intennolecular exchange reaction in which the bond joining two strongly coupled nuclei breaks and re-fomis at a series of rates, given beside tlie lineshape. In slow exchange, the typical spectrum of an AB spin system is shown. In the limit of fast exchange, the spectrum consists of two lines at tlie two chemical shifts and all the coupling has disappeared.

The hydration reaction has been extensively studied because it is the mechanistic prototype for many reactions at carbonyl centers that involve more complex molecules. For acetaldehyde, the half-life of the exchange reaction is on the order of one minute under neutral conditions but is considerably faster in acidic or basic media. The second-order rate constant for acid-catalyzed hydration of acetaldehyde is on the order of 500 M s . Acid catalysis involves either protonation or hydrogen bonding at the carbonyl oxygen. 

The reaction of the stabilized yUde 46 (a-vinyl substituted) with the cycloocta-dienyl Pd(II) allows the synthesis of a novel complex, the (rj -allyl)palladium 47, in which the olefmic double bond participates in the coordination (Scheme 20) [83]. The coordination of the bis-yUde 48 with the same starting Cl2Pd(COD) leads to the formation of another new palladium complex 49 via COD exchange reactions. A C-coordination mode takes place between the carbanionic centers of the bis-ylide and the soft palladium and two stereogenic centers of the same configuration are thus created [83]. In contrast to the example described in Scheme 19, the Cl2M(COD) (M=Pd or Pt), in presence of a slightly different car-... 

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