Narcissistic reaction

The [l,5]-hydrogen shift in Z-l,3-pentadiene is an example of a narcissistic reaction, with the reactant and product being identical. The TS is therefore located exactly at half-way, and has a symmetry different from either the reactant or product. By suitable constraints on the geometry the TS may therefore be located by a minimization within a symmetry consti ained geometry. 

A chemical reaction in which the reactant is converted into its mirror image, hence the name alluding to the self-admiring nature of the mythic Narcissus. In a narcissistic process, a chiral reactant can be converted into its enantiomer. Racemases catalyze the most obvious narcissistic biochemical reactions. Another example of a narcissistic reaction is degenerate rearrangement. 

Reactant conversion into its mirror image, NARCISSISTIC REACTION REACTING BOND RULES REACTING ENZYME CENTRIFUGATION REACTION COORDINATE DIAGRAM POTENTIAL ENERGY DIAGRAM SADDLE POINT... 

Figure 15.5 Transition-state structure for rate-determining hydrogen atom transfer in the methane metathesis reaction of methyllutetiocene. Note that the kinetics for this narcissistic reaction may be followed by using a label either in the reacting methane or in the methyl group of the starting organometallic...

Narcissistic reaction. 420 Pauli principle, 58 Quantum Mechanics-Molecular Mechanics ... 

Before this development took place the definition of the reaction pathway on the surface, with the concomitant characterization of the transition state had solicited considerable attention. Fukui [191] contributed the idea of the intrinsic reaction coordinate (IRC), but earlier Murrell [192] had discussed the possible symmetries of transition states. This would turn up again in Salem s [193] treatment of the so-called narcissistic reactions. Stanton and Mclver [194] and Pechukas [195] formulated general symmetry conditions for the transition vector. It was thought that symmetry could bring... 

The most common and important case are the narcissistic reactions. Under this type the degenerate transformations are classified [81] in which the structure of the products is viewed as a reflection of the structure of the reactants in a mirror... 

Rotation around a double bond is more complicated than rotation around a single bond. A double bond consists of a a bond and a n bond - on rotation, the jz bond is broken. Ethylene is a planar system, and, by symmetry, the transition state or highest energy point occurs when one CHa unit is perpendicular to the other. At this point, the system has D2d symmetry. Locating transition states in narcissistic reactions of this type is particularly simple. Calculating the electronic structure, however, is not so simple. 

Narcissistic reaction, 420 Natural Atomic Orbital (NAO), 230 Natural bond length, 11 Natural Bond OrbiM (NBO), 230 Natural internal coordinates, for optimization, 327... 

The directions of transition moments in every chromophore are dictated by molecular symmetry. For the cis tautomers of porphycene ( 2 point group), only three mutually orthogonal transition moment directions are allowed. On the other hand, the trans form is of 2 symmetry and, therefore, any direction in the molecular plane is possible, as well as the direction perpendicular to the plane. The determination of transition moment directions in such low symmetry molecules is not an easy task. However, in the case of narcissistic type of reactions exemplified by trans-trans conversion in 1, one can take advantage of an additional symmetry element introduced by the tautomerization process. Double hydrogen transfer converts the molecule into its image, with the horizontal and vertical mirror symmetry planes perpendicular to the molecular plane (Fig. 8.13). Thus, tautomerization results in the rotation of each in-plane transition moment direction. The angle of rotation is twice the value of the angle formed by a particular transition moment with the horizontal (or vertical) in-plane axis. It can be shown [80] that, for a fast excited state process, which results in equal population of both trans tautomers, the measured fluorescence anisotropy r will be expressed by the formula ... 

Just as the carbocyclic Diels-Alder reaction has its heterocyclic counterpart, so does the Cope rearrangement (Chapter 6). It will be recalled that in the archtypical Cope process (without heteroatoms), the narcissistic conversion of 1,5-hexadiene into itself is observed (Equation 9.32). 

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