Salem-Turro Analysis

[4 b) 4 a) Z2 =. ..[4 b) 4 a) D=...[4 b) 4 a) and D =. . . 4 b) 4 a) The first two states are zwitterionic, since the bond dissociates heterolytically. Also, since both electrons occupy the same orbital, both zwitterionic states are singlet states and will be totally symmetric with respect to any symmetry operation which may be preserved in the dissociation. By our assumption that ((iij) it is expected that 

E[Z ) E[Z2). The remaining two states arise from homolytic dissociation of the bond and therefore are diradical in character. Both singlet and triplet states arise. If any residual interaction persists (i.e., if the bond broken was a n bond or the products are held together in a solvent cage), then the triplet diradical state is lower than the singlet diradical state. Otherwise the two have the same energy. Since the electrons end up in different orbitals, the spatial symmetry of the diradical states is detennined by the symmetry properties of f) and The diradical is symmetric (S) if a and are both 

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Figure 15.3. (a) Orbital interaction diagram for the formation of a bond between molecule fragments a and b. (b) Orbitals for Dauben-Salem-Turro analysis of the rupture of the a—b bond left-hand side, orbitals of the bond with other occupied and unoccupied MOs of the reactant (molecule a—b) right-hand side, configurations which arise from the orbitals which made up the bond (other orbitals of fragments a and b not shown). 

Figure 15.5. Dauben-Salem-Turro analysis of the photochemical step of the Norrish Type II reaction. The reaction is efficient on the 3(nn ) surface to yield triplet diradical products. It is less efficient on the 1(nn ) surface since IC is relatively efficient.

This question involves the analysis of carbonyl photochemistry using Dauben-Salem-Turro state correlation diagrams. 

Photolysis of oe-chloro-o-methylacetophenones yields 1-indanones. The mechanism has been studied by laser flash photolysis (Netto-Ferreira, J. C. Scaiano, J. C., J. Am. Chem. Soc., 1991, 113, 5800). Develop a Dauben-Salem-Turro state correlation diagram for the photochemical step and, on the basis of your diagram, discuss the efficiency of the reaction on the singlet and triplet manifold. Do the experimental results agree with your analysis ... 

DABCO, see l,4-Diazabicyclo[2.2.2]octane Dative bond, 49, 262 Dauben-Turro-Salem analysis, 212-213 Norrish type I, 215-217 Norrish type II, 213-215 orbital interaction diagram, 213 Davidson correction, 240 Density, 22... 

The following very useful approach for the analysis of photochemical reactions is due to Dauben, Salem, and Turro [13]. A bond, a—b, made from fragment orbitals and of molecular fragments, a and b, is broken in the process under consideration. The relationship to the orbital interaction diagram is transparent (see Figure 15.3). The orbitals... 

DABCO, see 1,4-Diazabicyclo[2.2.2]octane Dative bond, 49, 262 Dauben-Turro-Salem analysis, 212-213... 

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