O’Ferrall-Jencks diagram for

Fig. 9 A hypothetical More-O Ferrall Jencks diagram for the attack of methoxide on O-aryl phosphate triesters (20) and 5-aryl phosphorothioates (21). Note that the diagram for attack of a metal-coordinated methoxide would be similar, but Mx +-coordination would push the TS toward the S-corner, possibly stabilizing the pentacoordinated intermediate to the point that the reaction occurs stepwise with the likely rate-limiting step being breakdown.

A depiction of a hypothetical potential energy surface for a reacting system as a function of two chosen coordinates (c.g., the lengths of two bonds being broken). Such diagrams are useful in assessing structural effects on transition states for stepwise or concerted pathways. An example of More O Ferrall-Jencks diagrams for j8-elimina-tion reactions is shown below. 

Fig. 1 More O Ferrall-Jencks diagram for the deprotonation of a nitroalkane. The curved line shows the reaction coordinate with charge delocalization lagging behind proton transfer.

Fig. 2 Modified More O Ferrall-Jencks diagram for the CH3N02/CH2=N02 system. The curved lines represent the reaction coordinates through the optimized and constrained transition state, respectively. The constrained transition state is less imbalanced as indicated by its location to the left of the optimized transition state.

Fig. 11.4 More O Ferrall-Jencks diagrams for nucleophilic addition to an aldehyde. (A) For general acid catalysis. (B) For general base catalysis. The symbol indicates an imposed decrease in energy of the state indicated.

Fig. 37 More O Ferrall-Jencks diagram for the Menschutkin reactions of 1-phenylethy] and benzyl chlorides with pyridine. The structures of transition states were optimized by ab initio MO calculation (RHF/b-Sf G ). O, substituted 1-phenylethyl chlorides with pyridine , benzyl chlorides with pyrindine , with 4-nitropyridine O, methyl and A, ethyl chlorides with pyridine (Fujio et al, unpublished).

Figure 11 More O Ferrall-Jencks diagram for the identity reactions of substituted phenolate ions with substituted phenyl esters (data from reference 24). See text for the identities of the three identity reactions...

Figure 5 More O Ferrall-Jencks diagram for the elimination reaction (Equation 17). A, El-like E2 mechanism B, synchronous E2 mechanism C, Elcb-like E2 mechanism. The vector (a.) corresponds to a Hammond (parallel) effect and (b) to a Thornton (perpendicular) effect...

Figure 22 More O Ferrall-Jencks diagram for base-catalysed elimination...

Figure 3.2 More O Ferrall-Jencks Diagram for nucleophilic displacements at saturated carbon.

Figure 3.5 Generalised three-dimensional More-O Ferrall-Jencks diagram for nucleophilic substitution at oxocarbenium ion centres. Because carbon cannot have more than eight electrons, only the front south-east tetrahedron is accessible, as shown.

Figure 3.16 More O Ferrall-Jencks diagram for the general acid catalysis of an acetal. The transition state position and reaction coordinate direction are those deduced for benzaldehyde alkyl acetals of acidic alcohols or phenols.

Figure 6.66 More O Ferrall-Jencks diagram for elimination reactions (like the general acid catalysis of acetals, this is a class e reaction and is drawn in the same way as Figure 3.16).

They were able to infer p for the identity reaction in which Ar = Ar, and interpreted the results in terms of a More O Ferrall-Jencks diagram of the type described in Section 5.3. 

O Ferrall-Jencks diagram and ab initio calculations with the 6-31G basis set. It is concluded that the transition state is slightly iilcB-like for (27) and more symmetrical for (28). 

This indicates a similar transition state in terms of leaving group bond fission for the reactions in water and in r-butanol. Fig. 6 shows a More-O Ferrall-Jencks diagram with the loose transition state for the aqueous hydrolysis denoted in the lower right-hand region. The reaction in t-butanol proceeds along the bottom axis via the intermediate in the lower right corner. 

Fig. 6 More-O Ferrall-Jencks diagram illustrating the mechanisms for the reactions of aryl phosphates with water (hydrolysis) and /-butanol. The hydrolysis reaction is concerted but not synchronous in the transition state, bond fission to the leaving group is ahead of bond formation to the nucleophile. In /-butanol, p-nitrophenyl phosphate undergoes reaction by a two-step Dn + An mechanism. The transition state for the rate-limiting first step is similarly late with regard to leaving group bond fission.

Together the Bronsted LFER and the KIE data indicate that transition states for phosphodiesters lie more toward the central area of the More-O Ferrall-Jencks diagram of Fig. 4 than the monoester transition state. The precise location is dependent upon nucleophile and leaving group, but the reactions of diester anions are concerted and exhibit more nucleophilic participation in the transition state, and less bond fission to the leaving group, than monoesters. 

Summary. In summary, the transition states for the uncatalyzed phosphoryl transfer reactions of the three classes of phosphate esters can be generally represented on the More-O Ferrall-Jencks diagram in Fig. 13. It has been noted that phosphoryl transfer reactions follow a trend for the phosphoryl group to bear a... 

The change in a and P can be understood from the More O Ferrall-Jencks diagrams (Figures 8 and 9) where the vector resulting from increasing nucleophilicity of HNu causes a shift to smaller a and smaller P for mechanisms A and B respectively. 

Figures (a) More O Ferrall-Jencks diagram the structure-reactivity surface of the displacement reaction (E - Yy + xY - lx + Values of p or f are normalised by division by or P, for each fundamental bond-forming or -fission...

The saddle point in the More O Ferrall-Jencks diagram has a shape which approximates a quadratic equation with a minimum in a direction perpendicular to the reaction coordinate (Figure A3b) and a quadratic equation with a maximum along the reaction coordinate (Figure A3c). In the illustrations the potential energies for movement in parallel and perpendicular directions are given by parallel = -OJx +(/ /10 + 3)x... 

Hoz, Yang and Wolfe (HYW) [38] made ingenious use of the gas-phase PES for the concerted addition of water to formaldehyde in order to obtain a Bronsted correlation for PT between oxygen atoms. PT from water to the carbonyl oxygen is endothermic in the reactant complex (Fig. 19.5, top left) but very exothermic in the zwitterionic species (bottom left) formed by nucleophilic attack at the carbonyl carbon, as shown by the More O Ferrall-Jencks diagram. There is a single true... 

Figure 19.5 More O Ferrall-Jencks diagram to illustrate how cross-sections of the potential energy surface for gas-phase hydration of formaldehyde yield a family of barriers from which a Br0nsted correlation may be generated (cf. Ref [38]).

Figure 2 A loose transition state for phosphoryl or sulfuryl transfer is one in which bond fission is ahead of bond formation to the nucleophile, and resides in the lower right region of the More-O Ferrall Jencks diagram. A tight transition state is the reverse situation, residing in the upper left region. If the sum of bond order to nucleophile plus leaving group is unity, the transition state will lie on the synchronicity diagonal.

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