Substitution reaction diagram

An interesting question concerns how much the posetic diagram might determine about the molecular structure of the species involved. In particular, what does the substitution reaction diagram for benzene imply about the... 

Particularly Komer in 1874 investigated permutational questions for the case of benzene using (at least implicitly) substitution reaction diagrams with an effort to avoid inadvertent geometrical assumptions. As an alternative to the hexagonal structure for benzene Ladenburg (1869) proposed a triagonal prismatic structure, as indicated in Fig. 2. 

Ivanciuc T, Klein DJ, Ivanciuc O (2005) Posetic Cluster Expansion for Substitution-Reaction Diagrams and its Application to Cyclobutane, J Math Chem, submitted... 

If the Lewis base ( Y ) had acted as a nucleophile and bonded to carbon the prod uct would have been a nonaromatic cyclohexadiene derivative Addition and substitution products arise by alternative reaction paths of a cyclohexadienyl cation Substitution occurs preferentially because there is a substantial driving force favoring rearomatization Figure 12 1 is a potential energy diagram describing the general mechanism of electrophilic aromatic substitution For electrophilic aromatic substitution reactions to... 

Figure 12.1 is a potential energy diagram describing the general mechanism of electrophilic aromatic substitution. For electrophilic aromatic substitution reactions to... 

Claisen rearrangement, 1194-1195 dehydration, 622 elimination reactions, 393 oxidation, 625-626 radical reactions, 243-244 characteristics of, 162-164 comparison with laboratory reactions, 162-164 conventions for writing, 162. 190 energy diagram of, 161 reduction, 723-725 reductive animation, 932 substitution reactions, 381-383 Biological reduction, NADH and, 610-611... 

JABLONSKI DIAGRAM ALLYLIC SUBSTITUTION REACTION ALPHA (a)... 

Probtom 11.12 (a) Draw enthalpy-reaction diagrams for the first step of electrophilic attack on benzene, toluene (meia and para) and nitrobenzene (meta and para). Assume all ground states have the same energy, (b) Where would the para and meta substitution curves for C HjCI lie on this diagram ... 

Fig. 18 Energy diagram for the first step of an electrophilic substitution reaction illustrating the crossing of DA and D +A" configurations. The effect of a substituent that stabilizes the D + A configuration (e.g. by improving the arene donor ability) is indicated by the dotted line. The diagram illustrates the correlation between AAv, the difference in excitation energies for the perturbed and unperturbed systems, and AE, the difference in activation energy for the two systems. (Avoided crossing deleted for clarity)...

Substitution of the central carbon of RX may induce significant mechanistic variations within the range of nucleophilic substitution reactions. For example, introduction of electron-releasing substituents on R will lead to a stabilization of the carbocation configuration [22]. An excellent illustration of this type of process is the reaction of methoxymethyl derivatives (83) taken from Jencks work (Knier and Jencks, 1980). The carbocation within [22] is stabilized by the resonance interaction (84). Thus the configuration diagram... 

A mathematical analysis of all four isomeric thiadiazoles by the simple molecular orbital method has provided molecular diagrams of the free base and conjugate acid of each thiadiazole, with electron densities, bond orders, and free valencies. On this basis, predictions have been made concerning the reactivities of the six non-equivalent carbon atoms, the basicities of the nitrogen atoms, and the delocalization energies in these molecules. The 5-position in free 1,2,4-thiadiazole should possess maximum reactivity in nucleophilic substitution reactions. The treatment also accounts for the order of the polarographic half-wave potentials and the position of the absorption maxima in the ultraviolet region of the spectra of 1,2,4- and 1,3,4-thiadiazoles.4... 

Substituents on the benzene rings exert their usual influence on the orientation and ease of electrophilic substitution reactions. For example, further nitration (HN03-H2S04-S03) of nitroquino-lines occurs meta to the nitro group as shown in diagrams (593) and (594). Friedel-Crafts acylation of 8-methoxyquinoline succeeds (cf. 595) although this reaction fails with quinoline itself. 

Sketch encrgy/reaction coordinate diagrams for ligand-substitution reactions in which products are more stable than reuci.int. and... 

Figure 29 presents an analysis of the data for p-phenyl groups in the Extended Selectivity Treatment. The reactivity of the para position increases significantly with an increase in the electron demand of the substitution reaction. This result is confirmed by an analysis of the data through the Selectivity Relationship in which a linear relationship is predicted for a diagram of log pfh against S (Fig. 30). Again, curvature is evident. It must be concluded that the substitution reactions of biphenyl do not adhere to a linear free-energy relationship (Eabom and Taylor, 1961b Stock and Brown, 1962a).

The silylation of all glassware that contacts the plant extract has proven to effectively reduce adsorption losses. As diagrammed in Figure 8, the hydroxyl adsorption sites on the silica surface can be coated with dichlordimethyl silane. The unreacted chloride groups are then displaced with methanol in a substitution reaction. A secondary advantage of the silyation process is that water will not adhere to the glass surface. Aqueous residues bead together, which allows more efficient sample transfers. 

Theoretical calculations using the simple MO method in the LCAO approximation have provided molecular diagrams of the free base and the conjugate acid (61CCC156). According to these calculations, the 5-position of the non-protonated 1,2,4-thiadiazole system should be the most reactive in nucleophilic substitution reactions. 

Potential energy diagram for a substitution reaction in the gas phase and in solution in water. Reproduced (modified), with permission from Mclver R.T., Sci. Am., 243,148,1980. 

For better understanding of the mechanism of a particular reaction, a two-dimensional More O Ferrall-Jencks (MOFJ) reaction coordinate diagram is most widely and conveniently used in the case of benzylic nucleophilic substitution reactions, the diagram requires separate coordinates for cleavage of the C-L bond (ordinate) and formation of the C-Nu bond to the... 

The TT-electron diagrams also illustrate that the electron density in the pyridine ring is greater than in pyridine itself, accounting for its increased resistance to nucleophilic attack. This is evidenced by the difficulty with which the 6-chloro compounds undergo substitution reactions or reduction, and by failure of the 4-methyl group to condense with aldehydes or to be oxidized. ... 

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