Possible reaction pathways

Example Researchers have used MX DO and. AMI setn i-etn pirical methods It) calculate possible reaction pathways for the interae-... 

Alternative algorithms employ global optimization methods such as simulated annealing that can explore the set of all possible reaction pathways [35]. In the MaxFlux method it is helpful to vary the value of [3 (temperamre) that appears in the differential cost function from an initially low [3 (high temperature), where the effective surface is smooth, to a high [3 (the reaction temperature of interest), where the reaction surface is more rugged. 

A strong argument in favor of the proposed mechanism (23) over other possible reaction pathways is that the enhanced driving force, present in the... 

In general however the various possible reaction pathways give rise to formation of a mixture of products. The type I-cleavage reaction is only of limited synthetic importance, but rather an interfering side-reaction—e.g. with an attempted Paterno-Buchi reaction, or when an aldehyde or ketone is used as sensitizer in a [2 -I- l -cy do addition reaction. 

The initial series of major tranquilizers consists of alkylated derivatives of 4-aryl-4-hydroxypiperidines. Construction of this ring system is accomplished by a set of rather unusual reactions. Condensation of methylstyrenes with formaldehyde and ammonium chloride afford the corresponding hexahydro-1,3-oxazines (119). Heating these oxazines in the presence of acid leads to rearrangement with loss of water to the tetrahydropyridines. Scheme 1 shows a possible reaction pathway for these transformations. Addition of hydrogen bromide affords the expected 4-bromo compound (121). This last is easily displaced by water to lead to the desired alcohol (122) The side chain (123) is obtained by Friedel-Crafts acylation of p-fluorobenzene with 4-chloro-butyryl chloride. Alkylation of the appropriate arylpiperidinol with 123 affords the desired butyrophenone derivative. Thus,... 

The mechanism for a non-surface-mediated hydrogen-tranfer from one hydrocarbon fragment to another cannot be identified in ambiguously from the current data alone. Possible reaction pathways include ... 

These three steps can combine in different ways to three possible reaction pathways, I, II, and III. We shall represent them as a table analogous to that in Section 13.1 ... 

On the basis of the previous data, possible reaction pathways may be proposed (Fig. 39.6). To confirm this hypothesis, the key intermediate 2-(ethoxymethoxy)phenol (2-EMP) was synthesized and fed, alone or together with water (Table 39.7). As expected, MDB was formed up to 47.0%, together with a smaller amount of 3-MC, confirming that 2-EMP is intermediate for both the above prodncts. Worthy of note is the formation of significant amounts of PYC, showing that the formation of 2-EMP is at equilibrinm with starting reagents. Lastly, the presence of water not only increased the amount of PYC, but also aided the formation of 2-MP. 

Figure 39.5. Possible reaction pathway in the synthesis of MDB by reaction of pyrocathechol (PYC) and diethoxy methane (DEM).

Devillanova and coworkers have also addressed this issue with some simple thiones and selones. Using spectroscopic analysis and quantum mechanical calculations, they examined the various possible reaction pathways shown in Fig. 5 [72,183]. The geometries and relative stabilities of the charge-transfer and T-shaped hypervalent adducts were compared using DFT cal-... 

The possible reaction pathways for the stereoselective E- and Z-allylation are illustrated in Scheme 7. 1-Silyl-l,3-dienes 22 react with a Ni-H species in the presence of PPI13 to provide a syn-it-allylnickel species 24, the least substituted allylnickel species, which undergoes nucleophilic addition to an aldehyde at the least substituted allylic terminus to provide ( )-allylsilanc ( )-23. It should be noted that the regioselectivities observed for the Ni-H addition to a diene 22 and nucleophilic addition of 24 to aldehydes are opposite to those observed so far in many precedents in this review (e.g., Eqs. 4 and 6). 

C02 elimination and the substitution with water were the most exothermic degradation reactions and this confirmed the observation of C02 evolved during degradation. Isomerisation reactions were also investigated and assessed for the possible reaction pathway exothermicity. The calculations did not try and assess the transition states or barriers along the reaction pathways. 

Detailed studies were carried out at the University of Pennsylvania to cast more light on the obscurities of the complex HCN polymers modern analytical methods were used, including thermochemolysis-GPC/MS. Two suggestions (Fig. 4.10) show possible reaction pathways leading from HCN to HCN polymers and other polymers (Minard et al., 1998). 

Fig. 10.9 Possible reaction pathway for the formation of a cell. The important precursors are an RNA replicase and a self-replicating vesicle. The combination of these two in a protocell leads to a rapid, evolutionary optimisation of the replicase. The cellular structure is completed if an RNA-coded molecular species, for example, a lipid-synthesised ribozyme, is added to the system (Szostak et al., 2001)... 

The following scheme was proposed for the possible reaction pathway, especially in the presence of a large excess of phosphine (96) ... 

FIGURE 3. Possible reaction pathway for Ge—C bond cleavage in amine 25... 

Schematic plots of the internal energy versus the reaction coordinate for both primary and secondary insertions and for generic aspecific, syndiospecific, and isospecific model complexes are sketched in Figures 1.11 a,b, and c, respectively. The minima at the centers and at the ends of the energy curves correspond to alkene-free intermediates, including a growing chain with n and n + 1 monomeric units, respectively. Movements from the central minima toward the left and the right correspond to possible reaction pathways leading to primary and secondary insertions, respectively. For the enantioselective complexes the reaction pathways for monomer enantiofaces being...

There are many possible reaction pathways between acrylonitrile and adiponitrile and, in each, there are several possible rate-determining steps. None of the reaction intermediates has yet been detected electrochemically or spectroscopically thus indicating very fast chemical processes with intermediates of half-lives of < 10-5 s. Bard and Feiming Zhou [104a] have recently detected the CH2 = CHCNT radical by Scanning Electrochemical Microscopy (SCEM) using a 2.5 fim radius Au electrode (1.5 mol CH2 = CHCN in MeCN/TBAPF6). The dimerization rate has been determined to 6.107 M-1 S l. 

Scheme 4. Possible reaction pathways for the hydrodimerization of acrylonitrile to adiponitrile. The asterisk indicates that electron transfer can be from the cathode or from [CH2CHCN] in homogeneous solution...

The first mode of the high resolution C-NMR of adsorbed molecules was recently reviewed Q-3) and the NMR parameters were thoroughly discussed. In this work we emphasize the study of the state of adsorbed molecules, their mobility on the surface, the identification of the surface active sites in presence of adsorbed molecules and finally the study of catalytic transformations. As an illustration we report the study of 1- and 2-butene molecules adsorbed on zeolites and on mixed tin-antimony oxides (4>3). Another application of this technique consists in the in-situ identification of products when a complex reaction such as the conversion of methanol, of ethanol (6 7) or of ethylene (8) is run on a highly acidic and shape-selective zeolite. When the conversion of methanol-ethylene mixtures (9) is considered, isotopic labeling proves to be a powerful technique to discriminate between the possible reaction pathways of ethylene. 

Conversion of methanol-ethylene mixtures The C isotopic labeling is a powerful technique to discriminate between the possible reaction pathways of ethylene (9,50). 

Scheme 9.20 Possible reaction pathways for additions of allenyltributylstannanes to aldehydes in the presence of SnCI4.

Figure 13.49 A possible reaction pathway for formation of the first C-C bond during MTO.

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