Reaction, identity

In a reaction, bonds are broken and made. In some cases free electrons are shifted also. The rcaciion center contains all the bond.s being broken or made during the reaction as well as all the electron rearrangement processes. The reaction uhstme-ture is the structural subunit of atoms and bonds around the reaction center that has to be present in a compound in order for the reaction to proceed in the foi"ward (synthesis) direction (Figure 10,3-32). Both characteristics of a reaction can be used to. search for reactions with an identical reaction center and reaction substructure but with different structural units beyond the reaction substructure. For example, this can be achieved by searching in a reaction database. 

In many cases, two identical reaction systems (e.g., a pilot plant scale and a full-scale commercial plant) exhibit different performances. This difference in performance may result from different flow patterns in the reactors, kinetics of the process, catalyst performance, and other extraneous factors. 

For the identity reactions, the intrinsic barriers are their free energies of activation, which can be determined by tracer studies or less directly by rate-equilibrium correlations. ... 

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. 

Curvature in a Br nsted-type plot is sometimes attributed to a change in transition state structure. This is not a change in mechanism rather it is interpreted as a shift in extent of bond cleavage and bond formation within the same mechanistic pattern. Thus, Ba-Saif et al. ° found curvature in the Br nsted-type plot for the identity reactions in acetyl transfer between substituted phenolates this reaction was shown earlier. They concluded that a change in transition state structure occurs in the series. Jencks et al." caution against this type of conclusion solely on the evidence of curvature, because of the other possible causes. 

Other measures of nucleophilicity have been proposed. Brauman et al. studied Sn2 reactions in the gas phase and applied Marcus theory to obtain the intrinsic barriers of identity reactions. These quantities were interpreted as intrinsic nucleo-philicities. Streitwieser has shown that the reactivity of anionic nucleophiles toward methyl iodide in dimethylformamide (DMF) is correlated with the overall heat of reaction in the gas phase he concludes that bond strength and electron affinity are the important factors controlling nucleophilicity. The dominant role of the solvent in controlling nucleophilicity was shown by Parker, who found solvent effects on nucleophilic reactivity of many orders of magnitude. For example, most anions are more nucleophilic in DMF than in methanol by factors as large as 10, because they are less effectively shielded by solvation in the aprotic solvent. Liotta et al. have measured rates of substitution by anionic nucleophiles in acetonitrile solution containing a crown ether, which forms an inclusion complex with the cation (K ) of the nucleophile. These rates correlate with gas phase rates of the same nucleophiles, which, in this crown ether-acetonitrile system, are considered to be naked anions. The solvation of anionic nucleophiles is treated in Section 8.3. 

Comparison of the dimerization of 1-butene with [(H-COD)Ni(hfacac)] in chloroaluminate ionic liquids with the identical reaction in toluene is quite instructive. First of all, the reaction in the ionic liquid solvent is biphasic with no detectable... 

Pd(0)-catalyzed hydrogenolysis of vinylepoxides offers an attractive regio- and dia-stereoselective route to homoallylic alcohols (Scheme 9.36) [104, 155, 156]. Thus, hydrogenolysis of ( ) olefin 88 affords syn isomer 89 with inversion of configuration at the allylic carbon, while subjection of (Z) isomer 90 to identical reaction conditions results in the anti isomer 91. The outcomes of these reactions are ex-... 

With OH and SH, the nucleophilic substitution of Cl has been reported. Thus, with NaOH, there is a report of successful nucleophilic substitution in 50% aq. acetone at room temperature to give the phenol complex in 36% yield. The latter is then spontaneously deprotonated to give the cyclohexadienyl complex (Eq. (24)). An identical reaction was carried out using NaSH in MeCN (50% yield) to give the thiophenol complex which was deprotonated [72] Eq. (25). These reactions would be especially valuable because direct synthesis of the phenol or thiophenol complexes from ferrocene is not possible due to the strong interaction between the heteroatom and A1C13 [11, 19]. Recent improvement and use of this reaction were achieved [88],... 

Two identical reaction solutions were prepared, one at T,(= 25.000 °C) in the sample compartment of a double-beam spectrophotometer, the other at T2( = 27.170 °C) in the reference beam. A direct recording of AAbs = Absi - Abs2 was made as a function of time while the difference in reaction temperature was maintained to 0.0001 °C. Evaluate kffk and AW1 for the run shown note this calculation is possible with an arbitrary time axis. 

Kinetic studies using 1,9-decadiene and 1,5-hexadiene in comparison widi catalyst 14 and catalyst 12 demonstrate an order-of-magnitude difference in their rates of polymerization, widi 14 being the faster of the two.12 Furdier, this study shows diat different products are produced when die two catalysts are reacted widi 1,5-hexadiene. Catalyst 14 generates principally lineal" polymer with the small amount of cyclics normally observed in step condensation chemistry, while 12 produces only small amounts of linear oligomers widi die major product being cyclics such as 1,5-cyclooctadiene.12 Catalyst 12, a late transition metal benzylidene (carbene), has vastly different steric and electronic factors compared to catalyst 14, an early transition metal alkylidene. Since die results were observed after extended reaction time periods and no catalyst quenching or kinetic product isolation was performed, this anomaly is attributed to mechanistic differences between diese two catalysts under identical reaction conditions. 

These results support the suggestion (20) that positive ion-molecule reactions can and do compete effectively with neutralization steps at pressures near 1 atm. It is, however, apparent that neutralization steps will compete quite effectively at dose rates greater than the relatively low ones used in this work. Since G( — CD4) and G( —ND3) are proportional to J 1/2, neutralization will compete on an equal footing for methanium and ammonium ions at dose rates of the order of 1016 e.v./cc. sec. in otherwise identical reaction mixtures, and the chain character of... 

In our previous studies on chlorination of toluene we had found that solvent had an important effect on the selectivity. In particular, the use of diethyl ether as a cosolvent was advantageous for the production of a high proportion of the para-isomer (ref. 9). An experiment in which the amount of ether in a tetrachloromethane/diethyl ether solvent mixture was varied under otherwise identical reaction conditions (Ih reaction at 18°C with 1.04 molar equivalent of tert-butyl hypobromite) demonstrated that diethyl ether also had a marked influence on the selectivity of the bromination reaction (Fig. 6). There was also an effect on the yield of the reaction as performed under these standard conditions. As the... 

In 2008, Grisi et al. reported three ruthenium complexes 65-67 bearing chiral, symmetrical monodentate NHC ligands with two iV-(S)-phenylethyl side chains [74] (Fig. 3.26). Three different types of backbones were incorporated into the AT-heterocyclic moiety of the ligands. When achiral triene 57 was treated with catalysts 65-67 under identical reaction conditions, a dramatic difference was observed. As expected, the absence of backbone chirality in complex 65 makes it completely inefficient for inducing enantioselectivity in the formation of 58. Similarly, the mismatched chiral backbone framework of complex 66 was not able to promote asymmetric RCM of 57. In contrast, appreciable albeit low selectivity (33% ee) was observed when the backbone possessed anti stereochemistry. 

An identical reaction to the previous one can be carried out with carbon tetrachloride either at 25-106°C and under 30-80 bar or in the presence of a radical initiator (peroxide) ... 

The bed void fraction and the Reynolds number were determined with the experimental procedures reported in literature [7]. Inprehminaty experiments, citral hydrogenation was investigated in six parallel reactors under identical reaction conditions, i.e., at 25°C and 6.1 bar hydrogen with the residence time of 156 s. The... 

Table 13-4. Complexation energy (AEC) and barrier heights (Al .oh and Al .h. see text) for the gas phase bimolecular Sn2 identity reaction CE + CH3C1 —> C1CH3 + Cl" [kcal/mol]. HF and DFT calculations were done with the 6-311+G(d,p) basis set and include zero-point vibrational contributions. 

Method Cyanide is destroyed by reaction with sodium hypochlorite under alkaline conditions. System component Reaction tanks, a reagent storage and feed system, mixers, sensors, and controls two identical reaction tanks sized as the above-ground cylindrical tank with a retention time of 4 h. Chemical storage consists of covered concrete tanks to store 60 d supply of sodium hypochlorite and 90 d supply of sodium hydroxide. 

As mentioned in the Introduction of this book, the quality of a domino process can be correlated to the number of steps involved and the increase of complexity compared to the starting material. Indeed, there are anionic transformations which consist of four and even live separate steps under identical reaction conditions. Again, most of these transformations start with a Michael addition. 

Isoenzymes Structurally related enzyme proteins that catalyse very similar or identical reactions (e.g., monoamine oxidase A and B, cytochrome P-450). 

H20, or colomanite Ca[B30(0H)3] H2O 1 are added under identical reaction conditions, the reaction mixture remains colourless even after two months, and ribose can be detected, apparently stabilized by boric acid. The corresponding ribose-diborate complex (with a molecular weight of 307) has been clearly identified (Ricardo et al., 2004). 

It is known that the oxidation potentials of diazodiphenylmethane and Cu(I) in acetonitrile are very similar. With CuBr2 however, no radical-chain reaction takes place. Contrary to the copper perchlorates, CuBr2 and CuBr initiate identical reaction pathways involving copper carbenoids. No definite answer to this discrepancy is available 402). 

Enantiomers have identical reaction rates with achiral reagents. 

Temperature measurement is achieved by means of a fiber-optic probe immersed in a single reference vessel. An available option is an IR sensor for monitoring the outside surface temperature of each vessel, mounted in the sidewall of the cavity about 5 cm above the bottom. The reaction pressure is measured by a pneumatic sensor connected to one reference vessel. Therefore, the parallel rotors should be filled with identical reaction mixtures to ensure homogeneity. 

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