Alkenes correlation table

Pericas and co-workers calculated the exothermicity of the cobaltacycle formation step and were able to correlate this with alkene strain (Table l).12... 

The results with dimethoxyearbene highlight an inherent deficiency of Eq. 4 it is an empirical correlation of parameters normalized to the electrophilic car-bene, CCI2. Its electrophilic heritage means that although the equation can predict values for highly resonance stabilized, nucleophilic carbenes such as (MeO)2C or Me2NCOMe, these are virtual selectivity indexes. The nucleophilic carbenes simply do not add to the aUcenes of the standard set. However, the equation helps us define the Wcxy regions in which electrophilic and nucleophilic carbenes reside. The electrophilic species, which react appropriately with the standard alkenes of Table 1, exhibit w xy values between 0.29 (BrCCOOEt) and... 

Chanical-Shift Ranges of Some Nuclei Reference Standards for Selected Nuclei H and C Chemical Shifts of Useful NMR Solvents Proton NMR Absorptions of Major Functional Groups Some Useful H Coupling Constants Additivity Rules in C NMR Correlation Tables Alkanes Alkenes Alkynes... 

Comparison of the data for methoxide with those for t-butoxide in Table 6.4 illustrates a second general trend Stronger bases favor formation of the less substituted alkene. " A stronger base leads to an increase in the carbanion character at the transition state and thus shifts the transition state in the Elcb direction. A linear correlation between the strength of the base and the difference in AG for the formation of 1-butene versus 2-butene has been established. Some of the data are given in Table 6.5. 

Radical cations can be derived from aromatic hydrocarbons or alkenes by one-electron oxidation. Antimony trichloride and pentachloride are among the chemical oxidants that have been used. Photodissociation or y-radiation can generate radical cations from aromatic hydrocarbons. Most radical cations derived from hydrocarbons have limited stability, but EPR spectral parameters have permitted structural characterization. The radical cations can be generated electrochemically, and some oxidation potentials are included in Table 12.1. The potentials correlate with the HOMO levels of the hydrocarbons. The higher the HOMO, the more easily oxidized is the hydrocarbon. 

Simple alkyl radicals such as methyl are considered to be nonnucleophilic. Methyl radicals are somewhat more reactive toward alkenes bearing electron-withdrawing substituents than towards those with electron-releasing substituents. However, much of this effect can be attributed to the stabilizing effect that these substiments have on the product radical. There is a strong correlation of reaction rate with the overall exothermicity of the reaction. Hydroxymethyl and 2-hydroxy-2-propyl radicals show nucleophilic character. The hydroxymethyl radical shows a slightly enhanced reactivity toward acrylonitrile and acrolein, but a sharply decreased reactivity toward ethyl vinyl ether. Table 12.9 gives some of the reactivity data. 

The structure of the reactant also influences the orientation, i.e. the ratio of 1- to 2-alkenes in the dehydration of 2-alkanols and the ratio of cis to trans alkenes. Table 4 shows that these ratios can also be correlated by the Taft equation. For the cis/trans ratio, a better fit was obtained with steric Es constants of substituents than with polar constants [127]. 

Fluorescence from the excited state complexes of t-1 and electron poor alkenes has been observed only with dimethylfuma-rate and fumaronitrile, both of which form weak ground state complexes with t-1 (76). Fluorescence of the same wavelength and lifetime is observed upon quenching of t or excitation in the charge-transfer absorption band of the complexes of t-1 with these acceptors. Some properties of these excited complexes and other exciplexes of t-1 are summarized in Table 7. Fluorescence maxima, like the absorption maxima, of related charge-transfer complexes, can be correlated with the donor ionization potentials (eq. 16). As shown in Fig. 3, the point for t-1 falls well below the line obtained by Shirota and co-workers (87) for the com-... 

The remaining chemical classes such as alkene (R2 < 0.51), amine (R2 < 0.90), aromatic hydrocarbon (R2 < 0.29), carboxylic acid (R2 < 0.06), and sulfonic acid (R2 < 0.77) do not correlate well. Table 7.6 shows all the QSAR models using ELUMO as the molecular descriptor. 

FIGURE 6. Extended Bronsted plot of ogkH+ vs pK%H for the protonation of some highly activated alkenes RC(X)=CH2, R = H, CH3, Ph see equations 55 and 56 in text, as well as Table 16. The squares represent alkenes with / -substituents these were not included in the correlation... 

The proximity of the diffusion limit also inhibits a detailed discussion of the data in Table 7, but a significant difference to the substituent effects discussed in Section III.D.4 is obvious. Whereas the reactivities of terminal alkenes, dienes, and styrenes toward AnPhCH correlate with the stabilities of the new carbenium ions and not with the ionization potentials of the 7r-nucleophiles [69], the situation is different for the reactions of enol ethers with (p-ClC6H4)2CH+ [136]. In this reaction series, methyl groups at the position of electrophilic attack activate the enol ether double bonds more than methyl groups at the new carbocationic center, i.e., the relative activation free enthalpies are not controlled any longer by the stabilities of the intermediate carbocations but by the ionization potentials of the enol ethers (Fig. 20). An interpretation of the correlation in Fig. 20 has not yet been given, but one can alternatively discuss early transition states which are controlled by frontier orbital interactions or the involvement of outer sphere electron transfer processes [220]. 

The equilibrium constants for a series of cycloalkenes decrease in the order norbomene > c -cyclooc-tene > cyclopentene > cycloheptene > cyclohexene, which correlates with the calculated strain energies as well as the kinetically determined relative adsorption constants on Pt (Table 2). Tolman states that electron donation from a filled metal rf-orbital to an empty alkene Tr -orbital is extremely important in determining the stability of these complexes. Steric effects of substituents are relatively unimportant compared to electronic effects, and resonance is more important than inductive interactions. The ability of the metal to back bond is lowered progressively in the series Ni° > Pt° > Rh > Pt" > Ag which reduces the importance of resonance and decreases the selectivity of the metal for different substituted alkenes. 

Table 1.30 summarizes the data available and Fig. 1.19 shows a plot of the activation energies against the ionization potential of the alkene. Walker et al. [70] have argued that the excellent correlation indicated in Fig. 1.19 provides clear evidence that the parameters in the table refer to the initial addition step. Kinetic data for RO2 + alkene have also been obtained by Waddington and co-workers [107,108]. 

Figure 10. Correlation between d and If for H abstractions from alkenes (Table 4).

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