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Electron affinity 1,3-butadiene

We saw previously that hydrated electrons react very rapidly with the conjugated 1,3-butadiene (k = 8 x 109 M-1 s 1). In less polar solvents the attachment of an electron to 1,3-butadiene (with adiabatic electron affinity of —0.62 eV20) will be slower. The... [Pg.334]

An examination of reported reactivity ratios (Table 6) shows that the behaviour rj > 1, r2 1 or vice versa is a common feature of anionic copolymerization. Only in copolymerizations involving the monomers 1,1-diphenylethylene and stilbene, which cannot homopolymerize, do we find <1, r2 <1 [212—215], and hence the alternating tendency so characteristic of many free radical initiated copolymerizations. Normally one monomer is much more reactive to either type of active centre in the order acrylonitrile > methylmethacrylate > styrene > butadiene > isoprene. This is the order of electron affinities of the monomers as measured polarographically in polar solvents [216, 217]. In other words, the reactivity correlates well with the overall thermodynamic stability of the product. Variations of reactivity ratio occur with different solvents and counter-ions but the gross order is predictable. [Pg.56]

Hohoyd and coworkers studied the attachment of excess electrons to 1,3-butadiene in n-hexane solution, and the detachment of an electron from the butadiene anion. It was found that the equilibrium constant K for equation 25 increases rapidly with pressure and decreases with increasing temperature, as was found earlier for other molecules with negative electron affinities in non-polar solvents. At —7°C attachment is observed at 1 bar. At high pressure it was found that the rate of the attachment is diffusion-controlled. Freeman and coworkers measured the free-ion yields in several liquid hydrocarbons, three of which were cyclic dienes, as a function of temperature. At room temperature they measured free-ion yields of 7.5 nmol and 23 nmolJ for 1,3- and 1,4-cyclohexadiene,... [Pg.335]

Selective solvation has been proved in many cases [233-235]. On the other hand, the behaviour r, 1, Y2 1 is a common feature of anionic copolymerization. One monomer is usually much more reactive to either type of active centre in the order acrylonitrile > methyl methacrylate > styrene > butadiene > isoprene, in agreement with its electron affinity [235]. [Pg.332]

Table 1.2 The Butadiene tc-system, with AN=N =4, frontier energetic quantities, ionization potential IP), electron affinity EA), electronegativity (x), and chemical hardness (rj) of Eqs. 1.7 and 1.8 - in electron volts (eV), and the resulted parabolic energy of Eq. 1.98, alongside with the 7t-related energy based on the Hiickel simplified (with Coulomb integrals set to zero, a = 0) expression of (1.97) for the experimental/Hiickel method and on the related energy form of Eq. 1.101 and the other semi-empirical methods CNDO, INDO, MINDO, MNDO, AMI, PM3, ZINDO) as described in the previous section - expressed in kilocalories per mol (kcal/mol) their ratio in the last column reflects the value of the actual departure of the electronegativity and chemical hardness parabolic effect from the pi-bonding energy, while for the first (Exp Hiickel) line it expresses the resonance contribution (and a sort of P factor integral) in (1.97) for the tt-bond in this system the eV to kcal/mol conversion follows the rule 1 eV = 23.069 kcal/mol... Table 1.2 The Butadiene tc-system, with AN=N =4, frontier energetic quantities, ionization potential IP), electron affinity EA), electronegativity (x), and chemical hardness (rj) of Eqs. 1.7 and 1.8 - in electron volts (eV), and the resulted parabolic energy of Eq. 1.98, alongside with the 7t-related energy based on the Hiickel simplified (with Coulomb integrals set to zero, a = 0) expression of (1.97) for the experimental/Hiickel method and on the related energy form of Eq. 1.101 and the other semi-empirical methods CNDO, INDO, MINDO, MNDO, AMI, PM3, ZINDO) as described in the previous section - expressed in kilocalories per mol (kcal/mol) their ratio in the last column reflects the value of the actual departure of the electronegativity and chemical hardness parabolic effect from the pi-bonding energy, while for the first (Exp Hiickel) line it expresses the resonance contribution (and a sort of P factor integral) in (1.97) for the tt-bond in this system the eV to kcal/mol conversion follows the rule 1 eV = 23.069 kcal/mol...
In order to obtain well-defined AB diblock copolymers by anionic polymerization and sequential monomer addition, some crucial conditions must be fulfilled (1) the carbanion formed by the second monomer must be more, or at least equally, stable than the one derived from the first monomer, and (2) the initiation of polymerization of the second monomer by the anion of the first monomer must be higher than the rate of propagation of monomer B. To fulfill these requirements, the monomers used must be added sequentially in the order of increasing electron affinity (e.g., a-methyl styrene (aMeSt) < St butadiene (Bd)< vinyl pyridine < methyl methacrylate (MMA)) and the nucleophilicity of the intermediate macromolecular carbanion A formed should at least match (though... [Pg.459]


See other pages where Electron affinity 1,3-butadiene is mentioned: [Pg.106]    [Pg.335]    [Pg.174]    [Pg.185]    [Pg.332]    [Pg.3631]    [Pg.106]    [Pg.161]    [Pg.191]    [Pg.1247]    [Pg.896]    [Pg.385]    [Pg.293]    [Pg.38]    [Pg.284]    [Pg.186]    [Pg.259]   
See also in sourсe #XX -- [ Pg.276 ]




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