Propylene resonances

Resonance theory can also account for the stability of the allyl radical. For example, to form an ethylene radical from ethylene requites a bond dissociation energy of 410 kj/mol (98 kcal/mol), whereas the bond dissociation energy to form an allyl radical from propylene requites 368 kj/mol (88 kcal/mol). This difference results entirely from resonance stabilization. The electron spin resonance spectmm of the allyl radical shows three, not four, types of hydrogen signals. The infrared spectmm shows one type, not two, of carbon—carbon bonds. These data imply the existence, at least on the time scale probed, of a symmetric molecule. The two equivalent resonance stmctures for the allyl radical are as follows ... 

Reaction Mechanism. High temperature vapor-phase chlorination of propylene [115-07-17 is a free-radical mechanism in which substitution of an allyhc hydrogen is favored over addition of chlorine to the double bond. Abstraction of allyhc hydrogen is especially favored since the allyl radical intermediate is stabilized by resonance between two symmetrical stmctures, both of which lead to allyl chloride. 

As shown, ia the case of chlotination of aEyl chloride, the resonance states of the chloroaEyl radical iatermediates are not symmetrical and their propagation reactions lead to the two different dichloropropene isomers ia an approximate 10 90 ratio (26). In addition, similar reactions result ia further substitution and addition with products such as trichloropropanes, trichloropropenes, tetrachloropropanes, etc ia diminisbing amounts. Propylene dimerization products such as 1,5-hexadiene, benzene, 1-chloropropane, 2-chloropropane, high boiling tars, and coke are also produced ia smaE amounts. 

Table III presents the relative rates of H2 transfer reactions from cyclo-C5H10 and C5H12 to propylene, ethylene, acetylene, and cyclopropane. These values were obtained by irradiating pentane-CwDm-02 mixtures with gamma rays, or with the argon resonance lines at 1048-1067 A. The results obtained by the two irradiation techniques are in fair agreement.

CHj)2N(CH2)2N(CH3XCH2)2N(CH3)2 proton magnetic resonance propylene-l,3-diamine, 1,3-H2NCH2CH2CH2NH2 positive... 

The exact enthalpy of polymerization for a particular monomer will depend on the steric and electronic effects imposed by the substituents attached to the E=E double bond. For olefins, resonance stabihzation of the double bond and increased strain in the polymer due to substituent interactions are the most important factors governing AHp For example, propylene has a calculated AH of -94.0 kJ moT, whereas the polymerization of the bulkier 2-methylpropene is less exothermic (-78.2 kJ moT ) [63]. Due to resonance effects, the experimentally determined AH of styrene (-72.8 kJ mol ) is less exothermic than that for propylene, while that for bulkier a-methylstyrene is even less favorable (-33.5 kJ moT ) [63]. In general, bulky 1,2-disubstituted olefins (i.e., PhHC= CHPh) are either very difficult or impossible to polymerize. 

NMR OU PEO Ph PFD PO Q rpm RT SAPO SBA SBU SDA Nuclear magnetic resonance Osaka University Polyethylene oxide Phenyl Pulsed laser deposition Propylene oxide Quinuclidene Revolutions per minute Room temperature Silicoaluminum phosphate Santa Barbara Secondary building unit Structure directing agent... 

Fig NMR spectra of propylene oxide in carbon tetrachloride solution (top) conventional spectrum and (bottom) double-resonance spectrum showing simplification resulting from collapse of the splitting due to coupling. 

High pressure free radical process is not suitable for propylene due to extensive hydrogen transfer to free radical which results in resonance stabilised alkyl radicals with reduced tendency to... 

Methyl end groups resulting from main-chain scission in ethylene-propylene copolymers have observed by their characteristic 13C NMR resonance and determined quantitatively to give values of G(scission). 

Frei and co-workers also extended this reaction to other zeolites showing that almost identical behavior was observed in BaY, BaX, and in the K+ and Ba " forms of zeolite L [45,46]. Xiang et al. [47] have also studied the photooxidations of a series of 1-alkenes in the more acidic BaZSM-5 [48] and Ba- 3. The extensive polymerization of propylene in these zeolites demonstrates the detrimental effect of Bronsted acid sites on the reaction selectivity. These workers also used ex situ nuclear magnetic resonance (NMR) allowing more detailed... 

This agrees with the theory that resonance-nonstabilized primary carban-ions are more stable than the corresponding secondary or tertiary carb-anions, whereas tertiary carbonium ions or radicals are more stable than the corresponding secondary and primary species. If radical intermediates were involved in a chain catalytic reaction of toluene with propylene, n-butylbenzene would be the product. 

An even simpler spectrum (a single resonance for sterically pure samples) was obtained from polymers of the two [(Z) and ( )] isomers of propylene-1,2,3,3,3-[Pg.35]

The mechanism is undoubtedly a free radical reaction that occurs very easily at the allyl site in propylene, forming the resonance-stabilized allyl radical. 

Many substituents stabilize the monomer but have no appreciable effect on polymer stability, since resonance is only possible with the former. The net effect is to decrease the exothermicity of the polymerization. Thus hyperconjugation of alkyl groups with the C=C lowers AH for propylene and 1-butene polymerizations. Conjugation of the C=C with substituents such as the benzene ring (styrene and a-methylstyrene), and alkene double bond (butadiene and isoprene), the carbonyl linkage (acrylic acid, methyl acrylate, methyl methacrylate), and the nitrile group (acrylonitrile) similarly leads to stabilization of the monomer and decreases enthalpies of polymerization. When the substituent is poorly conjugating as in vinyl acetate, the AH is close to the value for ethylene. 

Fig. 12. Correlation of the rate constant (fc) for the spin orbit relaxation of l(5QPy2) with the excitation energy [ (j3)] of the colliding olefin. (1) Tetramethylethylene. (2) cis-and t/ww-2-Butene. (3) Isobutene. (4) 1-Butene. (5) Propylene. (6) Ethylene. ( 3) = E (units of a resonance integral 3 for a standard C=C bond).133...

Fig. 45. Temperature dependence of 13C T, for the propylene oxide CHCH2 resonance in the linear (O, ) and crosslinked polyurethanes (A, 4k). The values are determined from the pulse sequences with cross-polarization ( , A) and the direct application of a carbon 90° degree pulse (O, A) (adapted from Ref.301 )...

The signal a of methyl protons consists of two doublet resonances. The weak doublet resonance (d, 8 1.98, JH H = 6.8 Hz) at lower field is related to the erythro (isotactic) placement of the last propylene unit (4-e), whereas the strong doublet resonance (d, 8 1.95, JH H = 6.8 Hz) at higher field is related to the threo (syndiotactic) placement of the same unit (4-t),... 

Poly(Propylene). In principle, resolution of individual carbon resonances in bulk polymers allows relaxation experiments to be performed which can be interpreted in terms of mainchain and side chain motions in the solid. This is a distinct advantage over the more common proton NMR relaxation experiments where efficient spin-diffusion usually results in the averaging of the relaxation behavior over the ensemble of protons. Thus, a direct... 

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