Methyl substituted ethylenes

For the methyl-substituted ethylenes, i.e. in the absence of any steric effects, there is a roughly linear relationship between the chemoselectivity and the 13C nmr chemical shift of the most substituted carbon atom of the bromonium ions (Dubois and Chretien, 1978). This selectivity is therefore discussed in terms of the magnitude of the charge on the carbon atom and the relative hardness of the competing nucleophiles, according to Pearson s theory (Ho, 1977). However, this interpretation does not take into account the substituent dependence of the nucleophilic solvent assistance, which must play a role in determining this chemoselectivity. 

Itoh, M. and Mulliken, R.S. (1969). Singlet-triplet absorption bands of methyl-substituted ethylenes. J. Phys. Chem. 73, 4332-A334... 

It is clear from these experiments that the presence of ethylene catalyses the fixation of nitrogen in lithium complexes. This assisted complexation was also observed with methyl-substituted ethylene and butadiene. It is a characteristic property of lithium-alkene complexes, as experiments performed with other lithium complexes have so far not yielded such ternary complexes. If one can easily anticipate that the fractional positive charge on the lithium in LiC2H4 and Li(C2H4)2 facilitates the coordination of N2 with, presumably, a a-donation to lithium, and possibly, to a weaker extent, p-donation from the metal, it is difficult to rationalize why LiC2H2 and LiC2H4 behave so differently with respect to nitrogen, for instance. 

Scheme 3.1 Heats of hydrogenation of ethylene and methyl-substituted ethylenes (82°C). 64...

Benzyloxy)methyl-substituted ethylene glycol, first prepared by Howe and Malkin (1951). has been used by many workers to prepare oligoethylene... 

Reaction of (benzyloxy)methyl-substituted ethylene glycol with chloroac-etic acid followed by reduction gave the substituted triethylene glycol. This... 

Bradshaw and Krakowiak have modified the reaction of a dihalide with A-ethyl or A-benzyl-substituted ethanolamine in the presence of a carbonate base in toluene to prepare A,A -diethyl- and A,A -dibenzyldiazapentaeth-ylene glycol in high overall yields (Bradshaw and Krakowiak, 1988 Bradshaw et al., 1988). These diols were reacted with (allyloxy)methyl-substituted ethylene oxide to form the diazahexaethylene glycol containing an (allyl-... 

In all cases, the quantum yield of the molecular elimination of either methane or hydrogen is considered to be smaller than O.OS. Thus, the main primary processes involve either the a(C-C) or the P(C-H) bond ruptures. This observation differs from that made for ethylene, where at least 40% of the fragmentation involves the molecular elimination of hydrogen. May this behavior be linked to the differences observed in the absorption spectra At least, it may be said that well-defined absorption bands, one of which is probably Rydberg in nature, are observed in the ethylene spectrum. Conversely, the spectra of methyl substituted ethylenes are rather unstructured (1). The UV absorption spectrum of 1-butene is shown in Figure 4. We shall come back lat to diis point. 

Rates of the cycloaddition of photoexcited phenanthroquinone to some methyl-substituted ethylenes were measured. Although the reaction gives other products, 1,4-dioxenes are the main ones their rate of formation increases with the number of methyl substituents on the double bond. 

In Table II are recorded the chemical shifts for the protons in a number of methyl-substituted ethylenes and in the corresponding AgBF. 2-olefinates, The proton chemical shifts in the complexed olefin are in every instance downfield from those of the uncomplexed olefin but the spectral pattern is essentially unchanged (some small changes of coupling constants observed) indicating retention of the olefinic character as observed by POWELL and SHEPPARD (3). The downfield change of chemical shift is attributed to proton... 

Polypropylene with the basic methyl substituted ethylene (i.e., propylene) as monomer is prepared industrially by the polymerization of propylene (C3H5) in a low pressure process using a mixture of aluminum triethyl [(C2H5)3A1] and titanium tetrachloride (TiClJ as catalysts. The polymerization reaction is very simple and can be written as follows ... 

There may be a third effect influencing the rate of radical addition, namely steric hindrance to product formation associated with resistance of groups to move into the direction of the initial conformation of the addition product. Examples of this effect appear in the addition of methyl radical to methyl substituted ethylenes as seen in Table II (13). The relative rates are ethylene (1.0), propylene (0.7), cis and trans- 2-butene (0.23 and 0.33), 1,1-dimethylethylene (1.1), trimethylethylene... 

Kawabata, Tsuruta, and Furukawa (121) have reported a linear relationship between the logarithms of their Q values and the logarithms of the methyl affinities of Szwarc and co-workers (111, 123, 124). James and MacCallum (125) have found a linear relationship between the logarithms of the Qo values calculated from the definition of Zutty and Burkhart (122) and the logarithms of the rates of addition of ethyl radicals to various substituted ethylenes. Similar... 

Other polydentate ligands are polyamines and related ligands. Stability constants of silver(I) complexes with polyamines in dimethyl sulfoxide,419 A-methyl-substituted 4-methyldiethylene-triamines,420 or ethylene- or N- or C-methylated ethylenediamine in aqueous solution have been reported.421 The structure of the silver 1,3-diaminopropane complex, [Ag NH2(CH2)3NH2 ]-C104,422 and complex formation with 1,4-diaminobutane and 1,5-diaminopentane have been reported.423 A dinuclear silver(I) compound with ethylenediamine [(enH)Ag(en)Ag(enH)2]4+ has... 

The regiochemistry of methyl radical attack (CH3) to a series of substituted ethylenes (Scheme 12.6) [33]. Generally, the radical attack occurs at the less substituted end of of the olefins. It has been found that while there is no correlation between the global softness (5) for radicals and the barrier heights for radical addition, the barrier tends to decrease with the increase in electronegativity of the radicals. 

Very few directly measured experimental enthalpies are available for methyl radical additions to substituted ethylenes. Reaction enthalpies are therefore normally estimated from other known thermochemical quantities (e.g. C-H BDEs), which often have considerable uncertainties [3], and the derivation generally involves the use of additivity approximations [42, 45], Therefore, theory may be able to provide more accurate values for these enthalpies. Tables 6.25 and 6.26 present reaction enthalpies determined at several levels of theory and compared with the experimental estimates. 

Methyl substitution leads to a decrease in the epoxidation barriers from 18.8 kcal moD for ethylene to 13.7 kcalmol" for isobutylene at the QCISD(T)/6-31G //QCISD/6-31G level. 

The preparation of heterocyclic-substituted ethylene derivatives by direct condensation of aldehydes with activated methyl groups, as, for example, in the formation of 2-styrylbenzoxazole (1) has long been known.1 However, the analogous reaction of aldehydes with those... 

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