5- -2,2-dimethyl Isoprene: 1,3-Butadiene, 2-methyl

Penultimate effects have been observed for many comonomer pairs. Among these are the radical copolymerizations of styrene-fumaronitrile, styrene-diethyl fumarate, ethyl methacrylate-styrene, methyl methacrylate l-vinylpyridine, methyl acrylate-1,3-butadiene, methyl methacrylate-methyl acrylate, styrene-dimethyl itaconate, hexafluoroisobutylene-vinyl acetate, 2,4-dicyano-l-butene-isoprene, and other comonomer pairs [Barb, 1953 Brown and Fujimori, 1987 Buback et al., 2001 Burke et al., 1994a,b, 1995 Cowie et al., 1990 Davis et al., 1990 Fordyce and Ham, 1951 Fukuda et al., 2002 Guyot and Guillot, 1967 Hecht and Ojha, 1969 Hill et al., 1982, 1985 Ma et al., 2001 Motoc et al., 1978 Natansohn et al., 1978 Prementine and Tirrell, 1987 Rounsefell and Pittman, 1979 Van Der Meer et al., 1979 Wu et al., 1990 Yee et al., 2001 Zetterlund et al., 2002]. Although ionic copolymerizations have not been as extensively studied, penultimate effects have been found in some cases. Thus in the anionic polymerization of styrene t-vinylpyri-dine, 4-vinylpyridine adds faster to chains ending in 4-vinylpyridine if the penultimate unit is styrene [Lee et al., 1963]. 

Dimethyl peroxide Diethyl peroxide Di-t-butyl-di-peroxyphthalate Difuroyl peroxide Dibenzoyl peroxide Dimeric ethylidene peroxide Dimeric acetone peroxide Dimeric cyclohexanone peroxide Diozonide of phorone Dimethyl ketone peroxide Ethyl hydroperoxide Ethylene ozonide Hydroxymethyl methyl peroxide Hydroxymethyl hydroperoxide 1-Hydroxyethyl ethyl peroxide 1 -Hydroperoxy-1 -acetoxycyclodecan-6-one Isopropyl percarbonate Isopropyl hydroperoxide Methyl ethyl ketone peroxide Methyl hydroperoxide Methyl ethyl peroxide Monoperoxy succinic acid Nonanoyl peroxide (75% hydrocarbon solution) 1-Naphthoyl peroxide Oxalic acid ester of t-butyl hydroperoxide Ozonide of maleic anhydride Phenylhydrazone hydroperoxide Polymeric butadiene peroxide Polymeric isoprene peroxide Polymeric dimethylbutadiene peroxide Polymeric peroxides of methacrylic acid esters and styrene... 

Complexes 17-19 can be written in one valence structure as a, /3-unsaturated carbonyl compounds in which the carbonyl oxygen atom is coordinated to a BF2(OR) Lewis acid. The C=C double bonds of such organic systems are activated toward certain reactions, like Diels-Alder additions, and complexes 17-19 show similar chemistry. Complexes 17 and 18 undergo Diels-Alder additions with isoprene, 2,3-dimethyl-1,3-butadiene, tram-2-methyl-l,3-pentadiene, and cyclopentadiene to give Diels-Alder products 20-23 as shown in Scheme 1 for complex 17 (32). Compounds 20-23 are prepared in crude product yields of 75-98% and are isolated as analytically pure solids in yields of 16-66%. The X-ray structure of the isoprene product 20 has been determined and the ORTEP diagram (shown in Fig. 3) reveals the regiochemistry of the Diels-Alder addition. The C-14=C-15 double bond distance is 1.327(4) A, and the... 

Butadiene, 2 -methyl -1,3-lmLadiene (uoprene), and 2,3-dimethyl-1,3-butadiene can yield mono- or diepoxides depending on ilie reactant ratio employed. 11 With isoprene the most substituted rlntible bond is attacked first (Eq. 7). 

Shima, Smid and Szwarc (56) studied the effect of the methyl substitution in the polymerization of butadiene, isoprene and dimethyl-butadiene. They showed that the electron-donating methyl group decreased the rate of polymerization catalysed by polystyrylsodium. This same electron releasing effect of the methyl is seen, since the 3.4-structure, not 1.2-structure, is produced predominantly from isoprene. This results from the anionic propagation mechanism of the alkali metal alkyl catalysed polymerization of dienes which produced 1.2 and 3.4-structures. 

Cyclobuten-Bildung findet auch bei zahlreichen substituierten 1,3-Buta-dienen statt (z.B. bei Isopren (92,277), 2,3-Dimethylbutadien-(l,3) (92, 277), trans-l,3-Pentadien (277), l-Cyclohexylbutadien-(l,3) (92), Sorbin-alkohol (92) und 2,3-Diphenyl-butadien (322)). Besonders erwahnt sei das 4-Methyl-l,3-pentadien (Formel 60), das bei der UV-Bestrahlung nicht 3,3-Dimethylcyclobuten-(l) (Formel 59), sondem 1,3-Dimethyl-cyclobuten-(l) (Formel 62) (92,126) liefert. 

Wiberg and coworkers published relative rate constants and the products of reaction of silene 6 with a number of alkenes and dienes in ether solution at 100 °C6 106-108. These data are listed in Table 2 along with an indication of the type of product formed in each case. As is the norm in Diels-Alder additions by more conventional dienophiles, the rate of [2 + 4]-cycloaddition of 6 to dienes increases with sequential methyl substitution in the 2- and 3-positions of the diene, as is illustrated by the data for 2,3-dimethyl-1,3-butadiene (DMB), isoprene and 1,3-butadiene. The well-known effects of methyl substitution at the 1- and 4-positions of the diene in conventional Diels-Alder chemistry are also reflected with 6 as the dienophile. For example, lruns-1,3-pen tadiene reacts significantly faster than the f/.v-isorrier, an effect that has been attributed to steric destabilization of the transition state for [2 + 4]-cycloaddition. In fact, the reaction of c/s-l,3-pentadiene with 6 yields silacyclobutane adducts, while the trans-diene reacts by [2 + 4]-cycloaddition108. No detectable reaction occurs with 2,5-dimethyl-2,4-hexadiene. The reaction of 6 with isoprene occurs regioselectively to yield adducts 65a and 65b in the ratio 65a 65b = 8.5 (equation 50)106,107. 

The rhodium-catalyzed addition of ethylene to 1,3-butadiene to yield 1,4-hexadiene (5a, 151) proceeds via a similar mechanism (151) with the exception that, upon formation of the alkylrhodium(III) species, the hexadiene synthesis proceeds without further change in the oxidation state of the metal. In these reactions with butadiene the coordinated alkyl groups are either chelate or 7r-allyl structures which appear to stabilize Rh(III) (151). The addition of propylene to butadiene and isoprene to produce [Pg.297]

Only one activating group on the alkyne is necessary for the cycloaddition to occur, and the monophosphorylated acetylene reacts as readily as the diphosphorylated one. Dienes such as isoprene, 2,3-dimethyl-l,3-butadiene, cyclopentadiene, l,3-cyclohexadiene, " anthracene, 9-methylanthracene, ° d-methyl-S-propoxyoxazole, l-phenyl-3,4-dimethylphosphole (Scheme 1.25), and a-pyronc have been employed. 

AuBer Butadien und Isopren wurden aueh cis- und fra ts-Pentadien-(l,3) und Cyelo-pentadien an Benzol photoaddiert, doch konnte die Struktur der entstehenden Addukte bisher nicht aufgeklart werden3. Mit 2,3-Dimethyl-butadien-(l, 3) entsteht endo-6-Methyl- sowie exo-6-Methyl-6-isopropenyl-tricydo 3.3.0.0z 8]octeM-(3) und 3,4-Dimethyl-bicyclo[4.2,2]decatrien-(3,7,9). ... 

During World War I German chemists, whose coxmoy was cut off from its sources of natural rubber by the British blockade, polymerized 3-methyl-isoprene (2,3-dimethyl-1,3-butadiene) units, (CH2=C(CH3)C(CH3)=CH2), obtained from acetone, to form an inferior substitute called methyl rubber. By the end of the war Germany was producing 15 tons (13.6 metric tons) of this rubber per month. The USSR (Union of Soviet Socialist Republics), which built a pilot plant at Leningrad (now St. Petersburg) in 1930 and three factories in 1932 and 1933, was the first country to institute a full-scale synthetic rubber industry. 

The reaction of dienes, 2,3-dimethyl-l,3-butadiene, isoprene, cyclopentadiene, and 1,3-cyclohexadiene, with cycloarsenic compounds, (AsCp3)4 43 or (AsCF3)5 44, led to the [4-1-2] cycloaddition products l,2-bis(trifluoro-methyl)-l,2,3,6-tetrahydro-l,2-diarsinine 45, 2,3-bis(trifluoromethyl)-2,3-diarsa-bicyclo[2.2.1]hept-5-ene 46, and 2,3-bis(trifluoromethyl)-2,3-diarsa-bicyclo[2.2.2]oct-5-ene 47 (Scheme 16) <1995ZNB189>. 

In formations of ternary complexes, the acceptor vinyl compound must have a double bond conjugated to a cyano or to a carbonyl group. Such acceptors are acrylonitrile, methacrylonitrile, acrylic and methacrylic esters and acids, methyl vinyl ketone, acrylamide, etc. Donor monomers are styrene, a-methyl styrene, butadiene, 2-3-dimethyl butadiene, isoprene, chloroprene, etc. 

Electron-withdrawing substituents in anionic polymerizations enhance electron density at the double bonds or stabilize the carbanions by resonance. Anionic copolymerizations in many respects behave similarly to the cationic ones. For some comonomer pairs steric effects give rise to a tendency to altemate. The reactivities of the monomers in copolymerizations and the compositions of the resultant copolymers are subject to solvent polarity and to the effects of the counterions. The two, just as in cationic polymerizations, cannot be considered independently from each other. This, again, is due to the tightness of the ion pairs and to the amount of solvation. Furthermore, only monomers that possess similar polarity can be copolymerized by an anionic mechanism. Thus, for instance, styrene derivatives copolymerize with each other. Styrene, however, is unable to add to a methyl methacrylate anion, though it copolymerizes with butadiene and isoprene. In copolymerizations initiated by w-butyllithium in toluene and in tetrahydrofuran at-78 °C, the following order of reactivity with methyl methacrylate anions was observed. In toluene the order is diphenylmethyl methacrylate > benzyl methacrylate > methyl methacrylate > ethyl methacrylate > a-methylbenzyl methacrylate > isopropyl methacrylate > t-butyl methacrylate > trityl methacrylate > a,a -dimethyl-benzyl methacrylate. In tetrahydrofuran the order changes to trityl methacrylate > benzyl methacrylate > methyl methacrylate > diphenylmethyl methacrylate > ethyl methacrylate > a-methylbenzyl methacrylate > isopropyl methacrylate > a,a -dimethylbenzyl methacrylate > t-butyl methacrylate. 

The kinetics of the reaction of NO3 with the following molecules have been investigated using the discharge-flow mass spectrometry method 2,3 dimethyl-2, butene ((CH3)2C=C(CH3)2), 1,3 butadiene (CH2=CH-CH=CH2), 2 methyl-1,3 butadiene (CH2=C(CH3)-CH=CH2, isoprene) and 2,3 dimethyl-1,3 butadiene (CH2=C(CH3)-C(CH3) = CH2). 

The olefins investigated were 1,1-diphenylethylene, stilbene, styrene, 2-methyl-propene, 2,3-dimethyl-2-butene, butadiene, pentadiene, and isoprene. The phenyl-substituted alkenes were chosen because the spectra of the expected carbonyl oxides are well known, the alkyl-substituted because of their relevance in tropospheric chemistry. 

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