Isoprene chemistry

Sequential Oxidation Products from Tropospheric Isoprene Chemistry MACR and MPAN at a NOt-Rich Forest Environment in the Southeastern United States, J. Geophys. Res., 103, 22463-22471 (1998). 

Nouaime, G S. B. Bertman, C. Seaver, D. Elyea, H. Huang, P. B. Shepson, T. K. Starn, D. D. Riemer, R. G. Zika, and K. Olszyna, Sequential Oxidation Products from Tropospheric Isoprene Chemistry MACR and MPAN at a NO,-Rich Forest Environment in the Southeastern United States, J. Geophys. Res., 103, 22463-22471 (1998). 

Hydrogenated Styrene-Diene Copolymers and Radial Isoprene Chemistry... 

The role of isoprene chemistry in controlling atmospheric composition and climate, and the influence of temperature and land use change on isoprene emissions, should not be underestimated. The field observations of OH in isoprene-rich, NO c-poor environments discussed above indicate that isoprene has a considerably smaller effect on OH concentrations than chemistry models predict. This conclusion, based on direct measurements of OH and comparison with model predictions, is also supported by observations of other atmospheric species undertaken in VOC rich NO poor environments. Discrepancies between isoprene concentration measurements and model predictions when constrained to isoprene emission inventories have been reported, as have discrepancies between model predictions of isoprene oxidation product concentrations and those measured. Large model underestimates of OH reactivity and SOA formation under isoprene-rich conditions also point towards significant uncertainties in the OH-initiated isoprene oxidation mechanism. 

The Mainz isoprene mechanism (Poschl et al., 2000) was based on and developed by intercomparison with the MCM, but it is highly condensed with only 16 species and 44 reactions. It was designed to provide a compact representation of the key isoprene chemistry in global models which incorporate explicit O3, NO , , HO , , CO, and CH4 chemistry. Table X-B-3 shows the MIM species included and the compounds they represent. Note that some important species formed in isoprene oxidation, such as CH2O and CH3OOH, are not included as separate species, because they are already included in the CH4 chemistry they appear in the 44 reaction mechanism of MIM as products only. Considerable simplification is introduced by including only MACR its rate coefficients with OH and O3 are taken as the arithmetic mean of those for methacrolein and methylvinylketone. 

The German chemist Otto Wallach (Nobel Prize m chemistry 1910) determined the structures of many terpenes and is credited with setting forth the isoprene rule ter penes are repeating assemblies of isoprene units normally joined head to tail... 

Polyisobutylene and isobutylene—isoprene copolymers are considered to have no chronic hazard associated with exposure under normal industrial use. Some grades can be used in chewing-gum base, and are regulated by the PDA in 21 CPR 172.615. Vulcanized products prepared from butyl mbber or halogenated butyl mbber contain small amounts of toxic materials as a result of the particular vulcanization chemistry. Although many vulcanizates are inert, eg, zinc oxide cured chlorobutyl is used extensively in pharmaceutical stoppers, specific recommendations should be sought from suppHers. 

Block copolymer chemistry and architecture is well described in polymer textbooks and monographs [40]. The block copolymers of PSA interest consist of anionically polymerized styrene-isoprene or styrene-butadiene diblocks usually terminating with a second styrene block to form an SIS or SBS triblock, or terminating at a central nucleus to form a radial or star polymer (SI) . Representative structures are shown in Fig. 5. For most PSA formulations the softer SIS is preferred over SBS. In many respects, SIS may be treated as a thermoplastic, thermoprocessible natural rubber with a somewhat higher modulus due to filler effect of the polystyrene fraction. Two longer reviews [41,42] of styrenic block copolymer PSAs have been published. 

Acyclic C5. The C5 petroleum feed stream consists mainly of isoprene which is used to produce rubber. In a separate stream the linear C5 diolefin, piperylene (trans and cis), is isolated. Piperylene is the primary monomer in what are commonly termed simply C5 resins. Small amounts of other monomers such as isoprene and methyl-2-butene are also present. The latter serves as a chain terminator added to control molecular weight. Polymerization is cationic using Friedel-Crafts chemistry. Because most of the monomers are diolefins, residual backbone unsaturation is present, which can lead to some crosslinking and cyclization. Primarily, however, these are linear acyclic materials. Acyclic C5 resins are sometimes referred to as synthetic polyterpenes , because of their similar polarity. However, the cyclic structures within polyterpenes provide them with better solvency power and thus a broader range of compatibility than acyclic C5s. 

Standard butyl rubber, which is a copolymer of isobutylene with about 2% of isoprene vulcanises in the same manner as natural rubber but, as it only contains a small proportion of polyisoprene, the cross-link percentage is much reduced. It is therefore not possible to make ebonite from a butyl rubber. The same vulcanisation chemistry, with some modifications, applies to ethylene-propylene terpolymers and brominated butyl rubber. 

Grosjean D, EL Williams II, E Grosjean (1993a) Atmospheric chemistry of isoprene and its carbonyl products. Environ Sci Technol 27 830-840. 

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... 

The major source of free-radicals is via 0(1D)+H20, although there is a substantial route to HO2 via HCHO photolysis. This observation is based on the measured concentrations of HCHO, which cannot be accounted for by methane chemistry under the conditions pertaining. Ayers et al. (1997) suggested that isoprene might act as a source, but this cannot explain [HCHO] on 7 February, because the measured isoprene concentrations were low (<2ppt). The... 

Steroid [75] and terpene [76] chemistry is undoubtedly a challenging topic of research that drives hundred of investigators all around the world. Terpenes are a large and structurally diverse family of natural products comprising C5 isoprene... 

Nordmeyer, T., W. Wang, M. L. Ragains, B. J. Finlayson-Pitts, C. W. Spicer, and R. A. Plastridge, Unique Products of the Reaction of Isoprene with Atomic Chlorine Potential Markers of Chlorine Atom Chemistry, Geophys. Res. Lett, 24, 1615-1618 (1997). 

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