Isoprene chemical structure

Camphor is a 10-carbon odoriferous natural product made from the joining of two isoprene units plus the addition of a ketone. Shown here is its chemical structure. Find and circle the two isoprene units. 

A more detailed analysis of the NMR signal from elastomer samples, addresses finer details such as the chemical structure of chain segments. In general a hierarchy of dipolar interaction between protons exists instead of a single chain-averaged dipolar interaction [34, 35]. For example, in cis-l,4-poly(isoprene) these different dipolar interactions can... 

Figure 9.9 Chemical structure of an isoprene (methylbuta-1,3-diene) unit containing five carbons.

Fig. 55 Chemical structure of complex formation between a phenolic resin and poly(2-vinylpyridine-b-isoprene). TEM-micrograph of the composite, indicating the microphase separation. Reprinted with permission from [201]...

The chemical structure of a polymer determines whether it will be crystalline or amorphous in the solid state. Both tacticity (i.e., syndio-tactic or isotactic) and geometric isomerism (i.e., trans configuration) favor crystallinity. In general, tactic polymers with their more stereoregular chain structure are more likely to be crystalline than their atactic counterparts. For example, isotactic polypropylene is crystalline, whereas commercial-grade atactic polypropylene is amorphous. Also, cis-pol3nsoprene is amorphous, whereas the more easily packed rans-poly-isoprene is crystalline. In addition to symmetrical chain structures that allow close packing of polymer molecules into crystalline lamellae, specific interactions between chains that favor molecular orientation, favor crystallinity. For example, crystallinity in nylon is enhanced because of... 

Chemical/Pharmaceutical/Other Class Terpene, closely related to isoprene Chemical Formula CioHig Chemical Structure ... 

Terpenes are are a class of compounds whose chemical structures are based on a number of isoprene units , derived from the hydrocarbon CH2=C(CH3)-CH=CH2 they may themselves be hydrocarbons, but may also contain alcohol (OH), aldehyde/ketone (CO) and carboxylic acid (COOH) groups. Monoterpenes are Cm compounds derived from two isoprene units, sesquiterpenes (Cu) are derived from three isoprene units, diterpenes (C20) from four and tritepenes (C30) from six. Terpenes are widespread in plants, where they are largely responsible for the odor, and they are the major constituents of plant-derived essential oUs . Among the best known terpenes are 3-pinene (turpentine), camphor, menthol and citroneUal (aU monoterpenes) and farnesol (a sesquiterpene that is a constituent of the essential oils of many plants). Certain terpenes have important biological roles vitamin A, for example, is a diterpene, and steroid hormones have a structure related to triterpenes (and are biosynthesized by a similar route). 

The chemical structure of naturally occurring ais polyisoprenes was determined by 13C NMR spectroscopy using acyclic terpenes and polyprenols as model compounds. The arrangement of the isoprene units along the polymer chain was estimated to be in the order dimethylallyl terminal unit, three trans units, a long block of ais units, and ais isoprenyl terminal unit. This result demonstrates that the biosynthesis of cis-polyisoprenes in higher plants starts from trans,trans,trarcs-geranylgeranyl pyrophosphate. ... 

Another name for isoprene is 2-methyl-1,3-butadiene. When illustrating the reactions of isoprene it is convenient to use the shorthand chemical structure (see Table 2.12),... 

The synthetic rubbers most frequently used for car tyres are emulsion and solution styreen/butadiene random copolymers (ESBR and SSBR) and butadiene rubber (BR). Truck tyres, however, often contain a certain amount of natural rubber (NR) or its synthetic version isoprene rubber (IR). The Tg-value of BR rubber as such can vary, depending on its chemical structure between -100°C and -20°C the Tg-value of SBR can, in principle, vary between -100°C and 100°C. 

The simple isoprene unit is the basis of an enormous range and a variety of chemical structures which we know as terpenoids. 

Butyl rubber consists mostly of isobutylene (95-98%) and about 2-5% isoprene units. 1 The isoprene unit is halogenated by either chlorine or bromine to obtain the corresponding halobutyl rubbers. Despite the superior elastomeric properties of halobutyl, the elastomer can easily undergo dehydrohalogenation leading to crosslinfang, and the isoprene unsaturation is subject to ozone cracking. To remedy these problems and to improve the halobutyl properties, a new class of elastomer poly(isobutylene-co-p-methylstyrene) [poly (IB-PMS)] was developed. Unlike butyl rubber, it contains no double bonds and therefore cannot be crosslinked unless otherwise functionalized. The chemical structures of butyl rubber and poly (IB-PMS) copolymers are shown below. 

Coenzyme Q is well defined as a crucial component of the oxidative phosphoiylation system in the mitochondria, where energy derived from the products of fatty acids and carbohydrates is converted into ATP to drive cellular machinery and biosynthetic processes (Figure 36.3). Coenzyme Q (also known as ubiquinone) was discovered by Fred Crane and his colleagues in 1957 in beef heart mitochondria. Karl Folkers and his associates elucidated its chemical structure in 1958. Coenzyme Q is composed of a homologous series of compounds differing in the length of the isoprene side chain, and coenzyme Qio, the homologue present in humans and several other species, has 10... 

Coenzyme Qio is a member of the ubiquinone family of compounds. All animals, including humans, can synthesize ubiquinones hence, coenzyme Qio cannot be considered a vitamin. The name ubiquinone refers to the ubiquitous presence of these compounds in living organisms and their chemical structure, which contains a functional group known as a benzoquinone. Ubiquinones are fat-soluble molecules with anywhere from 1 to 12 isoprene (5-carbon) units. The ubiquinone found in humans, ubidecaquinone or coenzyme Qio, has a tail of 10 isoprene units (a total of 50 carbon atoms) attached to its benzoquinone head (Figure 8.20). ... 

Fig. 2.8 a Unit cell of the Fddd structure found in diblock copolymers. (Reprinted with permission from Kim et al. [37], Copyright 2013 American Chemical Society) b Reconstructed three-dimensional image of a poly(styrene)-b-poly(isoprene) Fddd structure obtained by transmission electron microtomography. (Reproduced from Jung et al. [38] with permission of The Royal Society of Chemistry) c Brdl and stick model of the Pnna (No. 52). (Reproduced from Bluemle et al. [39] with permission of The Royal Society of Chemistry)... 

But the most important water-soluble non-isoprene is another carbohydrate called quebrachitol, or 2-0-methyl-L-inositol (see chemical structure in Figure 9.5.7), which can account for more than 1.2% of fresh weight. Its physiological function remains unknown. Quebrachitol can be used as a starting material to synthesize chiral drugs with therapeutic effects for the treatment of cancer, early ageing, diabetes and AIDS. An international patent for the extraction process has therefore been filed by a Malaysian team. ... 

Rubber hydrocarbon is the principle component of raw rubber. The subject is discussed in greater detail in Chapter 7. Natural rubber is 97% cw-l,4-polyisoprene. It is obtained by tapping the bark of rubber trees (Hevea brasiliensis) and collecting the exudate, a latex consisting of about 32-35% rubber. A similar material can also be found in the sap of many other plants and shrubs. The structure of natural rubber has been investigated over 100 years, but it was only after 1920, however, that the chemical structure was elucidated. It was shown to be a linear polymer consisting of head-to-tail links of isoprene units, 98% bonded 1,4. 

Chemical structure (Figure 1). Molecules formally composed of four isoprene units they naturally occur as an alcohol (retinol), an aldehyde (retinal), or as an acid (retinoic acid). From each of the three basic forms two variants exist vitamin A, with a jS-ionone ring and vitamin A2 with a dehydrated S-ionone ring. Native retinoids show cis-trans isomerism of the double bonds. Carotenoids are proforms of vitamin A (Figure 2). 

Poly(c/s-l,4-isoprene) has due to the lack of symmetry in its chemical structure (Fig. 21.8) non-zero components of... 

FIGURE 21.8. Chemical structure and dipole moment of poly(c/s-1,4-isoprene). 

The chains must be crosslinked to form a network (cf. Fig 7.16). In most elastomers containing double bonds, covalent bonds are introduced between chains. This can be done either with sulfur or polysulfide bonds (the well known sulfur vulcanisation of natural rubber is an example), or else by direct reactions between double bonds, initiated via decomposition of a peroxide additive into radicals. Double bonds already exist in the chemical structure of polyisoprene, polybutadiene and its copolymers. When this is not the case, as for silicones, ethylene-propylene copolymers and polyisobutylene, units are introduced by copolymerisation which have the property of conserving a double bond after incorporation into the chain. These double bonds can then be used for crosslinking. This is how Butyl rubber is made from polyisobutylene, by adding 2% isoprene. Butyl is a rubber with the remarkable property of being impermeable to air. It is used to line the interior of tyres with no inner tube. 

Natural rubber is an unsaturated hydrocarbon polymer. It is obtained commercially from the milky sap (latex) of the rubber tree. Its chemical structure was deduced in part from the observation that, when latex is heated in the absence of air, it breaks down to give mainly a single unsaturated hydrocarbon product, isoprene. 

The basic skeleton of isoprenoids may be modified by the introduction of a wide variety of chemical groups, by isomerization, shift of double bonds, methyl groups, etc. Hence a bewildering number of chemical structures arises. In addition compounds derived from other biogenic pathways may contain isoprene residues. For instance the K vitamins (D 8.1), ubiquinones (D 8.3), chlorophylls (D 10.1), plastoquinones, and tocopherylquinones (D 22.4) have isoprenoid side chains with up to ten isoprene units. Polyketides (D 3.3), alkaloids (D 8.4.2), and coumarins (D 22.2.2) may be substituted by dimethylallyl groups. The terpene residues are attached to nucleophilic sites, such as active methylene groups and phenolic oxygen atoms. 

The similarity in chemical structure to isoprene explains why these are quite compatible with natural rubber and synthetic isoprene-based polymers (or block copoljuners). The C-9 aromatic hydrocarbon resins include indene- and styrene-based oligomers. Because of the difference in chemical structure these will associate with the end-blocks in S-I-S copolymers, and thus have a reinforcing effect and improve high temperature performance. Finally, mixtures of aliphatic and aromatic hydrocarbon resins are commonly used as a way to tailor compatibility and physical properties of the resultant PSAs. 

It turns out that they are chemically related to each other, as you can imagine from the chemical structures shown in Fig. 12.1. They are called terpenes and terpenoids. They can be regarded as derivatives from a five-carbon compound called isoprene (2-methyl butadiene). Two isoprene molecules combine to form mono-terpene (ten-carbon compound). The fragrant oils mentioned above are all the derivatives of mono-terpene. Terpenes are derived from a common metabolic intermediate of glucose, acetyl-CoA (coenzyme A). By the way, a tri-terpene (which three terpene molecules combine to form) called squalene leads to the formation of steroids, and if you connect a large number of isoprene in a linear fashion, you will get natural rubber (Chap. 5). 

Over the ensuing years, many chemists tried to discover the chemical structure of rubber. It could be broken down by high temperature, and distillation would then yield an oil, which in turn gave rise to a liquid with a low boiling point. It turned out to be a pure substance, and was given the name isoprene with the formula... 

The question arises why cis-polyisoprene, different from poly(vinyl-acetate), shows in its dielectric spectrum the chain reorientation. The reason becomes clear when we look at the chemical constitution of polyisoprene, and focus in particular on the associated dipole moments. Figure 5.22 displays the chemical structure. The main point is that isoprene monomers are polar units which possess a longitudinal component p of the dipole moment, which always points in the same direction along the chain. As a consequence, the longitudinal components of the dipoles of all monomers become added up along the contour, giving a sum which is proportional to the end-to-end distance vector R. In the dielectric spectrum the kinetics of this total dipole of the chain is observable, hence also the chain reorientation as described by the time dependence R t). 

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