Pinenes molecular structure

C5H8, and may be either acyclic or cyclic with one or more benzenoid groups. They are classified as mono-cyclic (dipentene), dicyclic (pinene), or acyclic (myr-cene), according to the molecular structure. Many terpenes exhibit optical activity. Terpene derivatives (camphor, menthol, terpineol, bomeol, geraniol, etc.) are called terpenoids many are alcohols. 

Molecular structures of monoterpenoids are present as three major types acyclic, monocyclic and bicyclic. Oxygenated derivatives of acyclic monoterpenes are more widespread in nature than acyclic monoterpenes themselves. Such derivatives are the monoterpene alcohols citronellol and geraniol, or the monoterpene aldehydes citronellal and geranial. Mononocyclic monoterpene hydrocarbons are exemplified by limonene, which is a major component of orange and lemon peel oils, and p-phellandrene, which is emitted by conifer trees under biotic stress. These compounds are relatively common in nature. Bicyclic monoterpenes are represented by the aforementioned a-pinene, one of the most abundant and important monoterpenes. 

Of the two pinene monomers (Fig. Ij, k), which can be isomerized into each other (cf. Scheme 3), the a-isomer exhibits an endocychc double bond and is thus the less reactive (and also less frequently used) in polymerization reactions. However, the polymerization of a-pinene was reported as early as 1937, using AICI3 as catalyst in hydrocarbon (i.e., benzene, toluene, xylene, or hexane) solution at <15°C, yielding 75%. Polymerization in the presence of aromatics, with AICI3 as Friedel-Crafts catalyst, takes place without the interaction of aromatic and terpene. However, structures and MWs of the polymers formed were not given [80]. A later comparative study shows that the polymerization of a-pinene produces 35% or less solid polymer with MWs of 0.6-0.7 kg/mol, depending on the catalyst used (p-pinene yield up to 96%, MW = 0.8-3.1 kg/mol). The molecular structure of the oligo(a-pinene) was, however, not provided [66]. 

FIGURE 2.1. Molecular structures of a-pinene enantiomers and d-limonene. 

In the present work the synthesis of highly dispersed niobium or titanium containing mesoporous molecular sieves catalyst by direct grafting of different niobium and titanium compounds is reported. Grafting is achieved by anchoring the desired compounds on the surface hydroxyl groups located on the inner and outer surface of siliceous MCM-41 and MCM-48 mesoporous molecular sieves. Catalytic activity was evaluated in the liquid phase epoxidation of a-pinene with hydrogen peroxide as oxidant and the results are compared with widely studied titanium silicalites. The emphasis is directed mainly on catalytic applications of niobium or titanium anchored material to add a more detailed view on their structural physicochemical properties. 

Other cyclic monoterpenes, e.g. pinenes, form bridged structures, but the molecular formula is still C10H. ... 

As discussed in the introducticm to the fint p r of this series, erne of the objectives of this study was the synthesis of a series of novel hi molecular wei t cc edymen of isobutylene and pinene having useful physical prcf>erties. The physical properties of these copolymers were to reflect soff isobutylene and hard 0 wene structural units. 

Figure 7.13. Transition structure for hydroboration of a cis alkene with Ipc2BH. (a) The alkene substituents must be syn to one of the pinenes (R ). (b) Schematic representation of the lowest energy conformation, (c) Molecular mechanics - derived structure, with the rear (distal) pinene deleted for clarity. Reprinted with permission from ref. [141], copyright 1984, Elsevier Science, Ltd.

A detailed structure characterization of isobutylene and 0-pinene copolymers has been carried out including homogeneity studies (by GPC), quantitative composition and sequence analysis (by PMR and reactivity ratios) and molecular weight determinations (by osmometry and viscometry). Analysis of our data leads us to conclude that isobutylene and 0-pinene can be readily copolymerized to reasonably high molecular weight materials and that the products are perfectly random, statistical copolymers showing no detectable tendency for blockiness . 

Among the various classes of natural products, perhaps none is as extensive as the collection of structures that derive ifom the union and rearrangement of terpene building blocks. Indeed, whether in the form of a relatively small compound such as pinene or a far more complex and biochemically relevant steroid hormone, these secondary metabohtes are ubiquitous throughout Nature. Despite their widespread presence, however, their structures are far from ordinary, as many possess molecular architectures so exotic that even the most inventive of chemists would have a hard time imagining them prior to their full structural elucidation. 

The blocking of pores by PVC impregnation was carried out by treatment of the active carbons with suspensions of PVC in alcohol under reflux followed by carbonization at 600°C. This resulted in the deposition of appreciable amounts of carbonaceous material into the microporous structure causing a reduction in pore dimensions and producing carbon molecular sieves. These MSC were found to permit the adsorption of smaller molecules such as benzene or cyclohexane but prevented the adsorption of larger molecules such as isooctane and a-pinene. 

It was clearly shown that beta-pinene resins were equivalent to an alternating copolymer of isobutylene and cyclohexene units as proposed originally by Roberts and Day. Dipentene resin structure was shown to be compact and stiff by comparison of softening point and molecular weight. The determination of olefin content and model monomer studies showed a structure not of the type to be predicted by polymerization via the pendant olefin. The size difference and rigidity of these two types of terpene resins appear to be the outstanding properties which result in the predominant use of beta-pinene resins for pressure sensitive use and dipentene resins for hot melt use. 

The crystal structure of the p-pinene allyl compound [Pd(T 3-CioHi5)(S-(+)-BINAP)]+[CF3S03]- has been determinedl39 and multinuclear NMR measurements and molecular mechanics calculations on the related compound [Pd(Ti3-C]oH s)(5,5-CHIRAPH0S)]+[CF3S03]- presentedl o. 

The ozonolysis of the monoterpenes, biogenic species of molecular formula CioHm (e.g., a- and /3-pinene), provides a significant source of secondary organic aerosol. A number of multi-functional organic acids, such as norpinic acid from j8-pinene ozonolysis, and pinonic acid and pinic acid from a-pinene ozonolysis, have been conclusively identified as components of the organic aerosol formed (e.g., Presto et al., 2005 and references therein). As summarized in table VI-F-1, these acidic species possess very low vapor pressures (typically < 10 " Pa at 298 K, Bilde and Pandis, 2001), and thus have a strong tendency to partition to the condensed phase, where they are removed via depositional processes. The low vapor pressures preclude any studies of their gas-phase kinetics. However, the structure-activity relations (SARs) of Kwok and Atkinson (1995) can be used to estimate rate coefficients of about (1-5) xl0 cm ... 

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