Encyclopedia of Renewable Energy. James G. Speight

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СКАЧАТЬ Propylene -158 -48 1-Butene -6.5 1-Pentene 30 1-Hexene -138 63.5 0.643 1-Heptene -119 93 0.675 1-Octene -104 122.5 0.698 1-Nonene 146 0.716 1-Decene -87 171 0.731 Cis-2-butene -139 4 0.743 Trans-2-butene -106 1 Isobutylene -141 -7 Cis-2-pentene -151 37 2-Methyl-2-butene -123 39 0.655 2,3-Dimethyl-2-butene -74 73 0.660 Cyclopentene -93 46 0.705 Cyclohexene -104 83 0.774 1,3-Cyclopentadiene -85 42 0.810 1,3-Cyclohexadiene -49 87 0.798 0.847

      Owing to the presence of a double bond, the alkene undergoes a large number of addition reactions, but under special conditions, they also undergo substitution reactions. Alkene is readily hydrogenated under pressure in the presence of a catalyst. Platinum and palladium are effective at room temperature. Addition polymerization occurs between molecules containing double or triple bonds. The following are some reactions of aliphatic hydrocarbons to enhance its properties.

      See also: Alkanes, Alkenes.

      Alkalinity

      Alkalinity is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. Alkalinity is closely related to the acid neutralizing capacity (ANC) of a solution, and it is the acid neutralizing capacity that is often incorrectly used to refer to alkalinity.

      The alkalinity of a system is equal to the stoichiometric sum of the bases in solution. In the natural environment, carbonate alkalinity tends to make up most of the total alkalinity due to the common occurrence and dissolution of carbonate rocks and presence of carbon dioxide in the atmosphere.

      Alkalinity is sometimes incorrectly used interchangeably with basicity as when the pH of a solution can be lowered by the addition of carbon dioxide. This will reduce the basicity; however, the alkalinity will remain unchanged.

      Alkaloids

      Alkaloids are a class of nitrogenous organic compounds of plant origin which have pronounced physiological actions on humans and include many drugs (morphine, quinine) and poisons (atropine, strychnine). Alkaloids are naturally occurring chemical compounds containing basic nitrogen atoms and are produced by a large variety of organisms, including bacteria, fungi, plants, and animals.

The alkaloids are perhaps the last class of organic compounds which originate in plants that are of any importance in the formation of the organic substance of coal. These compounds all contain basic nitrogen in the molecule with the nitrogen frequently occurring in a cyclic system; in addition, most of the alkaloids also contain oxygen functions.

      Alkaloids are biologically active, organic compounds that contain a nitrogen atom which compounds have many structural frameworks, and are therefore highly variable. Alkaloids occur in the roots, bark, leaves, and within the cells of many plants. The structural chemistry of the alkaloids is variable because of the many locations in which nitrogen can occur in organic systems. However, it is generally recognized that the alkaloids may be based on any one of several individual (or even on a combination of two or more) systems.

      Alkaloids are divided into the several large groups, such as pyrrolidine, pyridine, quinoline, isoquinoline, indole, and quinazoline. They are often divided into main groups including peptides and cyclopeptide alkaloids, and true-alkaloids, proto-alkaloids, polyamine-alkaloids, and pseudo-alkaloids. Although most alkaloids are pharmacologically active or poisonous in high doses, there are some alkaloids in foods that are often consumed daily, of which the common examples are caffeine, theobromine, and theophylline (members of the purine alkaloid family) which are mainly found in coffee, cocoa beans, and tea leaves.

      Alkaloids have been isolated as crude extracts from plants for many millennia as part of folk medications. However, since the 20^th Century, individual alkaloids with defined and scientifically verified pharmacological properties have been purified and produced commercially as fine chemicals.

      The complexity of the chemical structures of the alkaloids makes them, in most cases, impossible to produce by chemical synthesis, so extraction from a crude plant mixture remains the most economically viable strategy. However, plants normally produce complex mixtures of alkaloids (rather than a single alkaloid) with the desirable types often at low levels, with the result that commercially produced specific alkaloids are expensive. As the genetic manipulation of plants becomes more sophisticated, research has focused on the engineering of alkaloid biosynthesis to generate transgenic or cell lines that overproduce specific alkaloids. This can be achieved by increasing the synthesis of a particular alkaloid and/or inhibiting the synthesis of related compounds to increase the ease of purification.

      Alkanes

      Alkanes СКАЧАТЬ