Alkenes are nonpolar , since they contain nothing but carbon-carbon and carbon-hydrogen bonds, and are not soluble in water; they are also generally less dense than water. Many alkenes are isolated from petroleum, and may serve as the starting points for the synthesis of more complex molecules.
Ethene is more commonly known under the trivial name ethylene. It is the simplest of the alkenes, consisting of two carbon atoms connected by a double bond. This leaves each carbon free to bond to two hydrogen atoms.
Since both carbon atoms are trigonal planar in shape, all six atoms lie in the same plane, and ethylene is a flat molecule. It is a colorless gas bp It is synthesized during the cracking of hydrocarbons at high temperatures, and can also be produced from the dehydration of ethanol.
It is used in the manufacture of the plastic polyethylene see section on Addition Polymers. The release of ethylene stimulates the beginning of the ripening process in many plants; some fruits and vegetables are picked while unripe, when they are less fragile, and ripened when they reach their destination by exposure to ethylene gas.
Propene Propylene 3D Download 3D Propene , more commonly known as propylene , is a colorless gas bp It is used in the manufacture of the polymer polypropylene. Because carbon 1 has two of the same substituent in this case, H , 1-butene does not exhibit geometric isomerism, unlike its structural isomer, 2-butene see below. Because free rotation is not possible around carbon-carbon double bonds, there are two isomers of 2-butene: one in which the two methyl groups at the end are pointing to the same side of the molecule, known as cis butene : Download 3D and one in which the two methyl groups are pointing to opposite sides of the molecule, known as trans butene : Download 3D Molecules which exhibit this kind of isomerism are known as geometric isomers or cis-trans isomers.
Despite the close similarity between these two structures, they are distinctly different compounds: the cis isomer boils at 3. Chloroethene Vinyl chloride 3D Download 3D Chloroethene , or vinyl chloride , is a carcinogenic gas manufactured from ethylene. It is used in the manufacture of the plastic polyvinyl chloride PVC.
Tetrachloroethylene Perchloroethylene, "Perc" 3D Download 3D Tetrachloroethylene , better known as perchloroethylene "Perc" , and more officially as tetrachloroethene , is a non-flammable organic solvent, widely used in dry cleaning; it is also used as an industrial solvent, degreaser, and paint remover.
Muscalure 3D Download 3D Muscalure , or cistricosene, is the sex pheromone of the female common housefly Musca domestica. Molecules with carbon-carbon double bonds adjacent to each other are referred to as conjugated alkenes ; molecules with large numbers of conjugated double bonds are responsible for many of the colors that we see in the world around us see the section on Terpenes for examples. In fact, the common name of 1,2-propadiene is allene. An interesting feature in the shape of these molecules is that the interior "double-double-bonded" carbon is sp -hybridized, and the two pi-systems of the double bonds are perpendicular to each other; therefore the substituents on the exterior double bonded carbon atoms are at right angles to each other.
Cyclopropene 3D Download 3D Cyclopropene is an example of a cycloalkene , a cyclic structure containing a carbon-carbon double bond. In cycloalkenes smaller than cyclohexene, the double bond can only exist in the cis -configuration, since the ring strain would be too great to accommodate a trans double bond. Cyclohexene 3D Download 3D Cyclohexene rings are considerably less strained than the smaller cycloalkenes, and occur commonly in nature. Cyclooctene 3D cis -cyclooctene Download 3D Cyclooctene has a large enough ring that it can exist in both the cis and trans stereoisomers.
Since the ring is too small to accommodate two double bonds to the same carbon atom, the position numbers of 1 and 3 are often dropped from the name, since there is no other set of position numbers possible for the ring. Cyclopentadiene 3D Download 3D 1,3-Cyclopentadiene is a ring of five carbons containing two double bonds.
As with cyclobutadiene, the position numbers can be dropped from the name, since no other positioning of the double bonds is possible. When left to itself, cyclopentadiene undergoes a Diels-Alder reaction with itself, producing a dimer called dicyclopentadiene ; this is the form in which cyclopentadiene is usually sold.
By heating the dicyclopentadiene is a distillation apparatus, it is possible to "crack" the dimer back into the cyclopentadiene monomer, which distills out and can be collected in a cooled receiving flask.
Cyclopentadiene is a common reagent in organic labs for use as a reagent in various Diels-Alder reactions. Unlike benzene , it is not an aromatic compound, despite having an alternating series of double and single bonds. See the section on Annulenes on the Aromatic Rings page. The terpenes are a diverse group of natural products which can be considered as being composed of isoprene units although their biosynthesis does not actually involve the isoprene molecule. The monoterpenes contain 10 carbon atoms, the sesquiterpenes have 15, the diterpenes have 20, the triterpenes have 30, the tetraterpenes have 40, and so on.
A number of related molecules also contain oxygen, and are classified as terpenoids. Terpenes and terpenoids are found in many plants, and often have distinctive flavors and aromas. Many of these molecules are components of common foods and perfumes.
They can often be obtained from natural sources by steam distillation, or other fairly simple purification techniques. Many of these compounds have important pharmaceutical and industrial uses, and may also be used as the starting point for the synthesis of other important compounds.
Isoprene more formally 2-methyl-1,3-butadiene can be considered the building block of the terpene family, although isoprene itself is not actually involved in the biosynthesis of these molecules. Instead, the natural precursor is isopentenyl pyrophosphate 3-methylbutenyl pyrophosphate. Two isopentenyl pyrophosphate units combine enzymatically to form geranyl pyrophosphate , which is the precursor for the monoterpenes; reaction with a third isopentenyl pyrophosphate molecule produces farnesyl pyrophosphate , the precursor for the sesquiterpenes.
Isopentenyl pyrophosphate Geranyl pyrophosphate Farnesyl pyrophosphate. Myrcene is found in bay leaves and oil of bay. Geraniol 3D Download 3D Geraniol is found in roses with 2-phenylethanol , citronella oil, pomerosa oil, geraniums, and other flowers. Citral Geranial 3D Download 3D Citral , or geranial , is found in oil of lemon; it is also secreted by some insects to repel predators.
It is used commercially in lemon-smelling perfumes and in the synthesis of Vitamin A. The structure shown here is citral-a; there is also a citral-b isomer, in which the aldehyde and methyl group on the bottom double bond are in a trans relationship.
The difference in orientation around the chiral carbon atoms gives these molecules a slightly different overall shape, resulting in slightly different odors when they interact with the olfactory receptors in the nasal passages. Thujene 3D Download 3D Thujene is found in oil of thuja, sage, tansy, and wormwood. Thujone 3D Download 3D Thujone is found in oil of thuja, sage, tansy, and wormwood.
Menthol 3D Download 3D Menthol is found in peppermint and other mint oils. It is used in cough drops, shaving lotion, and mentholated tobacco. Menthone is the oxidized form of menthol, and has a similar taste and physiological effect. It is the active component of medicinal eucalyptus oils. Camphene 3D Download 3D Camphene is found in turpentine oil, rosemary, cypress oil, and oil of citronella. It is used medicinally as a counter-irritant a substance which produces a superficial inflammation to reduce deeper inflammation and an anti-itching agent.
It produces a cooling sensation, because it stimulates cold receptors see menthol. Its strong odor inspires deep breathing, but in large doses can lead to respiratory collapse. Caryophyllene 3D Download 3D Caryophyllene is found in oil of cloves. Vitamin A also known as retinol is a fat-soluble vitamin, which is produced by the breakdown of the carotenes especially b -carotene. It is found in liver, egg yolks, butter, and milk. It is a precursor to retinal see below , the primary dye involved in vertebrate vision.
It is also involved in cell growth and maintenance of healthy skin tissue, bones, and teeth. Download 3D Squalene is found in shark liver oil, and is also a major component of the lipids on the surface of human skin. Although it is not obvious from the way the structure above is drawn, squalene is a precursor for the biosynthesis of cholesterol.
Through a complex series of enzymatically controlled reactions, squalene is converted into an intermediate called lanosterol, which undergoes a number of subsequent reactions to become cholesterol. In addition to essential oils, terpenes and terpenoids are also found in naturally occurring dyes. Molecules which contain large numbers of carbon-carbon double bonds adjacent to each other a conjugated double bond system absorb light at lower frequencies than molecules with no double bonds or just a few double bonds; some of these compounds absorb light in the visible region of the electromagnetic spectrum, and produce colors which we can see.
Compare the structures of the molecules below with the ones in the section on the Chemistry of Vision. Download 3D Lycopene is a red pigment found in tomatoes, watermelon, guava, papaya, pink grapefruit, apricots, and rosehips. Unripe tomatoes are green in color because of their chlorophyll, but as they ripen, the chlorophyll breaks down, unmasking the red color of the lycopene.
Lycopene is a good antioxidant, and is more readily absorbed from cooked tomatoes and tomato paste, especially if the foods contain fat. This molecule, and the ones below, are structurally similar to that of carotene , and are referred to as carotenoids. Zeaxanthin Download 3D Zeaxanthin is a yellow pigment found in corn, egg yolk, orange juice, mangoes; also contributes to the yellowish color of animal fats. Carotenoids containing hydroxyl groups are sometimes referred to as xanthophylls.
Download 3D Astaxanthin is a pink pigment found in salmon, trout, red seabream and the carapaces of lobster and shrimp. In live shellfish, the astaxanthin forms a complex with a protein which gives it a blackish color; when the shellfish are boiled, the protein breaks down, unmasking the pink astaxanthin.
Canthaxanthin Download 3D Canthaxanthin is a pink pigment found in the feathers of American flamingos. It is obtained from shrimp in their diet; flamingos in captivity turn into plain white birds unless they are fed adequate amounts of shrimp. See entry above. The yellow color of butter and animal fats comes from carotene and related molecules.
Carotene is found along with chlorophyll in photosynthetic organisms; it protects cells by reacting with O 2 molecules. The yellow color of autumn leaves is due to the carotene, which is unmasked as the chlorophyll in the leaves breaks down.
It is broken down in the body into one molecule of Vitamin A. Retinal and Vision Retinal is the oxidized form of Vitamin A, having an aldehyde group at the end instead of an alcohol. Loading related content. Jump to main content. Jump to site search. You do not have JavaScript enabled. Please enable JavaScript to access the full features of the site or access our non-JavaScript page.
Issue 0, From the journal: Journal of the Chemical Society Resumed. An infra-red spectroscopic investigation of double-bond structure in simple acyclic terpenes and derivatives thereof. Barnard , L. Bateman , A. Harding , H. Koch , N. The first page of this article is displayed as the abstract. You have access to this article. Please wait while we load your content Something went wrong.
Try again? Cited by.
0コメント