General type of reaction is an electrophilic addition reaction. The electrons of the p bond are available for reaction, which has the net effect of replacing a p bond with a s bond and, therefore, is energetically favorable. It is convenient to classify reactions according to the overall type — addition, substitution, elimination and, where appropriate, the nature of the reagent which first interacts with the organic substrate.
We need to define two new terms, which describe this nature: electrophile and nucleophile. 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. It combines with the protein opsin to form rhodopsin , the primary light-gathering pigment in vertebrate retinas. When it absorbs a photon h n of light, one of the p -bonds is broken, causing the molecule to rotate and lock into the trans form, which has a completely different shape.
This starts a long chain of chemical processes which eventually results in a visual image in the brain. The trans -retinal molecule is then twisted back into the cis form by another enzyme. Atkins, Molecules , 2nd ed. Cambridge: Cambridge University Press, , p. Paula Yurkanis Bruice, Organic Chemistry , 4th ed. Upper Saddle River: Prentice Hall, , p. Marye Anne Fox and James K. Whitesell, Organic Chemistry , 3rd ed. Sudbury: Jones and Bartlett Publishers, p.
Maitland Jones, Jr. New York: W. Richard J. Lewis, Sr. New York: Van Nostrand Reinhold, Marc Loudon, Organic Chemistry , 4th ed. New York: Oxford University Press, , p. Englewood Cliffs: Prentice Hall, , p. Royston M. Roberts, John C. Gilbert, and Stephen F. Fort Worth: Saunders College Publishing, , p. Sharp, The Penguin Dictionary of Chemistry , 2nd ed. London: Penguin Books, Wade, Jr.
Martha Windholz ed. Isoprene 2-methyl-1,3-butadiene 3D Download 3D 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. Myrcene 3D Download 3D Myrcene is found in bay leaves and oil of bay.
Menthone 3D Download 3D Menthone is the oxidized form of menthol, and has a similar taste and physiological effect. Vitamin A Retinol 3D Download 3D Vitamin A also known as retinol is a fat-soluble vitamin, which is produced by the breakdown of the carotenes especially b -carotene.
Squalene Download 3D Squalene is found in shark liver oil, and is also a major component of the lipids on the surface of human skin. Lycopene Download 3D Lycopene is a red pigment found in tomatoes, watermelon, guava, papaya, pink grapefruit, apricots, and rosehips. Astaxanthin Download 3D Astaxanthin is a pink pigment found in salmon, trout, red seabream and the carapaces of lobster and shrimp. Vitamin A Retinol See entry above. The oxy-acetylene torch is one of the top tools for welding and cutting.
An alkene is a hydrocarbon with one or more carbon-carbon double covalent bonds. The simplest alkene is composed of two carbon atoms and is called ethene shown below. Each carbon is bonded to two hydrogen atoms, in addition to the double bond between them. All the atoms of the molecule lay in one plane. Like the alkane series, the names of alkenes are based on the number of atoms in the parent chain. Naming follows the same rules as for alkanes, with the addition of using a number to indicate the location of the double bond.
Alkenes are called unsaturated hydrocarbons. An unsaturated hydrocarbon is a hydrocarbon that contains less than the maximum number of hydrogen atoms that can possibly bond with the number of carbon atoms present.
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