Why the simplest alkene is ethene

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. With four single bonds, carbon has a tetrahedral structure, while with one double bond it's structure is trigonal planar, and with a triple bond it has a linear structure.

A single carbon atom can make up to four bonds, but by looking at its electron configuration this would not be possible because there are only two electrons available to bond with. The other two are in a lone pair state, making them much less reactive to another electron that is by itself.

The electron is not promoted spontaneously. It becomes promoted when a photon of light with the correct wavelength hits the carbon atom. All the bonds in Ethene are covalent, meaning that they are all formed by two adjacent atoms sharing their valence electrons. As opposed to ionic bonds which hold atoms together through the attraction of two ions of opposite charges.

Sigma bonds are created when there is overlap of similar orbitals, orbitals that are aligned along the inter-nuclear axis. Sites such as these are referred to as functional groups or functionalities.

Propylene is also an important industrial chemical. It is converted to plastics, isopropyl alcohol, and a variety of other products. Although there is only one alkene with the formula C 2 H 4 ethene and only one with the formula C 3 H 6 propene , there are several alkenes with the formula C 4 H 8.

Draw all of the possible bond line structures for alkenes with the formula C 4 H 8 including all possible structural and stereoisomers. Alkenes Nomenclature of alkenes is covered in chapter 3.

Structure of Ethene - the simplest alkene Ethene is not a very complicated molecule. Rigidity in Ethene There is rigidity in the ethene molecule due to the double-bonded carbons. The alkenes are unsaturated hydrocarbons:. It is responsible for the typical reactions of alkenes. Alkenes The alkenes form a homologous series. Like all homologous series, the alkenes: have the same general formula differ by CH 2 in molecular formulae from neighbouring compounds show a gradual variation in physical properties , such as their boiling points have similar chemical properties General formula The general formula for the alkenes is C n H 2n , where n is the number of carbon atoms in the molecule.

Worked example Decene is an alkene.