Hydrocarbons

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Methane, the simplest hydrocarbon, is composed of four hydrogen atoms surrounding a central carbon. The bond between the four hydrogen atoms and the central carbon spaced as far apart as possible. The resulting in a tetrahedral shape with hydrogen atoms projecting upward and off to three sides around the central carbon.
Methane has a tetrahedral geometry, with each of the four hydrogen atoms spaced 109.5° apart.

Source: OpenStax Biology 2e

OpenStax Biology 2e

Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen, such as methane (CH4) described above. We often use hydrocarbons in our daily lives as fuels—like the propane in a gas grill or the butane in a lighter. The many covalent bonds between the atoms in hydrocarbons store a great amount of energy, which releases when these molecules burn (oxidize). Methane, an excellent fuel, is the simplest hydrocarbon molecule, with a central carbon atom bonded to four different hydrogen atoms. The shape of its electron orbitals determines the shape of the methane molecule’s geometry, where the atoms reside in three dimensions. The carbons and the four hydrogen atoms form a tetrahedron, with four triangular faces. For this reason, we describe methane as having tetrahedral geometry.

– What is the simplest alkane and is the main constituent of natural gas?

As the backbone of the large molecules of living things, hydrocarbons may exist as linear carbon chains, carbon rings, or combinations of both. Furthermore, individual carbon-to-carbon bonds may be single, double, or triple covalent bonds, and each type of bond affects the molecule’s geometry in a specific way. This three-dimensional shape or conformation of the large molecules of life (macromolecules) is critical to how they function.

Some insects such as the Brazilian stingless bee use unique hydrocarbon “scents” in order to determine family from non-family.

Hydrocarbon Chains

Successive bonds between carbon atoms form hydrocarbon chains. These may be branched or unbranched. Furthermore, a molecule’s different geometries of single, double, and triple covalent bonds alter the overall molecule’s geometry as illustrated below. The hydrocarbons ethane, ethene, and ethyne serve as examples of how different carbon-to-carbon bonds affect the molecule’s geometry. The names of all three molecules start with the prefix “eth-,” which is the prefix for two carbon hydrocarbons. The suffixes “-ane,” “-ene,” and “-yne” refer to the presence of single, double, or triple carbon-carbon bonds, respectively. Thus, propane, propene, and propyne follow the same pattern with three carbon molecules, butane, butene, and butyne for four carbon molecules, and so on. Double and triple bonds change the molecule’s geometry: single bonds allow rotation along the bond’s axis; whereas, double bonds lead to a planar configuration and triple bonds to a linear one. These geometries have a significant impact on the shape a particular molecule can assume.

– What is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulfide, or helium?

Methane, the simplest hydrocarbon, is composed of four hydrogen atoms surrounding a central carbon. The bond between the four hydrogen atoms and the central carbon spaced as far apart as possible. This results in a tetrahedral shape with hydrogen atoms projecting upward and off to three sides around the central carbon. Ethane is composed of two carbons connected by a single bond. Each carbon also has three hydrogen atoms connected to it. The hydrogens are spaced as far apart from each other and from the other carbon so again the shape is tetrahedral. Ethene, like ethane, is composed of two carbon atoms, but in this case the carbons are connected by a double bond. Each carbon also has two hydrogen atoms connected to it, for a total of three bonds. The three bonds are spaced as far apart as possible around carbon, which means they are all on the same plane and pointing off in three directions. As a result, the molecule is planar, or flat.
When carbon forms single bonds with other atoms, the shape is tetrahedral. When two carbon atoms form a double bond, the shape is planar, or flat. Single bonds, like those in ethane, are able to rotate. Double bonds, like those in ethene, cannot rotate, so the atoms on either side are locked in place.

Source: OpenStax Biology 2e

Hydrocarbon Rings

So far, the hydrocarbons we have discussed have been aliphatic hydrocarbons, which consist of linear chains of carbon atoms. Another type of hydrocarbon, aromatic hydrocarbons, consists of closed rings of carbon atoms with alternating single and double bonds. We find ring structures in aliphatic hydrocarbons, sometimes with the presence of double bonds, which we can see by comparing cyclohexane’s structure to benzene in the figuew below. Examples of biological molecules that incorporate the benzene ring include some amino acids and cholesterol and its derivatives, including the hormones estrogen and testosterone. We also find the benzene ring in the herbicide 2,4-D. Benzene is a natural component of crude oil and has been classified as a carcinogen. Some hydrocarbons have both aliphatic and aromatic portions. Beta-carotene is an example of such a hydrocarbon.

– What is a form of bioremediation in which fungi-based technology is used to decontaminate the environment?

Four molecular structures are shown. Cyclopentane is a ring consisting of five carbons, each with two hydrogens attached. Cyclohexane is a ring of six carbons, each with two hydrogens attached. Benzene is a six-carbon ring with alternating double bonds. Each carbon has one hydrogen attached. Pyridine is the same as benzene, but a nitrogen is substituted for one of the carbons. No hydrogens are attached to the nitrogen.
Carbon can form five- and six-membered rings. Single or double bonds may connect the carbons in the ring, and nitrogen may be substituted for carbon.

Source: OpenStax Biology 2e
Some hydrocarbons also abundant in the solar system. Lakes of liquid methane and ethane have been found on Titan, Saturn’s largest moon, confirmed by the Cassini-Huygens Mission. Hydrocarbons are also abundant in nebulae forming polycyclic aromatic hydrocarbon compounds

Source:

Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/biology-2e

https://en.wikipedia.org/wiki/Methane

https://en.wikipedia.org/wiki/Hydrocarbon

https://en.wikipedia.org/wiki/Natural_gas


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Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/biology-2e

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