In IUPAC (International Union of Pure and Applied Chemistry) nomenclature, alkenes are indicated by changing the suffix from -ane to -ene. A number indicates the location of the double bond (the locant).
Alkanes are carbon molecules that only contain single bonds. The prefix indicates the number of carbons in the molecule, and alkenes are named similarly. The suffix changes from -ane to -ene to indicate the double-bond character of the molecule, and the prefixes stay the same. A number is used to show where the double bond is located, which is called the locant.
Double-bond carbon molecules have the suffix -ene. The double-bond location is indicated by the numeral prefix. The compound 1-butene has a double bond between the first and second carbon atoms.
Double-bond carbon molecules have the suffix -ene. The double-bond location is indicated by the numeral prefix. The compound cis-2-butene has a double bond between the second and third carbon atoms; cis indicates the methyl (CH3) substituents are located on the same side of the double bond.
In IUPAC nomenclature, E and Z are given as a prefix with the location at the very front of the name of the compound, and they are always in parentheses. The Z indicates that the higher-priority groups are on the same side of the double bond. The E indicates that the higher-priority groups are on opposite sides of the double bond.
In (E)-1-bromo-1,2-dichloroethene, the (E) indicates that the atoms with the highest priority on each carbon of the double bonds are opposite each other.
In (Z)-1-bromo-1,2-dichloroethene, the (Z) indicates that the atoms with the highest priority on each carbon of the double bonds are on the same side as each other.
Properties of Alkenes
Alkenes are very similar in physical properties to alkanes.
Alkenes have similar physical properties to alkanes. Alkenes are insoluble in water and soluble in nonpolar solvents, such as ether or benzene. They have a lower density than water, and like alkanes, the boiling point of alkenes generally rises with added carbons. Alkenes are also weakly polar and have London dispersion forces but do not exhibit dipole-dipole interactions or hydrogen bonding.
Alkenes are often used as feedstock for chemical manufacture, e.g., ethylene is a feedstock alkene used in the synthesis of poly(ethylene). LDPE is low-density polyethylene and is one of the most ubiquitous polymers. LDPE is used in making trash and grocery bags, squeeze bottles, some household items, and even toys.
Alkenes are very abundant in nature in both cyclic and acyclic form. Many pheromones are alkenes and are used in synthetic form as a pharmaceutical. Naturally occurring alkenes are also used extensively in the pharmaceutical industry. One common alkene is beta-carotene. Vitamin A is derived from beta-carotene and is essential for vision. Beta-carotene is also responsible for the color of carrots. Alkanes are generally obtained from petroleum and natural gas and then converted into alkenes.
Beta-carotene is an alkene found in nature. Vitamin A is essential for vision and is derived from beta-carotene.
