Write the IUPAC name of each cycloalkene. (a) (b) (c)

The first step in naming an organic compound involves recognizing the functional group present within the molecule. In the context of cycloalkenes, the functional group of interest is the carbon-carbon double bond, which identifies the compound as an alkene. Cycloalkenes specifically contain this double bond within a cyclic structure. The presence of the double bond is not just important for identification but also significantly influences the chemical properties of the compound, such as reactivity and polarity.

Knowing the functional group aids in predicting the molecule's behavior in reactions, such as addition reactions typical for alkenes, where atoms or groups of atoms are added across the double bond. This identification forms the foundation for naming the compound using IUPAC nomenclature rules.

Determining the size of the ring in a cycloalkene is a crucial step, as it forms the base of the compound's name. Carbon counting is performed by totaling the number of carbon atoms that make up the ring structure itself, ignoring any substituents or other attached groups initially.

The term 'cyclo' precedes the alkene naming convention to indicate a ring structure, followed by a prefix derived from the number of carbon atoms: 'prop' for three, 'but' for four, 'pent' for five, and so forth. This prefix then combines with 'ene', the suffix used for alkenes, to give a name like cyclopropene, cyclobutene, or cyclopentene, corresponding to rings with three, four, or five carbons, respectively.

When dealing with substituted cycloalkenes, it's imperative to assign numbers to the carbon atoms in the ring. The carbon atoms involved in the double bond take precedence and receive the lowest possible numbers, usually starting with carbon number 1 for one of the double-bonded carbons.

This numbering progresses either clockwise or counterclockwise around the ring to provide the lowest possible numbers to substituents, if present. For example, in methylcyclohexene, where a methyl group acts as a substituent on the ring, this group should be assigned the lowest possible carbon number following the one assigned to the double bond, according to the 'lowest number rule'. This rule helps to minimize the numbers used in naming, providing clarity and reducing ambiguity in the compound's nomenclature.

The International Union of Pure and Applied Chemistry (IUPAC) rules provide a systematic method for naming organic compounds. Once the functional group is identified, the carbon ring is counted, and the substituents are numbered, these elements are pieced together to form the complete name.

The substituents are mentioned in alphabetical order preceding the name of the cycloalkene. Numbers indicating the location of the substituents are then separated by hyphens from the substituent names and the root name. For example, a methyl group on the second carbon of a cyclohexene would yield the name '2-methylcyclohexene'. When multiple substituents are present, their locations are separated by commas. The IUPAC name thus constructed tells you not only the skeleton of the molecule but also gives detailed information about the placement of double bonds and other groups attached to the carbon ring.