Naming Other Substituents: Videos & Practice Problems

An alkyl halide consists of an alkyl group bonded to a halogen atom. In organic chemistry, halogens such as fluorine, chlorine, bromine, and iodine are treated as substituents on a carbon chain. When naming these compounds, the halogens are designated with specific prefixes: fluorine is referred to as fluoro, chlorine as chloro, bromine as bromo, and iodine as iodo.

When naming an organic compound, it is essential to identify the parent chain, which can vary in structure, such as being a six-membered chain or cyclic. The numerical location of the halogen substituents must be indicated in relation to the parent chain. This systematic approach to naming ensures clarity in identifying the structure and composition of alkyl halides, highlighting the importance of recognizing halogens as substituents within organic compounds.

To determine the systematic name of an alkane, the first step is to identify the longest carbon chain, known as the parent chain. In this case, the longest chain consists of nine carbon atoms, which corresponds to the alkane named nonane. The numbering of the carbon atoms begins from the end closest to a substituent to ensure the lowest possible numbers for the substituents.

In this example, there are three substituents: a three-carbon substituent, a one-carbon substituent, and a bromine atom. The three-carbon substituent is identified as isopropyl, while the one-carbon substituent is methyl. The bromine substituent is denoted as bromo. When naming the compound, it is essential to number the substituents according to their position on the parent chain and to list them alphabetically.

Following the rules of nomenclature, the substituents are numbered as follows: starting from the right side, the carbon chain is numbered 1 through 9. The isopropyl group is located at carbon 6, the methyl group at carbon 5, and the bromo group at carbon 3. Therefore, the systematic name of the compound is constructed by placing the substituents in alphabetical order, leading to the final name: 3-bromo-5-methyl-6-isopropylnonane.

The phenyl group is a crucial concept in organic chemistry, representing a benzene ring that acts as a substituent on a parent hydrocarbon chain. A benzene ring, with the molecular formula C₆H₆, consists of six carbon atoms arranged in a cyclic structure with alternating double and single bonds. When the benzene ring is attached to a longer carbon chain, it loses one hydrogen atom, resulting in the phenyl group with the formula C₆H₅.

This phenyl group can be connected to various types of parent chains, including alkanes, alkenes, or alkynes, provided that the parent chain contains more than six carbon atoms. The skeletal structure of benzene is characterized by a six-membered ring, where five of the carbon atoms are bonded to hydrogen atoms, while the sixth carbon is linked to the parent chain, allowing it to function as a substituent.

When naming compounds that include a phenyl group, the convention involves indicating the position of the phenyl group on the parent chain followed by the name of the parent hydrocarbon. This systematic approach ensures clarity in identifying the structure and composition of the compound. Understanding the phenyl group is essential for grasping more complex organic structures and their reactivity.

To systematically name the given alkane, we first identify the longest carbon chain, which consists of eight carbon atoms, making it an octane. In this case, since the carbon chain exceeds six carbons, it serves as the parent chain, while the benzene ring acts as a substituent. The benzene substituent is referred to as a phenyl group.

Next, we need to consider the substituents attached to the parent chain. There are two methyl groups present, which are carbon substituents. When numbering the carbon chain, we start from the end closest to the substituent. Thus, we label the carbons as follows: carbon 1 has the phenyl group, and we continue numbering to carbon 8.

In this structure, the methyl groups are located on carbon 5. To accurately convey the position of both methyl groups, we must indicate that they are both on carbon 5. Instead of simply stating "5 dimethyl," which could imply only one methyl group, we specify "5,5-dimethyl" to clarify that there are two identical substituents at that position.

Finally, we combine all the components to form the complete systematic name of the compound: 5,5-dimethyl-1-phenyl-octane. This name reflects the structure and substituents of the alkane accurately, adhering to the IUPAC naming conventions.