Mason Delacroix
Benzene, an aromatic compound, can have multiple names depending on its structure. The nomenclature of benzene-derived compounds can be confusing, and a single compound can have multiple names. For example, the benzene derivative with an -OH group attached is commonly known as phenol, with the hydroxyl group as a substituent expressed as a suffix ('ol'). The IUPAC name for this compound is benzene-1,2,4-triol, and its common name is hydroxyquinol. When the alkyl substituent is smaller than the benzene ring (six or fewer carbons), the compound is named as an alkyl-substituted benzene. However, if the alkyl group attached to the benzene has seven or more carbons, the compound is named as a phenyl-substituted alkane.
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What You'll Learn
The IUPAC naming system
The International Union of Pure and Applied Chemistry (IUPAC) has established a set of rules and guidelines for naming chemical compounds, known as the IUPAC nomenclature system. This system provides clear and consistent naming conventions that enable chemists to easily identify and communicate about specific compounds. Here is an overview of the IUPAC naming system, specifically focused on naming alcohols on a benzene ring:
Identifying the Parent Compound
The first step in naming an alcohol on a benzene ring is to identify the parent compound. In this case, when an -OH group is attached directly to a benzene ring, the parent compound is called "phenol." This is because the benzene ring serves as the foundation for various derivatives, and "phenol" is one of the few common names retained in the IUPAC nomenclature for this structure.
Numbering the Ring
Once the parent compound is identified, the next step is to number the ring to give the substituents the smallest possible number. This is important because the numbering affects the name and helps identify the position of the substituents on the ring.
Naming the Substituents
After numbering the ring, identify and name any substituents attached to the benzene ring. These substituents can be various functional groups, such as alkyl chains or halogens. The names of these substituents will be combined with the parent name ("phenol") to form the final compound name.
Alphabetical Order and Prefixes
When there are multiple substituents, it is important to list them in alphabetical order. Additionally, if there are multiple alcohol (-OH) groups present, use prefixes like "di" for two groups, "tri" for three groups, and so on. This indicates the number of -OH groups in the compound.
Using the IUPAC Name
Finally, assemble the IUPAC name by combining the parent name ("phenol") with the numbered and alphabetized substituents. For example, if there is a methyl group attached at the C2 position, the compound would be named "2-Methylphenol."
Common Names and Variations
It is worth noting that common names for benzene derivatives, such as "hydroxyquinol" or "phloroglucinol," are still in use. While IUPAC has retained some common names, they primarily rely on the simple benzene naming system for benzene-derived compounds. Additionally, the OMP (ortho-, meta-, para-) system is not accepted in the IUPAC nomenclature, and common names from this system should be converted to systematic names using the benzene naming conventions.
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Common names for benzene alcohol
Benzene is a cyclic ring compound with an alcohol (-OH) group attached to it. The IUPAC name for this compound is benzene-1,2,4-triol, but it is also commonly known as 1,2,4-trihydroxybenzene. The -OH group is the principal characteristic group and is expressed as the suffix 'ol'.
The common name for this compound is hydroxyquinol, and it is still widely used. The other two isomers of benzenetriol are benzene-1,3,5-triol, commonly known as phloroglucinol, and benzene-1,2,3-triol, commonly known as pyrogallol. These common names are used far more frequently than the systematic name 'benzenetriol'.
Phenols are benzene-derived compounds where an -OH group is attached to a phenyl group. Phenol is highly toxic to the body, even in small doses, but it can be used as an antiseptic in minute quantities. It is also used as a catalyst in the hydrogenation of benzene into cyclohexane.
Benzyl alcohol, also known as α-cresol, is an aromatic alcohol with the formula C6H5CH2OH. It is a colourless liquid with a pleasant, mild odour. It is naturally produced by many plants and is commonly found in fruits, teas, and essential oils. Benzyl alcohol is a useful solvent due to its polarity, low toxicity, and low vapour pressure.
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Using the numbering system
The ortho/meta/para (OMP) system is used to name simple disubstituted aromatic compounds. However, this system cannot be used when more than two substituents are present in the benzene ring. In such cases, the "numbering system" can be used instead.
When using the numbering system, the carbon where the substituent is attached on the base is given the first priority and is named as carbon #1 (C1). The normal priority rules then apply, and the rest of the substituents are given the lowest possible number. For example, the compound 2,4-difluorobenzyl chloride indicates that the substituents are attached to the second and fourth carbons on the benzene ring.
The International Union of Pure and Applied Chemistry (IUPAC) provides a guide for naming alcohols in organic chemistry. The basic steps are as follows:
- Identify the parent compound or the longest hydrocarbon chain (alkane) attached to the hydroxyl group (-OH).
- Use the IUPAC name for the alkane as the root word for the compound. For example, if there are five carbons in the carbon chain, the compound is called "pentane."
- Change the "-e" at the end of the alkane name to "-ol" to give it the IUPAC name of an alcohol. For example, "pentane" becomes "pentanol."
- Number the carbons in the alkane chain, starting from the end nearest the hydroxyl group.
- Use the number of the carbon attached to the hydroxyl group to indicate its position.
- Name any additional substituent groups with number prefixes to indicate their location in the chain. For example, 3-methyl-butanol indicates that the -OH group and the methyl group are attached to the third and first carbons, respectively.
It is important to note that the numbering system can also be used in combination with prefixes like ortho- (o-), meta- (m-), and para- (p-) when naming disubstituted benzenes. These prefixes indicate the relative positions of the substituents on the benzene ring.
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Naming the longest carbon chain
When naming an alcohol on a benzene ring, the general format is: (positions of substituents (if >1) - # (di, tri, ...) + substituent) n + benzene. For example, chlorine (Cl) attached to a phenyl group would be named chlorobenzene (chloro + benzene).
Now, to name the longest carbon chain in an alcohol on a benzene, follow these steps:
Step 1: Find the Longest Carbon Chain
The first step is to identify the longest continuous carbon chain in the molecule. This is because the name of the alkane chain will serve as the base name for the compound. The longest carbon chain should be chosen, as this is the most substituted and will contain a functional group.
Step 2: Number the Longest Chain
Once the longest chain is identified, it should be numbered consecutively, starting from the end nearest a substituent group. This is an important step as it helps designate the location of each substituent group.
Step 3: Identify and Name Attached Groups
Any groups attached to the longest carbon chain should be identified and named. Common alkyl groups include methyl, ethyl, and bromo. If the benzene ring has a substituent of more than six carbons attached, the name "benzene" is changed to "phenyl."
Step 4: Designate Locations of Substituent Groups
Each substituent group should be designated a number that corresponds to its location on the carbon chain. This is done by following the numbering assigned in Step 2.
Step 5: Assemble the Name
Finally, the name of the molecule is assembled by listing the groups identified in alphabetical order, followed by the name of the longest carbon chain. The prefixes di, tri, tetra, etc., are used for multiple groups of the same kind but are not considered when alphabetizing.
For example, if there is an alcohol (OH) group present in the molecule, the longest carbon chain is numbered starting at the end closest to it. The suffix would be "ol," indicating the presence of an alcohol group.
It is important to note that the IUPAC system requires names for simple unbranched carbon chains and simple alkyl groups that may be attached to these chains.
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Using prefixes
When naming alcohols on a benzene ring, there are several conventions to follow. Firstly, the position of the substituents must be considered. The substituents are given position numbers, and the numbering is repeated to achieve the lowest possible sum. The substituents are then listed alphabetically, and the prefix "di-", "tri-" or "tetra-" is used to indicate multiple occurrences of the same substituent. The position prefix (ortho-, meta-, para-) is used to indicate the relative positions of two substituents on the benzene ring: ortho- (o-): 1,2-, meta- (m-): 1,3-, para- (p-): 1,4-. When three or more substituents are present, a numbering system is typically applied instead of the ortho-, meta-, para- system.
The general format for naming benzene derivatives is: (positions of substituents if more than one)-(number of substituents, e.g., di, tri, tetra) + substituent + benzene. For example, 1,4-dimethylbenzene. When benzene is a substituent, it is called "phenyl". If benzene is connected to a carbon chain with six or more carbons, the carbon chain is considered the parent structure, and benzene becomes the substituent, indicated by the prefix "phenyl".
When naming alcohols, the suffix "-ol" is used. For example, the IUPAC name for a benzene with an OH group attached is benzene-1,2,4-triol, and the common name is hydroxyquinol. The OH group can also be indicated by the prefix "hydroxy", as in "5-bromo-7-chloro-6-hydroxy-2,2,5-trimethyl-7-octen-4-one".
Additionally, alcohols can be classified as primary (1o), secondary (2o), or tertiary (3o) depending on the number of alkyl substituents attached to the carbon bonded to the OH group. In a primary alcohol, the carbon carrying the OH group is attached to only one alkyl group.
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Frequently asked questions
The suffix 'ol' is added to the name of the parent alkane.
The preferred IUPAC name (PIN) for an alcohol on a benzene is benzene-1,2,4-triol.
The common name for an alcohol on a benzene is hydroxyquinol.
The prefix 'cyclo' is added to the parent chain's name.
