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Chapter 17: Problem 88

Explain how hydrocarbons containing an OH group are named.

Short Answer

Expert verified
To name hydrocarbons containing an OH group, first identify the parent hydrocarbon chain and name it according to the standard alkane conventions (meth-, eth-, prop-, etc.). Next, locate the position of the OH group(s), assigning the lowest possible number to the carbon atom connected to the OH group. Finally, change the ending of the parent hydrocarbon name from -ane to -ol and include the number(s) indicating the position of the OH group(s) in the compound's name. If more than one OH group is present, use prefixes like di-, tri-, or tetra- to indicate the number of OH groups and their positions. For example, propane-1-ol or pentane-1,4-diol.

Step by step solution

01

Identifying the parent hydrocarbon

First, it is essential to identify the parent hydrocarbon, which is the longest continuous chain of carbon atoms in the molecule. This chain serves as a base for naming the compound. The parent hydrocarbon is named according to the number of carbon atoms in the chain, following the standard alkane naming conventions: meth- (1), eth- (2), prop- (3), but- (4), pent- (5), and so on.
02

Recognizing the presence of an -OH group

Next, verify the presence of an OH group(s) in the hydrocarbon. Since the presence of an OH group distinguishes these types of hydrocarbons from others, it impacts the name of the compound. Hydrocarbons containing an OH group are referred to as alcohols.
03

Determining the position of the -OH group

Locate the position of the OH group(s) on the parent hydrocarbon chain. Count the carbon atoms from one end of the chain, and assign the lowest possible number to the carbon atom directly attached to the OH group. This number indicates the position of the OH group in the hydrocarbon and should be included in the compound's name.
04

Naming the compound using IUPAC conventions

Using IUPAC conventions, name the hydrocarbon by changing the ending of the parent hydrocarbon name from -ane to -ol (for alcohols). The name should include the number(s) determined in step 3, indicating the position of the OH group(s), and should be preceded by the parent hydrocarbon name determined in step 1. When multiple OH groups are present, use a prefix such as di-, tri-, or tetra- to indicate the number of OH groups, and the appropriate locants to specify their positions. For example: - A single OH group attached to a propene molecule would be named as propane-1-ol or propane-2-ol, depending on which carbon atom is connected to the OH group. - A molecule with two OH groups attached to a pentane molecule would be named as pentane-1,4-diol or pentane-2,3-diol, based on the positions of the two OH groups.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Hydrocarbon Chain
Understanding the structure of hydrocarbon chains is essential in organic chemistry, especially for naming compounds. A hydrocarbon chain consists of a series of carbon atoms connected by single, double, or triple bonds, and these carbon atoms may be bounded by hydrogen atoms. The key is to identify the longest, continuous chain, as it serves as the 'backbone' for naming the rest of the molecule.

When naming alcohols, this backbone dictates the base name of the compound. For instance, a hydrocarbon chain with four carbon atoms is called 'butane'. Learning to recognize and name these chains will not only make it easier to name alcohols but will also be helpful across all organic compounds.
OH Group in Hydrocarbons
The presence of an hydroxyl (-OH) group is what sets alcohols apart from other hydrocarbons. In an alcohol, the hydroxyl group is bonded to a carbon atom of the hydrocarbon chain. The carbon bonded to the -OH can be at the end or in the middle of the chain, which affects the naming of the alcohol. It's crucial to recognize these groups as they are pivotal in determining the class of compounds and how they react chemically. Alcohols are known for their wide range of uses, from antiseptics to fuels, due to the presence of this functional -OH group.
IUPAC Nomenclature
The IUPAC nomenclature system is a standardized way of naming chemical compounds, ensuring that every compound has a unique and universally accepted name. For alcohols, the IUPAC name is derived by modifying the end of the hydrocarbon chain's name to indicate the presence of the hydroxyl group. For example, replacing the 'e' in 'alkane' with 'ol' signifies an alcohol. The system also includes rules for prioritizing functional groups, designating stereochemistry, and specifying the positions of functional groups within the molecule, which helps avoid ambiguities in naming.
Alkane Naming Conventions
Alkanes serve as the reference point for naming many organic molecules, including alcohols. The alkane naming conventions involve using prefixes like 'meth-', 'eth-', 'prop-', and 'but-' to indicate the number of carbon atoms in the longest chain. To differentiate alcohols from alkanes, the suffix '-ol' is used in place of '-ane'. It's essential for students to familiarize themselves with these prefixes and to be able to distinguish alkanes as the foundational structures for naming other organic molecules.
Position of Functional Groups
Identifying the correct position of functional groups is a critical step in naming compounds correctly. When an -OH group is attached to the hydrocarbon chain, it's vital to specify its location by numbering the carbon atoms in the chain. This is done starting from the end closest to the -OH group. The position number comes before the compound's name in IUPAC nomenclature. For example, 'butan-1-ol' has its -OH group attached to the first carbon atom of a butane chain. Correctly positioning functional groups affects not only the name of the compound but also its physical and chemical properties.

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Most popular questions from this chapter

Benzene is a hydrocarbon that has the molecular formula \(\mathrm{C}_{6} \mathrm{H}_{6}\). The benzene molecule contains a six-carbon ring and three double bonds. Draw its structural formula.

Name the alkanes that do not use Greek prefixes in their names, and draw the structural formula for each.

What kind of hydrocarbons are called aliphatic and where does the word aliphatic come from?

There are three isomers that have the molecular formula \(\mathrm{C}_{5} \mathrm{H}_{12}\). Draw the structural formula for each one. Which do you expect to have the lowest boiling point? Explain.

Explain why the molecules 1 -hexene, 2 -hexene, and 3 -hexene exist, but the molecules 4 -hexene and 5 -hexene do not.
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