Question

Draw a structure for each alkane. \begin{equation}\begin{array}{l}{\text { a. } 3 \text { -ethylhexane }} \\\ {\text { b. } 3 \text { -ethyl- } 3 \text { -methylpentane }} \\ {\text { c. } 2,3-\text { dimethylbutane }} \\ {\text { d. } 4,7 \text { -diethyl- } 2,2 \text { -dimethylnonane }}\end{array}\end{equation}

Short answer

a. A chain of 6 carbons with a 2-carbon group on the 3rd carbon. b. A chain of 5 carbons with a 2-carbon group and a 1-carbon group on the 3rd carbon. c. A chain of 4 carbons with two 1-carbon groups on the 2nd and 3rd carbons. d. A chain of 9 carbons with two 2-carbon groups on the 4th and 7th carbons, and two 1-carbon groups on the 2nd carbon.

Step-by-step solution

Identifying the Main Carbon Chain

Identify the longest continuous chain of carbon atoms in the molecule. This is known as the parent chain. Name the parent chain according to the number of carbons it contains, using the appropriate alkane name.

Identifying and Naming Substituents

Identify all of the substituents (groups branching off of the main chain). Name the substituents according to the number of carbon atoms they contain, using the appropriate alkyl group names.

Determining the Number Positions of the Substituents

Assign a number to each carbon atom in the main chain, beginning with the end closest to a substituent. Use these numbers to indicate the positions of the substituents on the main chain.

Drawing the Structure for 3-ethylhexane

Start by drawing a chain of 6 carbon atoms (hexane). Then attach an ethyl group (a two-carbon chain) to the third carbon of the main chain. The structure will have 6 carbons in the longest chain with a 2 carbon side chain on the third carbon.

Drawing the Structure for 3-ethyl-3-methylpentane

Begin with a pentane chain (5 carbons). Attach an ethyl group to the third carbon and a methyl group (a one-carbon chain) to the same third carbon. The structure will have 5 carbons in the longest chain with an ethyl and a methyl on the third carbon.

Drawing the Structure for 2,3-dimethylbutane

Start with a butane chain (4 carbons). Attach a methyl group to the second carbon and another methyl group to the third carbon. The structure will have 4 carbons in the longest chain with a methyl on the second and third carbons.

Drawing the Structure for 4,7-diethyl-2,2-dimethylnonane

Begin with a nonane chain (9 carbons). Attach an ethyl group to the fourth and seventh carbons, and two methyl groups to the second carbon. The structure will have 9 carbons in the longest chain with two ethyl groups and two methyl groups at the specified positions.

Key concepts

Organic Chemistry

Organic chemistry is the branch of chemistry that deals with the structure, properties, composition, reactions, and preparation of carbon-containing compounds, which include not only hydrocarbons but also compounds with any number of other elements, including hydrogen (most compounds contain at least one carbon-hydrogen bond), nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur. Understanding organic molecules is crucial since they are the basis of life on Earth, and they also have vast industrial applications, ranging from pharmaceuticals to plastics and fuels.

At the heart of organic chemistry is the ability to draw structures that represent these molecules. The structure not only conveys the makeup of the molecule but also hints at its reactivity and properties. Therefore, drawing structures accurately is a fundamental skill for students and professionals in chemistry-related fields.

Hydrocarbon Nomenclature

Hydrocarbon nomenclature refers to the system used to name the various types of hydrocarbon molecules. It is a critical aspect of organic chemistry, facilitating clear and unambiguous communication of molecular structures among scientists. The International Union of Pure and Applied Chemistry (IUPAC) sets the rules for naming these organic compounds.

The basic naming process involves identifying the longest carbon chain (the parent chain) and naming it according to the number of carbons it possesses. Simple hydrocarbons with only carbon and hydrogen are called alkanes and have names ending in '-ane.' The substituents, or groups of atoms attached to the main chain, must also be named and their position on the chain indicated. This process ensures each compound has a unique name that reflects its structure.

Substituents Naming

In organic chemistry, substituents are atoms or groups of atoms that are attached to the main carbon chain (parent chain) of a molecule. They are like 'decorations' that change the molecule's properties and reactivity. The naming of substituents is based on the number of carbon atoms they contain. Typical substituent names include 'methyl' for a one-carbon group, 'ethyl' for a two-carbon group, and so on.

Methane, the simplest alkane with one carbon atom, does not possess substituents; but as the chains get longer, the complexity of potential substituents grows. For example, if an alkane has a four-carbon chain and a one-carbon substituent, the molecule could be named '2-methylbutane,' indicating a methyl group is attached to the second carbon of a butane chain.

Carbon Chain Identification

Central to drawing alkane structures and understanding their naming conventions is the identification of carbon chains. This involves finding the longest, continuous chain of carbon atoms within the molecule—this is known as the parent chain, and it determines the base name of the alkane. When multiple chains of equal length are present, select the one with the largest number of substituents to be the main chain.

Once the main chain is determined, the next step is to number the carbon atoms, starting from the end closest to a substituent. This numbering helps to position the substituents correctly in the molecule's name. For instance, in '3-ethylhexane,' the number 3 indicates that the ethyl group is attached to the third carbon of the hexane chain. Accurate identification and numbering of the carbon chain are essential for the proper naming and understanding of complex organic molecules.