Question

The following names are incorrect; draw a reasonable structure for the alkane and give the proper IUPAC name. (a) 5 -isopropyloctane (b) 2 -ethylpropane (c) 1,2 -dimethylpropane

Short answer

Question: Identify the improper naming of three alkanes, draw the correct structure, and provide the proper IUPAC names. Answer: The improper naming of alkanes and their corrected structures and IUPAC names are as follows: 1. Improper Name: 5-isopropyloctane Corrected Structure: [CH3-CH2-CH(CH3)-(CH2)3-CH(CH3)2] IUPAC Name: 5-(2-methylpropyl)octane 2. Improper Name: 2-ethylpropane Corrected Structure: [CH3-CH(CH2-CH3)-CH2-CH3] IUPAC Name: 2-methylpentane 3. Improper Name: 1,2-dimethylpropane Corrected Structure: [CH3-CH(CH3)-CH2-CH3] IUPAC Name: 2,2-dimethylpentane

Step-by-step solution

Identifying the improper naming

First, let's identify the incorrect part of each given name: (a) 5-isopropyloctane: The prefix "isopropyl" is not used in IUPAC naming. (b) 2-ethylpropane: This name would imply five carbon atoms in total, but propane only has three. (c) 1,2-dimethylpropane: This name would imply five carbon atoms as well, while propane has three.

Drawing the corrected structure for each alkane

Now, let's draw the corrected structure, taking the most stable conformation: (a) 5-isopropyloctane: Based on the name, there is an octane (8 carbon atoms in a continuous chain) with a isopropyl group (1 central carbon connected to 2 carbons) as a side chain at the 5th carbon. [CH3-CH2-CH(CH3)-(CH2)3-CH(CH3)2] (b) 2-ethylpropane: As we noted before, there should be 5 carbon atoms in total. To correct the structure, we will use pentane as the main chain instead of propane (pentane has 5 carbon atoms). [CH3-CH(CH2-CH3)-CH2-CH3] (c) 1,2-dimethylpropane: This one also has 5 carbon atoms in total. We will again correct it by using pentane as the main chain. [CH3-CH(CH3)-CH2-CH3]

Providing the proper IUPAC name for the correct structures

Now that we have drawn the correct structure, let's name them using IUPAC rules: (a) 5-isopropyloctane: IUPAC name: 5-(2-methylpropyl)octane (b) 2-ethylpropane: IUPAC name: 2-methylpentane (c) 1,2-dimethylpropane: IUPAC name: 2,2-dimethylpentane

Key concepts

Chemical Nomenclature

Chemical nomenclature is the systematic naming of chemical compounds based on their structure and composition. In organic chemistry, the International Union of Pure and Applied Chemistry (IUPAC) provides guidelines to ensure that each compound has a unique and standardized name. This helps to prevent confusion and allows chemists to communicate efficiently about different substances.

For alkanes, which are saturated hydrocarbons containing only carbon and hydrogen with single bonds, IUPAC naming involves identifying the longest carbon chain and naming it accordingly, then numbering the chain to assign the lowest possible numbers to the substituents. These substituents, which are groups attached to the main chain, are then listed in alphabetical order as prefixes to the name of the main chain. For instance, in the case of 2-methylpentane, 'pentane' represents a five-carbon chain, and the '2-methyl' indicates a methyl group attached to the second carbon.

Organic Chemistry

Organic chemistry is a branch of chemistry that deals with the study of the structures, properties, compositions, reactions, and synthesis of carbon-containing compounds. Central to understanding organic chemistry is the study of molecular structure and the hybridization of atomic orbitals to form bonds.

Alkanes, as simple organic compounds, serve as foundational building blocks in the study of organic chemistry. They demonstrate concepts such as isomerism, where compounds have the same molecular formula but different structural formulas. Exercises such as IUPAC naming reinforce the understanding of these compounds' systematic structure and how variations in the carbon chain or substituents can lead to different compounds with distinctive properties. For example, changing the position of a methyl group in a pentane molecule from the second to the third carbon changes the compound from 2-methylpentane to 3-methylpentane, reflecting the importance of correct structural representation.

Molecular Structure

The molecular structure of organic compounds, including alkanes, is essentially a 3D representation of the atoms in a molecule and the bonds between them. Bonds are depicted as lines, with each line representing a pair of shared electrons, and the angle of these lines indicating the bond angle. Understanding molecular structure is crucial for identifying the stability, reactivity, and physical properties of a compound.

The molecular structure dictates the IUPAC naming; for instance, branching at different carbons in a chain can significantly alter the compound's name and properties. In the corrected structure examples, the carbon chain is illustrated linearly for clarity, but in reality, these molecules have a three-dimensional shape that can affect their reactivity and interactions with other molecules. For example, compounds with the same molecular formula but different structural formulas are called isomers, which can have vastly differing chemical behaviors.