Question

Draw structures for 3 -ethylpentane and 2,3 -dimethylpentane.

Short answer

3-ethylpentane has an ethyl group on C3; 2,3-dimethylpentane has methyl groups on C2 and C3.

Step-by-step solution

Identify the Main Chain

For both compounds, we must first identify the main carbon chain. In the names of both compounds, ‘pentane’ indicates a chain with 5 carbon atoms. Thus, the skeleton of each structure will be a straight chain of 5 carbon atoms.

Locate Substituents

For 3-ethylpentane, the substituent 'ethyl' (C2H5 group) is located on the third carbon of the pentane chain. For 2,3-dimethylpentane, there are two 'methyl' (CH3 groups) substituents, one attached to the second carbon and another to the third carbon of the pentane chain.

Draw 3-Ethylpentane

Draw the main chain of 5 carbon atoms. On the third carbon atom, attach an ethyl group (CH2CH3). This forms the complete structure of 3-ethylpentane.

Draw 2,3-Dimethylpentane

Draw the main chain of 5 carbon atoms. On the second carbon atom, attach a methyl group (CH3), and on the third carbon atom, attach another methyl group (CH3). This forms the complete structure of 2,3-dimethylpentane.

Key concepts

Structural Isomers

Structural isomers are fascinating and fundamental in organic chemistry. They have the same molecular formula but different arrangements of atoms. This means they can differ in how atoms are connected to each other, resulting in different structures and properties. For example, ethanol ( C_2H_5OH ) and dimethyl ether ( CH_3OCH_3 ) share the same molecular formula (C_2H_6O) but are distinct compounds with unique smells and uses.
In the exercise given, 3-ethylpentane and 2,3-dimethylpentane are structural isomers. Both share a similar molecular backbone based on the number of carbon and hydrogen atoms, but with different connections. The only distinction lies in the position and type of substituents attached to the main carbon chain.

• 3-Ethylpentane features a longer ethyl group attached to the third carbon of a pentane main chain.
• 2,3-Dimethylpentane has two shorter methyl groups, one on the second and another on the third carbon.

These differences in structure lead to variations in their boiling points, density, and how they interact with other chemicals.

Organic Chemistry

Organic chemistry is a vast field that focuses on carbon-containing compounds. It's a key branch of chemical science that deals with the structure, properties, composition, reactions, and synthesis of organic materials. Carbon's unique ability to form stable bonds with other atoms, including itself, leads to the diversity of life and synthetic compounds.
The cardinal rule in organic chemistry is understanding how carbon atoms form chains and rings, connecting with others to create larger and more complex molecules like proteins, DNA, and carbohydrates. In this regard, the study of alkanes, like pentane, is essential because they are the simplest types of organic compounds.
Alkanes are hydrocarbons, meaning they consist solely of hydrogen and carbon atoms. Their simplicity makes them a starting point for learning organic chemistry. The ability to manipulate and identify structural isomers of alkanes like 3-ethylpentane and 2,3-dimethylpentane allows aspiring chemists to grasp the basics of constructing more complex molecules.

IUPAC Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) nomenclature is the standardized method of naming organic chemical compounds. This system provides a clear and uniform way to identify and differentiate between myriad possible molecules in organic chemistry. Understanding the nomenclature is crucial for accurate communication among chemists.
With IUPAC nomenclature, you start by identifying the longest carbon chain in the molecule; this forms the base name. For example, in both 3-ethylpentane and 2,3-dimethylpentane, the base name is 'pentane,' signifying a five-carbon chain. Substituents are other groups or atoms attached to this main chain and are named and numbered according to their position for clarity.

• In 3-ethylpentane, the substituent is 'ethyl,' a two-carbon group, located on the third carbon of the pentane chain.
• In 2,3-dimethylpentane, there are two 'methyl' groups, each consisting of just one carbon atom, attached to the second and third carbons respectively.

Being able to interpret these names correctly helps chemists predict molecular structures and understand reactivities and properties of different organic compounds.