Question

Draw the structural formulas for three isomers of pentane, \(\mathrm{C}_{5} \mathrm{H}_{12}\) $$ \begin{array}{cc} \hline \text { Droplet } & \text { Calculated Charge (wa) } \\ \hline \text { A } & 3.84 \times 10^{-8} \\ \text {B } & 4.80 \times 10^{-8} \\ \text {C } & 2.88 \times 10^{-8} \\ \text {D } & 8.64 \times 10^{-8} \\ \hline \end{array} $$ (c) Based on your answer to part (b), how many electrons are there on each of the droplets? (d) What is the conversion factor between warmombs and coulombs?

Short answer

The three isomers of pentane are: 1. n-pentane: H H H H H | | | | | H-C-C-C-C-C-H | | | | | H H H H H 2. Isopentane (2-methylbutane): H H H H | | | | H-C-C-C-C-H | | | | H H-C-H | H 3. Neopentane (2,2-dimethylpropane): H H H | | | H-C-C-C-C-H | | | H C-H H H | H-C | H

Step-by-step solution

Draw the straight-chain isomer of pentane

Draw five carbon atoms in a straight line, connected by single bonds. Add hydrogen atoms so that each carbon atom forms four bonds in total: H H H H H | | | | | H-C-C-C-C-C-H | | | | | H H H H H This is the straight-chain isomer, called n-pentane.

Draw the first branched isomer of pentane

Starting from n-pentane, move one hydrogen atom from the third carbon and replace it with a methyl group (CH3) attached to the second carbon. This new structure looks like this: H H H H | | | | H-C-C-C-C-H | | | | H H-C-H | H This is the first branched isomer, called isopentane or 2-methylbutane.

Draw the second branched isomer of pentane

Starting again from n-pentane, move one hydrogen atom from the third carbon and replace it with a methyl group (CH3) attached to the first carbon. This new structure looks like this: H H H | | | H-C-C-C-C-H | | | H C-H H H | H-C | H This is the second branched isomer, called neopentane or 2,2-dimethylpropane. We have successfully drawn the three isomers of pentane: n-pentane, isopentane (2-methylbutane), and neopentane (2,2-dimethylpropane).

Key concepts

Structural Formulas

Structural formulas are essential in the study of organic chemistry as they provide a visual representation of the molecular structure of a compound. Unlike simple chemical formulas, which list the types of atoms and their quantities, structural formulas show how those atoms are connected to each other.

For example, pentane, with a chemical formula of \(\mathrm{C}_5\mathrm{H}_{12}\), could describe any number of structures where five carbon atoms and twelve hydrogen atoms are bonded. But, structural formulas allow us to see the specific arrangement of the carbon and hydrogen atoms. The arrangement of atoms in different configurations leads to distinct substances known as isomers, each with unique properties despite having the same molecular formula.

As depicted in the textbook exercise, the straight-chain isomer is drawn with all carbon atoms connected in a row. For the branched isomers, structural formulas help us understand how moving a methyl group (\(\mathrm{CH}_3\)) creates a different compound, changing the molecular geometry and resulting in isopentane and neopentane.

Organic Chemistry

Organic chemistry is the branch of chemistry that studies the structure, properties, and reactions of organic compounds, which are defined by the presence of carbon atoms. Carbon is a unique element in its ability to form four bonds with other atoms, leading to a vast variety of carbon-based molecules, including hydrocarbons like pentane.

In organic chemistry, understanding isomers is crucial. Isomers have the same molecular formula but different structural or spatial arrangements, resulting in varied physical and chemical properties. For the case of pentane \(\mathrm{C}_5\mathrm{H}_{12}\), each of its isomers exhibits different characteristics such as boiling points and densities, which can influence their practical applications in industry.

The study of these differences is foundational for students of organic chemistry, as it provides insight into how slight changes in structure can lead to a different compound altogether. Recognition of the isomers of a given molecular formula, like those we identified for pentane, provides a concrete example of these fundamental organic chemistry principles.

Hydrocarbons

Hydrocarbons are organic chemical compounds consisting entirely of hydrogen and carbon atoms. They are the simplest form of organic compounds and serve as the foundation for more complex molecules. In organic chemistry, hydrocarbons are classified by the types of bonds between carbon atoms, with variations including alkanes, alkenes, and alkynes.

Pentane, the focus of our exercise, is a type of alkane, which is a hydrocarbon with single bonds between carbon atoms. Alkanes are known for their stability and are often used as fuels due to their tendency to undergo combustion reactions. Pentane itself, along with its isomers, is used in various applications from solvent production to being a reference substance in calibration.

The structural variance seen in the isomers of pentane showcases the diversity possible within hydrocarbons. Isomerism directly affects the physical properties of these substances, which is why understanding different hydrocarbon structures, as demonstrated in the textbook solution, is a key learning objective for students exploring organic chemistry.