Problem 129 - Chemistry The Science in Context

Question

Skunks The pungent smell of skunk spray is detected by receptors in the nose when the skunk secretes butanethiol, \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{SH} .\) Draw a carbon- skeleton structure for butanethiol.

Step-by-Step Solution

Answer

Question: Draw a carbon-skeleton structure for butanethiol and mention the atoms present in it. Answer: The carbon-skeleton structure for butanethiol is \(\mathrm{H}_{3}\mathrm{C} - \mathrm{CH}_{2} - \mathrm{CH}_{2} - \mathrm{CH}_{2} - \mathrm{S} - \mathrm{H}\). It contains 4 carbon atoms, 9 hydrogen atoms, and 1 sulfur atom.

Step 1: Identify the atoms in the molecular formula

The molecular formula given is \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{SH}\). We can see that there are: - 4 carbon atoms denoted by \(\mathrm{C}\) - 9 hydrogen atoms denoted by \(\mathrm{H}\) - 1 sulfur atom denoted by \(\mathrm{S}\)

Step 2: Connect the carbon atoms

In a carbon-skeleton structure, carbon atoms are connected in a chain. To make the chain, we need to place 4 carbon atoms next to each other, connected through single bonds. It will look like: \(\mathrm{C}\mathrm{-C}\mathrm{-C}\mathrm{-C}\)

Step 3: Attach the hydrogen atoms

Now we need to attach the hydrogen atoms to the carbon atoms. Each carbon atom should complete a total of 4 bonds in a fully saturated hydrocarbon: 1. The first carbon atom has one bond with the second carbon atom, so it can form 3 more bonds with 3 hydrogen atoms: \(\mathrm{H}_{3}\mathrm{-C}- \cdots\) 2. The second, and third carbon atoms already have one bond with adjacent carbons, they can form 2 bonds with hydrogen atoms: \(\mathrm{-CH}_{2}-\mathrm{CH}_2 \cdots\) 3. The fourth carbon atom has one bond with the third carbon atom; however, it also needs to make a bond with the sulfur atom. So it can form 2 bonds with hydrogen atoms: \(\cdots \mathrm{-CH}_{2}\)

Step 4: Attach the sulfur atom and the remaining hydrogen atom

As mentioned earlier, the fourth carbon atom needs to form a bond with the sulfur atom. To complete the molecule, we attach the sulfur atom to the fourth carbon atom, and then, the remaining hydrogen atom to the sulfur atom: \(\cdots \mathrm{-CH}_{2} - \mathrm{S} - \mathrm{H}\)

Step 5: Combine the components

Now that we have connected all the atoms, let's combine them to get the complete carbon-skeleton structure for butanethiol: \(\mathrm{H}_{3}\mathrm{C} - \mathrm{CH}_{2} - \mathrm{CH}_{2} - \mathrm{CH}_{2} - \mathrm{S} - \mathrm{H}\)

Key Concepts

Molecular Formula

The molecular formula provides essential information regarding the types and numbers of atoms comprising a compound. In the context of butanethiol, its molecular formula is expressed as \( \mathrm{CH}_{3}(\mathrm{CH}_{2})_{3} \mathrm{SH} \), indicating that the substance consists of four carbon (C) atoms, nine hydrogen (H) atoms, and one sulfur (S) atom.

Understanding the molecular formula is crucial for comprehending the overall makeup of butanethiol. It serves as a foundation for constructing the carbon-skeleton structure and identifying the compound's properties, such as whether it is a saturated hydrocarbon and the types of chemical bonding present.

Carbon-Skeleton Structure

A carbon-skeleton structure is a simplified representation of a molecule that highlights the arrangement of carbon atoms within the compound. For butanethiol, this consists of four carbon atoms connected linearly in a chain. The sequence begins with \( \mathrm{CH}_{3} \) and continues with three \( \mathrm{CH}_{2} \) groups before ending in a sulfur-hydrogen (\( \mathrm{SH} \) group).

As you visualize this structure, imagine a chain where each carbon atom represents a link, with the first carbon atom at one end (displaying three hydrogen atoms bonded to it) and the sulfur atom bonded to the fourth carbon atom at the other end. Implementing this representation aids in grasping the compound's arrangement and aides in further understanding its properties and reactivity.

Chemical Bonding

Chemical bonding pertains to the forces that hold atoms together in a compound. In butanethiol, carbon and hydrogen atoms are linked through single covalent bonds, which occur when two atoms share a pair of electrons. The compound features a covalent bond between the sulfur and hydrogen atoms, and single bonds connecting the linear chain of carbon atoms.

Such bonding assures the stability of the butanethiol molecule, designating each atom's specific location in the structure. It is through comprehending these bonds that one can deduce how molecules form and why they possess certain physical and chemical characteristics.

Saturated Hydrocarbons

Saturated hydrocarbons are compounds that consist solely of carbon and hydrogen atoms with single bonds between carbon atoms. However, butanethiol isn’t purely a saturated hydrocarbon due to the presence of a sulfur atom. Nevertheless, the carbon-hydrogen part of butanethiol is identical to that of saturated hydrocarbons, exemplified by the four carbon linear chain each making four bonds displaying no carbon-carbon double or triple bonds.

Understanding that saturated hydrocarbons, like the carbon-linked portion of butanethiol, are less reactive than their unsaturated counterparts, can help anticipate the chemical behavior of such compounds. Recognizing this difference will enable students to predict reactivity and potential reactions in which the compound might engage.