Problem 88 - Chemistry: The Central Science in SI Units, Global Edition

Question

Draw each molecule given its name and the following information. (a) Nitroglycerin, also known as 1,2,3-trinitroxypropane, the active ingredient in dynamite and a medication administered to people having a heart attack, (Hint: The nitroxy group is the conjugate base of nitric acid.) (b) Putrescine, also known as 1,4-diaminobutane, the compound responsible for the odor of putrefying fish, (c) Cyclohexanone, the precursor to Nylon, (d) 1,1,2,2 -tetrafluoroethene, the precursor to Teflon, (e) Oleic acid, also known as cis-9-octanedecenoic acid, a monounsaturated fatty acid found in many fats and oils. Draw the correct isomer.

Step-by-Step Solution

Answer

The structures of the five molecules are as follows: (a) Nitroglycerin: \[ \text{CH}_2\text{(ONO}_2\text{)-\text{CH}( \text{ONO}_2\text{)}_2 \] (b) Putrescine: \[ \text{NH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-NH}_2 \] (c) Cyclohexanone: \[ \begin{array}{cccc} & & \text{O} & \\ \\ & \text{C} & = & \text{C} \\ \\ \text{C} & - & \text{C} & \\ \\ & \text{C} & - & \text{C} \\ \\ & & \text{C} & \end{array} \] (d) 1,1,2,2-tetrafluoroethene: \[ \text{CF}_2=\text{CF}_2 \] (e) Oleic Acid: \[ \text{CH}_3\text{(CH}_2\text{)}_7\text{CH=CH(CH}_2\text{)}_8\text{COOH} \]

Step 1: (a) Drawing Nitroglycerin (1,2,3-trinitroxypropane)

1. Start by drawing propane, which has three carbon atoms in a straight chain. 2. Add an oxygen atom to each of the three carbon atoms to change them into oxy-propane. 3. Then, replace each hydrogen atom on the oxygens with a nitro group (NO2) from the conjugate base of nitric acid. This will create 1,2,3-trinitroxypropane. The structure of Nitroglycerin is shown below: \[ \text{CH}_2\text{(ONO}_2\text{)-\text{CH}( \text{ONO}_2\text{)}_2 \]

Step 2: (b) Drawing Putrescine (1,4-diaminobutane)

1. Start by drawing butane, which has four carbon atoms in a straight chain. 2. Replace the hydrogen atoms at the first and fourth carbon atoms with amine groups (NH2). The structure of Putrescine is shown below: \[ \text{NH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-NH}_2 \]

Step 3: (c) Drawing Cyclohexanone

1. Draw a six-membered ring with all carbon atoms and single bonds. 2. Replace one of the carbon-carbon single bonds with a double bond, and replace the hydrogen atom connected to that carbon with a double-bonded oxygen atom (to form a ketone group). The structure of Cyclohexanone is shown below: \[ \begin{array}{cccc} & & \text{O} & \\ \\ & \text{C} & = & \text{C} \\ \\ \text{C} & - & \text{C} & \\ \\ & \text{C} & - & \text{C} \\ \\ & & \text{C} & \end{array} \]

Step 4: (d) Drawing 1,1,2,2-tetrafluoroethene

1. Start with ethene (ethylene), which has a double bond between the two carbon atoms. 2. Replace two hydrogen atoms on each carbon atom with two fluorine atoms. The structure of 1,1,2,2-tetrafluoroethene is shown below: \[ \text{CF}_2=\text{CF}_2 \]

Step 5: (e) Drawing Oleic Acid (cis-9-octanedecenoic acid)

1. Draw an 18-carbon chain (octadecane) and change the eighth and ninth carbon groups to double bonds (cis-9-octadecene). 2. Replace the hydrogen atom at the first carbon with a carboxyl group (COOH) to create a carboxylic acid. The structure of Oleic Acid is shown below: \[ \text{CH}_3\text{(CH}_2\text{)}_7\text{CH=CH(CH}_2\text{)}_8\text{COOH} \]

Key Concepts

Molecular Drawing

Drawing molecules in organic chemistry is like creating a map of atoms and bonds. It's key for understanding how molecules are structured and how they interact. Let's explore how to translate the names of molecules into sketches that give insight into their chemical composition and properties.
In molecular drawing, we represent atoms as nodes and bonds as lines connecting these nodes:

• Start with the backbone of the molecule, which is often a chain of carbon atoms. This is your skeleton structure.
• Next, add functional groups like hydroxyls (-OH) or amino groups (-NH\(_2\)). This is important because it shows the active sites of the molecule.
• Molecules also contain bonds of varying lengths and angles. Visualize these in your drawing. Double and triple bonds are drawn as double or triple lines respectively.

For example, drawing 1,2,3-trinitroxypropane (Nitroglycerin) involves starting with a propane backbone of three carbon atoms. Each carbon then gets an oxygen atom attached before adding nitro groups (NO\(_2\)) to these oxygens. This reveals the entire molecule's layout and highlights how each section interacts.

Functional Groups

Functional groups are pivotal in determining how a molecule behaves chemically. They are specific groupings of atoms within molecules that have their own characteristic properties, regardless of the other atoms present in a molecule. Let's decode some common functional groups and their implications:

• Nitro Group (-NO\(_2\)): Found in explosives like nitroglycerin. This group is electron-withdrawing and adds polarity to the molecule, affecting its reactivity and stability.
• Amine Group (-NH\(_2\)): Present in compounds like putrescine. Amines, characterized by the nitrogen atom, are basic and can engage in hydrogen bonding, influencing solubility and boiling point.
• Carboxyl Group (-COOH): Seen in fatty acids such as oleic acid. This group makes molecules acidic and reactive, able to donate protons or form esters and amides.

To recognize these groups, look for patterns where the groups appear, and remember they will significantly influence the resulting molecule's chemical activity and interactions.

Isomer Identification

Isomers are fascinating variants of molecules that have the same molecular formula but different structures. Understanding these differences is crucial, especially when the properties and functions of the molecules vary with structure. Types of isomers include:

• Structural Isomers: Compounds with the same molecular formula but different connectivity. Oleic acid and its variants show how bonds and spatial arrangement can differentiate even simple hydrocarbons.
• Stereoisomers: These have the same bonds but differ in the arrangement of atoms in space. Cis and trans isomers, like those in oleic acid, where the hydrogen atoms are on the same side (cis) or opposite sides (trans) of the double bond, affect the shape and properties of molecules.
• Functional Group Isomers: Molecules with the same formula but possessing different functional groups. They showcase the diversity of molecular forms.

Recognizing isomers involves carefully analyzing the molecule's layout and ensuring that subtle differences do not escape your notice. This knowledge helps anticipate the behavior and reactivity of the compound in different environments.