Problem 54 - Chemistry Principles and Practice

Question

Draw the structure of each of the following molecules. (a) ethyl vinyl ether (b) 2 -bromopropanal (c) pentanoic acid (d) 3 -fluorophenol

Step-by-Step Solution

Answer

Draw each molecule by identifying functional groups and adding them to the carbon skeleton.

Step 1: Identify Functional Groups

For each molecule, identify the functional groups by analyzing the names given. (a) Ethyl vinyl ether consists of an ether group (-O-) between an ethyl and a vinyl group. (b) 2-Bromopropanal has an aldehyde group (carbonyl bonded to a hydrogen) on the terminal carbon and a bromine on the second carbon. (c) Pentanoic acid includes a carboxylic acid group (-COOH) on a five-carbon chain. (d) 3-Fluorophenol contains a phenol group (OH attached to a benzene ring) with a fluorine substituted at the third position.

Step 2: Draw the Basic Structures

Sketch the primary carbon chains or rings based on the naming. (a) Ethyl vinyl ether: Draw a two-carbon ethyl group attached to a two-carbon vinyl group. (b) 2-Bromopropanal: Sketch a three-carbon chain. (c) Pentanoic acid: Draw a straight five-carbon chain. (d) 3-Fluorophenol: Sketch a six-carbon benzene ring.

Step 3: Add Functional Groups

Place the functional groups on the base structures identified earlier. (a) Place an ether oxygen between the ethyl and vinyl group. (b) Attach an aldehyde group at the end of the chain and a bromine on the second carbon. (c) Add a carboxylic acid group on the end of the carbon chain. (d) Attach a hydroxyl group to the benzene ring and place a fluorine on the third carbon.

Step 4: Verify Connectivity and Count Electrons

Double-check that all carbon valencies are satisfied either by hydrogen or other atoms. Ensure the correct geometry around atoms, especially the sp² or sp³ hybridized carbons.

Key Concepts

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They play a crucial role in organic chemistry because they determine how molecules behave and react. In the exercise above, each compound contains distinct functional groups that define their chemical properties.

• Ether Group: Seen in ethyl vinyl ether, an ether group (-O-) separates the ethyl and vinyl components. This functional group is known for its relatively non-reactive nature but can partake in reactions like cleavage under certain conditions.
• Aldehyde Group: 2-Bromopropanal features a terminal aldehyde group, characterized by a carbonyl bonded to a hydrogen. Aldehydes are typically more reactive than ketones due to the hydrogen atom's electrophilic nature.
• Carboxylic Acid Group: Present in pentanoic acid, this group is known for acidity in organic compounds, due to the hydroxyl group's polarity and capability to donate a proton ( ext{H}^+).
• Phenol Group: In 3-fluorophenol, the phenol group consists of an -OH bonded to a benzene ring, making it more acidic than typical alcohols.

Functional groups are vital for identifying and predicting chemical behaviors, making the identification step in chemical drawing essential.

Molecular Structure

Understanding the molecular structure involves not only knowing the arrangement of atoms but also recognizing the spatial orientation. In the compounds from the exercise, the molecular structure was broken down using a step-by-step approach.

• Ethyl Vinyl Ether (C extsubscript{4}H extsubscript{8}O): Comprised of two carbon groups connected via an ether linkage, it adopts a linear structure with a slight angle at the oxygen atom due to its sp³ hybridization.
• 2-Bromopropanal (C extsubscript{3}H extsubscript{5}BrO): The molecule has a three-carbon backbone and, with bromine on the second carbon, the arrangement involves tetrahedral geometry around the carbon atoms, except for the carbon bonded to the aldehyde, which is trigonal planar.
• Pentanoic Acid (C extsubscript{5}H extsubscript{10}O extsubscript{2}): This features a five-carbon linear chain terminated by a carboxyl group, imparting a planarity to the terminal carbon due to sp² hybridization.
• 3-Fluorophenol (C extsubscript{6}H extsubscript{5}FO): A six-carbon benzene forms a planar hexagon with a hydroxyl and a fluorine substituent, maintaining the aromatic system intact.

These structures help predict the reactivity and physical properties of the molecules.

Chemical Drawing

Chemical drawing is a method to represent molecules visually, aiding chemists in understanding and communicating molecular details. For students, mastering this skill is fundamental.
Begin by constructing the carbon backbone, then add functional groups. For instance, in the exercise:

• For ethyl vinyl ether, sketch the two-carbon ethyl, then connect it to a similar two-carbon vinyl group where an oxygen (ether) bridges the gap.
• 2-Bromopropanal requires a linear approach with an aldehyde at the chain's end and bromine on the middle carbon, ensuring correct geometries as you go.
• With pentanoic acid, a simple straight chain is drawn, ending with a carboxylic acid, balancing both linearity and branching as necessary.
• Finally, 3-fluorophenol involves a hexagonal benzene ring, adding fluorine and a hydroxyl where required, highlighting how position can alter chemical properties.

Accurate chemical drawing is key to creating understandable molecular representations, necessary for both synthesis and analysis purposes.

Carbon Chains

Carbon chains form the backbone of organic molecules and can greatly influence their physical and chemical characteristics. These chains can be straight, branched, or cyclic, determining notable attributes of each compound.

• In ethyl vinyl ether, the carbon chain is composed of straight-connected carbons, leading to a flexible structure useful in many industrial applications.
• For 2-bromopropanal, the three-carbon saturated chain influences its reactivity, particularly in terms of how the bromine and aldehyde groups interact.
• Pentanoic acid's straight five-carbon chain facilitates its use in synthesizing various industrial chemicals, aided by its linear stability.
• Finally, the aromatic carbon configuration in 3-fluorophenol — a benzene ring — offers stability through resonance, providing particular properties such as enhanced acidity and unique reactivity patterns.

Carbon chains, due to their significance in determining the properties of compounds, are a major focus in organic chemistry, influencing both natural and synthetic processes.