Question

Draw a structural formula for each of the following. a. 3 -methylpentanoic acid b. ethyl methanoate c. methyl benzoate d. 2-bromobutanoic acid e. 3 -chloro- 2,4 -dimethylhexanoic acid

Short answer

a. 3-methylpentanoic acid: \[CH_3-\overset{O}{\underset{||}{C}}-CH_2-CH(CH_3)-CH_2-CH_3\] b. ethyl methanoate: \[\overset{O}{\underset{||}{C}}-\overset{H}{\underset{3}{C}}-O-CH_2-CH_3\] c. methyl benzoate: \[ \text{Ph} -\overset{O}{\underset{||}{C}}-CH_3\] d. 2-bromobutanoic acid: \[CH_3-\overset{O}{\underset{||}{C}}-CH(Br)-CH_2-CH_3\] e. 3-chloro-2,4-dimethylhexanoic acid: \[CH_3-\overset{O}{\underset{||}{C}}-CH(CH_3)-CH(Cl)-CH(CH_3)-CH_2-CH_3\]

Step-by-step solution

Understanding the Nomenclature

For each compound, analyze the name of the compound to identify the parent chain, functional groups, and substituents. Then, use this information to draw a basic skeletal structure. a. 3-methylpentanoic acid Parent chain: pentanoic acid (5 carbon chain with a carboxylic acid group) Substituent: Methyl group on the 3rd carbon. b. ethyl methanoate Parent chain: methanoic acid (1 carbon chain with a carboxylic acid group) Functional group: ester (name: ethyl methanoate) c. methyl benzoate Parent chain: benzoic acid (carboxylic acid group on a benzene ring) Functional group: ester (name: methyl benzoate) d. 2-bromobutanoic acid Parent chain: butanoic acid (4 carbon chain with a carboxylic acid group) Substituent: Bromine atom on the 2nd carbon. e. 3-chloro-2,4-dimethylhexanoic acid Parent chain: hexanoic acid (6 carbon chain with a carboxylic acid group) Substituents: Chlorine atom on the 3rd carbon, two methyl groups on the 2nd and 4th carbon.

Drawing the Structural Formulas

Now, we'll draw the structural formulas for each compound using the information gathered from the nomenclature: a. 3-methylpentanoic acid Structure: \[CH_3-\overset{O}{\underset{||}{C}}-CH_2-CH(CH_3)-CH_2-CH_3\] b. ethyl methanoate Structure: \[\overset{O}{\underset{||}{C}}-\overset{H}{\underset{3}{C}}-O-CH_2-CH_3\] c. methyl benzoate Structure: \[ \text{Ph} -\overset{O}{\underset{||}{C}}-CH_3\] (where Ph represents the phenyl group, which is a benzene ring) d. 2-bromobutanoic acid Structure: \[CH_3-\overset{O}{\underset{||}{C}}-CH(Br)-CH_2-CH_3\] e. 3-chloro-2,4-dimethylhexanoic acid Structure: \[CH_3-\overset{O}{\underset{||}{C}}-CH(CH_3)-CH(Cl)-CH(CH_3)-CH_2-CH_3\]

Key concepts

functional groups

In organic chemistry, understanding functional groups is crucial because they define the chemical and physical properties of molecules. A functional group is a specific group of atoms within a molecule that is responsible for the characteristic reactions of that compound.

For example, in carboxylic acids, the functional group is the carboxyl group (–COOH), which is a fusion of a carbonyl (C=O) and a hydroxyl (–OH) group. This group is pivotal in defining the acids' reactivity and acidity.

Similarly, esters have the functional group \(\overset{O}{\underset{||}{C}}-O-R'\), resulting from the combination of an acid and an alcohol, minus water. Recognizing these functional groups in compounds like methyl benzoate and ethyl methanoate helps predict their behavior and reactions.

• Carboxylic Acids: Presence of the carboxyl group.
• Esters: Formed through an ester linkage.
• Halides: Halogen atoms as substituents like bromine or chlorine.

Identifying functional groups gives insights into the molecular structure and reactivity of different organic compounds.

structural formula

A structural formula illustrates the specific connections between atoms within a molecule. It's a two-dimensional representation that shows the arrangement of atoms and the chemical bonds that hold them together.

The importance of structural formulas in organic chemistry can't be overstated as it helps in visualizing the molecule's shape and recognizing how atoms are connected, hence predicting the chemical behavior.

For instance, the structural formula for 3-methylpentanoic acid lets us see the carbon chain's length, the placement of the methyl group, and the carboxylic acid group's presence.

These representations provide clarity, especially when dealing with complex molecules like 3-chloro-2,4-dimethylhexanoic acid, allowing us to appreciate where each substituent or functional group is located within the carbon skeleton.

nomenclature

Nomenclature in organic chemistry is the system used to name chemical substances systematically. IUPAC (International Union of Pure and Applied Chemistry) provides a set of standard naming rules ensuring each molecule has a unique name.

The name of a compound reveals its structure. By breaking down names like "ethyl methanoate," you can deduce that it is an ester derived from methanoic acid with an ethyl group attached. Similarly, names such as 2-bromobutanoic acid give valuable hints about substituents and parent chains, indicating the presence of a bromine atom on the second carbon of a butanoic acid backbone.

Nomenclature helps in understanding the relationship between different parts of a molecule. Key guidelines involve identifying the longest carbon chain, considering functional groups, and accounting for other substituents. The clear structure and logic behind IUPAC names make understanding organic compounds more accessible.

carboxylic acid

Carboxylic acids are a class of organic compounds characterized by the presence of a carboxyl group (COOH) at the end of a carbon chain. This group is responsible for the acidic properties of these molecules.

In the formula \(R- ext{COOH}\), "R" represents the carbon chain, and the carboxyl group is the functional component. The acidity in carboxylic acids arises because the hydrogen in the hydroxyl can easily be lost, forming a carboxylate ion.

Compounds like 3-methylpentanoic acid and 2-bromobutanoic acid showcase this feature prominently. Their names reveal not just the carbon chain but the functional group that defines their chemical nature.

• Structural Aspect: Carboxylic acids always end with the COOH group.
• Reactions: They are known to engage in reactions like esterification.

Esterification is a process where an alcohol reacts with a carboxylic acid, resulting in an ester, such as in ethyl methanoate.

esters

Esters are organic compounds formed from an acid (typically a carboxylic acid) and an alcohol, facilitated through a dehydration reaction where water is eliminated. The general formula for an ester is \(R- ext{COO}-R'\), where "R" and "R'" are alkyl or aryl groups.

The formation of esters, known as esterification, involves the replacement of the hydroxyl in the carboxylic acid by an alkoxyl group from the alcohol.

For instance, in ethyl methanoate, methanoic acid (formic acid) reacts with ethanol, leading to the formation of the ester with an ethyl group attached. Similarly, in methyl benzoate, benzoic acid and methanol undergo the same transformation, delivering an aromatic ester.

• Structure: Presence of the ester linkage \(\overset{O}{\underset{||}{C}}-O-R'\).
• Uses: Esters are widely utilized for their aromas and flavors, making them popular in perfumes and food flavorings.

Understanding esters allows for comprehending a vast array of reactions and properties, central to organic chemistry.