Question

Draw a structural formula for each compound. (a) 1-Chloro-2-propanone (b) 3-Hydroxybutanal (c) 4 -Hydroxy-4-methyl-2-pentanone (d) 3-Methyl-3-phenylbutanal (e) 1,3 -Cyclohexanedione (f) 3 -Methyl-3-buten-2-one (g) 5-Oxohexanal (h) 2,2 -Dimethylcyclohexanecarbaldehyde (i) 3-Oxobutanoic acid

Short answer

Based on the step-by-step solution, complete the following structural formulas: (a) 1-Chloro-2-propanone: ClCH2-CO-CH3 (b) 3-Hydroxybutanal: CH3-CH2-CHOH-CHO (c) 4-Hydroxy-4-methyl-2-pentanone: CH3-CO-CH2-CH(OH)-C(CH3)3 (d) 3-Methyl-3-phenylbutanal: CH3-CH2-CH(C-CH3)(Ph)-CHO (e) 1,3-Cyclohexanedione: Cyclohexane 1,3-diketone (f) 3-Methyl-3-buten-2-one: CH2=C(=O)-CH=C(CH3)2 (g) 5-Oxohexanal: CH3-CH2-CH2-C(=O)-CHOH-CHO (h) 2,2-Dimethylcyclohexanecarbaldehyde: Cyclohexane carbaldehyde with two methyl groups at position 2 (i) 3-Oxobutanoic acid: CH3-CH2-C(=O)-CH2-COOH

Step-by-step solution

(a) 1-Chloro-2-propanone

Identify the parent chain as a three-carbon one (propane), with an aldehyde functional group (giving propanone). Then, add the chlorine atom at the one-carbon position. The structural formula for 1-Chloro-2-propanone is: ClCH2-CO-CH3

(b) 3-Hydroxybutanal

Here, the four-carbon (butane) chain has an aldehyde functional group (giving butanal), and a hydroxyl group at the three-carbon position. Draw the compound as: CH3-CH2-CHOH-CHO

(c) 4-Hydroxy-4-methyl-2-pentanone

In this case, start with the five-carbon (pentane) chain with a ketone functional group in the middle (giving pentanone). Add the hydroxyl group at the four-carbon position. Lastly, add the methyl group also to the four-carbon position. The structural formula for this compound is: CH3-CO-CH2-CH(OH)-C(CH3)3

(d) 3-Methyl-3-phenylbutanal

Start with a four-carbon (butane) chain with an aldehyde functional group (butanal). Next, add a methyl group at the three-carbon position, and a phenyl group also at the three-carbon position. The structural formula is: CH3-CH2-CH(C-CH3)(Ph)-CHO, where Ph represents the phenyl group

(e) 1,3-Cyclohexanedione

Draw a cyclohexane ring and add two ketone functional groups at the 1 and 3 positions. The structural formula for 1,3-cyclohexanedione is: Cyclohexane 1,3-diketone (ketone groups at positions 1 and 3 of the cyclohexane ring)

(f) 3-Methyl-3-buten-2-one

Begin with a five-carbon compound with two double bonds (butene). Then, place a ketone functional group at the two-carbon position and a methyl group at the 3-carbon position. The structural formula for 3-methyl-3-buten-2-one is: CH2=C(=O)-CH=C(CH3)2

(g) 5-Oxohexanal

For this compound, start with a six-carbon (hexane) chain with an aldehyde functional group (hexanal). Finally, add a ketone functional group at the fifth position: CH3-CH2-CH2-C(=O)-CHOH-CHO

(h) 2,2-Dimethylcyclohexanecarbaldehyde

Draw a cyclohexane ring and add two methyl groups at the 2-carbon position of the ring. Then, attach an aldehyde functional group to one of the carbons of the ring. The structural formula is: Cyclohexane carbaldehyde with two methyl groups at position 2

(i) 3-Oxobutanoic acid

Begin with a four-carbon (butane) chain with an acid functional group at one end (giving butanoic acid). Include a ketone functional group at the three-carbon position: CH3-CH2-C(=O)-CH2-COOH

Key concepts

Aldehyde Functional Group

An aldehyde functional group is a key concept in organic chemistry that defines a class of organic compounds. It’s composed of a carbon atom double-bonded to an oxygen atom (carbonyl group) and at least one hydrogen atom. The simplest aldehyde is formaldehyde (CH₂O), and it can be visually identified by the structure R-CHO, where R is any alkyl or aryl group.

Knowing how to recognize this group is crucial for understanding and drawing organic molecules, as aldehydes are involved in various chemical reactions, including oxidation and reduction processes. A functional group's identity greatly influences a molecule’s chemical behavior, and this is particularly true for aldehydes, which are typically quite reactive.

In the exercise presented, compounds like 3-Hydroxybutanal and 5-Oxohexanal showcase aldehyde groups at different positions, influencing their structural formulas and chemical properties.

Ketone Functional Group

Another vital player in organic chemistry is the ketone functional group. Similarly to aldehydes, ketones contain a carbonyl group. However, the key difference is that in ketones, the carbonyl carbon is bonded to two other carbon atoms (R-CO-R’). Common examples include acetone (propanone), which is the smallest and simplest ketone.

• The presence of a ketone impacts the reactivity and polarity of a molecule.
• Ketones can be identified by their IUPAC naming, typically ending in 'one', such as in butanone or pentanone.

The compounds 1,3-Cyclohexanedione and 3-Methyl-3-buten-2-one in the exercise are clear examples of structures featuring ketone groups. Learning to identify such groups is essential for understanding their roles in organic reactions, such as nucleophilic additions or their use in polymer production.

Hydroxyl Group in Organic Chemistry

The hydroxyl group is a fundamental functional group in organic chemistry represented by the formula –OH. It’s characteristic of alcohols and phenols and is known for its role in increasing the polarity and solubility of organic compounds in water. The hydroxyl group forms hydrogen bonds, which are vital for many biological processes.

• The –OH group is directly bonded to a carbon atom.
• Its presence influences the molecule's physical and chemical properties significantly.

For example, in the exercises, compounds like 3-Hydroxybutanal and 4-Hydroxy-4-methyl-2-pentanone, the hydroxyl group defines part of their structure, contributing to their chemical reactivity, such as in dehydration reactions or conversion to ethers.

Carbon Chain Identification

Understanding carbon chain identification is crucial in deciphering the structure of organic molecules. Carbon chains form the backbone of organic compounds and can vary in length, branching, and the types of bonds they contain (single, double, triple).

In organic chemistry, the length of the carbon chain and its branching pattern define the primary structure of a molecule, dictating its IUPAC name and properties. The structural formula is pieced together by identifying the longest chain of carbons (which may not always be straight), and noting any functional groups attached to this backbone.

When analyzing compounds from the exercise, such as 3-Methyl-3-phenylbutanal or 2,2-Dimethylcyclohexanecarbaldehyde, one must focus on identifying the main carbon chain to correctly interpret and draw the structural formula. Mastery of carbon chain identification is essential for organic synthesis and predicting molecular behavior.