Question

Each of the following compounds is either an aldehyde or a ketone (Section 1.3C). Which line-angle formulas represent the same compound? Which represent constitutional isomers? (a) CCC(C)=O (b) O=C1CCCC1 (c) CCC(=O)CC (d) CC(C)C=O (e) CCCC=O (f) CCCC(C)=O (g) O=C1CCCCC1 (h) O=CC1CCCC1

Short answer

Question: Determine the relationship between the given compounds and identify each as an aldehyde or a ketone: (a), (b), (c), (d), (e), (f), (g), and (h). Answer: The relationship between the compounds and their classification as an aldehyde or ketone is as follows: (a) Ketone; same compound as (d) (b) Aldehyde; constitutional isomer of (h) (c) Ketone; constitutional isomer of (f) (d) Aldehyde; same compound as (a) (e) Aldehyde; unique compound (f) Ketone; constitutional isomer of (c) (g) Aldehyde; unique compound (h) Aldehyde; constitutional isomer of (b)

Step-by-step solution

Identify the compounds

First, let's convert each line-angle formula into its molecular formula to better analyze the compounds: (a) C4H8O (b) C5H8O (c) C5H10O (d) C4H8O (e) C4H8O (f) C5H10O (g) C6H10O (h) C5H8O Now, let's determine if each compound is an aldehyde or a ketone: (a) Ketone (b) Aldehyde (c) Ketone (d) Aldehyde (e) Aldehyde (f) Ketone (g) Aldehyde (h) Aldehyde

Analyze the relationships between compounds

We will now discuss the relationships between the different compounds: • Same compound: Compounds with the same molecular formula and the same structural formula are the same compounds. Here, (a) and (d) are the same compounds (C4H8O, one carbonyl carbon with two carbon chains). • Constitutional isomers: Compounds with the same molecular formula but different connectivity of atoms. Among the given compounds, the following pairs are constitutional isomers: - (b) and (h) (C5H8O, one carbonyl carbon with different five-membered ring connectivity) - (c) and (f) (C5H10O, one carbonyl carbon with different connectivity to the carbon chains)

Key concepts

Line-Angle Formulas

Understanding line-angle formulas, also known as skeletal structures, is crucial when studying organic chemistry. These diagrams offer a simplified way to represent molecules by showing the carbon-carbon bonds as lines. The carbon atoms and hydrogen atoms bonded to them are often not drawn explicitly, which can make it a bit tricky to interpret these formulas at first glance. However, once you get the hang of it, line-angle formulas become a fast and efficient way to visualize organic compounds.

Each end of a line and every vertex represents a carbon atom. Carbon atoms not shown explicitly are assumed to have enough hydrogen atoms attached to complete their tetravalent state. Interpretation might require you to remember that each carbon makes four bonds. So, if you see two lines meeting, you can deduce that the carbon at that point has two hydrogen atoms attached if no other elements are shown. This knowledge aids in the conversion to molecular formulas and in determining isomeric relationships.

Molecular Formula

A molecular formula is the depiction of the number and types of atoms in one molecule of a compound but doesn't provide information on how these atoms are connected. For instance, both ethanol and dimethyl ether have the same molecular formula, C₂H₆O, but their physical and chemical properties are different because of their different structures. This is where isomers come into play. Isomers are compounds with the same molecular formula but different arrangements of atoms, as seen in the exercise with compounds (c) and (f), both having the molecular formula C₅H₁₀O but arranged differently in space making them constitutional isomers.

When comparing the molecular formulas of compounds in the given exercise, we were able to identify compounds that may be identical or isomers, based on matching molecular formulas. Distinguishing between identical compounds and isomers lays the foundation for a deeper understanding of the structural and functional diversity of organic molecules.

Aldehydes and Ketones

Aldehydes and ketones are two types of organic compounds characterized by the presence of a carbonyl group, which is a carbon double-bonded to an oxygen. In aldehydes, the carbonyl group is bonded to at least one hydrogen atom, making it typically found at the end of the carbon chain. Ketones, on the other hand, have the carbonyl group bonded to two carbon atoms, meaning it appears within the carbon skeleton.

An easy way to remember this is that aldehydes are like the 'alpha' of the alphabet and appear at the 'beginning' whereas ketones are 'key' to linking chains and appear 'within'. In the exercise, this distinction helped us to identify compound (b) as an aldehyde because the carbonyl group is connected to one of the ring ends while compounds like (a) are recognized as ketones since the carbonyl is connected to two other carbon atoms. Recognizing these functional groups is critical in the study of organic chemistry, as they largely define the chemical behavior and reactivity of the molecules in which they occur.