Question

Indicate whether the compounds in each set are constitutional isomers. (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\) CC(=O)CCCCC=O (c) CC(=O)CCCCCC(=O)O (d) CCC(=O)C(C)CC (e) CCCCCC(C)C1CCCC1 (f)

Short answer

Answer: For set (a), ethanol (\(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\)) and dimethyl ether (\(\mathrm{CH}_{3} \mathrm{OCH}_{3}\)) are constitutional isomers, as they have the same molecular formula (C2H6O) but different connectivity of atoms. For sets (b) to (f), there are no comparison molecules provided, so it is not possible to determine if these compounds are constitutional isomers with the given information.

Step-by-step solution

(a) Determine the molecular formula of the compounds

To find the molecular formula, we first translate the given chemical notations for the compounds: 1. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) is ethanol, with the molecular formula C2H6O. 2. \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\) is dimethyl ether, with the molecular formula C2H6O.

(a) Analyze the connectivity of atoms

Both compounds have the same molecular formula, C2H6O. However, the connectivity of their atoms is different: 1. In ethanol, the oxygen atom is bonded to one carbon atom and one hydrogen atom. 2. In dimethyl ether, the oxygen atom is bonded to two different methyl groups. Since both compounds have the same molecular formula but different connectivity, they are constitutional isomers.

(b-f) Translate SMILES notations

For the rest of the sets, we will first translate the given SMILES notations to their molecular structures, and then compare the molecular formula and connectivity of the atoms: (b) CC(=O)CCCCC=O is hexanoic acid (Molecular formula: C6H12O2), and there is no comparison molecule for (b). (c) CC(=O)CCCCCC(=O)O is an octanedioic acid (Molecular formula: C8H14O4), and there is no comparison molecule for (c). (d) CCC(=O)C(C)CC is a 3-methyl-2,4-hexanedione (Molecular formula: C7H12O2), and there is no comparison molecule for (d). (e) CCCCCC(C)C1CCCC1 is 4-cyclopentyl-3-methylheptane (Molecular formula: C12H24), and there is no comparison molecule for (e). (f) There is no molecule provided for this set. As there are no comparison molecules for sets (b) to (f), it is not possible to determine if these compounds are constitutional isomers with the given information.

Key concepts

Organic Chemistry

Organic chemistry is the study of carbon-containing compounds and their reactions. This branch of chemistry is crucial for understanding the structure, properties, and behavior of the molecules that make up living organisms and many materials we use every day.

Molecules in organic chemistry can have the same molecular formula but different structures. This leads to a concept known as isomerism, where compounds have the same atoms but arranged in different ways, thus leading to different chemical properties. One significant type of isomerism is constitutional isomerism. Here, molecules with the same molecular formula differ in the sequence in which the atoms are connected. An everyday example can be seen in the several structures that glucose and fructose can take, even though they have the same chemical formula of C6H12O6; their atoms are arranged differently, giving them distinct properties.

Understanding the subtleties of how atoms can be rearranged leads to a multitude of possibilities for creating new compounds in fields such as pharmaceuticals, plastics, and even the synthesis of new organic molecules for research purposes.

Molecular Formula

A molecular formula is a representation of the number and types of atoms present in a molecule. It does not show how atoms are connected to one another or the shape of the molecule, but it provides crucial information about the molecule's composition.

For instance, when looking at the molecular formula C2H6O from the exercise, we cannot determine the structure of the molecule directly from the formula itself. The formula simply tells us there are two carbon atoms, six hydrogen atoms, and one oxygen atom. These atoms can be arranged in different ways to form various substances. As demonstrated in the example exercise, C2H6O can represent both ethanol and dimethyl ether. While their molecular formulas are identical, their structures—how the atoms are connected—are what make them constitutional isomers.

To delve deeper into structural details, chemists use various notations and structural drawings. One such method, particularly useful in computer applications and databases, is the SMILES notation, which we will discuss next.

SMILES Notation

SMILES (Simplified Molecular Input Line Entry System) notation is a way to represent a chemical structure using a line of text. This notation can describe both the composition and the connectivity of a molecule, which is vital for distinguishing between isomers.

The SMILES notation uses a series of alphanumeric characters and punctuation marks to describe molecular structures: alphabetic characters for atoms (with 'C' for carbon, 'H' for hydrogen, etc.), '=' for double bonds, '#' for triple bonds, and parentheses for branching. Numbers are used to indicate ring structures. For example, in the problem given, CCC(=O)C(C)CC is the SMILES representation of 3-methyl-2,4-hexanedione. This system is particularly powerful when we consider its use in databases and algorithms that can predict properties of molecules or simulate reactions.

While SMILES is very informative, interpreting it can be quite challenging without proper training. Fortunately, computational tools can translate SMILES into visual structures, aiding chemists in visualizing and understanding complex molecules, which helps us to identify constitutional isomers, as seen in the exercise.