Question

For each compound, provide a name if the structure is given, or provide a structure if the name is given. (a) hexanoic acid CCCC(=O)O (c) CCCOC(=O)CC (d) butyl propanoate

Short answer

The structure for hexanoic acid is correctly given as 'CCCC(=O)O'. The second compound with the structure 'CCCOC(=O)CC' is named ethyl propanoate. The structure for butyl propanoate consists of a four-carbon butyl group attached to the oxygen of the ester linkage derived from propanoic acid.

Step-by-step solution

- Naming the compound from a given structure

For the structure represented by the SMILES string 'CCCC(=O)O', identify the functional groups and the longest carbon chain in the molecule. The structure has a carboxylic acid group (-COOH), indicated by '(=O)O', and a six-carbon chain (hexane), so the compound is named as a carboxylic acid with the parent chain 'hexane'. The name of the compound is hexanoic acid.

- Drawing the structure from a SMILES string

Translate the SMILES notation 'CCCOC(=O)CC' into a chemical structure. This notation tells us there is an ester functional group, indicated by 'OC(=O)', connecting two carbon chains. One chain has three carbons (propyl group) and the other has two carbons (ethyl group). The propyl group is on the alcohol-derived part of the ester, and the ethyl group comes from the acid part. Therefore, the ester is named ethyl propanoate.

- Drawing the structure for a given compound name

From the name butyl propanoate, identify the two parts of the ester. The 'butyl' part indicates a four-carbon alkyl group, and 'propanoate' indicates a derivative of propanoic acid where the acidic hydrogen has been replaced by another alkyl group. To draw the structure, create a three-carbon chain for the propanoate (acid part), with the carbonyl group (C=O) in the middle, and then attach a four-carbon butyl group to the oxygen atom of the ester linkage.

Key concepts

Chemical Structure Representation

Understanding the chemical structure representation is pivotal in organic chemistry, as it conveys crucial information about the molecule's identity and properties. When dealing with organic compounds, structural formulas allow chemists to visualize the arrangement of atoms within a molecule. These formulas can be depicted through various methods, including Lewis structures, line-angle (or skeletal) formulas, and space-filling models.

For students starting to learn about naming organic compounds, it's important to recognize the longest chain of carbon atoms — this identifies the compound's base name, which often ends with a suffix indicating the type of molecule, such as '-ane' for alkanes or '-oic acid' for carboxylic acids. Elements, such as oxygen or nitrogen, and functional groups, like double bonds or hydroxyl groups, are also represented in structures and denote further specific features and reactivity of the molecules.

In our example with hexanoic acid, the six-carbon chain forms the base name 'hexane', and the carboxylic acid group is represented by '(=O)O', concluding the name with '-oic acid'. Accurately interpreting these representations is essential for correctly naming the compound.

Functional Groups in Organic Chemistry

Functional groups are specific groupings of atoms within molecules that have their own characteristic properties, regardless of the other atoms or groups of atoms in the molecule. They are the key determinants of the chemical behavior of organic compounds and play a critical role in organic synthesis and compound identification.

The most common functional groups in organic chemistry include hydroxyl (-OH), carbonyl (C=O), carboxyl (-COOH), amino (-NH2), and ester (-COOR), among others. In the example of naming organic compounds, recognizing the presence of a functional group is the starting point for determining the compound's name.

For instance, the functional group in hexanoic acid is the carboxyl group, dictating that the molecule behaves as an acid and naming it accordingly. Similarly, the ester in the given SMILES 'CCCOC(=O)CC' is identified by the 'OC(=O)' part. Understanding these groups helps clarify the molecular structure and the naming conventions used in organic chemistry.

SMILES Notation

SMILES (Simplified Molecular Input Line Entry System) notation is a simplified chemical language used to represent a molecule's structure in a linear text format. It is a compact and computer-friendly way to describe the arrangement of atoms and bonds within a molecule without drawing out detailed structures.

SMILES strings are composed of symbols that represent atoms and their connectivity, and each string is unique to its respective molecule. Rings are described by breaking one bond and giving both atoms a matching numerical label. Various conventions are used to indicate the presence of double or triple bonds, branches, stereochemistry, and functional groups.

In our exercise, 'CCCC(=O)O' represents hexanoic acid, with 'CCCC' indicating a four-carbon chain and '(=O)O' denoting the carboxylic acid group. For 'CCCOC(=O)CC', we identify an ester functional group connecting an ethyl and a propyl chain. SMILES notation is a powerful tool for chemists, enabling them to communicate complex structures easily and efficiently. Mastering SMILES can significantly aid students in transitioning to more advanced topics in organic chemistry.