Question

Positive Tollen's test is observed for (A) O=Cc1ccccc1 (B) O=Cc1ccccc1 (C) O=C(O)C(c1ccccc1)c1ccccc1 (D) O=C(C=Cc1ccccc1)c1ccccc1

Short answer

(C) \texttt{O=C(O)C(c1ccccc1)c1ccccc1} is the correct answer because it contains an aldehyde group.

Step-by-step solution

- Identify the functional groups

Analyze the given SMILES strings and determine the functional groups present in each compound

- Determine the reactivity with Tollens' reagent

Tollens' test is used to detect the presence of an aldehyde group. The test is positive if the compound contains an aldehyde group that can be oxidized to a carboxylic acid. Assess which compounds have the aldehyde group necessary for a positive Tollens' test.

- Match compounds to SMILES strings

Compare the identified functional groups in each compound with the structure implied by their respective SMILES strings.

Key concepts

Functional Groups in Organic Chemistry

Organic chemistry is a branch of chemistry that studies the structure, properties, and reactions of organic compounds, which contain carbon. Central to understanding organic molecules is grasping the concept of functional groups. A functional group is a specific group of atoms within a molecule that is responsible for the characteristic reactions of that molecule.

Functional groups provide a way to classify organic compounds by their structural features and predict their reactive behavior. Common functional groups include hydroxyl (-OH), carboxyl (-COOH), amino (-NH₂), and aldehyde (-CHO) groups, among others. Each type of functional group behaves consistently in chemical reactions, which allows for the systematic study and classification of organic compounds.

Identifying Functional Groups

To identify functional groups, chemists look for specific patterns in the structure of a molecule. For instance, an aldehyde group is recognized by a carbonyl group (a carbon double-bonded to oxygen) with at least one hydrogen atom attached to the carbonyl carbon. Recognizing these groups aids in predicting how a molecule will react under different conditions, such as in the Tollen's test, which specifically detects the presence of an aldehyde.

Aldehydes and Ketones

Aldehydes and ketones are two closely related functional groups in organic chemistry. Both contain the carbonyl group, but aldehydes have the carbonyl group at the end of a carbon chain, while ketones have it within the carbon chain. The general formula for aldehydes is R-CHO, whereas ketones have the formula R-CO-R', where R and R' are alkyl or aryl groups.

The properties of aldehydes and ketones differ because of the placement of the carbonyl group. Aldehydes are typically more reactive than ketones due to the hydrogen atom that is attached to the carbonyl carbon, making them more susceptible to oxidation.

Detecting Aldehydes

The Tollen's test is an example of how this reactivity is used to distinguish aldehydes from ketones. Since Tollen's reagent reacts with aldehydes to produce a silver mirror on the test tube, it is a useful qualitative test in organic chemistry laboratories. Ketones, lacking the hydrogen attached directly to the carbonyl carbon, do not give a positive Tollen's test.

SMILES Notation

SMILES (Simplified Molecular Input Line Entry System) notation is a way to represent molecules using textual characters, depicting the structure in a linear form. It's widely used for its simplicity and effectiveness in describing molecular structures in databases and digital communication.

In SMILES, atoms are represented by their chemical symbols, double and triple bonds by '=' and '#', respectively, and branching by parentheses. Ring structures are denoted by numerical digits that indicate the beginning and end of a ring.

Understanding SMILES in Computer-Aided Chemistry

The notation is favored in computational chemistry due to its linear nature, making it easy for algorithms to parse and interpret the structure of compounds. For example, the SMILES string 'O=Cc1ccccc1' represents a molecule with a carbonyl group (C=O) adjacent to a benzene ring (c1ccccc1). Recognizing the SMILES notation enables students and chemists to rapidly identify the molecular structure and functional groups present in a compound, facilitating easier communication and analysis across various branches of chemistry.