Question

Arrange the following in the order of increasing acidity. Cc1cccc(C(=O)O)c1 Cc1ccc(C(=O)O)cc1 O=C(O)c1cccc(O)c1 O=C(O)c1ccccc1 \(\mathrm{A}\) \(C\) \(\mathrm{D}\) (a) \((\mathrm{A})<(\mathrm{D})<(\mathrm{B})<(\mathrm{C})\) (b) \((\mathrm{A})<(\mathrm{C})<(\mathrm{B})<(\mathrm{D})\) (c) \((\mathrm{C})<(\mathrm{D})<(\mathrm{A})<(\mathrm{B})\) (d) \((\mathrm{B})<(\mathrm{A})<(\mathrm{D})<(\mathrm{C})\)

Short answer

Question: Arrange the following molecules in the order of increasing acidity based on their SMILES notation: 1. Cc1cccc(C(=O)O)c1 2. Cc1ccc(C(=O)O)cc1 3. O=C(O)c1cccc(O)c1 4. O=C(O)c1ccccc1 Answer: The correct order of increasing acidity is Toluic Acid (A) < p-Toluic acid (C) < Benzoic acid (D) < Salicylic acid (B).

Step-by-step solution

Identify the molecules

The first step is to identify the molecules given by their SMILES notation: 1. Cc1cccc(C(=O)O)c1 -> Toluic Acid 2. Cc1ccc(C(=O)O)cc1 -> p-Toluic acid 3. O=C(O)c1cccc(O)c1 -> Salicylic acid 4. O=C(O)c1ccccc1 -> Benzoic acid Now that we have identified the molecules, we can move forward and analyze their acidity.

Analyze acidity

We will analyze the acidity of the molecules based on the presence of electron-withdrawing groups, electron-donating groups, and the stability of their conjugate bases: 1. Toluic Acid: Methyl group (-CH3) at ortho position (electron-donating group) 2. p-Toluic acid: Methyl group (-CH3) at para position (electron-donating group) 3. Salicylic acid: Hydroxyl group (-OH) at ortho position (electron-donating group) and Carbonyl group (C=O) (electron-withdrawing group) 4. Benzoic acid: Carbonyl group (C=O) (electron-withdrawing group) Now, let's arrange them in the order of increasing acidity.

Arrange in increasing acidity order

Electron-donating groups decrease acidity, while electron-withdrawing groups increase acidity. In addition, the conjugate base's stability directly affects the acidity of the molecule. Therefore, the order of increasing acidity would be as follows: \(A\) (Toluic Acid) < \(C\) (p-Toluic acid) < \(D\) (Benzoic acid) < \(B\) (Salicylic acid) So the correct order is given by option (b) \((\mathrm{A})<(\mathrm{C})<(\mathrm{B})<(\mathrm{D})\).

Key concepts

Organic Chemistry

Organic chemistry is all about understanding the structures, composition, and reactions of organic compounds. Organic compounds are mainly composed of carbon atoms, often combined with hydrogen, oxygen, nitrogen, and other elements. This branch of chemistry is vast and essential since it covers the chemistry of life, including everything from fuels to fabrics and pharmaceuticals. In organic chemistry, acidity is an important concept often examined through the lens of how molecular structure affects a compound's ability to donate a proton (H⁺). A deeper comprehension of acidity involves knowing how the molecular structure and substituents influence the compound's behavior in a reaction. In this context, substituents like electron-donating groups and electron-withdrawing groups play a key role, which can either increase or decrease the acidity of a compound.

Electron-Donating Groups

Electron-donating groups (EDGs) are atoms or groups of atoms that release or donate electrons into the molecule they are attached to. This process occurs through resonance or induction, predominantly in a conjugated system. In the context of acidity, EDGs reduce the acidity of a compound. This is because they make the conjugate base less stable by donating electron density, which destabilizes the negative charge.

• Common electron-donating groups include alkyl groups like the methyl group (-CH₃) and hydroxyl groups (-OH).
• The presence of an EDG often results in a compound holding onto its proton more tightly, thus making it less acidic.
• In the talk of the original problem, toluic acids have methyl groups, which are electron-donating, causing them to be less acidic compared to their counterparts with electron-withdrawing groups.

Electron-Withdrawing Groups

Contrary to electron-donating groups, electron-withdrawing groups (EWGs) pull electron density away from the rest of the molecule. This can stabilize the negative charge on a conjugate base, hence increasing the acidity of the original compound. EWGs accomplish this through resonance or induction.

• Typical EWGs include nitro groups (-NO₂), carbonyl groups (C=O), and halogens (F, Cl, etc.).
• When a molecule contains an EWG, the result is an increased tendency for the compound to release a proton, enhancing its acidity.
• In our example, benzoic acid contains a carbonyl group, which is an EWG, making it more acidic compared to toluic acids.

Conjugate Base Stability

The concept of conjugate base stability is pivotal in determining acidity. When an acid donates a proton, it forms a conjugate base. The more stable this conjugate base is, the stronger the original acid. This stability is highly influenced by the presence of substituents like electron-donating or electron-withdrawing groups.

• A stable conjugate base is one that has its negative charge dispersed or neutralized as effectively as possible.
• Electron-withdrawing groups can stabilize a conjugate base by delocalizing the negative charge across the molecule, enhancing acidity.
• Conversely, electron-donating groups can destabilize a conjugate base, reducing acidity by localizing additional electron density.
• In the initial question, salicylic acid is more acidic largely because the hydroxyl group can stabilize its conjugate base through hydrogen bonding and resonance.

Understanding these nuances helps predict and rationalize the acidity of different organic molecules.