Each of the three molecules shown here contains an OH group,...

Each of the three molecules shown here contains an OH group, but one molecule acts as a base, one as an acid, and the third is neither acid nor base.
(a) Which one acts as a base? (b) Which one acts as an acid? (c) Which one is neither acidic nor basic? [Sections 16.6 and 16.7$]$

Key Concepts

Bronsted-Lowry Acid?Base Theory

This theory defines acids as proton (H?) donors and bases as proton acceptors. In the context of organic chemistry, even molecules with similar functional groups can behave differently depending on their ability to donate or accept protons. The theory provides the framework for analyzing reactions where proton transfer occurs, making it fundamental to understanding why certain compounds exhibit acidic or basic behavior.

Resonance Stabilization and Conjugate Base Stability

The acidity of a compound is greatly influenced by the stability of its conjugate base. When an acidic proton is lost, a delocalized (resonance-stabilized) negative charge can increase the stability of the resulting species. This concept is particularly important in aromatic systems where the negative charge can be distributed over several atoms, enhancing the acidic character of the molecule through resonance stabilization.

Structural Influences on Acidity and Basicity

The chemical environment around a functional group, including inductive and steric effects, determines how easily a proton is donated or accepted. Electron-withdrawing groups can stabilize a negative charge, increasing acidity, while electron-donating groups can enhance basicity by increasing the electron density at the site of protonation. Understanding these structural effects helps explain why molecules with similar functional groups, such as OH groups, can behave as acids, bases, or remain neutral.

Functional Group Behavior in Organic Molecules

Even when molecules share the same functional group, such as an alcohol (OH), their acidic or basic properties depend on the overall molecular context. Factors such as the polarity of the surrounding structure, the presence of conjugated systems, and the type of bonding all play critical roles in determining whether the group will act primarily as a proton donor, acceptor, or remain mostly inert in acid-base interactions.

Transcript

00:01 All right.

00:01 Today we're doing chapter 16, problem 8 from chemistry, the central science, 14th edition by brown.

00:09 What this question is asking us is to look at the three molecules that they've given us below and to be able to answer which one's base, which one's acidic, and which one is neither aesthetic or basic.

00:25 And so looking at these molecules, we're just going to go one by one and draw them out in their loose asset.

00:31 Their lewy dot structure and be able to determine which one is what.

00:37 So molecule a is a nitrogen and connected to two hydrogens, connected to an oxygen, and another hydrogen.

00:58 All right.

00:59 And so with looking at this, in our lewdot structure, we can see that our nitrogen has two lone pair of electrons.

01:10 That would be easily being able to be donated if we were in a condition that had a proton to be able to be accepted to.

01:22 So this nitrogen, one pair of electrons, would be able to donate to this hydrogen over here, and it would be able to accept it.

01:33 So therefore, we consider this as a base.

01:36 And this is a base by the rule of the lewis acid and base and it being an electron donor.

01:48 So for molecule b, when we draw this structure, we have a carbon that is connected to hydrogen that is double bonded to an oxygen, which is bonded to another oxygen, which is bonded to a hydrogen...

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