In the following acid–base reactions,
1. draw Lewis structures of the reactants and the products.
2. determine which species are acting as electrophiles (acids) and which are acting as nucleophiles (bases).
3. use the curved-arrow formalism to show the movement of electron pairs in these reactions, as well as the imaginary movement in the resonance hybrids of the products.
4. indicate which reactions are best termed Brønsted–Lowry acid–base reactions.
(a)

검증된 단계별 안내

Draw the Lewis structures for acetaldehyde (CH3CHO) and HCl. Acetaldehyde has a carbonyl group (C=O) with a lone pair on the oxygen, and HCl is a simple diatomic molecule with a single bond between H and Cl, where Cl has three lone pairs.

Identify the electrophile and nucleophile. In this reaction, the carbonyl oxygen in acetaldehyde acts as the nucleophile due to its lone pairs, and HCl acts as the electrophile because the hydrogen can accept an electron pair.

Use curved-arrow formalism to show the movement of electron pairs. The lone pair on the oxygen of acetaldehyde attacks the hydrogen of HCl, forming a new O-H bond and resulting in the release of Cl- as a leaving group.

Draw the Lewis structures of the products: the protonated acetaldehyde (CH3C(=OH)H)+ and the chloride ion (Cl-). The oxygen in the protonated acetaldehyde now has a positive charge due to the additional hydrogen.

Determine if the reaction is a Brønsted–Lowry acid–base reaction. Since the reaction involves the transfer of a proton (H+) from HCl to acetaldehyde, it is classified as a Brønsted–Lowry acid–base reaction.

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Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They help visualize the arrangement of electrons and the connectivity of atoms, which is crucial for understanding chemical reactions. In the context of acid-base reactions, drawing Lewis structures allows one to identify the electron-rich and electron-deficient sites, aiding in the determination of nucleophiles and electrophiles.

Electrophiles and Nucleophiles

Electrophiles are species that accept electron pairs, typically acting as acids in chemical reactions, while nucleophiles are electron-rich species that donate electron pairs, acting as bases. In the given reaction, acetalaldehyde acts as a nucleophile due to the presence of a lone pair on the oxygen atom, while HCl serves as an electrophile. Understanding these roles is essential for analyzing acid-base reactions and predicting the outcome of chemical transformations.

Brønsted–Lowry Acid-Base Theory

The Brønsted–Lowry theory defines acids as proton donors and bases as proton acceptors. This framework is particularly useful for understanding reactions where protons are transferred between species. In the provided reaction, HCl donates a proton to acetalaldehyde, making it a classic example of a Brønsted–Lowry acid-base reaction. Recognizing these interactions is key to analyzing the behavior of acids and bases in organic chemistry.