Question

Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles: (a) \(\mathrm{CH}_{3} \mathrm{COOH}+\mathbf{H O}^{-} \rightarrow \mathrm{CH}_{3} \mathrm{COO}^{-}+\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}+\overline{\mathbf{C}} \mathbf{N} \rightarrow\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}(\mathrm{CN})(\mathrm{OH})\) (c) \(\mathrm{C}_{6} \mathrm{H}_{6}+\mathrm{CH}_{3} \stackrel{+}{\mathrm{C}} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COCH}_{3}\)

Short answer

(a) The bolded reagent is a nucleophile, (b) is a nucleophile, and (c) is an electrophile.

Step-by-step solution

Define Nucleophile and Electrophile

A *nucleophile* is an electron-rich species that tends to donate electrons, often characterized by lone pairs or pi bonds. An *electrophile* is an electron-deficient species that tends to accept electrons, usually having positive charge or partial positive charge.

Analyze Reaction (a)

In the reaction \(\mathrm{CH}_{3} \mathrm{COOH}+\mathbf{HO}^{-} \rightarrow \mathrm{CH}_{3} \mathrm{COO}^{-}+\mathrm{H}_{2} \mathrm{O}\), the bold \(\mathbf{HO}^{-}\) (hydroxide ion) is rich in electrons and has a negative charge. It seeks to donate electrons to \(\mathrm{CH}_{3} \mathrm{COOH}\), indicating that \(\mathbf{HO}^{-}\) is a nucleophile.

Analyze Reaction (b)

In the reaction \(\mathrm{CH}_{3} \mathrm{COCH}_{3}+\overline{\mathbf{C}} \mathbf{N} \rightarrow\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}(\mathrm{CN})(\mathrm{OH})\), the bold \(\overline{\mathbf{C}} \mathbf{N}\) (cyanide ion) has a lone pair on carbon, making it electron-rich and eager to donate electrons. This indicates that \(\overline{\mathbf{C}} \mathbf{N}\) is a nucleophile.

Analyze Reaction (c)

In the reaction \(\mathrm{C}_{6} \mathrm{H}_{6}+\mathrm{CH}_{3} \stackrel{+}{\mathrm{C}} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COCH}_{3}\), the bold \(\mathrm{CH}_{3} \stackrel{+}{\mathrm{C}} \mathrm{O}\) (acylium ion) has a positive charge on carbon, making it electron-deficient and likely to accept electrons. This indicates that \(\mathrm{CH}_{3} \stackrel{+}{\mathrm{C}} \mathrm{O}\) is an electrophile.

Key concepts

Organic Reactions

In the fascinating world of chemistry, organic reactions are fundamental processes where organic compounds undergo various transformations. These reactions can involve breaks and formations of chemical bonds. They are the core of organic chemistry and are categorized by the types of changes they promote in the molecular structure.

There are many types of organic reactions, such as substitution, addition, elimination, and rearrangement reactions. What's common among all these is the crucial role played by electron-rich and electron-deficient species, known as nucleophiles and electrophiles. Understanding who donates electrons and who accepts them helps predict the outcome of these reactions.

By knowing the nature of the reactive species, chemists can control and direct these reactions for desired synthetic applications, making an impact not only in laboratories but also in industry and medicine.

Chemical Reagents

Chemical reagents act as the main driving force in chemical reactions, helping break or form bonds between atoms. In organic reactions, these reagents can be either nucleophiles or electrophiles, depending on their electron status.

Reagents are essentially substances that are added to cause a chemical reaction or see if one occurs. In our exercise, examples include hydroxide ions (a strong nucleophile) and the acylium ion (an electrophile). The characteristics of reagents determine their behavior in the reaction process.

It's vital to understand these distinctions and how they function in different reactions. Nucleophilic reagents attack electron-deficient centers, while electrophilic reagents target electron-rich areas. This knowledge allows chemists to select appropriate conditions and substances to achieve a specific reaction product.

Electron-Rich Species

Electron-rich species are often termed nucleophiles, deriving from the Greek words "nucleus", meaning nucleus, and "philos", meaning loving. These species have an abundance of electrons, which they are willing to donate or share.

Such species typically feature a negative charge or lone pairs of electrons, making them attracted to positively charged or electron-deficient species. In the first example from our exercise, the hydroxide ion (\( ext{HO}^{-} \)) acts as a nucleophile, donating its electrons to acetic acid (\( ext{CH}_3 ext{COOH} \)) to form acetate and water.

Understanding nucleophiles is key for recognizing how organic reactions proceed. Their electron-rich nature means they look out for complementary partners who can accept those electrons, typically forming new chemical bonds in the process.

Electron-Deficient Species

In contrast to electron-rich species, electron-deficient species are called electrophiles. These molecules or ions lack electrons and are always on the hunt to acquire them from other sources.

Electrophiles often carry a positive charge or have an atom with a partial positive charge in their structure, rendering them eager to accept electrons. From our exercise, the acylium ion (\( ext{CH}_3 ext{C}^+ ext{O} \)) serves as a prime example, capturing electrons from an electron-rich benzene ring to form acetophenone.

Understanding the behavior of electrophiles in organic chemistry is as important as knowing nucleophiles, as the interaction between these two types of species dictates the progress and dynamics of many chemical reactions. Identifying electrophiles allows chemists to predict reaction pathways and outcomes with greater accuracy.