Question

2, 4-dinitrofluorobenzene is used in peptide chemistry because (a) it makes the amino acids insoluble in water and thus making them readily crystallizable (b) it undergoes electrophilic substitution (c) it undergoes nucleophilic substitution (d) it has a characteristic colour

Short answer

2, 4-dinitrofluorobenzene is used in peptide chemistry because it undergoes nucleophilic substitution, making option (c) correct.

Step-by-step solution

Understanding the Question

We are asked to identify why 2, 4-dinitrofluorobenzene is used in peptide chemistry. Several potential reasons are given, and we need to evaluate each one.

Chemical Properties of 2, 4-Dinitrofluorobenzene

2, 4-dinitrofluorobenzene has a fluorine atom attached to a benzene ring with two nitro groups at positions 2 and 4. The presence of nitro groups makes the fluorine a good leaving group in reactions.

Electrophilic vs. Nucleophilic Substitution

Electrophilic substitution typically occurs in benzene rings without strong electron-withdrawing groups like nitro groups. Here, the nitro groups make the ring less available for electrophilic substitution but more reactive to nucleophiles.

Evaluating Option C: Nucleophilic Substitution

The nitro groups on 2, 4-dinitrofluorobenzene increase the electron-deficient nature of the carbon bonded to the fluorine, making it susceptible to nucleophilic attack. This is vital in peptide chemistry to label amino groups in proteins.

Evaluating Other Options

Option A (crystallization) and Option D (color) do not directly relate to peptide chemistry utility, and Option B (electrophilic substitution) is unlikely due to the deactivating nitro groups on the ring.

Conclusion

2, 4-dinitrofluorobenzene's ability to undergo nucleophilic substitution is the reason for its use in peptide chemistry, as it will react with amino acids.

Key concepts

2, 4-dinitrofluorobenzene

2, 4-dinitrofluorobenzene is a chemical compound commonly used in peptide chemistry. Its structure consists of a benzene ring attached to two nitro groups (–NO₂) at the 2 and 4 positions, along with a fluorine atom at another position. The nitro groups play a special role. They are electron-withdrawing, meaning they pull electron density away from the benzene ring. This electron-withdrawing ability of the nitro groups makes the benzene ring electron-deficient. As a result, the carbon bonded to the fluorine atom becomes more susceptible to reactions with nucleophiles, which are substances with a pair of electrons that can be donated. This particular property enhances the chemical reactivity of 2, 4-dinitrofluorobenzene, making it useful in certain reactions in peptide chemistry. In addition to these reactivity properties, 2, 4-dinitrofluorobenzene is often chosen due to its capability to label amino groups within proteins and peptides. This helps researchers follow and analyze the behavior of proteins, which are crucial functions in the study of biochemistry and molecular biology.

Nucleophilic Substitution

Nucleophilic substitution is a common type of chemical reaction where a nucleophile forms a bond with a carbon atom by replacing a leaving group. In the context of 2, 4-dinitrofluorobenzene, the nucleophile is often an amino group from an amino acid or protein.

• Nucleophiles: These are typically molecules that have a negative charge or a lone pair of electrons, such as amino groups.
• Leaving Groups: These are atoms or groups that detach from the parent molecule during the reaction. In this case, it is the fluorine atom, which is a good leaving group due to the influence of nitro groups.

For 2, 4-dinitrofluorobenzene, the electron-withdrawing nature of the nitro groups makes the carbon-filtrated fluorine great for undergoing this substitution. As the nucleophile attacks, the fluorine detaches from the benzene ring, allowing for the amino acid or protein to be modified or labeled. This mechanism is significant since it allows scientists to track changes within proteins, enhancing our understanding of biological processes.

Amino Acid Labeling

Amino acid labeling is a critical application where 2, 4-dinitrofluorobenzene plays an essential role. This compound enables the selective attachment of labels to the amino groups in proteins and peptides, providing essential insights into protein structure and function. Labeling involves the nucleophilic attack of the amino group on the carbon atom to which the fluorine is attached in 2, 4-dinitrofluorobenzene. As a result of the reaction, the 2, 4-dinitrobenzene moiety attaches to the amino group. The purpose of amino acid labeling includes:

• Identifying specific amino acids within proteins.
• Studying the structural arrangement of proteins.
• Tracking reactions involving amino acids.

This labeling is a key tool in biochemistry, as it helps determine how proteins interact with other biomolecules, providing insights that are crucial for drug development and understanding disease mechanisms.

Electron-withdrawing Groups

Electron-withdrawing groups (EWGs) are functional groups attached to a molecule that attract electron density towards themselves, making other parts of the molecule more reactive. In 2, 4-dinitrofluorobenzene, the nitro groups are the electron-withdrawing groups.

• Effect: These groups increase the reactivity of adjacent positions on a benzene ring by decreasing their electron density.
• Outcome: This makes the carbon site more susceptible to nucleophilic attack, as less electron density means it can better accept electrons from a nucleophile.

In peptide chemistry, the electron-deficient carbon (due to the presence of EWGs) becomes an excellent target for nucleophiles, such as those found in amino acids and proteins. This unique feature is what makes certain compounds like 2, 4-dinitrofluorobenzene highly useful for labeling amino acids, allowing scientists to conduct further studies on protein dynamics and functionality.