Question

Dinitromethane, ${\mathrm{CH}}_2{\left({\mathrm{NO}}_2\right)}_2$ is a dangerously reactive substance that decomposes readily on warming. On the other hand, dichloromethane is relatively unreactive. Why is the nitro compound so reactive compared to the chloro compound? (Hint: Consider the oxidation numbers of the atoms involved and the possible products of decomposition.)

Short answer

Dinitromethane is more reactive than dichloromethane due to the presence of nitro groups with nitrogen in a high oxidation state (+3), which increases its reactivity upon breaking. Decomposition of dinitromethane also forms highly reactive intermediates like nitric oxide radicals (.$\mathrm{NO}$) and nitrogen dioxide radicals (.${\mathrm{NO}}_2$), further contributing to its reactivity. In contrast, dichloromethane has a lower overall oxidation state due to the presence of the less oxidizing chlorine atoms (-1) and decomposes into relatively stable products without forming highly reactive intermediates.

Step-by-step solution

Write down the formulas for dinitromethane and dichloromethane

The formulas for dinitromethane and dichloromethane are: 1. Dinitromethane: ${\mathrm{CH}}_2{\left({\mathrm{NO}}_2\right)}_2$ 2. Dichloromethane: ${\mathrm{CH}}_2{\mathrm{Cl}}_2$

Determine the oxidation numbers of the atoms involved in each compound

We can assign the oxidation numbers as follows: For dinitromethane: - Carbon (C): +2 (as it forms two single bonds with both hydrogen and nitro groups) - Hydrogen (H): +1 (as hydrogen is more electronegative than carbon) - Nitrogen (N): +3 (as it forms three covalent bonds in the nitro group) - Oxygen (O): -2 (as it forms two covalent bonds in the nitro group) For dichloromethane: - Carbon (C): +2 (forms two single bonds with hydrogen and chlorine atoms) - Hydrogen (H): +1 - Chlorine (Cl): -1 (as it forms one single bond with carbon)

Analyze the possible products of decomposition

Dinitromethane, upon breaking, can form various products, including highly reactive intermediates like nitric oxide radicals (.$\mathrm{NO}$) and nitrogen dioxide radicals (.${\mathrm{NO}}_2$). The formation of these intermediates tends to drive the decomposition process further, resulting in high reactivity. On the other hand, dichloromethane decomposes to form relatively stable products such as hydrochloric acid ($\mathrm{HCl}$) and carbon, which do not form any highly reactive intermediates.

Relate the oxidation numbers and products of decomposition to reactivity

In case of dinitromethane, the presence of the nitro groups with nitrogen in a high oxidation state increases its reactivity upon breaking. The formation of highly reactive intermediates from its decomposition also plays a significant role in its overall reactivity. In contrast, dichloromethane has a lower overall oxidation state due to the presence of the less oxidizing chlorine atoms and does not form highly reactive intermediates during decomposition. This results in its relatively lower reactivity compared to dinitromethane.

Key concepts

Dinitromethane

Dinitromethane, with the formula ${\mathrm{CH}}_2({\mathrm{NO}}_2{)}_2$, is a compound known for its high reactivity. This substance is characterized by the presence of nitro groups, which play a central role in its chemical behavior.

• The nitro groups contain nitrogen atoms in a relatively high oxidation state.
• The presence of these nitro groups makes the compound more prone to undergoing decomposition.

Upon the application of heat, dinitromethane readily decomposes, leading to the formation of various intermediate products. Such intermediates like nitric oxide radicals ($.\mathrm{NO}$) and nitrogen dioxide radicals ($.{\mathrm{NO}}_2$) contribute to the overall instability and reactivity of the compound. These radicals are highly reactive and can promote further chemical reactions almost immediately.

Dichloromethane

Dichloromethane, known by its chemical formula ${\mathrm{CH}}_2{\mathrm{Cl}}_2$, is significantly less reactive than dinitromethane. This compound features two chlorine atoms bonded to a central carbon atom.

• Chlorine atoms are more stable and less oxidizing than nitro groups.
• Dichloromethane does not easily break down into reactive intermediates.

Under normal conditions, this stability makes dichloromethane a popular choice as a solvent in chemical processes. Its decomposition products, such as hydrochloric acid ($\mathrm{HCl}$) and carbon, are relatively stable, contributing to its mild nature compared to more reactive substances like dinitromethane.

Oxidation Numbers

Oxidation numbers are a crucial concept in understanding the reactivity of chemical compounds. They represent the effective charge of an atom within a molecule, indicating how electrons are distributed among the atoms.

• Dinitromethane: Nitrogen has an oxidation number of +3, contributing to its high reactivity.
• Oxygen typically has an oxidation state of -2, which complements the positive charge of nitrogen.
• Dichloromethane: Chlorine has an oxidation number of -1, reflecting its tendency to accept electrons rather than donate them.

The higher oxidation states in dinitromethane align with its tendency to release energy through decomposition. The relatively lower and more stable oxidation numbers in dichloromethane point towards its more subdued reactivity.

Decomposition Products

Decomposition products are substances formed when a chemical compound breaks down. Understanding these products helps explain why some compounds are more reactive than others.

• For dinitromethane, the decomposition leads to highly reactive intermediates like $.\mathrm{NO}$ and $.{\mathrm{NO}}_2$.
• These intermediates participate in further reactions, amplifying the decomposition process.

In contrast, the decomposition of dichloromethane results in more stable products such as $\mathrm{HCl}$ and carbon. The stability of these products means that they do not cause rapid or further breakdown, which is why dichloromethane doesn't exhibit the same level of explosiveness as dinitromethane. Understanding the nature of the products formed through decomposition is essential for predicting the behavior of chemical compounds in practical applications.