Question

Draw and name the three isomers of dinitrobenzene,\(\mathrm{C}_{6} \mathrm{H}_{4}\left(\mathrm{NO}_{2}\right)_{2}\).

Short answer

The three isomers are 1,2-Dinitrobenzene (ortho), 1,3-Dinitrobenzene (meta), and 1,4-Dinitrobenzene (para).

Step-by-step solution

Understanding Isomers

Before we draw the isomers, we need to understand that isomers are compounds with the same chemical formula but different structural arrangements. In the case of dinitrobenzene, the difference lies in the positions of the nitro groups \(\mathrm{NO}_2\) on the benzene ring, \(\mathrm{C}_6\mathrm{H}_4\).

Identifying Possible Positions

On the benzene ring, substitute positions are numbered relative to each other. The positions are generally referred to as ortho (1,2-), meta (1,3-), and para (1,4-) positions. These positions will help us determine the arrangement of the \(\mathrm{NO}_2\) groups.

Drawing the Ortho-Isomer

In the ortho-isomer, the nitro groups are on adjacent carbon atoms. Thus, we place \(\mathrm{NO}_2\) groups on positions 1 and 2. Draw a benzene ring and label one carbon as 1, placing an \(\mathrm{NO}_2\) group there, then place another \(\mathrm{NO}_2\) group on the adjacent carbon, position 2.

Drawing the Meta-Isomer

For the meta-isomer, the nitro groups are placed on carbons 1 and 3. Draw a benzene ring as before, place the first \(\mathrm{NO}_2\) group on position 1, skip one carbon, and place the second \(\mathrm{NO}_2\) group on position 3.

Drawing the Para-Isomer

In the para-isomer, the nitro groups are positioned on opposite sides of the benzene ring. Place the first \(\mathrm{NO}_2\) group on carbon 1 and the second \(\mathrm{NO}_2\) group on carbon 4.

Naming the Isomers

Now, name the isomers based on their structural positions: the ortho-isomer is named 1,2-Dinitrobenzene, the meta-isomer is named 1,3-Dinitrobenzene, and the para-isomer is named 1,4-Dinitrobenzene.

Key concepts

Chemical Isomers

Chemical isomers are fascinating because they challenge the idea that identical molecular formulas always mean identical substances. While they share the same numbers and types of atoms, their atoms are connected differently, forming distinct structures. Think of it as building with the same LEGO blocks, but assembling different shapes. For dinitrobenzene, this means the presence of nitro groups (\(\text{NO}_2\)) on a benzene ring arranged in various patterns.Isomers can vary in physical or chemical properties due to their different structures, even when composed of the same elements. With dinitrobenzene isomers, the molecular formula stays constant (\(\mathrm{C}_{6} \mathrm{H}_{4}\left(\mathrm{NO}_{2}\right)_{2}\)), but the spatial arrangement changes, offering three distinct versions. These structural variations are crucial in chemistry because they influence reactivity and interaction with other chemicals.

Benzene Ring

The benzene ring is a hallmark structure in organic chemistry, often associated with aromatic compounds. It features a six-membered carbon ring, with alternating single and double bonds, though in reality, these bonds are equal due to resonance. This creates a stable ring system known for its aromaticity.Benzene rings provide a backbone onto which groups like nitro (\(\text{NO}_2\)) may attach, as in dinitrobenzene isomers. These attachments occur via a benzene ring’s carbon atoms, and understanding the ring's structure is essential to comprehend how these groups influence the compound's properties.Because of the delocalization of electrons in the benzene ring, it exhibits unique stability and resists reactions typical for alkenes, making the study of benzene fundamental for students of chemistry. The benzene ring provides a canvas for a variety of chemical modifications, broadening the range of possible compounds.

Substituent Positions

When modifying benzene, the positions of substituents, such as nitro groups (\(\text{NO}_2\)), dictate the compound's name and properties. In dinitrobenzene, substituent positions are often referred to as ortho, meta, and para, based on their relative locations on the ring.

• Ortho (1,2-): The substituents are adjacent on the benzene ring. For 1,2-dinitrobenzene, the \(\text{NO}_2\) groups are side by side, influencing their chemical environment and possible interactions with other molecules.
• Meta (1,3-): Here, a one-carbon gap exists between substituents. In 1,3-dinitrobenzene, this arrangement alters electronic distribution and can affect the reactivity pattern compared to other isomers.
• Para (1,4-): Positioned opposite, the \(\text{NO}_2\) groups are as far apart as possible on the ring. 1,4-dinitrobenzene reflects the balances of electronic effects, often resulting in symmetrical properties.

These differing positions play a role in determining the compound’s chemical behavior, boiling point, melting point, and solubility, impacting how chemists can use them in synthetic applications.