Problem 37 - General Chemistry: Principles and Modern Applications

Question

Supply condensed structural formulas for the following substances. (a) 2,4,6 -trinitrotoluene (TNT-an explosive) (b) methyl salicylate (oil of wintergreen) [Hint: Salicylic acid is \(o \text { -hydroxybenzoic acid. }]\) (c) 2 -hydroxy-1,2,3-propanetricarboxylic acid (citric \(\left.\operatorname{acid}, \mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7}\right)\).

Step-by-Step Solution

Answer

(a) 2,4,6 -trinitrotoluene = \(CH_3-C_6H_2(NO_2)_3\)\n(b) methyl salicylate = \(O=C(OCH_3)-C_6H_4-OH\)\n(c) 2 -hydroxy-1,2,3-propanetricarboxylic acid = \(-COOH-CH(OH)-COOH-CH_2-COOH\)

Step 1: Writing Structure for 2,4,6 -trinitrotoluene

Toluene is a methyl group attached to a benzene ring. Trinitrotoluene has three nitro groups \(-NO_2\).Their positions are indicated by the numbers 2,4 and 6, meaning positions opposite to the methyl groups on the Benzene ring. Thus, we have \(CH_3-C_6H_2(NO_2)_3\)

Step 2: Writing Structure for methyl salicylate

Salicylic acid is ortho-hydroxybenzoic acid which means a carboxylic acid \(-COOH\) and a hydroxyl group \(-OH\) on adjacent positions of a benzene ring. Methyl salicylate replaces the hydrogen in the carboxylic group with a methyl \(-CH_3\) group, giving the formula \(O=C(OCH_3)-C_6H_4-OH.\)

Step 3: Writing Structure for 2 -hydroxy-1,2,3-propanetricarboxylic acid

Propane indicates a 3-carbon backbone. The 1,2,3-tricarboxylic acid indicates three carboxylic acid groups on every carbon atom. The 2-hydroxy indicates a hydroxyl group attached to the second carbon atom. The formula thus becomes \(-COOH-CH(OH)-COOH-CH_2-COOH.\)

Key Concepts

Condensed Structural Formulas

Condensed structural formulas are a way to represent organic molecules in a simple, linear fashion, emphasizing the connections between atoms. This representation is especially helpful when dealing with more complex organic structures, as it provides a balance between detailed structural formulas and minimalistic molecular formulas.

To write condensed structural formulas, we group atoms by how they are attached to each other. For instance, in 2,4,6-trinitrotoluene, we simplify the benzene ring and highlight the nitro and methyl groups by writing it as \(CH_3-C_6H_2(NO_2)_3\). This tells us there's a benzene ring with a methyl group and three nitro groups.

This method is not only less cluttered but also allows for quick identification of functional groups and substituents in a molecule, aiding in understanding and discussion.

Nomenclature of Organic Compounds

The nomenclature of organic compounds is the system used to name the chemical compounds in a systematic way, ensuring each compound has a unique name. It's essential in chemistry to communicate complex structures easily and avoid confusion.

For example, in naming 2,4,6-trinitrotoluene (commonly known as TNT), each part of the name provides information:

• "Toluene" indicates a methyl group attached to a benzene ring.
• The "trinitro" indicates three nitro groups, and the numbers "2,4,6" specify their positions on the ring.

This systematic naming allows chemists to deduce the structure from the name. Understanding this system involves learning the various prefixes, suffixes, and numbering as shaped by IUPAC guidelines, which dictate rules for naming carbon chains, substituents, and functional group positions.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They provide specific properties and reactivity patterns and play a crucial role in naming organic compounds.

In our examples:

• The nitro group \(-NO_2\) in TNT significantly affects its explosive nature and the name trinitrotoluene.
• Methyl salicylate contains a hydroxyl \(-OH\), a carboxyl \(-COOH\), and an ester group \((OCH_3)\), each influencing its reactivity and aroma.
• Citric acid has carboxyl \(-COOH\) and hydroxyl \(-OH\) groups, contributing to its acidic properties.

Recognizing these groups helps chemists understand how molecules will behave in chemical reactions, predict their physical properties, and synthesize new compounds.

Chemical Structure Representation

Chemical structure representation is how we convey the 3D arrangement of atoms within a molecule using 2D drawings. This is vital for understanding the spatial and biochemical interactions of molecules.

There are different ways to represent this:

• Lewis Structures: Represent every bond and lone pair explicitly, offering detailed insights.
• Condensed Formulas: Simplify structures, suitable for longer chains and larger molecules as in our examples.
• Structural Formulas: Highlight the layout of atoms, showing connections between them without representing all of the hydrogen atoms.

Each method has its advantages and is suitable for different scenarios. For example, when speed and simplicity are needed, a condensed formula might suffice, while other times, complete spatial understanding is essential, calling for 3D models or detailed drawings. The choice depends on what needs to be communicated or understood in a given context.