Problem 115 - A Complete Resource Book in Chemistry for JEE Main

Question

Which is incorrectly matched? Common name \(\quad\) IUPAC name (a) Vanillin 4-hydroxy-3-methoxybenzaldehyde (b) Protocatechual- \(\quad 2,3\)-dihydroxydehyde benzaldehyde (c) Adipic acid hexanl, 6-dioic acid (d) Pyruvic acid \(\quad\) cis-2-methylbut-2-enoic acid

Step-by-Step Solution

Answer

Option (d) has an incorrect match: Pyruvic acid is not cis-2-methylbut-2-enoic acid.

Step 1: Analyze Each Option

Evaluate each common name and its corresponding IUPAC name to find inconsistencies. Compare the structures implied by the common names with the structures described by their IUPAC names.

Step 2: Examine Option (a)

Vanillin should be 4-hydroxy-3-methoxybenzaldehyde as it includes a methoxy and hydroxy group on a benzaldehyde. This is correctly matched.

Step 3: Examine Option (b)

Protocatechuic aldehyde actually corresponds to 3,4-dihydroxybenzaldehyde. The given IUPAC name is incorrect as it states 2,3-dihydroxybenzaldehyde.

Step 4: Examine Option (c)

Adipic acid should be known as hexanedioic acid, not hexanl, 6-dioic acid. But since common language may vary slightly, interpret it correctly as a match, or check context.

Step 5: Examine Option (d)

Pyruvic acid should have the IUPAC name of 2-oxopropanoic acid. The name given, cis-2-methylbut-2-enoic acid, is incorrect as it refers to a different compound.

Step 6: Conclusion

After checking all options, options (b) and (d) contain incorrect IUPAC names for the given common names. Typically, only one choice is expected in similar problems; however, if following the pattern, verify with text source or teacher for precise context intended.

Key Concepts

Common Names in Chemistry

Common names in chemistry are names traditionally used for chemicals that do not follow the systematic methods of the IUPAC. These names can often be historical, based on the substance's source, the person who discovered it, or even its purported effects. Common names are usually easier to remember and often used in casual settings by chemists.

For example:

• Acetic acid is commonly known as vinegar when diluted in water.
• Baking soda is the everyday term for sodium bicarbonate.

An interesting aspect of common names is that they provide insight into the historical context or practical use of the compound, hinting at its discovery or application.

However, common names do not provide information about the structure of the compounds, which can sometimes cause confusion. In formal and scientific settings, IUPAC names are preferred to ensure clear and precise communication.

Naming Organic Compounds

Naming organic compounds is a fundamental skill in chemistry, enabled by the IUPAC nomenclature system. It gives each compound a systematic name based on its molecular structure, detailing the number of carbon atoms, types of chemical groups, and their positions.

The rules of IUPAC ensure that each compound has one unique name, which helps in identifying and distinguishing it from others. This systematic approach avoids ambiguity, especially in research and publication.

For example, the compound commonly known as **Adipic acid** is systematically named **Hexanedioic acid** in IUPAC nomenclature. Here are the steps to name this compound:

• Identify the longest carbon chain: In this case, there are six carbons ("hexane").
• Recognize the functional groups present: Adipic acid is a diacid, so indicate with "dioic acid."

IUPAC naming allows chemists to decipher the structure of a compound just from its name, providing critical information about possible reactions and properties.

Identifying Chemical Structures

Identifying chemical structures involves understanding how atoms are bonded together in a molecule and their spatial arrangement. This skill is crucial for interpreting both common and IUPAC names.

Often, the IUPAC name gives detailed hints about the structure. For instance, the name "4-hydroxy-3-methoxybenzaldehyde" tells us:

• There's a benzaldehyde, which is a benzene ring with an aldehyde group attached.
• A hydroxy group (-OH) is on the fourth carbon of the ring.
• A methoxy group (-OCH₃) is on the third carbon.

Understanding these details allows chemists to draw the molecular structure accurately, which is vital in predicting chemical behavior and reactions.

The ability to translate names into structures, and vice versa, is a fundamental skill for chemists, ensuring precision in communication and experimentation.