Problem 182 - A Complete Resource Book in Chemistry for JEE Main

Question

The IUPAC name of the compound shown below is [2006] ClC1CCCC(Br)C1 (a) 2-bromo-6-chlorocyclohex-1-ene (b) 6 -bromo-2-chlorocyclohexene (c) 3-bromo-1-chlorocyclohexene (d) 1-bromo-3-chlorocyclohexene

Step-by-Step Solution

Answer

The IUPAC name is 1-bromo-3-chlorocyclohexene (option d).

Step 1: Draw the Compound

Convert the SMILES notation "ClC1CCCC(Br)C1" to a structural diagram. The molecule is a six-membered cyclohexane ring with a chlorine atom and a bromine atom attached as substituents.

Step 2: Identify the Substituents

Determine the positions of the chlorine and bromine on the cyclohexane ring. In the drawn structure, observe that the chlorine (Cl) is attached to carbon-1 and the bromine (Br) is attached to carbon-3.

Step 3: Assign Numbering to the Cyclohexane

According to IUPAC rules, the ring should be numbered to give the substituents the lowest possible numbers. Start numbering from the chlorine (as '1') and follow around the ring to place the bromine at '3'.

Step 4: Name the Compound

Formulate the IUPAC name using the positions and names of the substituents: The name is "1-chloro-3-bromocyclohexene," which corresponds to option (d) "1-bromo-3-chlorocyclohexene" after ordering the substituents alphabetically as per IUPAC convention.

Key Concepts

Understanding SMILES Notation

SMILES notation stands for Simplified Molecular Input Line Entry System. It is a way to describe a chemical structure using a string of text. It is exceptionally useful for computers because it allows complex molecules to be represented in a simple, text-based format.
In this exercise, for example, the SMILES string `ClC1CCCC(Br)C1` describes a molecule. Each letter or character represents an atom or bond in the molecule. Here:

• `Cl` and `Br` represent chlorine and bromine atoms respectively.
• `C` stands for carbon atoms.
• The numbers `1` indicate the atoms are part of a ring, specifically a six-atom ring here.

With SMILES, it's easier to digitally work with chemical structures, essential for database searches and computational chemistry. Learning SMILES can enhance your understanding of chemistry software and data sharing.

Substituents in Organic Compounds

In organic chemistry, substituents are atoms or groups of atoms attached to the main carbon skeleton of a molecule. They can influence the physical and chemical properties of the molecule.
When naming a compound using IUPAC nomenclature, substituents are crucial. They determine how the molecule is named as they often require specific numbering and alphabetical ordering. In our example, the molecule contains two substituents on the cyclohexane ring:

• Chlorine (`Cl`), which is referred to as a 'chloro' substituent.
• Bromine (`Br`), a 'bromo' substituent.

Substituents affect the compound's final name, so positioning and proper identification are essential. It's important to understand how to assign priorities and positions according to IUPAC rules to ensure accurate naming.

The Cyclohexane Ring and Its Numbering

A cyclohexane ring is a common cyclic structure in organic chemistry. It consists of six carbon atoms bonded in a ring. The ring can form the backbone of many organic compounds and often has various substituents attached to it.
When naming a compound with a cyclohexane ring, it's important to assign numbers to each carbon atom to correctly identify the positions of attached substituents. According to IUPAC rules, numbering should provide the lowest possible numbers to the substituents. In this exercise, numbering starts from chlorine, giving it position '1', and continues around the ring until bromine is identified at position '3'.
The numbering process helps avoid confusion and ensures that every chemist uses the same conventions when describing a compound, making communication clearer in chemical literature and studies.