Question

Write structures for the following compounds: (a) 2,2 -dibromo- 3,3 -dichloro-5,5-difluoro6,6 -diiodobicyclo[2.2.1]heptane (b) bicyclo[1.1.1]pentan-1,3-diol (c) hexamethylbicyclo \([2.2 .0]\) hexa- 2,5 -diene

Short answer

Structures are: (a) Add halogens to bicyclo[2.2.1]heptane; (b) Add OH groups to bicyclo[1.1.1]pentane; (c) Add CH3 groups and double bonds to bicyclo[2.2.0]hexa.

Step-by-step solution

Understand the Nomenclature

Begin by understanding how the names of the chemical compounds given correspond to their structures. Bicyclic compounds have two rings that share two or more atoms.

Drawing 2,2-dibromo-3,3-dichloro-5,5-difluoro-6,6-diiodobicyclo[2.2.1]heptane

The bicyclo[2.2.1]heptane structure consists of two 6-carbon rings connected by a single carbon atom. Each number in the name refers to the position on the bicyclic structure, where substituents are added:1. Draw the base structure for bicyclo[2.2.1]heptane.2. Add dibromo groups at positions 2.3. Add dichloro groups at positions 3.4. Add difluoro groups at positions 5.5. Add diiodo groups at positions 6.

Drawing bicyclo[1.1.1]pentan-1,3-diol

Bicyclo[1.1.1]pentane consists of a triangular core with three fused cyclopropane rings. At positions 1 and 3, add hydroxyl (--OH) groups:1. Draw the base structure for bicyclo[1.1.1]pentane.2. Add hydroxyl groups (–OH) at positions 1 and 3.

Drawing hexamethylbicyclo[2.2.0]hexa-2,5-diene

This structure includes a bicyclo[2.2.0] framework with two double bonds and six methyl groups:1. Draw the base bicyclo[2.2.0]hexa-2,5-diene structure, ensuring double bonds are between carbons 2 and 3, and 5 and 6.2. Add six methyl groups, ensuring they are properly placed around the bicyclic framework.

Key concepts

Bicyclic Compounds

Chemical nomenclature plays a crucial role in identifying and constructing chemical compounds. It’s a standardized way to name molecular structures and represent them visually.
When dealing with complex structures like the ones in the provided exercises, understanding the nomenclature allows us to draw the correct compounds easily.

• Substituents: These are the atoms or groups of atoms added to the main structure. They’re listed in alphabetical order along with their positions on the parent structure.
• Bicyclo nomenclature: Names often start with 'bicyclo-' and include a bracketed numbers system indicating how many carbons are in each ring, excluding the bridgehead carbons.

**Steps to follow**:

• Identify the parent structure.
• Number the positions on the parent structure sequentially, ensuring the substituents get the lowest possible numbers.
• Include substituents and their positions in the compound’s name.
• **Example: 2,2-dibromo-3,3-dichloro-5,5-difluoro-6,6-diiodobicyclo[2.2.1]heptane:
• This name gives specific locations for bromine (2), chlorine (3), fluorine (5), and iodine (6) on a heptane structure.

Structural Drawing

Structural drawing is essential for visualizing and understanding chemical compounds. When approached methodically, this task becomes straightforward and rewarding.
Follow these steps to draw structures based on their chemical names:
Understand the Base Structure:

Decipher the base bicyclo framework from the nomenclature.

Examples include bicyclo[2.2.1]heptane or bicyclo[1.1.1]pentane.

• For the simpler base structures,
  • draw a triangle for bicyclo[1.1.1]pentane and a more complex structure for bicyclo[2.2.1]heptane.
  
  Add Substituents: Positions for substituents are dictated by numbers in the compound’s name. Insert these atoms or groups (e.g., bromine, chlorine, methyl groups) at the specified positions.


For instance, 1:
1. First, draw bicyclo[2.2.1]heptane, then add bromine on position 2, further with chlorine on 3, fluorine on 5, and iodine on 6.

Finally, refine and check your drawing:
• Ensure all atoms and bonds are placed correctly. Double-check for the right number of bonds at each carbon position.

With practice, structural drawing becomes intuitive. Keep engaging with different structures to improve your skills.