Question

Draw the structure of each of the following compounds: (a) 2,3 -dimethylhexane (b) 2,3 -dimethyloctane (c) 3 -ethylheptane (d) 3 -ethyl-2-methylhexane

Short answer

Draw each main chain and add substituents based on their positions: (a) 6C with 2 methyls at C2,C3; (b) 8C with 2 methyls at C2,C3; (c) 7C with ethyl at C3; (d) 6C with ethyl at C3 and methyl at C2.

Step-by-step solution

Understand the Number of Carbon Atoms in the Main Chain

The main chain in a hydrocarbon name is indicated by the suffix. In these names: - Hexane means a 6-carbon chain. - Octane means an 8-carbon chain. - Heptane means a 7-carbon chain. Identify the length of the carbon chain for each compound: (a) Hexane (6 carbons) (b) Octane (8 carbons) (c) Heptane (7 carbons) (d) Hexane (6 carbons)

Draw the Straight Chain of Carbon Atoms

Draw a horizontal line of carbon atoms for each main chain: (a) Draw 6 carbon atoms in a row for hexane. (b) Draw 8 carbon atoms in a row for octane. (c) Draw 7 carbon atoms in a row for heptane. (d) Draw 6 carbon atoms in a row for hexane.

Number the Carbon Atoms in the Chain

Start from the left to number each carbon atom in the chain: (a) Number the 6-carbon hexane chain from 1 to 6. (b) Number the 8-carbon octane chain from 1 to 8. (c) Number the 7-carbon heptane chain from 1 to 7. (d) Number the 6-carbon hexane chain from 1 to 6.

Add Substituents According to the IUPAC Name

Add appropriate substituents at their respective positions: (a) 2,3-dimethylhexane means adding a methyl group at carbon 2 and carbon 3. (b) 2,3-dimethyloctane means adding a methyl group at carbon 2 and carbon 3. (c) 3-ethylheptane means adding an ethyl group at carbon 3. (d) 3-ethyl-2-methylhexane means adding an ethyl group at carbon 3 and a methyl group at carbon 2.

Verify the Structure

Ensure each carbon has four bonds (considering hydrogens where needed). Verify the positions of each branch: - Methyl group represents -CH₃. - Ethyl group represents -CH₂CH₃. Make sure all positions are in correct numerical order as per IUPAC naming.

Key concepts

Hydrocarbon Structure

Hydrocarbons are organic compounds consisting solely of hydrogen and carbon atoms. These compounds form the backbone of organic chemistry. By combining carbon and hydrogen in different configurations, hydrocarbons can take on various structures that define their chemical properties and uses.

Understanding hydrocarbon structure is fundamental because it affects everything from chemical reactivity to boiling points. Hydrocarbon chains can be:

• Straight (linear chains like hexane or octane)
• Branched (such as those involving methyl or ethyl groups)
• Cyclic (forming rings)

In the given exercise, we focus on alkanes, which are saturated hydrocarbons characterized by linear or branched chains of single-bonded carbon atoms. Their simplicity allows them to serve as building blocks for more complex molecules.

IUPAC Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) nomenclature is a systematic way of naming chemical compounds. This system provides a uniform method that ensures clarity and helps chemists communicate about the compound structure efficiently.

Understanding IUPAC nomenclature entails recognizing:

• The base name that indicates the length of the carbon chain (hexane, octane, heptane).
• The prefixes that reveal the presence and position of additional groups, called substituents (like methyl or ethyl).
• Numbers in the name that specify where substituents are attached.

For example, in 2,3-dimethylhexane, 'hexane' tells us there's a 6-carbon chain. The '2,3-dimethyl' part indicates two methyl groups attached at carbons 2 and 3.

Proper application of IUPAC rules leads to a clear understanding of molecular structure, which is crucial for drawing and identifying organic molecules.

Carbon Chains

Carbon chains serve as the backbone of hydrocarbon molecules, determining their overall structure and properties. Composed of carbon atoms linked together, these chains can vary in length and branching, influencing properties like the boiling point and melting point.

There are a few key things to note about carbon chains:

• The length of the chain determines the base name in IUPAC nomenclature (e.g., hexane for 6 carbons).
• Straight chains have a simpler structure, often found in foundational hydrocarbons like those in the exercise.
• Branched chains arise from substituents like methyl or ethyl groups that branch off the main chain.

Chains are usually depicted as linear for simplicity, as in the given exercise instructions. However, in reality, these chains are somewhat zigzagged due to the tetrahedral geometry of carbon-hydrogen bonds.

Chemical Substituents

Chemical substituents are groups of atoms that attach to the main carbon chain, modifying its structure and characteristics. In organic chemistry, these substituents can dramatically change the chemical properties of the molecule, like its reactivity or its boiling point.

Key aspects of chemical substituents include:

• Identifying the substituent, such as a methyl group (\( -CH_3 \)) or an ethyl group (\( -C_2H_5 \)).
• Understanding their placement on the carbon chain, as indicated by numbers in their IUPAC names.
• Adding these groups as side chains without disrupting the main carbon framework.

In the exercise examples, substituents like methyl and ethyl groups are added to specified locations on the main chain (e.g., 2,3-dimethylhexane). Recognizing where they attach helps distinguish one compound from another, giving each its unique identity in organic chemistry.