Question

Draw the condensed structural formula for each of the following molecules: a. 3 -ethylhexane b. 2,3 -dimethylpentane c. 1,3 -dichloro- 3 -methylheptane

Short answer

a. CH3CH2CH(C2H5)CH2CH2CH3; b. CH3CH(CH3)CH(CH3)CH2CH3; c. CH2ClCH2C(Cl)(CH3)CH2CH2CH2CH3

Step-by-step solution

Identify the Parent Chain

For each molecule, determine the longest continuous carbon chain which will serve as the parent structure. Then number the chain from the end nearest to the substituents.

Identify and Place Substituents

Identify the substituents (branches, halogens, etc.) and their position on the parent chain from the name given.

Construct the Condensed Structural Formula for 3-ethylhexane

The parent chain is hexane (6 carbons). An ethyl group is attached to the 3rd carbon. The condensed formula is: CH3CH2CH(C2H5)CH2CH2CH3.

Construct the Condensed Structural Formula for 2,3-dimethylpentane

The parent chain is pentane (5 carbons). Methyl groups are attached to the 2nd and 3rd carbons. The condensed formula is: CH3CH(CH3)CH(CH3)CH2CH3.

Construct the Condensed Structural Formula for 1,3-dichloro-3-methylheptane

The parent chain is heptane (7 carbons). Chlorine atoms are attached to the 1st and 3rd carbons, and a methyl group is attached to the 3rd carbon. The condensed formula is: CH2ClCH2C(Cl)(CH3)CH2CH2CH2CH3.

Key concepts

organic chemistry

Organic chemistry is the branch of chemistry that focuses on the study of carbon-containing compounds. These compounds aren't limited to just hydrocarbons; they also include various other elements such as hydrogen, oxygen, nitrogen, and halogens. The beauty of organic chemistry lies in the versatility and complexity of carbon-based molecules. Quite often, understanding these molecules involves knowing the common structures, bonding patterns, and nomenclature.

hydrocarbons

Hydrocarbons are the simplest class of organic compounds, consisting entirely of hydrogen and carbon atoms. There are different types of hydrocarbons:

• Alkanes: Saturated hydrocarbons with single bonds.
• Alkenes: Unsaturated hydrocarbons with one or more double bonds.
• Alkynes: Unsaturated hydrocarbons with one or more triple bonds.
• Aromatics: Hydrocarbons containing conjugated ring systems like benzene.

Understanding hydrocarbons is essential because they form the backbone of more complex organic molecules. In the given exercise, we mainly deal with alkanes.

nomenclature

Nomenclature in organic chemistry involves the systematic naming of compounds based on their structure. The IUPAC system is the most widely used. Here are the basic steps to follow:

• Identify the parent chain: The longest continuous carbon chain forms the base of the name.
• Number the chain: Start numbering from the end nearest to the substituents.
• Name and number the substituents: Attach prefixes like 'methyl-', 'chloro-', etc., based on their position and type.

For example, in '3-ethylhexane', 'hexane' is the parent chain with an ethyl group on the third carbon. Carefully naming the compounds helps in precisely constructing their structural formulas.

chemical structures

Chemical structures represent the spatial arrangement of atoms in a molecule. Visualizing these structures helps in understanding the matter's chemical behavior.
Condensed structural formulas provide a shorthand representation by grouping atoms and showing the connectivity without drawing every single bond.
For example, 'CH3CH2CH(C2H5)CH2CH2CH3' breaks down as follows:

• CH3 (methyl group)
• CH2 (methylene group repeating)
• CH(C2H5): This shows a point of branching where C2H5 (ethyl group) is attached.

Understanding these representations is crucial for visualizing and predicting chemical reactions and properties.