Question

Draw a condensed structural formula for each of the following alkanes: a. 3,3 -dimethylpentane b. \(2,3,5\) -trimethylhexane c. 3 -ethyl- 2,5 -dimethyloctane d. 1 -bromo-2-chloroethane e. 2 -bromo-3-chlorobutane

Short answer

a. (CH\textsubscript{3})\textsubscript{2}CCH\textsubscript{2}CH\textsubscript{2}CH\textsubscript{3} b. (CH\textsubscript{3})\textsubscript{2}CHCH(CH\textsubscript{3})CH\textsubscript{2}CH\textsubscript{3} c. CH\textsubscript{3}CH(CH\textsubscript{3})CH(CH\textsubscript{3})CH\textsubscript{2}C(CH\textsubscript{2}H)CH(CH\textsubscript{3}) d. CClBrCH\textsubscript{3} e. BrCH\textsubscript{2}CClH

Step-by-step solution

Identify the main carbon chain

Find the longest continuous chain of carbon atoms in each compound. This will be the parent chain.

Identify and position the substituents

Determine the substituents (alkyl groups, halogens, etc.) attached to the main carbon chain, and note their positions based on the provided naming.

Draw the main carbon chain

Draw the carbon atoms of the main chain in a linear arrangement, denoting each carbon with a bare minimum of hydrogen atoms.

Add substituents to the main chain

Attach the substituents at their specified positions on the main chain and finalize the structure.

Verify and condense the structure

Ensure all hydrogen atoms are added to each carbon to make the valence complete (each carbon must have 4 bonds). Then condense the formula by grouping hydrogens and atoms attached to each carbon.

Key concepts

alkanes

Alkanes are a fundamental concept in organic chemistry. These are hydrocarbons, which means they are compounds made entirely of carbon (C) and hydrogen (H) atoms.

The defining feature of alkanes is that they have only single bonds between the carbon atoms, making them 'saturated.' In simpler terms, each carbon atom forms four single bonds (either with other carbon atoms or hydrogen atoms).

Some notable properties of alkanes include:

• They are relatively inert and do not react easily.
• They are non-polar, making them not very soluble in water.
• They are less dense than water and usually float on its surface.

Understanding alkanes helps in grasping more complex organic chemistry concepts.

condensed structural formula

Condensed structural formulas are a simplified way of representing the molecular structure of organic compounds.

Instead of drawing out each individual bond, you write the structure in a line, grouping like atoms together. For example, instead of drawing each carbon and hydrogen atom separately, you would write them in a bonded group, such as CH₃-(CH₂)₄-CH₃ for hexane.

This form helps quickly convey the structure while saving space and time. Here are some things to remember when writing condensed structural formulas:

• Group similar atoms together (like all hydrogens attached to a carbon).
• Use parentheses to indicate repeating units or branches.
• Keep the main chain in a linear arrangement for clarity.

With practice, these formulas become second nature and are very useful for complex molecules.

substituents

Substituents are atoms or groups of atoms that replace hydrogen atoms on a carbon chain. They are significant in determining the properties and reactivity of a molecule.

Some common substituents include:

• Alkyl groups like methyl (CH₃-) and ethyl (CH₃CH₂-).
• Halogens like chlorine (Cl) and bromine (Br).
• Functional groups like hydroxyl (OH-) or carboxyl (-COOH).

Substituents are named and numbered based on their position on the carbon chain. The carbon chain is numbered such that the substituents get the lowest possible numbers.

For example, in 2-bromo-3-chlorobutane, 'bromo' and 'chloro' are substituents on the butane carbon chain. The numbers indicate they are on the second and third carbons, respectively.

This system helps in clearly defining the molecule’s structure.

carbon chain

The carbon chain is the backbone of an organic molecule. It can vary in length and complexity, affecting the molecule's properties and categorization.

Here’s what to keep in mind:

• Identify the longest continuous chain of carbon atoms. This is usually the 'parent' chain and determines the root name of the molecule (e.g., hexane for a six-carbon chain).
• Branches or 'substituents' off this main chain are noted and named separately.
• The chain can be straight (linear) or contain branches.

For example, in 3,3-dimethylpentane, the longest chain is pentane (five carbons), and there are two methyl groups (CH₃) attached to the third carbon.

Recognizing the main carbon chain is crucial for systematically naming and understanding organic compounds according to IUPAC conventions.