Question

Draw both the condensed and line structures for the cis and trans isomers of 3,4 -dimethylhex-3-ene.

Short answer

Cis: Condensed - CH₃CH(CH₃)C=C(CH₃)CH₂CH₂CH₃; Trans: Condensed - CH₃CH=CH(CH₃)C(CH₃)CH₂CH₂CH₃.

Step-by-step solution

Identify the Main Carbon Chain

The compound name is 3,4-dimethylhex-3-ene. The main carbon chain is 'hex', which means it consists of 6 carbon atoms. Structure this chain in a linear form.

Determine the Location of Double Bond

Since the name indicates 'hex-3-ene', the double bond is between the 3rd and 4th carbon atoms in the chain. Represent this double bond within the linear carbon chain.

Add Methyl Groups

Add a methyl group (CH₃) to both the 3rd and 4th carbon atoms. These are the substituents given by '3,4-dimethyl' in the compound's name.

Draw the Cis Isomer Structure

In the cis isomer, the substituents (methyl groups) are on the same side of the double bond. Draw the structure so that both methyl groups are either both above or both below the carbon chain.

Draw the Trans Isomer Structure

In the trans isomer, the substituents (methyl groups) are on opposite sides of the double bond. Draw the structure with one methyl above and one below the carbon chain.

Write Condensed Structural Formula

For the cis isomer, write the condensed formula as CH₃CH(CH₃)C=C(CH₃)CH₂CH₂CH₃. Do the same for the trans isomer: CH₃CH=CH(CH₃)C(CH₃)CH₂CH₂CH₃.

Write Line Structure for Both Isomers

For the cis isomer, sketch a zig-zag line where both methyl groups are oriented towards the same side at the double bond. For the trans isomer, orient one methyl above and one below the zig-zag line at the double bond location.

Key concepts

Organic Chemistry

Organic chemistry is a branch of chemistry focused on the study of carbon-based compounds. Carbon's ability to form stable covalent bonds with other elements, including itself, makes it incredibly versatile. In fact, organic chemistry is central to our understanding of the structure, properties, and reactions of different carbon compounds in both biological and synthetic processes.

A primary feature of organic compounds is the presence of functional groups, which are specific groupings of atoms that confer distinct chemical properties. For instance, in the compound 3,4-dimethylhex-3-ene, the 'ene' suffix indicates the presence of a carbon-carbon double bond. These double bonds introduce a degree of rigidity in the molecule, leading to different spatial arrangements called geometric isomers—such as the cis-trans isomerism explored in this exercise.

• Organic molecules are typically characterized by their unique structures and bonding patterns.
• Functional groups determine much of a compound's reactivity and properties.
• Cis-trans isomerism stems from the arrangement of groups around a double bond.

Structural Isomers

Structural isomers are compounds that have the same molecular formula but different structural arrangements of atoms. These variations can lead to dramatically different chemical and physical properties. In the realm of organic chemistry, there are many types of structural isomers, including chain isomers, position isomers, and functional isomers.

Cis-trans isomerism, as seen in 3,4-dimethylhex-3-ene, is a type of geometric isomerism that specifically involves the spatial arrangement of atoms around a double bond. By changing the configuration of the methyl groups attached to the double-bonded carbons, you can switch between the cis (same side) and trans (opposite sides) isomers. Despite having the same connectivity and molecular formula, the different spatial orientations result in distinct compounds.

• Cis isomers: Methyl groups on the same side of the double bond.
• Trans isomers: Methyl groups on opposite sides.
• Isomers can exhibit different chemical reactivities and physical properties like boiling and melting points.

Double Bond Positioning

The positioning of double bonds in a carbon chain can significantly influence the properties and reactivity of a compound. In the context of the exercise, the double bond's location is critical for determining the correct structural configuration of 3,4-dimethylhex-3-ene.

The name 'hex-3-ene' suggests that the double bond lies between the 3rd and 4th carbon atoms. This imposes restrictions on the rotation around the bond, leading to the possibility of cis-trans isomerism. With the double bond established on the specified carbon atoms, the orientation of the substituents—methyl groups in this case—decides whether we have the cis or trans isomer.

• A double bond is rigid compared to a single bond, preventing rotation and leading to isomerism.
• Cis-trans isomerism arises only when two different groups are attached to each carbon of the double-bond.
• The position of the double bond can affect the compound's shape, reactivity, and even its smell or taste.