Question

Draw the structure of 4 -ethyl \(-3,4\) -dimethyl \(-2\) -hexene.

Short answer

The structure of 4-ethyl-3,4-dimethyl-2-hexene is: \[ \footnotesize{\text{CH}_2= \text{CH-CH} (\text{CH}_3)_2-\text{CH} (\text{CH}_2\text{CH}_3)-\text{CH}_2-\text{CH}_3} \]

Step-by-step solution

Draw the hexene backbone

First, draw a straight chain of 6 carbons, labeling them with numbers 1 to 6. Now, place a double bond between carbons 2 and 3 to represent the hexene structure: \[ \footnotesize{\text{CH}_2= \text{CH-CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_3} \]

Add the ethyl group

An ethyl group is a two-carbon chain, \(\footnotesize{\text{CH}_2 \text{CH}_3 }\). Attach the ethyl group to carbon 4 on the main chain: \[ \footnotesize{\text{CH}_2= \text{CH-CH}_2-\text{CH} (\text{CH}_2 \text{CH}_3)-\text{CH}_2-\text{CH}_3} \]

Add the two methyl groups

Methyl groups consist of one carbon atom and three hydrogen atoms \(\footnotesize{ \text{CH}_3 }\). Attach one methyl group to each of carbon 3 and carbon 4: \[ \footnotesize{\text{CH}_2= \text{CH-CH} (\text{CH}_3)_2-\text{CH} (\text{CH}_2\text{CH}_3)-\text{CH}_2-\text{CH}_3} \] The complete structure of 4-ethyl-3,4-dimethyl-2-hexene is now drawn: \[ \footnotesize{\text{CH}_2= \text{CH-CH} (\text{CH}_3)_2-\text{CH} (\text{CH}_2\text{CH}_3)-\text{CH}_2-\text{CH}_3} \]

Key concepts

Hexene Structure

Understanding the hexene structure is vital in grasping organic chemistry nomenclature. Hexene is a type of alkene, which means it contains at least one carbon-to-carbon double bond. Alkenes are unsaturated hydrocarbons because they have fewer hydrogen atoms than alkanes, their saturated counterparts.

When we say 'hexene', we're referring to an alkene with a six-carbon backbone. The 'hex' part of the word indicates the number of carbon atoms, while 'ene' signifies the presence of a double bond. In the provided exercise, we focus on a particular hexene known as '2-hexene.' This denotes that the double bond begins at the second carbon of the chain.

To depict hexenes, you often draw them as a straight or branched carbon chain. In our case, 2-hexene is drawn with a straight chain. Here, carbon atoms are represented as 'C' and the double bond is shown between carbon 2 and carbon 3, which influences the chemical's properties and reactivity. Understanding where the double bond is located helps in predicting the molecule's behavior during chemical reactions.

Ethyl Group

The ethyl group, a fundamental unit in organic chemistry, is comprised of two carbon atoms bound together and to other atoms. It is denoted by the molecular formula \( C_2H_5 \). This structure qualifies it as an alkyl group, which is simply a hydrocarbon chain functioning as a substituent on larger molecules.

An important aspect of the ethyl group is its ability to attach to a carbon chain, such as in the '4-ethyl' part of our molecule. When attached, the ethyl group brings along its two carbons and five hydrogens, extending the carbon chain and influencing the molecule's physical and chemical properties. For instance, as depicted in our exercise solution, the ethyl group attaches to the fourth carbon of the hexene backbone, which impacts the molecule's boiling point, solubility, and other characteristics.

Methyl Group

The methyl group – another alkyl group – is smaller than the ethyl group, consisting of only one carbon atom bonded to three hydrogen atoms. Represented by the formula \( CH_3 \), it's often considered the simplest alkyl group and is extremely common in organic chemistry.

Adding methyl groups to a molecule, as shown in the '3,4-dimethyl' component of the exercise's molecule, can impact the molecule's shape, reactivity, and overall behavior. Each methyl group is attached to the main carbon chain, introducing additional branching. This branching can affect how the molecule interacts with other molecules and its overall stability. In the context of the exercise, two methyl groups are added to the hexene structure, specifically at carbon atoms 3 and 4, creating a more complex branched structure.