Question

Give the structure for each of the following. a. 3 -hexene b. 2,4 -heptadiene c. 2 -methyl-3-octene

Short answer

a. 3-hexene: \(\mathrm{CH_2=CH(CH_2)_3CH_3}\) b. 2,4-heptadiene: \(\mathrm{CH_2=CHCH_2CH=CH(CH_2)_2CH_3}\) c. 2-methyl-3-octene: \(\mathrm{CH_3CH(CH_3)CH=CH(CH_2)_4CH_3}\)

Step-by-step solution

Draw the main carbon chain

Based on the prefix in each compound, we will draw the main carbon chain with the correct number of carbon atoms. a. Hex (6 carbon atoms) b. Hept (7 carbon atoms) c. Oct (8 carbon atoms)

Add double bonds

Next, we will add the double bonds to the main chain according to the suffix and position numbers given in the compound name. a. 3-hexene: Add a double bond between carbons 3 and 4. b. 2,4-heptadiene: Add a double bond between carbons 2 and 3 and another between carbons 4 and 5. c. 2-methyl-3-octene: Add a double bond between carbons 3 and 4.

Add additional groups

Now we will add any additional groups (such as methyl) to the main carbon chain, at the positions indicated in the compound name. a. 3-hexene: No additional groups. b. 2,4-heptadiene: No additional groups. c. 2-methyl-3-octene: Add a methyl group to carbon 2.

Draw the structures

With all the necessary components in place, we can now draw the structures of the given compounds. a. 3-hexene: \(\mathrm{CH_2=CH(CH_2)_3CH_3}\) b. 2,4-heptadiene: \(\mathrm{CH_2=CHCH_2CH=CH(CH_2)_2CH_3}\) c. 2-methyl-3-octene: \(\mathrm{CH_3CH(CH_3)CH=CH(CH_2)_4CH_3}\)

Key concepts

Understanding Carbon Chains

A carbon chain is a series of carbon atoms connected to each other, forming the backbone of many organic compounds. These chains can vary in length and can be straight or branched. In the case of alkenes, such as 3-hexene, 2,4-heptadiene, and 2-methyl-3-octene, the carbon chain is crucial for determining the compound's identity and properties.

When naming alkenes, the carbon chain's length is indicated by a prefix: "hex-" for six carbons, "hept-" for seven carbons, and "oct-" for eight carbons. The main carbon chain is chosen to be the longest continuous chain that contains the double bond(s).

Keep in mind:

• The prefix denotes the number of carbon atoms in the longest chain with necessary functional groups.
• The carbon chain is numbered starting from the end nearest a double bond for positioning clarity.

The Role of Double Bonds

Double bonds are covalent bonds where two pairs of electrons are shared between atoms. In alkenes, one double bond is always present, giving these compounds their characteristic features. For example, in 3-hexene, the name indicates a double bond between the 3rd and 4th carbon atoms.

Key characteristics of double bonds include:

• They restrict rotation around the bond, providing alkenes with distinct geometric shapes (cis/trans isomerism).
• They are typically more reactive than single bonds, allowing alkenes to undergo addition reactions.

When placing the double bonds:

• Look for position numbers in the name, such as 3 in 3-hexene and 2,4 in 2,4-heptadiene, which indicate where to place the double bonds along the carbon chain.
• Ensure the double bonds are incorporated into the main carbon chain, not side branches.

Introduction to the Methyl Group

A methyl group is a small alkyl group consisting of one carbon atom bonded to three hydrogen atoms, represented as -CH₃. This group can be attached to the main carbon chain, influencing the structure and properties of the molecule.

When examining alkenes like 2-methyl-3-octene:

• The number preceding "methyl" tells you which carbon atom of the main chain has the methyl group attached. In 2-methyl-3-octene, the methyl group is attached to the second carbon.
• The addition of the methyl group can impact the boiling point and solubility of the compound.
• The presence of such groups can also influence the compound’s spatial structure due to steric hindrance (crowding between atoms).

Understanding methyl groups allows for more insights into the branching and functionalization of organic compounds, leading to diverse molecules with varied chemical behaviors.