Question

Give the line drawing and molecular formula for: (a) 3 -methylpentane (b) 2,3 -dimethyl-2-butene (c) 3 -methyl-1-pentene (d) 5 -methyl-1-hexyne

Short answer

(a) Line drawing: ``` CH_3 | CH_3-CH-CH_2-CH_3 ``` Molecular formula: \(C_6H_{14}\) (b) Line drawing: ``` CH_3 CH_3 | | CH_2=C-CH_2-CH_3 ``` Molecular formula: \(C_6H_{12}\) (c) Line drawing: ``` CH_3 | CH_2=CH-CH_2-CH_3 ``` Molecular formula: \(C_6H_{12}\) (d) Line drawing: ``` CH_3 | CH≡C-CH_2-CH_2-CH_2-CH_3 ``` Molecular formula: \(C_7H_{12}\)

Step-by-step solution

(a) 3-Methylpentane

First, identify the main carbon chain in the name, which is "pentane", meaning a 5-carbon chain. Next, locate the substituent(s) and their position(s). We see the prefix "3-methyl", indicating a methyl (CH_3) group at position 3. Draw a 5-carbon chain and add a methyl group at position 3. The line drawing and molecular formula are: Line drawing: ``` CH_3 | CH_3-CH-CH_2-CH_3 ``` Molecular formula: \(C_6H_{14}\)

(b) 2,3-Dimethyl-2-butene

The main carbon chain is "butene", meaning a 4-carbon chain with a carbon-carbon double bond. The position of the double bond is unspecified, so it will be at position 1. There are two substituents, both methyl groups, located at positions 2 and 3 on the chain. Draw a 4-carbon chain with a double bond at position 1 and two methyl groups at positions 2 and 3. The line drawing and molecular formula are: Line drawing: ``` CH_3 CH_3 | | CH_2=C-CH_2-CH_3 ``` Molecular formula: \(C_6H_{12}\)

(c) 3-Methyl-1-pentene

The main carbon chain is "pentene", meaning a 5-carbon chain with a carbon-carbon double bond. Since the double bond is specified at position 1, it will be at the first carbon. The substituent is a methyl group at position 3. Draw a 5-carbon chain with a double bond at position 1 and a methyl group at position 3. The line drawing and molecular formula are: Line drawing: ``` CH_3 | CH_2=CH-CH_2-CH_3 ``` Molecular formula: \(C_6H_{12}\)

(d) 5-Methyl-1-hexyne

The main carbon chain is "hexyne", meaning a 6-carbon chain with a carbon-carbon triple bond. Since the triple bond is specified at position 1, it will be at the first carbon. The substituent is a methyl group at position 5. Draw a 6-carbon chain with a triple bond at position 1 and a methyl group at position 5. The line drawing and molecular formula are: Line drawing: ``` CH_3 | CH≡C-CH_2-CH_2-CH_2-CH_3 ``` Molecular formula: \(C_7H_{12}\)

Key concepts

Molecular Formula

A molecular formula is a straightforward representation that shows the number of each type of atom in a molecule. For chemistry students, understanding how to derive a molecular formula from a chemical name is essential.
For example, when given a compound like hexane, it indicates six carbon atoms. Applying basic principles, one can include the matching number of hydrogen atoms.
Typically, the formula is organized with the carbon (C) number first, followed by hydrogen (H), and then any other elements in alphabetical order. Utilizing the molecular formula can help deduce structural properties and clarify how a molecule is built.

IUPAC Nomenclature

The IUPAC nomenclature is a standardized way to name chemical substances, ensuring a universal understanding. This system assists in representing a molecule's structure with ease.
In organic chemistry, IUPAC names inform us about the carbon chain's length and functional groups present. For instance, in '3-methylpentane', 'pentane' hints at a five-carbon chain structure. The '3-methyl' cue tells us about a single CH₃ group attached to the third carbon.
Utilizing IUPAC names helps chemists understand a molecule's structure instantly and predict possible reactions or properties.

Structural Isomers

Structural isomers are compounds with the same molecular formula but different structural arrangements. This variability can significantly impact the compound's chemical and physical properties.
For instance, 'butane' and 'isobutane' both share the molecular formula C₄H₁₀. However, butane has a straight chain, while isobutane includes a branched structure.
Recognizing isomers is crucial as they exhibit unique behaviors despite having identical molecular compositions. Analyzing line drawings can swiftly help identify isomeric variations and their ramifications.

Hydrocarbons

Hydrocarbons are simple organic compounds consisting exclusively of carbon and hydrogen atoms. They serve as basic building blocks in organic chemistry.
Classified into alkanes, alkenes, and alkynes, each type of hydrocarbon is defined by its type of carbon bond—single, double, or triple, respectively. Alkanes follow the formula CₙH₂ₙ₊₂, while alkenes and alkynes adhere to more complex bond arrangements.
Hydrocarbons are fundamental in generating energy sources, such as fuels. Understanding their structures and characteristics helps students grasp broader organic chemistry concepts.