Problem 85 - General Chemistry: Principles and Modern Applications

Question

Write structural formulas for the following. (a) 2,4 -dimethyl- 1,4 -pentadiene (b) 2,3 -dimethylpentane (c) 1,2,4 -tribromobenzene (d) methylethanoate (e) butanone

Step-by-Step Solution

Answer

The structural formulas for these compounds can be drawn as follows: (a) A five carbon chain with a double bond at the 1st and 4th carbon and a methyl group at the 2nd and 4th carbon. (b) A five carbon chain with methyl branches at the 2nd and 3rd carbon. (c) A benzene ring with bromine atoms at the 1st, 2nd, and 4th positions. (d) A two carbon backbone with a methyl group attached to the carbonyl carbon atom and an oxygen atom joining the carbonyl and methyl groups. (e) A four carbon chain with a carbonyl group at the 2nd carbon position.

Step 1: Identifying compound (a) 2,4 -dimethyl- 1,4 -pentadiene

Here, pentadiene means a five carbon chain with two double bonds at 1 and 4, and dimethyl indicates two methyl groups at positions 2 and 4. Draw this out on a piece of paper.

Step 2: Identifying compound (b) 2,3 -dimethylpentane

Pentane signifies a five carbon atom chain. The term dimethyl means there are two methyl branches on the carbon chain at the 2nd and 3rd carbon atom. Draw this as specified.

Step 3: Identifying compound (c) 1,2,4 -tribromobenzene

Benzene is a six-carbon ring with alternating double bonds, and tribromo suggests there are three bromine atoms at positions 1, 2, and 4 of the benzene ring. Illustrate this accordingly.

Step 4: Identifying compound (d) methylethanoate

Methylethanoate has a two carbon backbone (ethanoate) with a methyl group (meth-) attached to the carbonyl carbon atom, and an oxygen atom joining the carbonyl and methyl groups. Draw this correctly.

Step 5: Identifying compound (e) butanone

Butanone is an organic compound with a four carbon chain and a carbonyl group at the 2nd carbon position. Draw an illustration as described.

Key Concepts

Structural Formulas

Structural formulas are quite helpful when working with organic chemistry. They allow us to visualize the arrangement of atoms in molecules. By using structural formulas, chemists can easily see which atoms are connected and how.
For example, molecules can be displayed differently like in this exercise, using condensed formulas, line-bonded structures, or expanded diagrams.
In structural formulas, carbon chains are formed by connecting carbon atoms to each other along with hydrogen, oxygen, nitrogen, and any other functional group present. You can often spot hydrogen atoms bonded to the carbon atoms or other atoms completing four bonds for each carbon.
Visualizing structures is important because it helps in understanding the properties and reactions of specific molecules. Make sure to always confirm atom counts and bonds when drawing to ensure accuracy.

Hydrocarbons

Hydrocarbons are organic compounds composed solely of carbon and hydrogen atoms. They play a central role in organic chemistry due to their diverse structures and properties.
Two main categories of hydrocarbons exist: aliphatic and aromatic. Aliphatic hydrocarbons can be further classified into alkanes, alkenes, and alkynes.
Alkanes, like 2,3-dimethylpentane from the exercise, have single covalent bonds between carbon atoms, making them saturated. Alkenes, such as 2,4-dimethyl-1,4-pentadiene, have one or more double bonds, indicating they are unsaturated and more reactive.
These structures directly influence their chemical behavior and applications. The naming is crucial, using the International Union of Pure and Applied Chemistry (IUPAC) rules to identify and differentiate the many unique hydrocarbon structures.

Benzene Derivatives

The structure of benzene is a perfect example of aromatic hydrocarbons. The benzene ring consists of six carbon atoms, each connected to a hydrogen atom, with alternating double and single bonds forming a hexagonal shape.
This special structure creates unique electronic stability and reactivity properties known as resonance. Benzene derivatives, like 1,2,4-tribromobenzene, result when hydrogen atoms on the benzene ring are replaced by other groups or atoms, such as bromine in this case.
The position of these substituents is described with numbers or prefix terms like ortho, meta, and para, indicating their placement on the ring. Understanding benzene derivatives is crucial in fields like pharmaceuticals, where altering the benzene structure can greatly affect a compound's activity.

Carbonyl Compounds

Carbonyl compounds are a group of organic compounds characterized by the presence of a carbon atom double-bonded to an oxygen atom, known as the carbonyl group. This distinctive structure is found in several important classes of organic compounds.
Depending on the atoms bonded to the carbonyl carbon, the compound may be classified differently. Ketones, such as butanone from the exercise, have the carbonyl group flanked by carbon atoms, while esters like methylethanoate involve the carbonyl adjacent to an oxygen atom bridging to another carbon structure.
These differences influence the physical and chemical properties of the compounds. Carbonyl groups are crucial as they are frequently part of larger and more complex molecules, playing key roles in reactions like oxidation and reduction. Understanding carbonyl chemistry is essential for exploring various synthesis reactions in organic chemistry.