Question

Isooctane can be obtained by joining (A) Isopropyl and neo-pentyl (B) Isobutyl and Tertiary butyl (C) neo-hexyl and Tertiary butyl (D) None is correct

Short answer

The correct combination to obtain Isooctane, an isomer of octane with the chemical formula C8H18 and IUPAC name 2,2,4-trimethylpentane, is by joining Isobutyl and Tertiary butyl (option B). This combination results in an 8-carbon molecule with the desired branched structure and three methyl groups.

Step-by-step solution

Understanding Isooctane Structure

Isooctane is known for its branched structure. Its IUPAC name is 2,2,4-trimethylpentane, which indicates that it is made up of an alkyl group and three methyl groups attached to the carbon chain. This structure enables Isooctane to have a relatively higher octane rating, making it preferred in the fuel industry.

Analyzing the Options

Now, let's analyze the given options to determine the correct combination: (A) Isopropyl and neo-pentyl: Isopropyl has 3 carbons, and neo-pentyl has 5 carbons. Joining them would give a molecule with 8 carbons. However, the structure would lack the required three methyl groups. (B) Isobutyl and Tertiary butyl: Isobutyl has 4 carbons, and Tertiary butyl has 4 carbons as well. Joining them would give an 8-carbon molecule, and it would possess the required three methyl groups. (C) neo-hexyl and Tertiary butyl: neo-hexyl has 6 carbons, and Tertiary butyl has 4 carbons. Joining them would result in a molecule with 10 carbons, which is too many carbons for Isooctane.

Conclusion

By examining the structure of Isooctane, we can conclude that the correct combination to obtain the compound is given by option (B), i.e., Isobutyl and Tertiary butyl. This combination results in an 8-carbon molecule with the desired IUPAC name of 2,2,4-trimethylpentane.

Key concepts

IUPAC Nomenclature

Understanding the IUPAC nomenclature is crucial for anyone delving into organic chemistry. The International Union of Pure and Applied Chemistry (IUPAC) developed a systematic method for naming organic chemical compounds. The main goal of IUPAC naming is to provide a unique and unambiguous name for each compound, avoiding the confusion that may arise from the use of common names.

Take the compound isooctane as an example. Its IUPAC name is '2,2,4-trimethylpentane'. This name carries a lot of information about the structure of the compound. The prefix 'pentane' tells us that the longest continuous carbon chain in the molecule contains five carbons. The numbers '2,2,4-' inform us about the positioning of the branches, or substituents on the carbon chain; in this case, three methyl groups (-CH3). Two of these are on the second carbon, and one is on the fourth carbon. With IUPAC nomenclature, once the name is understood, the structure of the molecule can be drawn accurately.

Parsing the name helps in solving organic chemistry problems: by identifying the components and their placement from the name, students can more easily visualize or even predict the molecular structure. This is why IUPAC nomenclature is not only a naming convention but also a language of communication among chemists worldwide.

Organic Chemistry Problem Solving

In organic chemistry, problem-solving often involves analyzing molecular structures and understanding their interactions. When faced with an option of groups to combine to achieve a target molecule, as in the isooctane exercise, students must apply their knowledge of molecular structures and counting carbon atoms to find the correct combination.

For example, one skill required in the step by step solution is recognizing that an isooctane molecule (2,2,4-trimethylpentane) requires an eight-carbon molecule with specific branches. By visualizing and drawing the requisite number of carbons and their respective positions, a student can deduce the right combination from the options provided.

Approaching Organic Problems

• Analyze the given molecular fragments (e.g., isopropyl, neopentyl, isobutyl, tertiary butyl).
• Count the number of carbon atoms in each fragment.
• Consider the necessary molecular structure and the number of carbon atoms for the final molecule.
• Combine fragments that result in the accurate structure and correct number of carbon atoms as per IUPAC naming.

Each of these steps helps break down the larger problem into smaller, manageable pieces. Students should always check that their final structure matches the common name and IUPAC nomenclature, ensuring their solution is correct.

Octane Rating

The octane rating of a fuel is a measure of its ability to resist 'knocking' or 'pinging' during combustion, which is caused by the premature ignition of the fuel-air mixture in the engine. This rating is important for optimizing engine performance and preventing damage.

Isooctane plays a significant role in this context due to its high octane rating, which makes it an ideal substance for fuel. In an engine, a higher octane-rated fuel can withstand more compression before detonating, which allows for higher engine efficiency and performance. In reference to the exercise, the isooctane structure, or 2,2,4-trimethylpentane, has an octane rating of 100, which is used as a standard reference point.

When fuels are examined for their anti-knock properties, they are compared to the performance of isooctane, and thus the octane rating scale is born. The relevance of studying isooctane in chemistry textbooks goes beyond understanding its structure: it explains the standard against which all other fuel components are measured, highlighting the profound intersection between organic chemistry and practical applications such as automotive engineering.