Question

Which of the following alkenes on catalytic hydrogenation yield 2 -methyl pentane? (1) 4 -methyl-1-pentene (2) 4 -methyl pentene-2 (3) 2 -methyl pentene-2 (4) 2 -methyl pentene-1 (5) All of the above

Short answer

(3) 2-methylpentene-2 and (4) 2-methylpentene-1

Step-by-step solution

- Understand the question

The problem asks which of the given alkenes will yield 2-methylpentane upon catalytic hydrogenation. Catalytic hydrogenation converts alkenes (double bonds) to alkanes (single bonds). We need to identify the structure of each compound and see if it will result in 2-methylpentane after the addition of hydrogen.

- Identify 2-methylpentane

2-methylpentane is a hydrocarbon with the following structure: CH3-CH(CH3)-CH2-CH2-CH3 It has a main chain of five carbon atoms with a methyl group attached to the second carbon atom.

- Analyze each compound

Evaluate each alkene to determine if its hydrogenation will produce 2-methylpentane. (1) 4-methyl-1-pentene: Structure - CH3-CH2-CH2-CH(CH3)-CH=CH2 Hydrogenation will yield 4-methylhexane, not 2-methylpentane. (2) 4-methylpentene-2: Structure - CH3-CH2-CH(CH3)-CH=CH2 Hydrogenation will yield 4-methylpentane, not 2-methylpentane. (3) 2-methylpentene-2: Structure - CH3-CH(CH3)-CH=CH-CH3 Hydrogenation will yield 2-methylpentane. (4) 2-methylpentene-1: Structure - CH3-CH(CH3)-CH2-CH2-CH=CH2 Hydrogenation will yield 2-methylpentane. (5) All of the above: Not all compounds produce 2-methylpentane.

- Conclusion

Based on the structures, only compounds (3) and (4) yield 2-methylpentane upon catalytic hydrogenation. Therefore, the correct answer is (3) 2-methylpentene-2 and (4) 2-methylpentene-1.

Key concepts

alkenes to alkanes conversion

Catalytic hydrogenation is a process that converts alkenes into alkanes. In this reaction, the double bond in an alkene breaks, and hydrogen atoms are added to the carbons. This changes the alkene with its double bond into an alkane with single bonds.

The catalyst (often metals like platinum or palladium) is key in this reaction. It lowers the activation energy, making the reaction faster and easier to carry out. Catalytic hydrogenation is widely used in organic chemistry to ‘saturate’ molecules, meaning to convert all double or triple bonds into single bonds.

Imagine you have an alkene like 1-hexene (CH3-CH2-CH2-CH2-CH=CH2). When you add hydrogen in the presence of a catalyst, the double bond between the last two carbons breaks. Hydrogen atoms then attach to these carbons, resulting in hexane (CH3-CH2-CH2-CH2-CH2-CH3).

This process is essential for changing the properties of organic compounds. Alkanes are usually less reactive than alkenes because they lack double bonds. This makes them more stable and useful in different applications. Knowing how to carry out and predict the results of catalytic hydrogenation is fundamental in organic chemistry.

2-methylpentane

2-methylpentane is an example of a branched alkane. Its chemical structure provides a good example of how branching works in hydrocarbons.

The structure of 2-methylpentane consists of a main chain of five carbon atoms. The key feature is a methyl group (CH3) attached to the second carbon atom. The full chemical formula is:

CH3-CH(CH3)-CH2-CH2-CH3

In this formula:

• CH3- indicates a methyl group.
• -CH- represents a single carbon connected to two other groups -- one being another CH3, and the other being a part of the larger carbon chain.

Understanding the structure of 2-methylpentane is crucial because it helps visualize what the products of various reactions will look like. In catalytic hydrogenation, ensuring your product aligns with 2-methylpentane's structure confirms whether the correct reactions have occurred.

chemical structure analysis

Analyzing chemical structures is a fundamental skill in organic chemistry. Let’s look at how to analyze the structures of given alkenes and predict the results of their hydrogenation.

Consider the following compounds:

• 4-methyl-1-pentene: CH3-CH2-CH2-CH(CH3)-CH=CH2
• 4-methylpentene-2: CH3-CH2-CH(CH3)-CH=CH2
• 2-methylpentene-2: CH3-CH(CH3)-CH=CH-CH3
• 2-methylpentene-1: CH3-CH(CH3)-CH2-CH2-CH=CH2

For each compound, you need to visualize the structure and locate the double bond. During catalytic hydrogenation, the double bond breaks, and hydrogen atoms attach to the carbons initially bonded by the double bond.

For instance, in 2-methylpentene-2 (CH3-CH(CH3)-CH=CH-CH3), the hydrogenation will break the double bond between the third and fourth carbons, yielding 2-methylpentane.

Similarly, in 2-methylpentene-1 (CH3-CH(CH3)-CH2-CH2-CH=CH2), the double bond breaks, and the resulting product is again 2-methylpentane. This structure analysis confirms that only these specific alkenes (2-methylpentene-2 and 2-methylpentene-1) will yield 2-methylpentane upon catalytic hydrogenation.