Question

The alkane from below having two secondary hydrogens is:

• A. 2,2,4,4-Tetramethylhexane
• B. 2,2,3,3-Tetramethylpentane
• C. 4-Ethyl-3,4-dimethyloctane
• D. 2,2,4,5-Tetramethylheptane

Hint:

When identifying secondary hydrogens, look for the carbon atoms attached to two other carbon atoms. These positions will have the secondary hydrogens.

Answer 1

The Correct Option is B

To find the alkane with two secondary hydrogens, we need to understand what a secondary hydrogen atom is. A secondary hydrogen is attached to a secondary carbon, which is a carbon atom bonded to two other carbon atoms. 

1. Examine the structure of each given alkane by understanding the names and using IUPAC nomenclature rules:
   • 2,2,4,4-Tetramethylhexane: A hexane backbone with four methyl groups attached at the 2nd and 4th positions. No secondary hydrogens are present because all hydrogen atoms are bonded to either tertiary or quaternary carbons due to heavy branching.
   • 2,2,3,3-Tetramethylpentane: A pentane backbone with four methyl groups at the 2nd and 3rd positions. Here, we find two secondary hydrogens attached to the 4th carbon atom, which is connected to two other carbons.
   • 4-Ethyl-3,4-dimethyloctane: This compound has a long octane chain with substituents. The branching forms mostly tertiary carbon atoms, meaning fewer secondary hydrogens.
   • 2,2,4,5-Tetramethylheptane: Like the other branched alkanes, the substituents lead to either quaternary or tertiary carbon centers, leaving no secondary hydrogens.
2. Conclusion: Based on this analysis, only 2,2,3,3-Tetramethylpentane has two secondary hydrogens.

Answer 2

Identifying secondary hydrogens in alkanes involves understanding the structure of each carbon atom and its connected hydrogen atoms. A secondary hydrogen atom is attached to a secondary carbon. A secondary carbon is bonded to two other carbon atoms. Let's analyze each option:

1. 2,2,4,4-Tetramethylhexane: The structure of this alkane does not have any secondary carbons, as all carbons hosting hydrogens are either primary or quaternary.
2. 2,2,3,3-Tetramethylpentane: This alkane has a structure where the 2nd and the 3rd carbon in the parent chain are secondary, each bonded to two other carbons. Therefore, it houses secondary hydrogens.
3. 4-Ethyl-3,4-dimethyloctane: Although it has complex branching, secondary hydrogens are minimal and scattered, not fulfilling the requirement of having two secondary hydrogens effectively derived from a single parent carbon chain.
4. 2,2,4,5-Tetramethylheptane: This alkane predominantly contains primary and tert-carbon atoms, with limited secondary hydrogen accessibility.

Given these insights, the alkane 2,2,3,3-Tetramethylpentane is the correct answer as it distinctly contains two secondary hydrogens due to the presence of adequate secondary carbon atoms in its structure.