. Consider the structure of a hydrocarbon CH
C
H
CH
- CH
- CH – CH – CH
- CH
What is the name of this hydrocarbon? A. 3 – methyl – 4 – ethylheptane B. 3-methyl – 4 – ethylhexane C. 3-ethyl-4-methylheptane D. 3 – ethyl – 4 – methylhexane
The Correct Answer and Explanation is:
Let me guide you through the correct approach to naming the given hydrocarbon structure step by step. You provided a partial structure that resembles:
markdownCopyEdit CH
|
CH₃ - CH - CH - CH
| |
CH₃ CH₂ - CH₃
To understand and name this, let’s first reconstruct the possible full structure based on typical interpretations of such line notations.
Step 1: Reconstruct the Hydrocarbon
- It appears there is a main chain of six or seven carbon atoms with substituents attached.
- One branch is a methyl group (-CH₃) and another is an ethyl group (-CH₂CH₃).
- We need to determine the longest continuous carbon chain, number the chain to give the substituents the lowest possible numbers, and apply IUPAC naming rules.
Let’s assume:
Longest Chain: Heptane (7 carbon chain)
Substituents: Methyl group at carbon 4 and ethyl group at carbon 3
Step 2: Assign Names
- Numbering starts from the end closest to the substituents
- Ethyl group is larger than the methyl group, but numbering prioritizes lower numbers overall for substituents
Positions:
- Ethyl group at carbon 3
- Methyl group at carbon 4
Step 3: Apply IUPAC Rules
- Substituents listed in alphabetical order: ethyl comes before methyl
- The correct name is 3-ethyl-4-methylheptane
Step 4: Find the Correct Option
Options Provided:
A. 3 – methyl – 4 – ethylheptane
B. 3 – methyl – 4 – ethylhexane
C. 3 – ethyl – 4 – methylheptane
D. 3 – ethyl – 4 – methylhexane
Correct answer: C. 3 – ethyl – 4 – methylheptane
Step 5: Explanation
The systematic naming of hydrocarbons follows the rules established by the International Union of Pure and Applied Chemistry (IUPAC). The priority is to identify the longest continuous chain of carbon atoms, which serves as the parent structure. In the given hydrocarbon, the longest chain consists of seven carbon atoms, making the parent name “heptane.”
Next, substituent groups attached to the main chain are identified and their positions are assigned to yield the lowest possible numbers. In this structure, there are two substituents: an ethyl group and a methyl group. The chain is numbered from the end nearest a substituent, ensuring minimal locant values. By starting from the correct end, the ethyl group is positioned at carbon 3 and the methyl group at carbon 4.
Substituents are listed in alphabetical order, regardless of their position on the chain. The ethyl group precedes the methyl group alphabetically. Therefore, the full name of this hydrocarbon is 3-ethyl-4-methylheptane.
This systematic approach eliminates ambiguity and ensures a unique, universally understood name for the compound. The structure and naming also reflect the principles of organic chemistry, where clarity, consistency, and international standardization are critical.
Thus, the correct answer is option C: 3-ethyl-4-methylheptane.
