Naming Alkanes - Worksheet #1

To name these alkanes correctly, we follow the IUPAC rules:
1. Find the longest carbon chain (the parent chain). This determines the base name (like methane, ethane, propane, butane, pentane, hexane, heptane, octane).
2. Number the chain starting from the end that gives the substituents (branches) the lowest possible numbers.
3. Identify and name the substituents (methyl, ethyl, propyl, etc.).
4. Assemble the name: List substituents in alphabetical order (ignoring prefixes like di-, tri-) with their position numbers, followed by the parent name.

Let's go through each structure one by one.

---

Structure 1:
```
CH3
|
CH3 - CH - CH2 - CH3
```
- Longest chain: 4 carbons → butane.
- Numbering: Start from left to give methyl group position 2 (vs. 3 from right). So, it’s 2-methyl.
- Name: 2-methylbutane

✔ Correct as written? The worksheet says “2-methylbutane” — yes, correct.

---

Structure 2:
```
CH3 CH3
| |
CH3 - CH2 - CH - CH - CH2 - CH3
```
Wait — let me count atoms carefully.

Actually, looking at the diagram:

It shows:
```
CH3 CH3
| |
CH3 - CH2 - CH - CH - CH2 - CH3
```

That’s a 6-carbon chain: positions 1 to 6.

Substituents: methyl groups on carbon 3 and carbon 4.

Numbering: If we number left to right → methyls at 3 and 4.
If we number right to left → methyls at 3 and 4 again (symmetrical).

So, 3,4-dimethylhexane

But wait — is there a longer chain? No, 6 is max.

Alphabetical: dimethyl comes before hexane.

Name: 3,4-dimethylhexane

Worksheet says: “3,4-dimethylhexane” — ✔ correct.

---

Structure 3:
```
CH3
|
CH3 - CH2 - CH - CH2 - CH3
|
CH3
```

Longest chain: 5 carbons → pentane

Substituents: two methyl groups on carbon 3 → 3,3-dimethyl

Name: 3,3-dimethylpentane

Worksheet says: “3,3-dimethylpentane” — ✔ correct.

---

Structure 4:
```
CH3
|
CH3 - CH2 - CH2 - CH - CH2 - CH3
|
CH3
```

Longest chain: 6 carbons → hexane

Substituent: methyl on carbon 4? Let’s number properly.

If we number left to right: methyl on C4.
If we number right to left: methyl on C3 → better!

So, number from right:

Rightmost CH3 = C1
Then CH2 = C2
Then CH (with methyl) = C3
Then CH2 = C4
Then CH2 = C5
Then CH3 = C6

So methyl is on C3

Name: 3-methylhexane

Worksheet says: “3-methylhexane” — ✔ correct.

---

Structure 5:
```
CH3 CH3
| |
CH3 - CH - CH - CH2 - CH3
```

Longest chain: 5 carbons → pentane

Substituents: methyl on C2 and methyl on C3 → 2,3-dimethyl

Name: 2,3-dimethylpentane

Worksheet says: “2,3-dimethylpentane” — ✔ correct.

---

Structure 6:
```
CH3
|
CH3 - CH2 - CH - CH3
```

Longest chain: 4 carbons → butane

Methyl on C2 → 2-methylbutane

Wait — this looks identical to Structure 1!

Yes, same molecule.

Worksheet says: “2-methylbutane” — ✔ correct.

---

Structure 7:
```
CH3
|
CH3 - C - CH2 - CH3
|
CH3
```

Longest chain: 4 carbons → butane

Two methyl groups on C2 → 2,2-dimethyl

Name: 2,2-dimethylbutane

Worksheet says: “2,2-dimethylbutane” — ✔ correct.

---

Structure 8:
```
CH3
|
CH3 - CH2 - CH - CH2 - CH2 - CH3
```

Longest chain: 6 carbons → hexane

Methyl on C3 (if numbered left to right) or C4 (right to left) → choose lower number → 3-methylhexane

Same as Structure 4.

Worksheet says: “3-methylhexane” — ✔ correct.

---

Structure 9:
```
CH3 CH3
| |
CH3 - CH - CH - CH3
```

Longest chain: 4 carbons → butane

Methyls on C2 and C3 → 2,3-dimethylbutane

Worksheet says: “2,3-dimethylbutane” — ✔ correct.

---

Structure 10:
```
CH3
|
CH3 - CH2 - CH2 - CH - CH2 - CH2 - CH3
```

Longest chain: 7 carbons → heptane

Methyl on C4 (numbering either way gives same result due to symmetry)

Name: 4-methylheptane

Worksheet says: “4-methylheptane” — ✔ correct.

---

All names provided in the worksheet are actually correct.

But since the instruction says “Name the following branched alkanes”, and the worksheet already has answers filled in, perhaps the task was to verify them? Or maybe the student is supposed to write them?

Given that all are correct, and no errors were found, the final answer is simply confirming each name.

However, if the user expects us to list the correct names (even though they’re already given), we’ll reproduce them accurately.

Final Answer:

1. 2-methylbutane
2. 3,4-dimethylhexane
3. 3,3-dimethylpentane
4. 3-methylhexane
5. 2,3-dimethylpentane
6. 2-methylbutane
7. 2,2-dimethylbutane
8. 3-methylhexane
9. 2,3-dimethylbutane
10. 4-methylheptane

All match the worksheet.