Worksheet for naming branched alkanes with structural formulas.

Here's the solution to naming each of the branched alkanes using IUPAC nomenclature rules.

---

IUPAC Naming Rules Summary:

1. Find the longest continuous carbon chain → this gives the parent name (methane, ethane, propane, butane, pentane, hexane, heptane, octane, etc.).
2. Number the chain to give the lowest possible numbers to substituents.
3. Name and number the substituents (methyl, ethyl, propyl, etc.).
4. List substituents in alphabetical order (ignoring prefixes like di-, tri-).
5. Use commas between numbers and hyphens between numbers and words.

---

## 1.

```
H₃C—CH—CH₃
|
CH₃
```

- Longest chain = 3 carbons → propane
- One methyl group on carbon #2
- Name: 2-methylpropane

> ✔ Answer: 2-methylpropane

*(Note: This is also called "isobutane" in common naming, but IUPAC requires "2-methylpropane")*

---

## 2.

```
H₃C—CH—CH₃
|
CH₂—CH₃
```

- Longest chain = 4 carbons → butane (if you go through the ethyl group: C–C–C–C)
- Substituent: ethyl group on carbon #2
- But wait — if we number the chain as:

CH₃–CH–CH₂–CH₃
|
CH₃

That’s actually a 4-carbon chain with a methyl on carbon #2 → 2-methylbutane

Wait — let’s redraw properly:

Original structure:

CH₃
|
CH₃–CH–CH₃
|
CH₂–CH₃

This is actually:

CH₃–CH–CH₂–CH₃
|
CH₃

Because the longest chain is 4 carbons: from left CH₃ → CH → CH₂ → CH₃ (with a methyl on carbon 2).

So correct numbering:

Carbon 1: leftmost CH₃
Carbon 2: CH (with methyl)
Carbon 3: CH₂
Carbon 4: CH₃

→ 2-methylbutane

> ✔ Answer: 2-methylbutane

*(Common name: isopentane)*

---

## 3.

```
H₃C—CH₂—CH₂—CH—CH₂—CH₂—CH₃
|
CH₂—CH₃
```

- Longest chain: 7 carbons → heptane
- Ethyl group on carbon #4
- Numbering: from left to right, ethyl is on C4; from right to left, it would be on C4 too → same.
- Name: 4-ethylheptane

> ✔ Answer: 4-ethylheptane

---

## 4.

```
H₃C—CH₂—CH₂—CH—CH—CH₂—CH₃
| |
CH₃ CH₂—CH₃
```

Let’s write it clearly:

Chain: CH₃–CH₂–CH₂–CH–CH–CH₂–CH₃
| |
CH₃ CH₂–CH₃

So substituents:
- Methyl on carbon 4
- Ethyl on carbon 5

Longest chain: 7 carbons → heptane

Now number the chain to give lowest numbers to substituents.

Option A: Left to right → methyl on C4, ethyl on C5 → numbers 4,5

Option B: Right to left → ethyl on C3, methyl on C4 → numbers 3,4 → better!

So renumber:

Carbon 1: rightmost CH₃
Carbon 2: CH₂
Carbon 3: CH (with ethyl)
Carbon 4: CH (with methyl)
Carbon 5: CH₂
Carbon 6: CH₂
Carbon 7: CH₃

Substituents: ethyl on C3, methyl on C4 → 3-ethyl-4-methylheptane

Alphabetical order: ethyl before methyl → correct.

> ✔ Answer: 3-ethyl-4-methylheptane

---

## 5.

```
H₃C—CH₂—CH—CH₂—CH—CH₂—CH₃
| |
CH₃ CH₂—CH₂—CH₃
```

Structure:

CH₃–CH₂–CH–CH₂–CH–CH₂–CH₃
| |
CH₃ CH₂–CH₂–CH₃

Substituents:
- Methyl on C3
- Propyl on C5

Longest chain: 7 carbons → heptane

Numbering:

Left to right: methyl on C3, propyl on C5 → numbers 3,5

Right to left: propyl on C3, methyl on C5 → numbers 3,5 → same total.

But alphabetical: methyl before propyl → so we list methyl first.

Name: 3-methyl-5-propylheptane

Wait — is that correct? Let’s check if there’s a longer chain.

What if we include the propyl group? The propyl is –CH₂–CH₂–CH₃ → 3 carbons.

If we go: from left CH₃–CH₂–CH–CH₂–CH–CH₂–CH₃
| |
CH₃ CH₂–CH₂–CH₃

The longest chain is still 7 carbons. No longer path.

So yes: 3-methyl-5-propylheptane

BUT — IUPAC rule: when substituents are different, list alphabetically.

“methyl” comes before “propyl” → correct.

> ✔ Answer: 3-methyl-5-propylheptane

---

## 6.

```
H₃C—CH₂—CH₂—CH₂—CH₂
|
H₃C—CH₂—CH₂—CH₂—C—CH₂—CH₃
|
CH₃
```

This is a central carbon with 4 groups:

- Left: CH₂–CH₂–CH₂–CH₃ (butyl)
- Right: CH₂–CH₃ (ethyl)
- Down: CH₃ (methyl)
- Up: CH₂–CH₂–CH₂–CH₃ (butyl)

Actually, let’s count the longest chain.

It’s symmetric. The central carbon is bonded to:

- CH₂–CH₂–CH₂–CH₃ (4 carbons)
- CH₂–CH₃ (2 carbons)
- CH₃ (1 carbon)
- CH₂–CH₂–CH₂–CH₃ (4 carbons)

Longest chain: go from one butyl through central C to the other butyl → 4 + 1 + 4 = 9 carbons → nonane

Central carbon is C5.

Substituents on C5: ethyl and methyl.

Numbering: from either end, C5 is middle.

So: 5-ethyl-5-methylnonane

Alphabetical: ethyl before methyl → 5-ethyl-5-methylnonane

> ✔ Answer: 5-ethyl-5-methylnonane

---

## 7.

```
CH₂—CH₂—CH₃
|
H₂C—CH—CH₂—CH—CH₃
| |
CH₃ CH₂—CH₂—CH₃
```

Let’s rewrite for clarity:

Carbon 1: CH₃– (left)
Carbon 2: CH– (with CH₃ below)
Carbon 3: CH₂
Carbon 4: CH– (with CH₂–CH₂–CH₃ below)
Carbon 5: CH₃

Also, Carbon 2 has a branch: CH₂–CH₂–CH₃ (propyl) above?

Wait — original:

CH₂—CH₂—CH₃
|
H₂C—CH—CH₂—CH—CH₃
| |
CH₃ CH₂—CH₂—CH₃

So:

- Left: CH₃–CH–CH₂–CH–CH₃
| |
CH₃ CH₂–CH₂–CH₃

AND on the second carbon (from left), there’s also a propyl group: CH₂–CH₂–CH₃ attached upward.

So carbon 2 has two branches: methyl and propyl.

Carbon 4 has a propyl branch.

Longest chain: let’s trace.

Option: start from top propyl: CH₃–CH₂–CH₂– (attached to C2) → then C2–C3–C4–C5 (CH₃) → that’s 3 (propyl) + 1 (C2) + 1 (C3) + 1 (C4) + 1 (C5) = 7? Not quite.

Better: the main chain is from left CH₃–CH–CH₂–CH–CH₃ → 5 carbons.

Branches:

- On C2: methyl and propyl
- On C4: propyl

So total substituents: one methyl, two propyls.

Longest chain: is there a longer one?

Try going from top propyl → C2 → C3 → C4 → bottom propyl → that’s 3 (top) + 1 (C2) + 1 (C3) + 1 (C4) + 3 (bottom) = 8 carbons? Wait, no — C2 and C4 are part of the chain.

Actually, the longest continuous chain is:

Start at top propyl: CH₃–CH₂–CH₂– (this is attached to C2)
Then C2–C3–C4–C5 (CH₃) → that’s 3 + 1 + 1 + 1 + 1 = 7? Still not.

Let me draw it linearly.

The molecule is:

CH₂–CH₂–CH₃
|
CH₃–CH–CH₂–CH–CH₃
| |
CH₃ CH₂–CH₂–CH₃

So atoms:

- C1: CH₃– (left)
- C2: CH– (bonded to C1, C3, CH₃, and CH₂–CH₂–CH₃)
- C3: CH₂– (bonded to C2 and C4)
- C4: CH– (bonded to C3, C5, and CH₂–CH₂–CH₃)
- C5: CH₃

So longest chain: C1–C2–C3–C4–C5 → 5 carbons → pentane

Substituents:

- On C2: methyl and propyl
- On C4: propyl

So: 2-methyl-2-propyl-4-propylpentane? That’s messy.

But we can have a longer chain!

Try: from top propyl (CH₃–CH₂–CH₂–) → attached to C2 → C3 → C4 → bottom propyl (CH₃–CH₂–CH₂–)

That’s: CH₃–CH₂–CH₂–C2–C3–C4–CH₂–CH₂–CH₃ → 3 + 1 + 1 + 1 + 3 = 9 carbons? Wait — C2, C3, C4 are single carbons.

So: CH₃–CH₂–CH₂– (branch) — but that’s not continuous unless we go through C2.

Actually, the longest continuous chain is:

Start at top propyl’s end: CH₃–CH₂–CH₂– (this is attached to C2)
Then C2–C3–C4– (then to bottom propyl’s CH₂–CH₂–CH₃)

So: CH₃–CH₂–CH₂–C2–C3–C4–CH₂–CH₂–CH₃ → that’s 3 (top) + 1 (C2) + 1 (C3) + 1 (C4) + 3 (bottom) = 9 carbons → nonane

And what’s attached?

At C2: originally had a methyl → now that methyl is a substituent.

At C4: originally had nothing extra? Wait — in this new chain, C2 and C4 are part of the main chain.

In this 9-carbon chain:

Positions:

1. CH₃ (top propyl end)
2. CH₂
3. CH₂
4. C2 (now this carbon has a methyl group attached)
5. C3
6. C4
7. CH₂ (bottom propyl)
8. CH₂
9. CH₃

So substituent: methyl on carbon #4.

Numbering: from top to bottom, methyl on C4.

From bottom to top, methyl on C6 → so better to number from top: methyl on C4.

Name: 4-methylnonane

Wait — but we ignored the fact that in the original, C4 had a propyl, but in this chain, that propyl is now part of the main chain.

Yes! So by choosing the longest chain (9 carbons), we’ve incorporated both propyl groups into the main chain.

And the only substituent is the methyl on C4.

So final name: 4-methylnonane

> ✔ Answer: 4-methylnonane

---

## ✔ Final Answers:

1. 2-methylpropane
2. 2-methylbutane
3. 4-ethylheptane
4. 3-ethyl-4-methylheptane
5. 3-methyl-5-propylheptane
6. 5-ethyl-5-methylnonane
7. 4-methylnonane

Let me know if you’d like structural diagrams or explanations for any specific one!