Naming Alkanes - Worksheet #1 - PHA 212 - Studocu - Free Printable

Let’s go through each problem one by one. We’re naming branched alkanes — that means we need to find the longest carbon chain (the parent chain), number it correctly, and then name any branches (substituents) with their positions.

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Problem 1:

Structure:
H₃C–CH(CH₃)–CH₃
That’s a 3-carbon chain with a methyl group on carbon #2.

Longest chain = 3 carbons → propane
Branch = methyl on carbon 2 → 2-methylpropane

✔ Correct answer: 2-methylpropane

*(Note: The student wrote “1-methyl propane” — that’s wrong because you always number from the end closest to the branch. Also, no space in “methylpropane”.)*

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Problem 2:

Structure:
H₃C–CH(CH₃)–CH₂–CH₃
Longest chain = 4 carbons → butane
Methyl group on carbon #2 → 2-methylbutane

✔ Correct answer: 2-methylbutane

*(Student got this right! Good job.)*

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Problem 3:

Structure:
H₃C–CH₂–CH₂–CH(CH₂CH₃)–CH₂–CH₂–CH₃
Wait — let’s count the longest chain. If we go straight across: 7 carbons? But look at the branch: it’s –CH₂–CH₃ (ethyl group). So if we include that ethyl in the main chain, we might get longer?

Actually, let’s trace:

From left: C1–C2–C3–C4(–CH₂–CH₃)–C5–C6–C7 → that’s 7 carbons in a row, plus an ethyl on C4.

But wait — what if we go down the ethyl? Then: C1–C2–C3–C4–C(ethyl part)–C(ethyl part) → that’s only 6. So 7 is still longest.

So parent = heptane
Ethyl group on carbon #4 → 4-ethylheptane

BUT — the student wrote “4-methyl heptane” — that’s wrong! The branch is ethyl (–CH₂–CH₃), not methyl (–CH₃).

✔ Correct answer: 4-ethylheptane

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Problem 4:

Structure:
H₃C–CH₂–CH₂–CH(CH₃)–CH(CH₂CH₃)–CH₂–CH₃
Let’s find the longest chain.

If we go straight: 7 carbons? Let’s label:

Left to right:
C1–C2–C3–C4(–CH₃)–C5(–CH₂CH₃)–C6–C7 → yes, 7 carbons.

Branches:
- Methyl on C4
- Ethyl on C5

Now, number the chain so substituents have lowest numbers.

If we number left to right: methyl on 4, ethyl on 5 → 4,5
If we number right to left: ethyl on 3, methyl on 4 → 3,4 → better!

So renumber:
Right end as C1:
C1–C2–C3(–CH₂CH₃)–C4(–CH₃)–C5–C6–C7

So: ethyl on 3, methyl on 4 → alphabetically: ethyl before methyl → 3-ethyl-4-methylheptane

✔ Correct answer: 3-ethyl-4-methylheptane

*(Student wrote “3-ethyl 4-methyl heptane” — close, but should be hyphenated and no spaces: 3-ethyl-4-methylheptane)*

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Problem 5:

Structure:
H₃C–CH₂–CH(CH₃)–CH₂–CH(CH₂CH₂CH₃)–CH₂–CH₃
Longest chain? Let’s see.

Straight chain: 7 carbons?
C1–C2–C3(–CH₃)–C4–C5(–CH₂CH₂CH₃)–C6–C7 → yes.

Branches:
- Methyl on C3
- Propyl on C5

Numbering: left to right → 3,5
Right to left → propyl on 3, methyl on 5 → same numbers. Alphabetical order: methyl before propyl → so 3-methyl-5-propylheptane

Wait — but propyl is larger, but alphabetically “m” comes before “p”, so methyl first.

✔ Correct answer: 3-methyl-5-propylheptane

*(Student wrote “5-methyl 3-propyl heptane” — they numbered backwards and didn’t follow alphabetical order. Should be 3-methyl-5-propylheptane.)*

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Problem 6:

Structure:
H₃C–CH₂–CH₂–CH₂–C(CH₃)(CH₂CH₃)–CH₂–CH₃
Central carbon has two branches: methyl and ethyl.

Longest chain: let’s try going through the central carbon.

Option 1: Left side: 4 carbons + central + right side 2 carbons = 7?
C1–C2–C3–C4–C5(central)–C6–C7 → yes, 7 carbons.

On C5: attached are –CH₃ and –CH₂CH₃ → so methyl and ethyl groups.

So: 3-methyl-3-ethylheptane? Wait — where is C5?

Numbering: if we number left to right:
C1–C2–C3–C4–C5(branches)–C6–C7 → branches on C5.

But if we number right to left:
C1(right)–C2–C3(central)–C4–C5–C6–C7(left) → branches on C3 → lower number!

So: ethyl and methyl both on C3 → 3-ethyl-3-methylheptane

Alphabetical: ethyl before methyl → 3-ethyl-3-methylheptane

✔ Correct answer: 3-ethyl-3-methylheptane

*(Student wrote “3-methyl 3-pentyl heptane” — totally wrong. The branch is ethyl, not pentyl. Pentyl would be 5 carbons — here it’s just ethyl (2 carbons).)*

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Problem 7:

Structure:
H₂C(CH₃)–CH(CH₂CH₂CH₃)–CH₂–CH(CH₂CH₂CH₃)–CH₃
Wait — let’s write it clearly:

It’s:
CH₃–CH(propyl)–CH₂–CH(propyl)–CH₃? No — looking at drawing:

Actually, it’s:
Carbon 1: CH₂ with a CH₃ below → so it’s –CH(CH₃)– but wait, labeled H₂C– with CH₃ under it → that’s a –CH– group with a methyl substituent? Actually, standard notation: H₂C– usually means terminal, but here it’s drawn with a branch.

Looking again:
The structure is:

CH₂–CH₂–CH₃ (propyl)
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H₂C – CH – CH₂ – CH – CH₃
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CH₃ CH₂–CH₂–CH₃ (propyl)

So carbon 1: H₂C– with a CH₃ attached → so it’s actually a –CH– group? Wait, H₂C implies two H’s, but if it has a CH₃ branch, it should be HC– with three bonds.

I think there’s a typo in drawing. Probably meant:

Carbon 1: CH₃–CH– (with another CH₃? No)

Better interpretation:

The main chain is 5 carbons:
C1 – C2 – C3 – C4 – C5

With:
- On C1: a methyl group? But it says H₂C– with CH₃ under it → that would make C1 have three carbons? Impossible.

Wait — looking at student’s labeling: they circled a 5-carbon chain and called it pentane, with branches: methyl on C1, propyl on C2, propyl on C4.

But in standard naming, you can’t have a substituent on C1 of the parent chain — because C1 is an end carbon, and if you attach something to it, it becomes part of the chain.

Actually, let’s redraw properly:

The structure is:

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

No — original drawing:

"H₂C—CH—CH₂—CH—CH₃" with:
- Under first H₂C: CH₃ → so that carbon has: H₂C– (which is unusual) — probably it's meant to be CH₃–CH– with the CH being carbon 2.

Standard way: the first carbon is CH₃– (if it were normal), but here it's written as H₂C– with a CH₃ attached — that suggests the first carbon is actually a CH group with two hydrogens and one methyl? That doesn't make sense.

Perhaps it's:

Carbon 1: CH₃– (but drawn as H₂C with CH₃ under — maybe it's a mistake).

Looking at student’s work: they identified a 5-carbon chain: C1 to C5, with:
- On C1: methyl group → but that would make it a 6-carbon chain if included.
- On C2: propyl
- On C4: propyl

Actually, the correct longest chain: if you go from the bottom methyl on left, up to C2, then to C3, C4, then down the propyl on C4 — that could be longer.

Let’s count atoms:

Start from left-bottom CH₃ (call it C1) – connected to CH (C2) – connected to CH₂ (C3) – connected to CH (C4) – connected to CH₃ (C5) — that’s 5.

But C2 also has a propyl: CH₂–CH₂–CH₃ (3 more carbons)
C4 also has a propyl: CH₂–CH₂–CH₃ (3 more)

So total carbons: 5 + 3 + 3 = 11, but we need longest continuous chain.

What if we go: from left propyl end: CH₃–CH₂–CH₂– (attached to C2) – then C2–C3–C4– then down right propyl: CH₂–CH₂–CH₃ → that’s 3+1+1+1+3 = 9 carbons? Let's map:

Chain:
C1 (end of left propyl) – C2 – C3 – C4 (the CH that was C2 in original) – C5 (CH₂) – C6 (CH) – C7 – C8 – C9 (end of right propyl)

Yes! So longest chain is 9 carbons → nonane.

Now, what branches? In this chain, at C4 (which was original C2), there is a methyl group (the CH₃ that was attached to original C1). And at C6 (original C4), there is a methyl group (the CH₃ at the end of the original chain).

Original structure simplified:

The molecule is symmetric:
It’s 4-methyl-6-methylnonane? But let's define the chain.

Set the long chain as:
CH₃–CH₂–CH₂–CH–CH₂–CH–CH₂–CH₂–CH₃
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CH₃ CH₃

Because:
- From left propyl: CH₃–CH₂–CH₂– (carbons 1,2,3)
- Attached to CH (carbon 4) which has a CH₃ (branch)
- Then CH₂ (carbon 5)
- Then CH (carbon 6) which has a CH₃ (branch)
- Then CH₂–CH₂–CH₃ (carbons 7,8,9)

Yes! So parent = nonane
Branches: methyl on C4 and methyl on C6 → 4,6-dimethylnonane

And since both are methyl, we say dimethyl.

✔ Correct answer: 4,6-dimethylnonane

*(Student wrote “2,4-dipropyl 1-methyl pentane” — completely wrong. They didn’t find the longest chain. The longest chain is 9 carbons, not 5.)*

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Now, compiling all correct answers:

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

Final Answer:
1. 2-methylpropane
2. 2-methylbutane
3. 4-ethylheptane
4. 3-ethyl-4-methylheptane
5. 3-methyl-5-propylheptane
6. 3-ethyl-3-methylheptane
7. 4,6-dimethylnonane