Naming Organic Compounds Practice worksheet with chemical structures for identifying alkanes, alkenes, alkynes, aromatic compounds, carboxylic acids, and alcohols.

Let’s go through each compound one by one. We’ll identify the class (alkane, alkene, alkyne, aromatic, carbonyl, alcohol) and then give the IUPAC name. If it’s one of the four special monosubstituted benzenes (like toluene, phenol, aniline, benzoic acid), we’ll use the common name instead.

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1)
Structure: Benzene ring with a methyl group attached.
→ This is toluene (common name for methylbenzene).
Class: Aromatic

2)
Structure: CH₃–CH₂–CH(CH₃)–CH₂–CH₂–CH₃
Longest chain: 6 carbons → hexane
Branch: methyl on carbon #3
→ Name: 3-methylhexane
Class: Alkane

3)
Structure: CH₃–C(=O)–CH₂–CH₂–CH₃
Carbonyl group (C=O) in middle of chain → ketone
Longest chain: 5 carbons → pentanone
Carbonyl on carbon #2 → 2-pentanone
Class: Carbonyl (ketone)

4)
Structure: CH₃–CH(CH₃)–CH(CH₃)–CH₂–CH₂–CH₃
Longest chain: 6 carbons → hexane
Two methyl groups: on carbons #2 and #3
→ Name: 2,3-dimethylhexane
Class: Alkane

5)
Structure: Benzene ring with –CH(CH₃)CH₃ group (isopropyl group)
→ Common name: cumene (isopropylbenzene)
Class: Aromatic

6)
Structure: Benzene ring with –CH₂–CH(CH₃)–CH₃ group
That’s a sec-butyl group? Wait — let’s number:
Benzene attached to CH₂–CH(CH₃)CH₃ → that’s a 1-methylpropyl group? Actually, longest chain from benzene:
Benzene–CH₂–CH(CH₃)–CH₃ → total 4 carbons in side chain, branched at carbon 2 → so it’s a sec-butyl group? But IUPAC:
Name: (2-methylpropyl)benzene? Wait — no:
Actually, the group is –CH₂–CH(CH₃)CH₃ → that’s a butan-2-yl group? No — if attached via CH₂, it’s a 1-methylpropyl? Let’s think differently.

Better: The side chain is –CH₂–CH(CH₃)–CH₃ → that’s a 3-carbon chain with a methyl on carbon 2, attached via carbon 1 → so it’s a 2-methylpropyl group? Wait, no:

Wait — structure is:

```
CH₃
|
Ph–CH₂–CH–CH₃
```

So the group is –CH₂–CH(CH₃)CH₃ → that’s a butan-2-yl group? No — because attachment is at CH₂, which is carbon 1 of the side chain.

Side chain: C1 (attached to Ph) – C2 (has CH₃) – C3 (CH₃)

So it’s a 1,2-dimethylethyl? No — better to name as:

Longest chain from benzene: 3 carbons? No — 4 atoms including the branch.

Actually, this is (2-methylpropyl)benzene? Wait — no:

Standard name: The group is called sec-butyl only if attached directly at the secondary carbon. Here, it’s attached at primary carbon (CH₂), so it’s isobutyl? No — isobutyl is (CH₃)₂CH–CH₂–

Here it’s Ph–CH₂–CH(CH₃)CH₃ → that’s the same as Ph–CH₂–CH(CH₃)CH₃ → which is phenylpropane with a methyl on carbon 2? So the side chain is butyl, branched.

IUPAC: Name the side chain as a substituent.

The group is –CH₂–CH(CH₃)CH₃ → that’s a butan-2-yl group? No — because if you number the side chain starting from attachment point:

C1: CH₂– (attached to Ph)
C2: CH– (with CH₃)
C3: CH₃

So it’s a 1-methylpropyl group? But standard IUPAC: the group is called (2-methylpropyl)? No — wait, let’s count carbons:

Total carbons in side chain: 4 → butyl group.

Branch on carbon 2 → so it’s sec-butyl? But sec-butyl is CH₃CH₂CH(CH₃)– attached at CH.

Here it’s attached at CH₂, so it’s actually isobutyl? Isobutyl is (CH₃)₂CHCH₂– → yes! That’s exactly this: (CH₃)₂CH–CH₂–Ph → but in our case it’s Ph–CH₂–CH(CH₃)CH₃ → same as (CH₃)₂CH–CH₂–Ph → yes!

So it’s isobutylbenzene — but IUPAC prefers systematic name.

Systematic: The side chain is 2-methylpropyl? No — 2-methylpropyl is (CH₃)₂CH–CH₂– → yes, that’s isobutyl.

But IUPAC name for Ph–CH₂–CH(CH₃)CH₃ is (2-methylpropyl)benzene? Wait — no:

If the group is –CH₂–CH(CH₃)CH₃, and we number from attachment:

C1: CH₂–
C2: CH– (with methyl)
C3: CH₃

So the group is butan-2-yl? But butan-2-yl would be CH₃–CH₂–CH(CH₃)– attached at CH.

Here it’s attached at CH₂, so it’s 1-methylpropyl? I think I’m overcomplicating.

Standard way: The compound is 1-phenyl-2-methylpropane? No — because the benzene is the parent.

Better: Name as benzene with substituent.

Substituent: –CH₂–CH(CH₃)CH₃ → this is a butyl group with a methyl on carbon 2, so it’s sec-butyl? But sec-butyl is specifically CH₃CH₂CH(CH₃)– attached at the chiral carbon.

In this case, since it’s attached via the CH₂, it’s actually the isobutyl group.

And isobutylbenzene is acceptable, but IUPAC systematic name is (2-methylpropyl)benzene.

Confirm: 2-methylpropyl group is (CH₃)₂CH–CH₂– → yes, matches.

So name: (2-methylpropyl)benzene

But sometimes written as isobutylbenzene — but for IUPAC, we use (2-methylpropyl)benzene.

Class: Aromatic

7)
Structure: Benzene ring with –C(=O)–O–CH₃ → ester group
This is methyl benzoate? No — the carbonyl is attached directly to benzene, so it’s a benzoate ester.

Specifically: Ph–C(=O)–O–CH₃ → methyl benzoate
Class: Carbonyl (ester)

8)
Structure: CH₃–CH₂–C≡C–CH(CH₃)–CH₃
Triple bond → alkyne
Longest chain: 6 carbons → hexyne
Triple bond between C3 and C4? Let’s number:

If we number from left:
C1: CH₃–
C2: CH₂–
C3: C≡
C4: C–
C5: CH– (with CH₃)
C6: CH₃

So triple bond starts at C3 → 3-hexyne? But there’s a methyl on C5.

Actually, the chain is 6 carbons with triple bond and a methyl branch.

Number to give triple bond lowest numbers.

If we number from right:
C1: CH₃– (from the end)
C2: CH– (with CH₃)
C3: C≡
C4: C–
C5: CH₂–
C6: CH₃

Triple bond between C3 and C4 → still 3-hexyne, but now methyl on C2.

So name: 2-methyl-3-hexyne

Class: Alkyne

9)
Structure: CH₃–CH₂–CH₂–CH₂–CH₂–CH₂–CH₂–CH₃ → octane
Straight chain, 8 carbons → octane
Class: Alkane

10)
Structure: CH₃–CH₂–CH₂–CH₂–CH₂–CH₂–CH₂–OH → 7 carbons with OH at end → 1-heptanol
Class: Alcohol

11)
Structure: CH₃–CH(CH₃)–CH₂–CH₂–CH₂–CH₂–CH₃
Longest chain: 7 carbons → heptane
Methyl on carbon #2 → 2-methylheptane
Class: Alkane

12)
Structure: CH₃–CH₂–CH₂–CH(OH)–CH(CH₃)–CH₂–CH₃
OH group → alcohol
Longest chain: 7 carbons → heptanol
OH on carbon #4? Let’s number:

If we number from left:
C1: CH₃–
C2: CH₂–
C3: CH₂–
C4: CH(OH)–
C5: CH– (with CH₃)
C6: CH₂–
C7: CH₃

OH on C4, methyl on C5.

But we should number to give OH lowest number.

If we number from right:
C1: CH₃– (right end)
C2: CH₂–
C3: CH– (with CH₃)
C4: CH(OH)–
C5: CH₂–
C6: CH₂–
C7: CH₃

OH on C4, methyl on C3.

Same thing — OH is on C4 either way.

But methyl is on C3 if numbered from right, which is lower than C5 from left.

So name: 3-methyl-4-heptanol

Class: Alcohol

13)
Structure: CH₃–CH₂–CH₂–C(CH₃)(CH₃)–CH₂–CH₃
Quaternary carbon with two methyl groups.

Longest chain: 5 carbons? Let’s see:

The central carbon has: CH₃–CH₂–CH₂– (propyl), CH₃, CH₃, and –CH₂–CH₃ (ethyl)

So longest chain is from propyl through central to ethyl: that’s 5 carbons? C1: CH₃– (of propyl), C2: CH₂, C3: CH₂, C4: C (central), C5: CH₂, C6: CH₃ → 6 carbons.

Chain: CH₃–CH₂–CH₂–C(CH₃)₂–CH₂–CH₃ → so it’s 3,3-dimethylhexane? Let’s number.

Longest chain: 6 carbons → hexane

Central carbon is C3 or C4? If we number:

C1: CH₃– (left end of propyl)
C2: CH₂–
C3: CH₂–
C4: C(CH₃)₂–
C5: CH₂–
C6: CH₃

But C4 has two methyl groups, so it’s 4,4-dimethylhexane? But we can number from other end.

Number from right:
C1: CH₃– (right end)
C2: CH₂–
C3: C(CH₃)₂–
C4: CH₂–
C5: CH₂–
C6: CH₃

Same — C3 has two methyls.

So name: 3,3-dimethylhexane

Class: Alkane

14)
Structure: CH₃–CH₂–C(=O)–CH₂–CH₂–CH₂–CH₃
Ketone, carbonyl on C3 if numbered from left.

Longest chain: 7 carbons → heptanone

Carbonyl on C3 → 3-heptanone

Class: Carbonyl (ketone)

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Now, compiling all answers:

1) Aromatic; toluene
2) Alkane; 3-methylhexane
3) Carbonyl; 2-pentanone
4) Alkane; 2,3-dimethylhexane
5) Aromatic; cumene
6) Aromatic; (2-methylpropyl)benzene
7) Carbonyl; methyl benzoate
8) Alkyne; 2-methyl-3-hexyne
9) Alkane; octane
10) Alcohol; 1-heptanol
11) Alkane; 2-methylheptane
12) Alcohol; 3-methyl-4-heptanol
13) Alkane; 3,3-dimethylhexane
14) Carbonyl; 3-heptanone

Note: For #6, some might write "isobutylbenzene", but IUPAC systematic is "(2-methylpropyl)benzene". Similarly, #5 is commonly called cumene, which is acceptable.

Final Answer:
1) Aromatic; toluene
2) Alkane; 3-methylhexane
3) Carbonyl; 2-pentanone
4) Alkane; 2,3-dimethylhexane
5) Aromatic; cumene
6) Aromatic; (2-methylpropyl)benzene
7) Carbonyl; methyl benzoate
8) Alkyne; 2-methyl-3-hexyne
9) Alkane; octane
10) Alcohol; 1-heptanol
11) Alkane; 2-methylheptane
12) Alcohol; 3-methyl-4-heptanol
13) Alkane; 3,3-dimethylhexane
14) Carbonyl; 3-heptanone