Organic Chemistry interactive worksheet - Free Printable

Let's solve this step by step. The task is to identify the circled functional groups in each of the three molecules shown.

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1. First Molecule

Here are the circled parts and their functional group identities:

#### a) HO–C(=O)–CH₂
- This is a carboxylic acid group: `–COOH`
→ Carboxylic acid

#### b) –C(=O)–NH–
- A carbonyl (C=O) bonded to a nitrogen (N): `–CONH–`
→ Amide

#### c) Aromatic ring (benzene)
- Six-membered ring with alternating double bonds
→ Aromatic (or benzene ring)

#### d) –C(=O)–O–CH₃
- Carbonyl (C=O) bonded to an oxygen that is bonded to a methyl group: `–COOR`
→ Ester

#### e) –NH₂
- Nitrogen bonded to two hydrogens
→ Amino group

#### f) –CH₂– attached to aromatic ring
- This is just a methylene group, but since it’s connected to a benzene ring, it's part of a benzyl group. However, the functional group here is not significant, but if we're focusing on what's circled — the circle includes the benzene ring, so we already identified it above.

But wait — let's recheck: there are six circles in total.

Let’s label them clearly:

1. Leftmost: HO–C(=O)– → Carboxylic acid
2. Middle top: –C(=O)–NH– → Amide
3. Top right: Benzene ring → Aromatic ring
4. Right side: –C(=O)–O–CH₃ → Ester
5. Bottom left: –NH₂ → Amino group
6. Center CH₂? Wait — no, the sixth circle is around the –CH– carbon with H and N, but it's not a functional group. Wait — actually, the fifth circle is H₂N, and the sixth is the ester.

Wait — looking carefully:

- There are five red circles:
1. HO–C(=O)–CH₂ → Carboxylic acid
2. –C(=O)–NH– → Amide
3. Benzene ring → Aromatic ring
4. –C(=O)–O–CH₃ → Ester
5. –NH₂ → Amino group

So five functional groups.

✔ Final Answer for #1:
- Carboxylic acid
- Amide
- Aromatic ring
- Ester
- Amino group

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2. Second Molecule

This molecule has two circled groups:

#### a) –OH group attached to a benzene ring
- Hydroxyl group directly bonded to an aromatic ring → Phenol

#### b) Oxygen bridging two rings
- The structure shows a six-membered ring with O in the ring, forming a dioxane-like or tetrahydropyran ring, but more importantly, the oxygen is part of an ether linkage between two carbon atoms.
- Specifically, it's an oxygen atom connecting two carbon atoms → Ether

Also note: the ring with O is a cyclic ether, but the functional group is still ether.

✔ Final Answer for #2:
- Phenol
- Ether

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3. Third Molecule

This one has four circles:

#### a) Methoxy group (–OCH₃) attached to benzene ring
- Oxygen bonded to methyl group and aromatic ring → Alkoxy group (specifically methoxy), which is a type of ether

→ Ether (or methoxy group)

#### b) –NH– group attached to benzene ring and a double bond
- Nitrogen bonded to hydrogen and two carbons → Amine, but specifically, since it's attached to a benzene ring and a carbon chain, and the circle is around the –NH–
→ Amine (more precisely, secondary amine)

But also, look at the double bond adjacent to the NH — that suggests an imidazole-like structure?

Wait — actually, the circled N–H is part of a pyrrole-like or indole-like ring system.

The structure shows a benzene ring fused to a five-membered ring with N and double bonds.

This looks like indole or tryptamine derivative.

But let’s focus on the circles:

1. CH₃O– attached to benzene ring → Methoxy group → Ether
2. N–H in a five-membered ring with double bonds → This is a pyrrole-type nitrogen → Amine (specifically aromatic amine, or secondary amine)
3. Double bond in the five-membered ring → Alkene (but it's part of an aromatic system — actually, the ring is aromatic, so it's a conjugated double bond in a heterocycle)
- But since it's circled separately, likely alkene or aromatic system
- However, in context, this is part of indole, so it's aromatic.
- But the circle is around the double bond, so → Alkene (though aromatic)

Better interpretation: the circle around the double bond is highlighting a carbon-carbon double bond, so → Alkene

4. –NH–C(=O)– → Amide (since it's –NH–C=O)

So the four circles:

1. –OCH₃ → Ether (or alkoxy)
2. –NH– → Amine
3. C=C double bond → Alkene
4. –NH–C(=O)– → Amide

But wait — the fourth circle is around –NH–C(=O)–, which is amide

And the third circle is around the double bond in the five-membered ring — yes, it's a double bond, so alkene

But in reality, the five-membered ring is aromatic (like indole), so the double bond is part of an aromatic system, but functionally, it's still considered alkene unless specified otherwise.

However, in organic chemistry, such systems are often classified as aromatic.

But the question asks for functional groups, so:

- Alkene is acceptable
- Or aromatic?

But the aromatic ring is already implied in the benzene ring.

But the circle is only around the double bond, so likely alkene

Alternatively, the five-membered ring may be considered heteroaromatic, but again, the circle is small.

Let’s assume the circled parts are:

1. CH₃O– → Ether
2. N–H → Amine
3. C=C → Alkene
4. –NH–C(=O)– → Amide

But wait — the fourth circle is around –NH–C(=O)–, which is amide

Yes.

But the third circle is around the double bond, which is alkene

So final list:

✔ For #3:
- Ether (methoxy)
- Amine (secondary amine)
- Alkene
- Amide

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✔ Final Answers:

#### 1.
- Carboxylic acid
- Amide
- Aromatic ring
- Ester
- Amino group

#### 2.
- Phenol
- Ether

#### 3.
- Ether (or methoxy)
- Amine
- Alkene
- Amide

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Summary Table:

| Problem | Functional Group |
|--------|------------------|
| 1 | Carboxylic acid, Amide, Aromatic ring, Ester, Amino group |
| 2 | Phenol, Ether |
| 3 | Ether, Amine, Alkene, Amide |

You can now fill in the blanks accordingly on the worksheet.