IUPAC nomenclature practice worksheet featuring structural formulas and names of organic compounds.

Here's the IUPAC nomenclature for each compound shown in your worksheet, with a clear explanation for each:

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1. First Compound (already named: butane)

Structural Formula:
H₃C–CH₂–CH₂–CH₃

✔ Name: Butane

Explanation:
This is a straight-chain alkane with 4 carbon atoms. According to IUPAC rules:
- The prefix for 4 carbons is “but-”
- Since it’s an alkane (only single bonds), the suffix is “-ane”
→ Butane

*(You already wrote this correctly!)*

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2. Second Compound

Structural Formula:
A cyclobutane ring with an –OH group attached.

✔ Name: Cyclobutanol

Explanation:
- The parent structure is a 4-membered carbon ring → “cyclobutane”
- The –OH group indicates an alcohol functional group → replace “-e” with “-ol”
- No numbering needed since there’s only one substituent (the OH), so position 1 is implied.
→ Cyclobutanol

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3. Third Compound

Structural Formula:
A benzene ring with a Br (bromine) and an OH (hydroxyl) group attached.

✔ Name: 2-Bromophenol (or *o*-Bromophenol)

Explanation:
- The base structure is a benzene ring with an –OH group → “phenol”
- Bromine is a substituent. In phenol, the carbon with the OH is position 1.
- The Br is adjacent to the OH → position 2
→ 2-Bromophenol

*Note: “ortho-” (o-) is common shorthand for 1,2-substitution on benzene, so “o-bromophenol” is also acceptable, but IUPAC prefers numbered names.*

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4. Fourth Compound

Structural Formula:
A 6-membered ring (cyclohexane) with a ketone (=O) and an ethyl group (–CH₂CH₃) attached.

✔ Name: 2-Ethylcyclohexanone

Explanation:
- Parent chain: cyclohexane ring with a ketone → “cyclohexanone”
- The ketone carbon is position 1 (by priority)
- Ethyl group is attached to carbon #2
→ Numbering starts at the ketone, then goes to give the substituent the lowest number → 2-Ethylcyclohexanone

*(Important: The ketone has higher priority than alkyl groups, so it defines carbon #1.)*

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5. Fifth Compound

Structural Formula:
CH₃–C(=O)–CH(CH₃)–CH₂CH₃
(A ketone with a methyl branch on the alpha carbon)

✔ Name: 3-Methylpentanone — Wait! This is incorrect. Let’s fix it.

Actually, we must number the chain to give the ketone the lowest possible number.

The longest chain including the carbonyl is 5 carbons:
- CH₃–C(=O)–CH(CH₃)–CH₂–CH₃
- Numbering from left: C1=CH₃, C2=C=O, C3=CH(CH₃), C4=CH₂, C5=CH₃ → ketone at C2 → correct
- Methyl group on C3

✔ Correct Name: 3-Methylpentanone? — NO!

IUPAC requires specifying the position of the ketone!

→ The correct name is: 3-Methyl-2-pentanone

Explanation:
- Longest continuous chain including the carbonyl = 5 carbons → “pentane”
- Ketone functional group → change “-e” to “-one”, and indicate its position → “2-pentanone”
- Methyl group on carbon 3 → “3-methyl”
→ 3-Methyl-2-pentanone

*(Note: You cannot omit the ketone position if it’s not at the end — here it’s at C2, which is necessary to specify.)*

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6. Sixth Compound

Structural Formula:
H–C(=O)–CH₂–CH₂–CH₃
(Aldehyde with 4 carbons total)

✔ Name: Butanal

Explanation:
- Aldehydes have the –CHO group, which must be at carbon 1
- Longest chain = 4 carbons → “butane”
- Change “-e” to “-al” for aldehyde → Butanal

*(Note: No number needed for aldehyde since CHO is always at C1.)*

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## ✔ Final Answer Table:

| Name | Structural Formula (as given) |
|-----------------------|-------------------------------------|
| Butane | H₃C–CH₂–CH₂–CH₃ |
| Cyclobutanol | Cyclobutane with –OH |
| 2-Bromophenol | Benzene with Br and OH (adjacent) |
| 2-Ethylcyclohexanone | Cyclohexanone with ethyl at C2 |
| 3-Methyl-2-pentanone | Ketone with methyl on C3 |
| Butanal | H–C(=O)–CH₂–CH₂–CH₃ |

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Let me know if you’d like drawn structures or further clarification on any naming rule!