Class 10 Organic Chemistry Nomenclature Worksheet with compounds for IUPAC naming practice.

Here is the IUPAC naming for each compound shown in the worksheet, with a clear explanation for each.

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Top Left:

Structure:
`H₃C — CH₂ — CH₂ — CH₃`
→ This is a straight-chain alkane with 4 carbon atoms.

✔ IUPAC Name: Butane

> *Explanation:* For alkanes, the prefix indicates the number of carbons: 1=meth, 2=eth, 3=prop, 4=but. Since it’s saturated and unbranched, it’s simply “butane”.

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Top Right:

Structure:
`H₃C — CH₂ — CH₂ — CH(CH₃) — CH₂ — CH₃`
→ Longest chain has 6 carbons (hexane). There is a methyl group on carbon #3.

✔ IUPAC Name: 3-Methylhexane

> *Explanation:*
- Find longest continuous carbon chain → 6 carbons = hexane.
- Number the chain to give substituent the lowest number → methyl on C3.
- Name: [position]-[substituent][parent chain] → 3-Methylhexane

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Second Row Left:

Structure:
`H₃C — CH₂ — CH=CH — CH₃`
→ 5-carbon chain with a double bond between C3 and C4.

✔ IUPAC Name: Pent-2-ene or 2-Pentene

> *Explanation:*
- Parent chain: 5 carbons = pentane → change suffix to “-ene” for alkene.
- Double bond starts at C2 → so “pent-2-ene”.
- Numbering from left gives double bond at C2–C3; numbering from right would give C3–C4 → we choose lower number → C2.

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Second Row Right:

Structure:
`H₃C — CH=CH — CH(CH₃) — CH₃`
→ 5-carbon chain with double bond and methyl branch.

✔ IUPAC Name: 3-Methylpent-2-ene

> *Explanation:*
- Longest chain including double bond = 5 carbons → pentene.
- Double bond between C2–C3 → so pent-2-ene.
- Methyl group on C3 → so 3-Methylpent-2-ene.
- Note: We number to give double bond lowest numbers first, then substituents.

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Third Row Left:

Structure:
`H₃C — CH₂ — CH₂ — C≡CH`
→ 5-carbon chain with triple bond at end.

✔ IUPAC Name: Pent-1-yne or 1-Pentyne

> *Explanation:*
- Parent chain: 5 carbons → pentane → “-yne” for alkyne.
- Triple bond at C1–C2 → so pent-1-yne.
- Always number to give triple bond lowest possible number.

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Third Row Right:

Structure:
`H₃C — CH₂ — CH(OH) — CH₂ — OH`
→ 4-carbon chain with two OH groups (diol).

✔ IUPAC Name: Butane-1,2-diol

> *Explanation:*
- Parent chain: 4 carbons → butane.
- Two –OH groups at C1 and C2 → suffix “-diol”.
- Position numbers: 1 and 2 → butane-1,2-diol.
- The “e” in butane is retained before “diol” per IUPAC rules.

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Fourth Row Left:

Structure:
```
OH
|
H₃C — C — CH₂ — CH₃
|
OH
```
→ 3-carbon chain with two OH groups on C2.

✔ IUPAC Name: Propane-1,1-diol? Wait — let's check!

Actually, this structure is:

`HO — CH(CH₃) — CH₂ — CH₃`? No — wait, the drawing shows:

Central carbon has:
- One CH₃ (methyl)
- One CH₂CH₃ (ethyl)
- Two OH groups

So the central carbon is bonded to: CH₃, CH₂CH₃, OH, OH → that’s 4 bonds → correct.

Parent chain: longest chain including both OHs → 3 carbons (if we take CH₃–C–CH₂CH₃, that’s 3 carbons total).

But actually, the longest chain is 3 carbons: from ethyl side → C–C–C, with two OHs on middle carbon.

Wait — better way: The central carbon is C2, attached to:
- CH₃ (C1)
- CH₂CH₃ (C3–C4)

So longest chain is 4 carbons: CH₃–C(OH)₂–CH₂–CH₃ → that’s 4 carbons.

✔ Correct IUPAC Name: Butane-2,2-diol

> *Explanation:*
- Longest chain: 4 carbons → butane.
- Two OH groups on C2 → so butane-2,2-diol.
- The central carbon is C2, with two OH groups → geminal diol.

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Fourth Row Right:

Structure:
```
OH CH₂—CH₃
| |
H₃C — CH — CH — CH₂ — CH₃
```
→ 5-carbon chain with OH on C2 and ethyl on C3.

✔ IUPAC Name: 3-Ethylpentan-2-ol

> *Explanation:*
- Longest chain including OH: 5 carbons → pentane → “-ol” for alcohol.
- OH on C2 → pentan-2-ol.
- Ethyl group on C3 → 3-Ethylpentan-2-ol.
- Numbering: OH gets priority → start from left so OH is on C2. Ethyl is then on C3.

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Fifth Row Left:

Structure:
`H₃C — CH₂ — CH₂ — C(=O) — H`
→ 4-carbon aldehyde.

✔ IUPAC Name: Butanal

> *Explanation:*
- Aldehydes: parent chain includes carbonyl carbon.
- 4 carbons → butane → replace “e” with “al” → butanal.
- Carbonyl carbon is always C1 → no need to number.

---

Fifth Row Right:

Structure:
`HC≡C — CH₂ — CH₂ — C(=O) — H`
→ 5-carbon chain with triple bond at C1 and aldehyde at C5.

✔ IUPAC Name: Pent-4-ynal

> *Explanation:*
- Functional group priority: aldehyde > alkyne → so suffix is “-al”.
- Parent chain: 5 carbons → pentane → pentanal.
- Triple bond between C4–C5 → but since aldehyde carbon is C1, we number from aldehyde end:
- C1: CHO
- C2: CH₂
- C3: CH₂
- C4: C≡CH → so triple bond starts at C4 → pent-4-ynal

> ✔ Note: In IUPAC, when multiple functional groups are present, the highest priority group determines the suffix. Aldehyde > alkyne → so “-al” is suffix, “-yne” is infix.

---

Sixth Row Left:

Structure:
```
CH₃
|
H₃C — CH — C(=O) — H
```
→ 3-carbon chain with methyl branch and aldehyde.

✔ IUPAC Name: 2-Methylpropanal

> *Explanation:*
- Parent chain: 3 carbons including carbonyl → propanal.
- Methyl group on C2 → 2-Methylpropanal.
- Numbering: carbonyl is C1, so adjacent carbon is C2 → methyl on C2.

---

Sixth Row Right:

Structure:
`H₃C — CH₂ — CH₂ — CH₂ — C(=O) — H`
→ 5-carbon straight-chain aldehyde.

✔ IUPAC Name: Pentanal

> *Explanation:*
- 5 carbons → pentane → aldehyde → pentanal.
- No branches → straightforward.

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## ✔ Final Answer Summary:

| Compound | IUPAC Name |
|----------|------------------------|
| Top Left | Butane |
| Top Right | 3-Methylhexane |
| 2nd Left | Pent-2-ene |
| 2nd Right | 3-Methylpent-2-ene |
| 3rd Left | Pent-1-yne |
| 3rd Right | Butane-1,2-diol |
| 4th Left | Butane-2,2-diol |
| 4th Right | 3-Ethylpentan-2-ol |
| 5th Left | Butanal |
| 5th Right | Pent-4-ynal |
| 6th Left | 2-Methylpropanal |
| 6th Right | Pentanal |

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