Solved Worksheet: Identifying Isomers 1. For each pair of | Chegg.com - Free Printable

Let's analyze each structure one by one to determine whether it is cis, trans, cis/trans does not apply, or cis/trans may apply, but cannot be determined from info given.

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Rules for cis/trans isomerism:

- Cis/trans isomerism (geometric isomerism) occurs in alkenes when each carbon of the double bond has two different groups attached.
- If both carbons of the double bond have two identical groups, then cis/trans does not apply.
- If one carbon has two identical groups, then cis/trans does not apply.
- If both carbons have two different substituents, then cis/trans may apply.
- Cis: similar groups are on the same side of the double bond.
- Trans: similar groups are on opposite sides.
- In some cases, if the stereochemistry isn't shown (e.g., no wedges/dashes), we cannot determine if it’s cis or trans — so the answer would be "cannot be determined".

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Now let's go through each molecule:

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1.

```
CH₃
\
C = C
/ \
H CH₂CH₃
```

This is:
CH₃–C(H)=C(CH₂CH₃)–H → Actually, better written as:
CH₃–C(H)=C(H)–CH₂CH₃

Wait — the carbon on the left has:
- CH₃ and H
- The right carbon has: H and CH₂CH₃

So both carbons of the double bond have two different groups:
- Left: CH₃ and H
- Right: H and CH₂CH₃

→ So cis/trans applies.

But no stereochemistry is indicated (no wedges/dashes). So we don’t know if the H atoms are on the same side or opposite.

✔ Answer: cis/trans may apply, but cannot be determined from info given

---

2.

```
CH₃
\
C = C
/ \
CH₃ CH₃
```

Structure: (CH₃)₂C=C(CH₃)₂

Each carbon of the double bond has two methyl groups.

So both carbons have identical substituents (two CH₃ groups).

→ No geometric isomerism possible.

✔ Answer: cis/trans does not apply

---

3.

```
CH₃
|
CH₂–CH₂
|
CH₃
```

This is a saturated compound — no double bond!

It’s butane with a methyl group on carbon 2, i.e., 2-methylbutane.

No double bond → no cis/trans isomerism.

✔ Answer: cis/trans does not apply

---

4.

```
CH₃–CH₂–CH=CH–CH₂–CH₃
```

This is hex-3-ene.

The double bond is between C3 and C4.

- C3: attached to CH₂CH₃ and H
- C4: attached to CH₂CH₃ and H

So both carbons have: H and CH₂CH₃

→ Both carbons have two different groups, so cis/trans applies.

But again, no stereochemistry is shown (no wedges/dashes).

So we cannot determine if it's cis or trans.

✔ Answer: cis/trans may apply, but cannot be determined from info given

---

5.

```
CH₃
|
CH₃–CH₂–C=C–H
|
H
```

Better written as:
CH₃–CH₂–C(CH₃)=CH₂ → Wait, no.

Actually:
Left carbon of double bond: bonded to CH₃–CH₂– and CH₃ (and double bond)

So:
- Left carbon: CH₃CH₂– and CH₃
- Right carbon: H and H? Wait, no.

Look at the drawing:

```
CH₃
|
CH₃–CH₂–C=C–H
|
H
```

So the double bond is between the carbon with CH₃CH₂ and CH₃, and the carbon with H and H?

Wait — that can't be.

Let me interpret carefully.

The carbon on the left of the double bond is attached to:
- CH₃–CH₂– (ethyl)
- CH₃ (methyl)
- Double bond to next carbon

So it has two alkyl groups: ethyl and methyl → so two different groups

The right carbon of the double bond is attached to:
- H
- H? No — the drawing shows:
- One bond to H (written as –H)
- One bond down to H (written below)
- And double bond

Wait — this is confusing.

Actually, the structure is:

```
CH₃
|
CH₃–CH₂–C = C–H
|
H
```

So the right carbon has two hydrogens? That would make it: –CH₂–, but it's part of a double bond.

If the right carbon has two H atoms, then it's CH₂ group.

So the double bond is:
R–C(CH₃)(CH₂CH₃)=CH₂

So:
- Left carbon: CH₃CH₂– and CH₃ → two different groups
- Right carbon: H and H → two identical groups

→ Since one carbon has two identical groups (H and H), cis/trans isomerism does NOT apply.

Even though the other carbon has two different groups, if one carbon has two identical substituents, there is no geometric isomerism.

✔ Answer: cis/trans does not apply

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6.

```
CH₃–CH₂–CH₂–C=C–CH₂–CH₃
| |
CH₃ H
```

Double bond between two carbons:
- Left carbon: bonded to CH₃CH₂CH₂– and CH₃
- Right carbon: bonded to CH₂CH₃ and H

So:
- Left carbon: two different groups → ethylpropyl and methyl
- Right carbon: CH₂CH₃ and H → two different groups

So both carbons have two different substituents → cis/trans applies

But no stereochemistry is shown (no wedges/dashes), so we cannot determine if it's cis or trans.

✔ Answer: cis/trans may apply, but cannot be determined from info given

---

7.

```
cyclohexyl
\
C=C
/
propyl
```

More precisely: cyclohexylidene-propylalkene?

Wait — it's drawn as:

A cyclohexyl ring connected to a double bond, which connects to a three-carbon chain.

So it's: cyclohexyl–CH=CH–CH₂–CH₂–CH₃

Wait — actually, the double bond is between two sp² carbons, one attached to cyclohexyl, one to propyl.

But the structure shows:

```
cyclohexyl
\
C=C
/
CH₂CH₂CH₃
```

And the double bond has no indication of stereochemistry.

So the two carbons of the double bond:
- Left: bonded to cyclohexyl and H (assumed)
- Right: bonded to CH₂CH₂CH₃ and H

So both carbons have two different groups:
- Left: cyclohexyl and H
- Right: propyl and H

→ So cis/trans is possible

But no stereochemistry shown → cannot tell if cis or trans.

✔ Answer: cis/trans may apply, but cannot be determined from info given

---

8.

```
CH₃–CH₂–CH₂–CH₂–CH₂–CH₃
```

This is hexane, a straight-chain alkane.

No double bond → no cis/trans isomerism

✔ Answer: cis/trans does not apply

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✔ Final Answers:

| Structure | Classification |
|---------|----------------|
| 1. CH₃–C(H)=C(H)–CH₂CH₃ | cis/trans may apply, but cannot be determined from info given |
| 2. (CH₃)₂C=C(CH₃)₂ | cis/trans does not apply |
| 3. CH₃–CH₂–CH(CH₃)–CH₃ | cis/trans does not apply |
| 4. CH₃CH₂CH=CHCH₂CH₃ | cis/trans may apply, but cannot be determined from info given |
| 5. CH₃CH₂C(CH₃)=CH₂ | cis/trans does not apply |
| 6. CH₃CH₂CH₂C(CH₃)=CHCH₂CH₃ | cis/trans may apply, but cannot be determined from info given |
| 7. Cyclohexyl–CH=CH–CH₂CH₂CH₃ | cis/trans may apply, but cannot be determined from info given |
| 8. CH₃(CH₂)₄CH₃ | cis/trans does not apply |

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Summary:

- cis/trans does not apply: Structures 2, 3, 5, 8
- cis/trans may apply, but cannot be determined: Structures 1, 4, 6, 7

✔ All classifications based on presence of double bond and substituent diversity, and lack of stereochemical indication.