Draw all structurally isomeric alkenes with molecular formula `C_(4)H_(8)`

Answer

To find all structurally isomeric alkenes with the molecular formula C4H8, we will follow these steps:

### Step 1: Identify the General Structure of Alkenes
Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). The general formula for alkenes is CnH2n, which fits our molecular formula C4H8 (where n=4).

### Step 2: Determine the Possible Carbon Skeletons
For C4H8, we can have straight-chain and branched-chain alkenes. The main carbon skeletons we can consider are:
1. Straight-chain (butene)
2. Branched-chain (isobutylene)

### Step 3: Draw the Straight-Chain Alkenes
1. **1-Butene**:
- Structure: CH2=CH-CH2-CH3
- Description: The double bond is between the first and second carbon atoms.

2. **2-Butene**:
- Structure: CH3-CH=CH-CH3
- Description: The double bond is between the second and third carbon atoms. This can exist in two geometric isomers:
- **Cis-2-butene**: Both methyl groups (CH3) are on the same side of the double bond.
- **Trans-2-butene**: The methyl groups are on opposite sides of the double bond.

### Step 4: Draw the Branched-Chain Alkene
3. **Isobutylene (or 2-Methylpropene)**:
- Structure: CH2=C(CH3)-CH3
- Description: The double bond is between the first carbon and the second carbon, with a methyl group branching off the second carbon.

### Summary of Isomeric Alkenes
1. **1-Butene** (CH2=CH-CH2-CH3)
2. **Cis-2-Butene** (CH3-CH=CH-CH3)
3. **Trans-2-Butene** (CH3-CH=CH-CH3)
4. **Isobutylene (2-Methylpropene)** (CH2=C(CH3)-CH3)

### Final Note
Cyclic compounds like cyclobutane and methylcyclopropane were mentioned but are not alkenes, as they do not contain a C=C double bond.