What are the reactive species involved in `S_(N^1)` reactions ?

Explanation

To answer the question about the reactive species involved in SN1 reactions, we can break it down into a step-by-step explanation.

### Step-by-Step Solution:

1. **Understanding SN1 Reaction**:
- SN1 stands for unimolecular nucleophilic substitution. It involves two main steps: the formation of a carbocation and the nucleophilic attack.

2. **Formation of the Carbocation**:
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