Identify Z in the following reaction sequence
`C_(2)H_(5)Ioverset(alc.KOH)toXoverset(Br_(2))toYoverset(KCN)toZ`

Options

A. `Br-CH_(2)-CH_(2)-CN`
B. `CH_(3)CH_(2)-CN`
C. `CN-CH_(2)-CH_(2)-CN`
D. BrCH = CHCN

Explanation

To identify the compound Z in the given reaction sequence, we will follow the steps outlined in the video transcript. Let's break it down step by step.

### Step 1: Reaction of C₂H₅I with Alcoholic KOH
- **Starting Material:** Ethyl iodide (C₂H₅I)
- **Reagent:** Alcoholic KOH
- **Reaction Type:** Elimination reaction (dehydrohalogenation)

In this step, the alcoholic KOH acts as a base and removes a hydrogen atom from the ethyl iodide, leading to the formation of an alkene. The reaction can be represented as follows:

\[ C_2H_5I + alc.KOH \rightarrow C_2H_4 + HI \]

**Product X:** Ethylene (C₂H₄)

### Step 2: Reaction of X (C₂H₄) with Br₂
- **Starting Material:** Ethylene (C₂H₄)
- **Reagent:** Bromine (Br₂)
- **Reaction Type:** Electrophilic addition

When ethylene reacts with bromine, a bromonium ion intermediate is formed, followed by the attack of bromide ion on the more substituted carbon. The reaction can be represented as follows:

\[ C_2H_4 + Br_2 \rightarrow C_2H_4Br_2 \]

**Product Y:** 1,2-Dibromoethane (C₂H₄Br₂)

### Step 3: Reaction of Y (C₂H₄Br₂) with KCN
- **Starting Material:** 1,2-Dibromoethane (C₂H₄Br₂)
- **Reagent:** Potassium cyanide (KCN)
- **Reaction Type:** Nucleophilic substitution (SN2 mechanism)

In this step, the cyanide ion (CN⁻) acts as a nucleophile and attacks the carbon atom bonded to bromine, leading to the substitution of bromine with the cyanide group. Since there are two bromine atoms, two moles of KCN will react:

\[ C_2H_4Br_2 + 2 KCN \rightarrow C_2H_4(CN)_2 + 2 KBr \]

**Product Z:** 1,2-Dicyanoethane (C₂H₄(CN)₂)

### Final Answer:
**Z is 1,2-Dicyanoethane (C₂H₄(CN)₂)**

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