Alkyl halides are formed when thionyl chloride and _____ are refluxed in presence of pyridine. The order of reactivity `(3^(@)gt2^(@)gt1^(@))` is due to +1 effect of the alkyl group which____ the polarity of C-X bond.

Options

A. acids, decreases
B. alcohols, increases
C. aldehydes, changes
D. ketones, decreases

Answer

To solve the given question step by step, we need to fill in the blanks and understand the concepts involved.

### Step 1: Identify the reactants
The question states that alkyl halides are formed when thionyl chloride is refluxed with another compound in the presence of pyridine. The common reactant that reacts with thionyl chloride to form alkyl halides is **alcohol**.

**Hint:** Think about common reactions involving thionyl chloride and what it typically reacts with to form alkyl halides.

### Step 2: Write the reaction
When alcohol (ROH) reacts with thionyl chloride (SOCl2), the reaction can be represented as follows:
\[ \text{ROH} + \text{SOCl}_2 \rightarrow \text{RCl} + \text{SO}_2 + \text{HCl} \]
This shows that alcohol is converted into alkyl halide (RCl), along with the byproducts sulfur dioxide (SO2) and hydrogen chloride (HCl).

**Hint:** Recall the products formed when alcohol reacts with thionyl chloride.

### Step 3: Understand the order of reactivity
The question mentions an order of reactivity: \(3^\circ > 2^\circ > 1^\circ\). This order indicates that tertiary alkyl halides are more reactive than secondary, which are more reactive than primary. This is due to the +I (positive inductive) effect of alkyl groups.

**Hint:** Consider how the structure of alkyl groups affects the stability of the carbocation formed during the reaction.

### Step 4: Explain the +I effect
The +I effect refers to the electron-donating nature of alkyl groups. When an alkyl group is attached to a carbon atom bonded to a halogen (C-X bond), it increases the electron density around the carbon atom. This effect enhances the polarity of the C-X bond, making it easier for the bond to break during the reaction.

**Hint:** Think about how electron-donating groups influence the stability of bonds and the reactivity of compounds.

### Step 5: Fill in the second blank
The second blank in the question states that the +I effect of the alkyl group ______ the polarity of the C-X bond. Since the +I effect increases the electron density, it actually **increases** the polarity of the C-X bond.

**Final Answer:**
Alkyl halides are formed when thionyl chloride and **alcohol** are refluxed in the presence of pyridine. The order of reactivity \(3^\circ > 2^\circ > 1^\circ\) is due to the +I effect of the alkyl group which **increases** the polarity of the C-X bond.

### Summary of Answers:
1. First blank: **alcohol**
2. Second blank: **increases**