This is a high-weightage concept from alcohols + organometallics.

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General Reaction:

$$\text{Epoxide} + RMgX \xrightarrow{\text{dry ether}} \text{alkoxide} \xrightarrow{H_3O^+} \text{alcohol}$$

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Core Mechanism:

• Grignard reagent (RMgX) behaves like R⁻ (strong nucleophile)
• Attacks epoxide → ring opening (SN2 type)
• Final step: acidic hydrolysis → alcohol

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Golden Rules (VERY IMPORTANT):

Attack Position:

✔ Always attacks LESS substituted carbon (SN2 mechanism)

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Product Type:

✔ Alcohol is formed at the carbon where O⁻ was present
✔ Nature depends on epoxide structure:

• Ethylene oxide → Primary alcohol
• Substituted epoxide → Secondary / tertiary alcohol

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Chain Extension Trick:

✔ Adds +2 carbons (only with ethylene oxide clearly)
✔ With other epoxides → chain increases but depends on structure

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Important Cases:

1. Ethylene Oxide:

$$RMgX \rightarrow R-CH_2-CH_2-OH$$

Always primary alcohol
+2 carbon extension (fixed)

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2. Unsymmetrical Epoxide (e.g., Propylene oxide):

$$RMgX \rightarrow R-CH_2-CH(R’)-OH$$

Attack at less hindered carbon
Usually secondary alcohol

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• JEE/NEET Quick Summary:

✔ RMgX = nucleophile (R⁻)
✔ Epoxide opening = SN2 reaction
✔ Attack = less substituted carbon
✔ Product = alcohol after H₃O⁺

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