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Organic Chemistry I - Summary of Preparations

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    Study Guide Organic Chemistry I – Summary of Preparations 1. Preparations : Alkenes Alkenes can be prepared using different reactions. Let’s look at three main methods : 1. Dehydrohalogenation of Alkyl Halides • What happens? In this reaction, an alkyl halide (a molecule with a halogen atom attached to a carbon chain) undergoes elimination of a hydrogen atom and a halide ion (X). • What’s used? A strong base like KOH in alcohol is used under heat. • Reaction : 2. Dehydration of Alcohols • What happens? In a dehydration reaction, an alcohol loses a water molecule , forming a double bond between the carbon atoms. • What’s used? This reaction requires concentrated sulfuric acid (H ₂ SO ₄ ) and heat. • Reaction :

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    Study Guide 3. Dehalogenation of Vicinal Dihalides • What happens? When a vicinal dihalide (a molecule with two halogen atoms on adjacent carbon atoms ) is treated with zinc (Zn), the halogen atoms are removed, and a double bond forms between the two carbon atoms. • What’s used? Zinc (Zn) is the key reagent for this reaction. • Reaction : Key Takeaway s • Dehydrohalogenation : Alkyl halides lose hydrogen and halide to form alkenes, using a strong base like KOH . • Dehydration of alcohols : Alcohols lose water to form a double bond with the help of H ₂ SO ₄ and heat. • Dehalogenation : Vicinal dihalides lose halogens (usually via zinc ) to form alkenes. 2. Preparations : Alkynes Alkynes, like alkenes, can be prepared using a variety of reactions. Below are three common methods for preparing alkynes: 1. Dehydrohalogenation of Vicinal Dihalides • What happens?

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    Study Guide A vicinal dihalide (a molecule with two halogen atoms on adjacent carbon atoms ) undergoes elimination of hydrogen and halide ions to form an alkyne (a molecule with a triple bond between two carbon atoms). • What’s used? A strong base like KOH in alcohol, heated under strong conditions . • Reaction : 2. Dehydrohalogenation of Geminal Dihalides • What happens? In this reaction, a geminal dihalide (where both halogens are on the same carbon ) undergoes elimination of hydrogen and halide ions to form an alkyne. • What’s used? KOH in alcohol, with heat. • Reaction : 3. Dehalogenation of Vicinal Tetrahaloalkanes • What happens? A vicinal tetrahaloalkane (with four halogens on adjacent carbon atoms ) undergoes dehalogenation , where the halogens are replaced by hydrogen atoms, leading to the formation of an alkyne.

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