ochem 2 lab exam 1

Grignard Reaction**

**Q: What are Grignard reagents, and why are they important?**

**A:** Grignard reagents are organomagnesium compounds used to form carbon-carbon bonds. They are essential for synthesizing alcohols, carboxylic acids, and hydrocarbons due to their strong nucleophilic nature.

**Q: What roles do bromobenzene, magnesium, and diethyl ether play in a Grignard reaction?**

**A:**

- **Bromobenzene**: Forms the phenyl group for the Grignard reagent.

- **Magnesium**: Facilitates the carbon-metal bond formation.

- **Diethyl Ether**: Stabilizes the Grignard reagent and acts as a solvent.

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### **Oxidation and Reduction**

**Q: What is the difference between oxidation and reduction reactions?**

**A:**

- **Oxidation**: Loss of electrons, typically adding oxygen or removing hydrogen.

- **Reduction**: Gain of electrons, typically adding hydrogen or removing oxygen.

**Q: What are the main reagents used in oxidation and reduction reactions in the lab?**

**A:**

- **Oxidation**: Sodium hypochlorite (NaOCl).

- **Reduction**: Sodium borohydride (NaBH₄), with lithium aluminum hydride (LiAlH₄) being a stronger reducing agent.

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### **Kinetic and Thermodynamic Products**

**Q: What is the difference between kinetic products and thermodynamic products?**

**A:**

- **Kinetic Products**: Form quickly with lower activation energy but are less stable.

- **Thermodynamic Products**: Form slowly with higher stability and require higher temperatures.

**Q: Which product, endo or exo, is the major product in a Diels-Alder reaction and why?**

**A:** The **endo product** is the major product because of secondary orbital interactions that stabilize the transition state, following the endo rule.

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### **Diels-Alder Reaction**

**Q: What is the Diels-Alder reaction?**

**A:** It’s a [4+2] cycloaddition reaction between a diene and a dienophile, producing a cyclohexene derivative by forming two new carbon-carbon sigma bonds in a concerted, stereospecific manner.

**Q: Why is the Diels-Alder reaction a syn addition?**

**A:** Because the reaction is concerted, all new bonds are formed on the same face of the reactants, resulting in stereospecificity.

**Q: Does the Diels-Alder reaction have stereoselectivity?**

**A:** Yes, it exhibits high stereoselectivity and regioselectivity due to its concerted mechanism, preserving the stereochemistry of the reactants.

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### **Practical and Theoretical Calculations**

**Q: How do you calculate the theoretical yield of a reaction?**

**A:**

1. Determine moles of the limiting reactant.

2. Use the stoichiometry of the reaction to calculate moles of product.

3. Convert moles of product to grams using molar mass.

**Q: How do you calculate the percent yield of a reaction?**

**A:**

\text{Percent Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100

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### **Lab Techniques and Reagents**

**Q: What is the purpose of glacial acetic acid and anhydrous sodium sulfate in lab reactions?**

**A:**

- **Glacial Acetic Acid**: Enhances reaction efficiency by providing an acidic medium.

- **Anhydrous Sodium Sulfate**: Removes residual water during the workup step.

**Q: How does water affect the melting point of semicarbazones?**

**A:** Water lowers the melting point by introducing impurities, disrupting the crystal lattice structure.