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Experiment 8 - Hydroboration Introduction A reaction mechanism is the step-by-step description of how a reaction actually occurs. Even though we often draw reactions as just starting materials and products, the process is much more complicated. Reactions mechanisms are one of the most important parts of organic chemistry because they help to explain why reactions occur in the way that they do. Additionally, they can often help us to find answers when reactions do not work in the way that we expect them to. There are numerous methods of probing the mechanism of a reaction, however we will be using some familiar techniques in this experiment. In this experiment, you will be exploring the hydroboration reaction and analyzing the results to verify some of mechanistic information presented in the lecture portion of this course. In this experiment you will be running a hydroboration in order to explore the regiochemical and stereochemical outcome of the reaction. Other hydration reactions of alkenes that we have learned (e.g. acid catalyzed and oxymercuration) often give the Markovnikov (the hydrogen adds to the less substituted carbon and the X group adds to the more substituted carbon) addition product. 3 H₂O*, H₂O, heat or 1. Hg(OAc)2, H₂O 2. NaBH4 However, we have learned that the hydroboration reaction class gives a product based on steric effects. This means that the hydroboration reaction generally yields the anti-Markovnikov addition product. In the case of 1-methyl-1-cyclohexene, this can be easily tested as the three possible products can be easily differentiated on the basis of the fingerprint regions of their infrared spectra. There are three possible products from this experiment: the Markovnikov addition product (1- methylcyclohexanol), and the two anti-Markovnikov addition products ((1S,2R)-2-methyl-1- cyclohexanol and (1R,2R)-2-methyl-1-cyclohexanol). Upon isolation of the product, you will be able to identify the regiochemistry of the product as well as the stereochemistry based on the infrared spectrum. 1. BH 3 THF 2. H₂O₂, NaOH 1-methyl-1-cyclohexene 3 OH OH or 3 OH or 3 OH

Experiment 8 - Hydroboration Introduction A reaction mechanism is the step-by-step description of how a reaction actually occurs. Even though we often draw reactions as just starting materials and products, the process is much more complicated. Reactions mechanisms are one of the most important parts of organic chemistry because they help to explain why reactions occur in the way that they do. Additionally, they can often help us to find answers when reactions do not work in the way that we expect them to. There are numerous methods of probing the mechanism of a reaction, however we will be using some familiar techniques in this experiment. In this experiment, you will be exploring the hydroboration reaction and analyzing the results to verify some of mechanistic information presented in the lecture portion of this course. In this experiment you will be running a hydroboration in order to explore the regiochemical and stereochemical outcome of the reaction. Other hydration reactions of alkenes that we have learned (e.g. acid catalyzed and oxymercuration) often give the Markovnikov (the hydrogen adds to the less substituted carbon and the X group adds to the more substituted carbon) addition product. 3 H₂O*, H₂O, heat or 1. Hg(OAc)2, H₂O 2. NaBH4 However, we have learned that the hydroboration reaction class gives a product based on steric effects. This means that the hydroboration reaction generally yields the anti-Markovnikov addition product. In the case of 1-methyl-1-cyclohexene, this can be easily tested as the three possible products can be easily differentiated on the basis of the fingerprint regions of their infrared spectra. There are three possible products from this experiment: the Markovnikov addition product (1- methylcyclohexanol), and the two anti-Markovnikov addition products ((1S,2R)-2-methyl-1- cyclohexanol and (1R,2R)-2-methyl-1-cyclohexanol). Upon isolation of the product, you will be able to identify the regiochemistry of the product as well as the stereochemistry based on the infrared spectrum. 1. BH 3 THF 2. H₂O₂, NaOH 1-methyl-1-cyclohexene 3 OH OH or 3 OH or 3 OH

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**Experiment 8 – Hydroboration** **Introduction** A reaction mechanism is the step-by-step description of how a reaction actually occurs. Even though we often draw reactions as just starting materials and products, the process is much more complicated. Reaction mechanisms are one of the most important parts of organic chemistry because they help to explain why reactions occur in the way that they do. Additionally, they can often help us to find answers when reactions do not work in the way that we expect them to. There are numerous methods of probing the mechanism of a reaction, however we will be using some familiar techniques in this experiment. In this experiment, you will be exploring the hydroboration reaction and analyzing the results to verify some of the mechanistic information presented in the lecture portion of this course. In this experiment, you will be running a hydroboration in order to explore the regiochemical and stereochemical outcome of the reaction. Other hydration reactions of alkenes that we have learned (e.g. acid catalyzed and oxymercuration) often give the Markovnikov (the hydrogen adds to the less substituted carbon and the X group adds to the more substituted carbon) addition product. \[ \text{H}_3\text{O}^+, \text{H}_2\text{O, heat} \] or \[ \text{1. Hg(OAc)}_2 , \text{H}_2\text{O} \] \[ \text{2. NaBH}_4 \] However, we have learned that the hydroboration reaction class gives a product based on steric effects. This means that the hydroboration reaction generally yields the anti-Markovnikov addition product. In the case of 1-methyl-1-cyclohexene, this can be easily tested as the three possible products can be easily differentiated on the basis of the fingerprint regions of their infrared spectra. There are three possible products from this experiment: the Markovnikov addition product (1-methylcyclohexanol), and the two anti-Markovnikov addition products ((1S,2R)-2-methyl-1-cyclohexanol and (1R,2R)-2-methyl-1-cyclohexanol). Upon isolation of the product, you will be able to identify the regiochemistry of the product as well as the stereochemistry based on the infrared spectrum. **Diagram Explanation** The diagram illustrates the hydroboration reaction process
Transcribed Image Text:**Experiment 8 – Hydroboration** **Introduction** A reaction mechanism is the step-by-step description of how a reaction actually occurs. Even though we often draw reactions as just starting materials and products, the process is much more complicated. Reaction mechanisms are one of the most important parts of organic chemistry because they help to explain why reactions occur in the way that they do. Additionally, they can often help us to find answers when reactions do not work in the way that we expect them to. There are numerous methods of probing the mechanism of a reaction, however we will be using some familiar techniques in this experiment. In this experiment, you will be exploring the hydroboration reaction and analyzing the results to verify some of the mechanistic information presented in the lecture portion of this course. In this experiment, you will be running a hydroboration in order to explore the regiochemical and stereochemical outcome of the reaction. Other hydration reactions of alkenes that we have learned (e.g. acid catalyzed and oxymercuration) often give the Markovnikov (the hydrogen adds to the less substituted carbon and the X group adds to the more substituted carbon) addition product. \[ \text{H}_3\text{O}^+, \text{H}_2\text{O, heat} \] or \[ \text{1. Hg(OAc)}_2 , \text{H}_2\text{O} \] \[ \text{2. NaBH}_4 \] However, we have learned that the hydroboration reaction class gives a product based on steric effects. This means that the hydroboration reaction generally yields the anti-Markovnikov addition product. In the case of 1-methyl-1-cyclohexene, this can be easily tested as the three possible products can be easily differentiated on the basis of the fingerprint regions of their infrared spectra. There are three possible products from this experiment: the Markovnikov addition product (1-methylcyclohexanol), and the two anti-Markovnikov addition products ((1S,2R)-2-methyl-1-cyclohexanol and (1R,2R)-2-methyl-1-cyclohexanol). Upon isolation of the product, you will be able to identify the regiochemistry of the product as well as the stereochemistry based on the infrared spectrum. **Diagram Explanation** The diagram illustrates the hydroboration reaction process
**Procedure** 1. In a clean, dry test tube, add 0.5 mL of 1-methyl-1-cyclohexene and a stir bar. Place a stopper in the test tube and move the test tube to an ice bath. Bring your test tube and ice bath to the hood and add 2.5 mL of 1 M BH₃:THF solution via syringe. Record your test tube and warm the solution to room temperature by removing the ice bath. Allow the reaction solution to stir for 45 minutes. During this time, you should heat a water bath to 50 – 60 °C in preparation for the second part of the reaction. 2. After 45 minutes have elapsed, cool the reaction mixture to 0 °C by placing it on ice for 5 minutes in the hood and add 10 – 15 drops of water slowly. **This should be done cautiously as hydrogen gas will be evolved during this step.** The test tube should remain uncorked for the remainder of the experiment. Next, add 0.7 mL of 3 M NaOH followed by 1 mL of 30% H₂O₂. Heat the reaction mixture at 50 – 60 °C for 20 minutes with stirring and then cool the reaction solution to room temperature. Your reaction solution should now contain 2 layers (If THF is your organic solvent, which layer will be on top?). 3. Place the reaction contents in a separatory funnel and add 2 mL of brine. Drain the aqueous layer out (bottom layer) and place the top organic layer into a clean and dry Erlenmeyer flask. Return the aqueous to the separatory funnel and add 3 mL of ether, mix the contents of the funnel and combine the top organic layer with the organic layer that was previously collected. Dry the organic layers over MgSO₄ (magnesium sulfate works in the exact same way that sodium sulfate works). 4. Pass this solution through a 3 cm column of silica gel/AgNO₃ (the column should be wet first with ether and then the level of solvent should be drained to the top of the silica gel). Once all of the ether solution (your dried solution from the previous step) has penetrated the column add CH₂Cl₂ as the eluent (5 mL total), and collect all of the solution in a preweighed
Transcribed Image Text:**Procedure** 1. In a clean, dry test tube, add 0.5 mL of 1-methyl-1-cyclohexene and a stir bar. Place a stopper in the test tube and move the test tube to an ice bath. Bring your test tube and ice bath to the hood and add 2.5 mL of 1 M BH₃:THF solution via syringe. Record your test tube and warm the solution to room temperature by removing the ice bath. Allow the reaction solution to stir for 45 minutes. During this time, you should heat a water bath to 50 – 60 °C in preparation for the second part of the reaction. 2. After 45 minutes have elapsed, cool the reaction mixture to 0 °C by placing it on ice for 5 minutes in the hood and add 10 – 15 drops of water slowly. **This should be done cautiously as hydrogen gas will be evolved during this step.** The test tube should remain uncorked for the remainder of the experiment. Next, add 0.7 mL of 3 M NaOH followed by 1 mL of 30% H₂O₂. Heat the reaction mixture at 50 – 60 °C for 20 minutes with stirring and then cool the reaction solution to room temperature. Your reaction solution should now contain 2 layers (If THF is your organic solvent, which layer will be on top?). 3. Place the reaction contents in a separatory funnel and add 2 mL of brine. Drain the aqueous layer out (bottom layer) and place the top organic layer into a clean and dry Erlenmeyer flask. Return the aqueous to the separatory funnel and add 3 mL of ether, mix the contents of the funnel and combine the top organic layer with the organic layer that was previously collected. Dry the organic layers over MgSO₄ (magnesium sulfate works in the exact same way that sodium sulfate works). 4. Pass this solution through a 3 cm column of silica gel/AgNO₃ (the column should be wet first with ether and then the level of solvent should be drained to the top of the silica gel). Once all of the ether solution (your dried solution from the previous step) has penetrated the column add CH₂Cl₂ as the eluent (5 mL total), and collect all of the solution in a preweighed
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