Student Name: Aleycna Jerame APPLY Experiment 15: Nucleophilic Substitution Reactions Questions - Please answer the following questions. Limited partial credit will be given for the questions. 1. Usually, bimolecular nucleophilic substitution \( \left(\mathrm{S}_{\mathrm{N}} 2\right) \) reactions occur under basic conditions. The \( \mathrm{S}_{\mathrm{N}} 2 \) reaction of 1-butanol by a halide ion is a rare example of a \( \mathrm{S}_{\mathrm{N}} 2 \) reaction under acidic conditions. Of course, halide ions were not the only nucleophiles in your reaction medium. Draw the acidcatalyzed \( \mathrm{S}_{\mathrm{N}} 2 \) reaction mechans molecules of 1-butanol. dibutyl ether from two molecules of 1-butanol. 2. Explain the difference in boiling point between the isomers 1-chlorobutane and 2-methyl-2chloropropane in terms of structure. Since 1-chlorobutane has stranger intermolccular forces, it requires more energy to overcome these farces 1 transition into the gaseous phese Also 1-chlonobutane is a straight-chain molecule, allowing for grecter sarface is a branched motecule, reducing the surface contact leading to weater von der wails. 3. A \( 2: 1: 1 \) mixture of 2-chloro-2-methylpropane (MW: \( 106.59 \mathrm{~g} / \mathrm{mol} \), density \( 0.866 \mathrm{~g} / \mathrm{mL}, \mathrm{bp} 85^{\circ} \mathrm{C} \) ), 1-chlorohexane (MW: \( 120 \mathrm{~g} / \mathrm{mol} \), density \( 0.87 \mathrm{~g} / \mathrm{mL} \), bp \( 133^{\circ} \mathrm{C} \) ), and 1-chlorooctane (MW: 148 \( \mathrm{g} / \mathrm{mol} \), density \( 0.87 \mathrm{~g} / \mathrm{mL} \), bp \( 183^{\circ} \mathrm{C} \) ) was injected into a GC. What is the order that the compounds will elute (flow through) the column? Please draw the chromatograph and clearly label the peaks. 4. 2-methyl-2-propanol \( (0.0100 \mathrm{~mol}) \) is reacted with \( \mathrm{NH}_{4} \mathrm{Br}(0.0175 \mathrm{~mol}) \) and \( \mathrm{NH}_{4} \mathrm{Cl}(0.0350 \mathrm{~mol}) \) in the presence of \( \mathrm{H}_{2} \mathrm{SO}_{4}(0.100 \mathrm{~mol}) \). What is the expected ratio of the products 2-bromo-2methylpropane and 2-chloro-2-methylpropane? Explain. 2-bromo-2-methylpropane: 1 Since the recction follow SN1 2-chlore-2-mcthy|propanc: 2 mectrnism be of tertiany carbocection its Cetermined by the nudeolliles \( \left(s_{0}-1, c c^{-}\right) \). And-Cl is prosont twice then- \( B r \). UNIVERSITYATALBANY ratiois 1:2 State University of New York 147
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NUCLEOPHILIC ALIPHATIC SUBSTITUTION: SYNTHESIS OF 1-BROMOBUTANE OBJECTIVES: To synthesize 1-bromobutane through a nucleophilic aliphatic substitution. To understand the use of distillation and extraction in the context of the synthesis. To characterize the desired product with GC-MS. Experimental 1) In the 10 mL round-bottomed flask, dissolve 3.0 g of NaBr in 3.4 mL of water, and 1.8 g of butanol. Add a boiling chip 2) While swirling, add 2.5 mL of concentrated sulfuric acid, dropwise. 3) Reflux the reaction gently for 45 min (keep the Variac at a low setting - usually between 50-60) 4) Increase the temperature, and distill (set up the distillation apparatus—set up 50) until all organic material has come over, up to about 115°C. 5) As soon as the distillation is over, clean the round-bottomed flask and rinse the distillation head with acetone. Set aside to dry. 6) Add 2 mL of H2O to the distillate, transfer it to the separatory funnel. Slowly, drain out the lower layer into a small Erlenmeyer flask, being careful not to collect any of the top layer. Add enough CaCl2 pellets to cover the bottom of the flask. Let it sit for about 2 minutes. 7) DO THIS STEP ONLY IF TIME ALLOWS IT. Pipet the dry bromobutane layer into your clean 10 mL round-bottomed flask. Add a boiling chip and distill the product without the condenser into a pre-weighed vial. (bp should be about 102°C). Weight the distillate and report the percent yield. 8) Run a GC trace to obtain the percent of product and starting material in your distillate. Note: o H2SO4 is a very strong acid and it should be handled carefully. One of the most common tasks in organic laboratory is the purification of desired compounds. The goal is to separate the target molecule from undesired byproducts and impurities. Several techniques are available and sometimes more than one is utilized in the same protocol (like in this case) Extraction: involves the use of two immiscible solvents (S' and S"), one is generally water and the other one is an organic solvent. The solute partitions between the two phases, that forms two layers, with the denser phase at the bottom. Liquid-liquid extractions are characterized by a partition coefficient, D, that is defined as: C"/C'=D where C" is the concentration of solute in solvent S" and C' is the concentration of solute in solvent S'. the partition coefficient Figure 1. Reaction scheme: synthesis of 1-bromobutane from 1-butanol Background A substitution reaction occurs when a suitable substrate undergoes a substitution by a nucleophile. In order for this to occur, the substrate must possess a good leaving group. Substitution reactions are classified as SN1 and SN2 depending on the mechanism of the reaction itself (unimolecular or bi-molecular). SN2 occurs via a concerted mechanism involving substrate and nucleophile while SN1 reactions take place with the formation of an intermediate carbocation. Therefore, the nature of substrate, nucleophile, electrophile and solvent have an impact on whether a reaction will occur via SN1 or SN2 mechanism. Methyl and primary substrate favor SN2 due to steric hindrance of the transition state, whereas tertiary substrates favor SN1 due to the stability of the intermediate carbocation. Secondary substrate can proceed via SN1 or SN2, depending on the reaction conditions. Additionally, SN2 reaction are stereospecific and characterized by inversion of configuration (If a chiral center is present) due to the fact that the nucleophile attacks from the backside and never from the frontside. In this experiment you will synthesize 1-bromobutane from 1-butanol utilizing HBr (generated in situ by reacting NaBr and sulfuric acid). Figure 2 Inversion of configuration for an SN2 reaction
Sri K.
Define an electrophilic addition. Thoroughly explain how hydrogenation of an alkene (reaction of an alkene with H2) fits this definition. Consider the electrophilic addition of an alkene with a diatomic halogen molecule. Rank the rate of reactivity of the different halogens (F2, Cl2, Br2) in the electrophilic addition reaction. In the electrophilic addition reaction, is the halogen acting as the nucleophile or the electrophile? Electrophilic additions involving hydracids, such as HCl or HBr, are known as "hydrohalogenations". In them, the alkene is first protonated by the HX acid, which produces a halide anion and a carbocation. Explain why the proton from the hydracid ends up on the less-substituted carbon of the double bond. Will this reaction happen faster for HBr or HCl? Explain (hint: look up the pKa of each acid). Define the role the halide anion plays in the next step of the mechanism. Draw the mechanism of the electrophilic addition of HBr to 2-methylbut-2-ene. Draw the product of 2-butene when it is reacted with HCl. Will a hydrohalogenation reaction produce an enantiomeric, racemic mixture, or an achiral product? Explain. Define halohydrin and list the reagents needed to produce it using electrophilic addition of an alkene. Explain the rate of reaction difference between methyl-1-propene and propene in an acid-catalyzed hydration reaction.
The following reactions underwent SN2 : 1-bromobutane + NaI in acetone The following reactions underwent SN1: 2-chlorobutane + AgNO3 in ethanol 1- bromobutane + AgNO3 in ethanol 2-bromobutane + AgNO3 in ethanol 2-chloro-2-methyl-propane + AgNO3 in ethanol In addition, the tube with 1- bromobutane + NaI in acetone was cloudy at the time of recording the results, which means it was about to undergo SN1. Most likely, given extra time, this compound would have undergone an SN1 reaction. The following reactions underwent neither SN1 or SN2: 1-chlorobutane + NaI in acetone 2-chlorobutane + NaI in acetone 2-chloro-2-methylpropane + NaI in acetone 2-bromobutane + NaI in acetone bromobenzene + NaI in acetone 1-chlorobutane + AgNO3 in ethanol bromobenzene + AgNO3 in ethanol For SN2 reactions: Rank fastest to slowest theoretically and Explain theory with respect to, the structure of alkyl halide and leaving group For SN1 reactions: Rank fastest to slowest theoretically and Explain theory with respect to, the structure of alkyl halide and leaving group Explain theoretically why SN1 of 2-chloro-2-methylpropane with silver nitrate in ethanol/water would be faster than reaction of 2-chloro-2-methylpropane with silver nitrate in ethanol alone.
Adi S.
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