Experiment 12 PDF

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Hajar Ferrasse 3rd August 2020 CHM 2210L Prof Pablo Sacasa SN1 and SN1 Reactions EXPERIMENT: The objective of this lab is to convert 1-butanol and hydrobromic acid to 1bromobutane using a SN2 reaction. In the SN2 reaction, 11.100g of sodium bromide, 10mL of water, and 10mL of 1-butanol are mixed and cooled in an ice bath before addingthe 10mL sulfuric acid. The sulfuric acid will react with the sodium bromide to produce HBr which is one of the reactants in the conversion. The addition of sulfuric acid also drives the reaction to the right and converts –OH into a good leaving group. The SN2 reaction will occur through the reflux of the solution. The product will be isolated through simple distillation of the solution, the repetitive washing of the product, and the shortpath distillation of the product. IntroductionSN2 stands for Nucleophilic Substitution (bi-molecular). Nucleophilic substitution is a reaction in which a nucleophile, which contains at least one lone pair, reacts with a sp3hybridized electrophile, which contains a leaving group. This reaction causes that group to leave and the nucleophile to bond by donating electrons to the accepting electrophile. The carbon-leaving group bond is broken and the carbon-nucleophile bond is formed simultaneously. Nucleophiles can be negatively charged or neutral. SN2 reactions prefer a leaving group that can best stabilize the negative charge of the transition state, for example, conjugate bases of strong acids. The concentrations of both the nucleophile and the leaving group affect the rate-

determining step of the reaction. Both the nucleophile and the leaving group are present in the transition state, which is therate-determining step. This is what makes the reaction bi-molecular. During the reaction, the nucleophile directly attacks the carbon bonded to the leaving group from an 180o, back-side approach. This approach causes the inversion of stereochemistry. Steric hindrance limits the SN2 reaction by slowing the rate of the reaction. Steric hindrance occurs from the presence of substrates around the leaving group. Tertiary substrates are the most hindered with the slowest reaction rate. Primary substrates are the least hinderedwith the fastest reaction rate. Tertiary substrates are favored by and will undergo substitution primarily by the SN1 mechanism and primary substrates are favored by and will undergo substitution primarily by the SN2 mechanism. Secondary substrates may react through either mechanism. The SN2 reaction also prefers polar aprotic solvents which reduce the rate of reaction. In contrast, a protic solvent will increase the rate of reaction. SN2 reactions are also limited by competing E2 reactions. E2 reactions results ina loss of a hydrogen and the formation of an alkene. The alkene product is not the desiredproduct in this lab....