Pure (R)-2-bromo-1-fluorobutane reacts with sodium cyanide in aqueous ethanol to form pure (R)-2-(fluoromethyl)butanenitrile.
CH3CH2CHCNCH2F2-(fluoromethyl)butanenitrile
a. What is the probable mechanism of this reaction? Explain your reasoning.
I think the mechainsm is Sn2
b. Based on your choice of mechanism, explain how both the substrate and the product can have the R configuration.
pure substrate
Please help me, I am really having hard time with this question
a. The probable mechanism for this reaction is indeed the SN2 (substitution nucleophilic bimolecular) mechanism. This mechanism involves a one-step concerted reaction in which the nucleophile attacks the substrate, leading to simultaneous breaking of the carbon-bromine bond and formation of the carbon-nitrogen bond.
In this case, the nucleophile is the cyanide ion (CN-) and the substrate is the (R)-2-bromo-1-fluorobutane. The SN2 mechanism is favored when the substrate is primary or secondary, as in this case, where the carbon with the leaving group (bromine) is attached to only one other carbon. Additionally, the presence of a polar solvent like aqueous ethanol promotes the SN2 mechanism by stabilizing the transition state.
b. The SN2 mechanism leads to inversion of configuration at the chiral center. However, the product still has the R configuration. This can be explained by the presence of an "intramolecular" SN2 process that follows the initial SN2 reaction. In this intramolecular process, the formed nitrile group (CN) attacks the adjacent carbon, breaking the carbon-fluorine bond and making a new carbon-carbon bond with the fluoromethyl group, resulting in the product with the R configuration.
The key concept here is that the intramolecular process occurs after the initial SN2 reaction and does not involve any stereocenter inversion. It is important to note that this intramolecular process is not considered in the forefront of the reaction mechanism but rather as an additional step that takes place in the reaction pathway.
Overall, it is the combination of the SN2 mechanism followed by this intramolecular process that results in the formation of the pure (R)-2-(fluoromethyl)butanenitrile with the same configuration as the starting material.