What is a good method (an easy method that gives a pure product in good yield) for carrying out the following transformation? $$ \mathrm{R}-\mathrm{CH}_{2}-\mathrm{Br} \rightarrow \mathrm{R}-\mathrm{CH}_{2}-\mathrm{NH}_{2} $$

To transform an alkyl bromide (R-CH2-Br) into an amine (R-CH2-NH2), we need to replace the bromine atom (Br) with an amine group (NH2). This type of reaction is called nucleophilic substitution, as the nucleophile (the amine group) replaces the leaving group (the bromine atom) in the starting molecule.

A suitable nucleophile to use in this reaction is ammonia (NH3). We will be using excess ammonia in a solution, as it will not only serve as the nucleophile but also act as a solvent for the reaction.

To obtain a good yield and pure product, it is important to ensure that the reaction conditions are optimal. In this case, carry out the reaction at low temperature (around 0°C) and under an inert atmosphere (such as nitrogen or argon) to prevent side reactions or decomposition of the reactants and product.

Combine the alkyl bromide (R-CH2-Br) with excess ammonia in a suitable vessel under an inert atmosphere, and slowly cool the mixture to 0°C. Allow the reaction to proceed until it is complete, which could take several hours. You can monitor the progress by using techniques like thin-layer chromatography (TLC) or nuclear magnetic resonance (NMR).

Once the reaction is complete, you can isolate the desired amine product (R-CH2-NH2). First, remove the excess ammonia by evaporating it off under reduced pressure. Next, extract the product using an appropriate solvent (such as ethyl acetate) and separate the organic layer. Finally, dry the organic layer with a drying agent (such as magnesium sulfate), and evaporate the solvent under reduced pressure to obtain the pure amine product (R-CH2-NH2). In summary, the reaction can be carried out efficiently by using a nucleophilic substitution reaction with excess ammonia as the nucleophile, under low temperature and inert atmosphere conditions. Following this procedure will result in the desired transformation with a good yield and purity of the product.