See, the best is always, no doubt to understand the concept very clearly, if you do that there will be no need to mug up the reactions. However if there is any absolute necessity, you can try the 'memory places technique'.Here, we associate things we want to remember with images, rather than words. So, if for example you need to remember the
Sandmeyer Reaction, associate it with a beach, where you get lots of sand, and as for meyer, you think of a mayor. This is a effective way too.