 You may have learned about functional groups, which are sites in a molecule where a reaction occurs. Some molecules may have more than one functional group. Now, this may be a problem if you're carrying out a reaction, but you only want the reaction to occur at one particular functional group. To prevent the other functional groups from reacting, we must protect them. So to do so, we must add a protecting group or a derivative. These groups are also called blocking groups. This can be an issue because it costs time and energy to add and remove these protecting groups. As well, a lot of unnecessary waste is produced in this process. Think about a small stain on your shirt. It would be unnecessary to clean the entire shirt when there is only one small stain. It would be a waste of water, laundry detergent, and energy. These chemists, in an effort to be more environmentally friendly, are developing chemo-selective methods and synthesis. This means that the reaction will happen only at a particular functional group. So there is not a need to block the other functional groups that may be present.