A chemist can protect a specific functional group in a molecule during a chemical reaction by using protecting groups. Protecting groups are temporary chemical modifications that shield a reactive functional group from unwanted reactions while still allowing other desired reactions to occur. Once the desired reaction is complete, the protecting group can be removed to restore the original functional group.A specific example of a protecting group used in organic synthesis is the tert-butyldimethylsilyl TBS group, which is commonly used to protect alcohols. The TBS group can be added to an alcohol by reacting it with tert-butyldimethylsilyl chloride TBSCl in the presence of a base, such as imidazole. This reaction converts the alcohol R-OH into a silyl ether R-OTBS , which is less reactive and can withstand various reaction conditions that would otherwise react with the unprotected alcohol.Once the desired reactions have been carried out on the molecule, the TBS protecting group can be removed to regenerate the original alcohol. This can be achieved by treating the silyl ether R-OTBS with a fluoride source, such as tetra-n-butylammonium fluoride TBAF or hydrogen fluoride HF in pyridine. The fluoride ion acts as a nucleophile, attacking the silicon atom in the TBS group and displacing the alcohol, which is then released as the original functional group R-OH .In summary, protecting groups like the TBS group can be used to temporarily shield reactive functional groups from unwanted reactions during organic synthesis. Once the desired reactions are complete, the protecting group can be removed to restore the original functional group.