When there are two functional groups of unequal reactivity within a molecule, the more reactive group can be made to react alone, but it may not be possible to react the less reactive functional group selectively. A group the use of which makes possible to react a less reactive functional group selectively in presence of a more reactive group is known as protecting group.
A protecting group blocks the reactivity of a functional group by converting it into a different group which is inert to the conditions of some reaction s that is to be carried out as part of a synthetic route. The SlideShare family just got bigger. Home Explore Login Signup. Successfully reported this slideshow. We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime. Next SlideShares. You are reading a preview.
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A protective group also referred to as "protecting group" is a reversably formed derivative of an existing functional group in a molecule. The protective group is temporarily attached to decrease reactivity so that the protected functional group does not react under synthetic conditions to which the molecule is subjected in one or more subsequent steps.
As an example, whereas amines are nucleophiles and react with electrophiles, the amino group is no longer nucleophilic after being converted to a carbamate. Protecting an amine as a carbamate therefore enables other functional groups to undergo selective reactions with electrophiles whereby the carbamate protected amino group is left intact.
However, two additional synthetic steps are needed to achieve this protection: the step to form the protected intermediate and a deprotection once the additional selective synthetic steps have been completed. In addition, the nature of the protective group must be chosen carefully to ensure adequate stability throughout all the intermediary synthesis steps. Moreover, the conditions for the protection and deprotection steps and the nature of the protective group itself mustn't interfere with other functional groups present in the molecule.
If more than one functional group of the same type is present in a molecule, subtle differences in reactivity - for example caused by steric effects - can help to achieve the selective protection of just one functional group while another such functional group remains unprotected.
Alternatively, a second such functional group could be protected with a different protecting group that has a different reactivity profile.
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