What does NH2 mean in Chemistry?

amidogen

In chemistry, the amino radical, ·NH2, also known as the aminyl radical or azanyl radical, is the neutral form of the amide ion (NH−2). Aminyl radicals are highly reactive and consequently short-lived, like most radicals; however, they form an important part of nitrogen chemistry. In sufficiently high concentration, amino radicals dimerise to form hydrazine. While NH2 as a functional group is common in nature, forming a part of many compounds (e.g. the phenethylamines), the radical cannot be isolated in its free form.

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