Just as delocalization stabilizes the allyl cation and anion (at least some of the electrons in conjugated systems end up in lower energy orbitals than they would have done without con jugation) so too is the amide group stabilized by the conjugation of the nitrogen’s lone pair with the carbonyl group. This makes an amide C=O one of the least reactive carbonyl groups (we shall discuss this in Chapter 10). Furthermore, the nitrogen atom of an amide group is very different from that of a typical amine. Most amines are easily protonated. However, since the lone pair on the amide’s nitrogen is conjugated into the π system, it is less available for proto nation or, indeed, reaction with any electrophile. As a result, when an amide is protonated (and it is not protonated easily, as you will see in the next chapter) it is protonated on oxygen rather than nitrogen. The consequences of conjugation for reactivity extend far and wide, and will be a running theme through many chapters in this book.

مواضيع ذات صلة

? What makes benzene special

Aromaticity

The amide group

Delocalization over three atoms is a common structural feature The carboxylate anion

The allyl system, The allyl anion

The colour of pigments depends on conjugation

UV and visible spectra

The molecular orbitals of butadiene

Conjugation

Multiple double bonds not in a ring

Molecules with more than one C=C double bond Benzene has three strongly interacting double bonds

The structure of ethene (ethylene, CH2=CH2)