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Pyrrole is an extremely weak base for an amine, with a conjugate acid pK a of −3.8. The most thermodynamically stable pyrrolium cation (C 4 H 6 N +) is formed by protonation at the 2 position. Substitution of pyrrole with alkyl substituents provides a more basic molecule—for example, tetramethylpyrrole has a conjugate acid pK a of +3.7.
with regards to acid-base reactions, electron-rich species have high pKa's and react with weak Lewis acids. [4] with regards to nucleophilic substitution reactions, electron-rich species are relatively strong nucleophiles, as judged by rates of attack by electrophiles. For example, compared to benzene, pyrrole is more rapidly attacked by ...
Polypyrrole Pyrrole can be polymerised electrochemically. [1] Polypyrrole (PPy) is an organic polymer obtained by oxidative polymerization of pyrrole. It is a solid with the formula H(C 4 H 2 NH) n H. It is an intrinsically conducting polymer, used in electronics, optical, biological and medical fields. [2] [3]
The reaction employs an organic acidic medium such as acetic acid or propionic acid as typical reaction solvents. Alternatively p-toluenesulfonic acid or various Lewis acids can be used with chlorinated solvents. The aldehyde and pyrrole are heated in this medium to afford modest yields of the meso tetrasubstituted porphyrins [RCC 4 H 2 N] 4 H 2.
Their antiaromatic character entails strong electrophilicity of the boron center resulting in even weak donors such as ethers or nitriles being capable of forming stable Lewis acid–base adducts. Moreover, boroles' highly activated carbon backbone readily participates in Diels–Alder reactions and is prone to two-electron reductions affording ...
Additionally, the metal is often not centered in the N 4 plane. [6] For free porphyrins, the two pyrrole protons are mutually trans and project out of the N 4 plane. [7] These nonplanar distortions are associated with altered chemical and physical properties. Chlorophyll-rings are more distinctly nonplanar, but they are more saturated than ...
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Tetrapyrroles are a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by (= (CH)-or -CH 2-units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four carbon atoms and one nitrogen atom.