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This difference is partly related to the lower symmetry of the individual pyridine molecule (C 2v vs D 6h for benzene). A trihydrate (pyridine·3H 2 O) is known; it also crystallizes in an orthorhombic system in the space group Pbca, lattice parameters a = 1244 pm, b = 1783 pm, c = 679 pm and eight formula units per unit cell (measured at 223 K).
Compared to benzene, the rate of electrophilic substitution on pyridine is much slower, due to the higher electronegativity of the nitrogen atom. Additionally, the nitrogen in pyridine easily gets a positive charge either by protonation (from nitration or sulfonation) or Lewis acids (such as AlCl 3) used to catalyze the reaction. This makes the ...
Typical simple aromatic compounds are benzene, indole, and pyridine. [1] [2] Simple aromatic rings can be heterocyclic if they contain non-carbon ring atoms, for example, oxygen, nitrogen, or sulfur. They can be monocyclic as in benzene, bicyclic as in naphthalene, or polycyclic as in anthracene.
The pyridine analog is quinoline or isoquinoline, and the class of analogues with two nitrogen atoms is known as the benzodiazines. For azepine, benzazepine is the preferred name. Likewise, the compounds with two benzene rings fused to the central heterocycle are carbazole , acridine , and dibenzoazepine.
Replacing one CH with N gives the compound pyridine, C 5 H 5 N. Although benzene and pyridine are structurally related, benzene cannot be converted into pyridine. Replacement of a second CH bond with N gives, depending on the location of the second N, pyridazine, pyrimidine, or pyrazine. [65]
The theory predicts the molecular orbitals for π-electrons in π-delocalized molecules, such as ethylene, benzene, butadiene, and pyridine. [ 1 ] [ 2 ] [ 3 ] It provides the theoretical basis for Hückel's rule that cyclic, planar molecules or ions with 4 n + 2 {\displaystyle 4n+2} π-electrons are aromatic .
Heteroarenes are aromatic compounds, where at least one methine or vinylene (-C= or -CH=CH-) group is replaced by a heteroatom: oxygen, nitrogen, or sulfur. [3] Examples of non-benzene compounds with aromatic properties are furan, a heterocyclic compound with a five-membered ring that includes a single oxygen atom, and pyridine, a heterocyclic compound with a six-membered ring containing one ...
Benzene will react under aggressive conditions but deactivated rings such as pyridine are difficult to formylate effectively. Many formylation reactions will select only the ortho product (e.g. salicylaldehyde), attributed to attraction between the phenoxide and the formylating reagent.