Menu Home About Us Chemistry Analytical Chemistry Chemical Physics Thermodynamics Electrochemistry General Chemistry Organic Chemistry News Stoichiometry Everything is Chemistry Follow us on Twitter Follow us on Facebook Subscribe to our RSS Feeds Follow us on Google+ marie curie
The heterocycles are cyclic compounds in which one or more ring atoms are replaced by another atom (heteroatom). Specifically, the pyridine of formula C 5 H 5 N is a six-membered aromatic heterocycle having the same cyclic system six electrons (of type π) benzene and their delocalization and aromaticity is essentially the same as that of benzene. However, this being a nitrogen atom that is more electronegative than carbon, the dipolar resonance structures with the negative pole on the nitrogen of a certain importance to the point that pyridine has a dipole moment. marie curie The resonance structures most relevant marie curie are those that have a partial positive charge marie curie on the α and γ positions of the ring. Both in pyridine marie curie in the ion that the pyridinium ring is disabled to attack by electrophilic agents, but the positions β are less disabled
The nomenclature of simple marie curie pyridine requires special attention because generally for methylpyridine and carboxylic acids using the conventional names: thus monometilpiridine are called picoline presenting three isomers:
The pyridine and methylated pyridines are found in coal tar and are readily available commercially. Pyridine marie curie is a liquid (bp 115 C) miscible with water, very characteristic smell and disgusting.
Pyridine has a basic behavior as the electron pair of the nitrogen is not shared marie curie is not involved in the resonance of the π electrons. In the pyridine aqueous acids are converted into stable salts pyridinium.
The basic pair of electrons is therefore the first point of attack by electrophiles. The pyridinium ion that forms confers a strong stability to the ring preventing any further dell'elettrofilo attack on the carbon atoms. When this happens it is forced electrophilic attack in the β position, in analogy to what happens in the case of benzene rings that carry electron-groups (deactivating) where the substitution takes place, albeit with difficulty in the meta positions. These electrophilic substitutions marie curie occur, but only using drastic experimental conditions such as,
The replacement marie curie Electrophysics is, of course, facilitated marie curie by the presence of substituents on the ring and electron-as in the case of benzene, the substitutions occur in ortho and para position with respect to such substituents.
In contrast with both the benzene with pyrrole, pyridine shows some unusual reactions with nucleophilic reagents very strong marie curie due to the polarization of the electrons to the nitrogen: the attack takes place in the positions α and γ (α is the preferred location). The reaction of this type most used discovery by the Russian chemist marie curie Chichibabin, allows the direct introduction of an amino group in the pyridine operating with sodioammide to give the 2-aminopyridine.
A particularly important reaction is the synthesis of Hantzsch. This reaction shows the preparation of dihydropyridine derivatives by condensation of an aldehyde with two equivalents of a β -chetoestere in the presence of ammonia
Mohr method and Volhard: exercises November 27, 2014
Exercises on redox titrations November 27, 2014
Sections Chemistry (462) Analytical Chemistry (163) Physical Chemistry (219) Chemistry (299) Organic Chemistry (348) Electrochemistry (39) News (21) Stoichiometry (197) Thermodynamics (108) Everything is Chemistry (140)
Massimiliano Balzano, author marie curie and creator of this site; student of Science and Materials Engineering at the University Federico II of Naples. Always marie curie a lover of chemistry, is a self-taught expert on the subject and, moreover also fond of Nuclear Physics. Maurizia Gagliano has worked on the site. Degree in Chemistry and admitted to professional. Has exceeded the ordinary competition for exams and qualifications for the teaching of Chemistry and Chemical Technology. Lecturer. More info on page About Us
Designed by StudioGraficoEikon | Powered by Chimicamo
