Nitro group

Nitro compound with simplified formula (left) and the structural formula (right). The radical R is an organyl radical ( aryl radical , alkyl radical, arylalkyl radical, etc.). The nitro group is marked in blue .

In organic chemistry, the nitro group is the functional NO ₂ group that is bound to the organic radical R via the nitrogen atom .

The isomer to the nitro group is the functional ester group of nitrous acid . In these esters, the bond to the organic radical R takes place via an oxygen atom (R – O – N = O). Often nitric acid esters , R – O – NO _{2, are also} referred to as nitro compounds, although these compounds belong to the nitrate class . Examples are the incorrectly designated explosives nitroglycerin (correct name glycerol trinitrate) and nitrocellulose (correct name cellulose nitrate ).

properties

In the mesomerism-stabilized nitro group, one oxygen atom has a negative charge and the nitrogen atom has a positive charge. Since two double bonds to the nitrogen atom are forbidden according to the octet rule , the structural formula has to be represented with a neutral and a charged oxygen atom.

The nitro group as a substituent therefore decreases the electron density of aromatic compounds and shows an −M effect . The aromatic system is thus deactivated in the case of electrophilic aromatic substitution and activated in the case of a potential nucleophilic aromatic substitution .

Nitro groups have an oxidizing effect due to the nitrogen atom in the high oxidation state . This applies to many explosives compounds. TNT (tri nitro toluene) is so explosive because the compound contains three nitro groups for every seven carbon atoms. The molecule therefore has the properties of an oxidizing agent - the nitro groups (high oxidation state) - and a reducing agent - the carbon atoms (low oxidation state).

The anti- luxochromic effect in colored compounds is based on the –M effect of the nitro group , e.g. B. in picric acid . The yellow coloration ( xanthoprotein reaction ) that occurs when proteins are treated with concentrated nitric acid is caused by the nitration of aromatic amino acids, the absorption of which is shifted to the visible range of light .

See also

• Organic nitro compound

literature

• Hans Beyer, Wolfgang Walter: Textbook of organic chemistry , 19th edition, S. Hirzel Verlag, Stuttgart, ISBN 3-7776-0356-2 .
• Siegfried Hauptmann : Organic Chemistry , 2nd edition, VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig 1985, ISBN 3-342-00280-8 , pp. 513-522.
• Peter Sykes: reaction mechanisms - an introduction , 8th edition, VCH, Weinheim 1982, ISBN 3-527-21090-3 .

Individual evidence

1. ↑ Eberhard Breitmeier, Günther Jung: Organic chemistry . Basics, substance classes, reactions, concepts, molecular structure. 5th edition. Georg Thieme Verlag, Stuttgart 2005, ISBN 3-13-541505-8 , p. 223, 406 ( limited preview in Google Book search).