The oxoacid from which an amidine is derived must be of the form RnE(=O)OH, where R is a substituent. The −OH group is replaced by an −NH2 group and the =O group is replaced by =NR, giving amidines the general structure RnE(=NR)NR2.
Carboxamidines are frequently referred to simply as amidines, as they are the most commonly encountered type of amidine in organic chemistry. The simplest amidine is formamidine, HC(=NH)NH2.
Examples of amidines include:
The most common way to make primary amidines is by the Pinner reaction. Reaction of the nitrile with acidic alcohol gives an iminoether; treatment of this with ammonia then completes the conversion to the amidine.
Protonation occurs onto the sp² hybridized nitrogen. This occurs because the positive charge can be delocalized onto both nitrogen atoms. The resulting cationic species is known as a amidinium ion and possesses identical C-N bond lengths.
A notable subclass of amidinium ions are the formamidinium cations; which can be represented by the chemical formula [R2N-CH=NR2]+. Deprotonation of these gives stable carbenes which can be represented by the chemical formula R2N-C:-NR2.
An amidinate salt has the general structure M+[RNRCNR]− and can be accessed by reaction of a carbodiimide with an organometallic compound such as methyl lithium. They are used widely as ligands in organometallic complexes.
- Guanidines — a similar group of compounds where the central Carbon is bonded to three Nitrogens.
- Imidazolines contain a cyclic amidine.
- IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "amidines".
- IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "carboxamidines".
- IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "sulfinamidines".
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