Amidine

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Amidines are a class of oxoacid derivatives.

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.[1][2][3]

Carboxamidines[edit]

The skeletal formula of acetamidine (acetimidamide)

When the parent oxoacid is a carboxylic acid, the resulting amidine is a carboxamidine or carboximidamide (IUPAC name), and has the following general structure:

The general structure of a carboxamidine

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 DBU, diminazene, and benzamidine.

The most common way to make primary amidines is by the Pinner reaction.

Properties[edit]

Amidines are much more basic than amides and are among the strongest neutral bases.[4]

Protonation occurs onto the sp² hybridized nitrogen. This occurs because the positive charge can be delocalized onto both nitrogen atoms:

Amidineresonance.png

The amidinium cation has identical C-N bond lengths.

Amidinate salts[edit]

An amidinate salt has the general structure M+[RNRCNR]- [5] 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.

See also[edit]

  • Guanidines - a similar group of compounds where the central Carbon is bonded to three Nitrogens.

References[edit]

  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "amidines".
  2. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "carboxamidines".
  3. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "sulfinamidines".
  4. ^ Clayden; Greeves; Warren (2001). Organic chemistry. Oxford university press. p. 202. ISBN 978-0-19-850346-0. 
  5. ^ Chemistry and Technology of Carbodiimides Henri Ulrich