Cyclopropenyl cation

Structure of the cyclopropenyl cation (left). The delocalization of the two π electrons and the positive charge are marked in red

The cyclopropenyl cation is a cyclic and planar cation with the empirical formula C ₃ H ₃ ⁺ . It is stable and a great many derivatives of this cation have already been detected and synthesized. Furthermore, the cyclopropenyl cation fulfills all the conditions to be considered an aromatic, which explains the stability of this compound.

Hückel rule

According to Hückel's rule, cyclic, conjugated π systems with 4n + 2 delocalized electrons are considered aromatic. The cyclopropenyl cation (n = 0) is therefore also one of the aromatics. Strictly speaking, this is the smallest carbocyclic, aromatic system. The resulting boundary structures ensure that the cyclopropenyl cation is one of the most stable carbenium ions .

Mesomeric boundary structures of the cyclopropenyl cation and an associated anion (tetrafluoroborate). The positive charge and the π double bond are marked in red

synthesis

3-Chlorocyclopropene can be obtained from tetrachlorocyclopropene with the aid of 3 equivalents of tributyltin hydride . In the second step, 3-chlorocyclopropene reacts with a strong Lewis acid such as antimony (V) chloride or silver tetrafluoroborate to form the cyclopropenyl cation:

Individual evidence

1. ↑ ^{a b} Cyclopropenylium cation . In: Jürgen Falbe (Ed.): Römpp . 8th edition. Georg Thieme Verlag, Stuttgart 1990, ISBN 3-13-734709-2 , p. 855 .
2. ^ Adalbert Wollrab: Organic chemistry . Springer Spectrum, Berlin 2014, ISBN 978-3-642-45143-0 , p. 254 , doi : 10.1007 / 978-3-642-45144-7_6 .
3. ↑ Ronald Breslow, John T. Groves: Cyclopropenyl cation. Synthesis and characterization . In: Journal of the American Chemical Society . tape 92 , no. 4 , 1970, pp. 984-987 , doi : 10.1021 / ja00707a040 .
4. ↑ Eberhard Breitmaier, Günther Jung: Organic chemistry . 7th edition. Thieme-Verlag, Stuttgart 2012, ISBN 978-3-13-541507-9 , p. 574 .