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The analogous cyclic system appears to have even more resonance stabilized, as the negative charge can be delocalized across three carbons instead of two. However, the cyclopropenyl anion has 4 π electrons in a cyclic system and in fact has a substantially higher pK a than 1-propene because it is antiaromatic and thus destabilized. [3]
In 2011, Jordi Poater and Miquel Solà expanded the rule to open-shell spherical compounds, finding they were aromatic when they had 2n 2 + 2n + 1 π-electrons, with spin S = (n + 1/2) - corresponding to a half-filled last energy level with the same spin. For instance C 60 1– is also observed to be aromatic with a spin of 11/2. [16]
Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp 3 hybridized carbon atom. Although this sp 3 center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties ...
[1] [2] The lowest triplet state of an annulene is, according to Baird's rule, aromatic when it has 4n π-electrons and antiaromatic when the π-electron count is 4n + 2, where n is any positive integer. This trend is opposite to that predicted by Hückel's rule for the ground state, which is usually the lowest singlet state (S 0).
With two π electrons, the cyclopropenium cation class obeys Hückel’s rules of aromaticity for 4n + 2 electrons since, in this case, n = 0. Consistent with this prediction, the C 3 H 3 core is planar and the C–C bonds are equivalent. In the case of the cation in [C 3 (SiMe 3) 3] + SbCl − 6, [3] the ring C–C distances range from 1.374(2 ...
3 Cyclopropenyl anion. 2 comments. 4 Peer review and responses during the educational assignment in Fall 2013. 5 Peer Review 1. 1 comment Toggle Peer Review 1 subsection.
Two orbital models were proposed to describe the bonding situation. The Coulson-Moffit model uses bent bonds. The C-C bonds are formed by overlap of two sp-hybrid orbitals. To adapt to the small bond angle, there is some rehybridization resulting in sp ~5-hybrids for the ring bonds and sp ~2 for the C-H bonds. This model resembles the banana ...
A related process is the cyclisation of 1,3-dibromopropane via a Wurtz coupling. This was used for the first synthesis of cyclopropane by August Freund in 1881. Originally this reaction was performed using sodium, [20] however the yield can be improved by exchanging this for zinc. [21] BrCH 2 CH 2 CH 2 Br + 2 Na → (CH 2) 3 + 2 NaBr