The carbenium ion is a kind of positive ion with the structure RR′R″C, that is, a chemical species with carbon atom having three covalent bonds, and it bears a +1 formal charge. Carbenium ions are a major subset of carbocations, which is a general term for diamagnetic carbon-based cations. In parallel with carbenium ions is another subset of carbocations, the carbonium ions with the formula R5. In carbenium ions charge is localized. They are isoelectronic with monoboranes such as B(CH3)3.
HINT:
👉 Carbenium ion in the context of Carbocations
Carbocation is a general term for ions with a positively charged carbon atom. In the present-day definition given by the IUPAC, a carbocation is any even-electron cation with significant partial positive charge on a carbon atom. They are further classified in two main categories according to the coordination number of the charged carbon: three in the carbenium ions and five in the carbonium ions. Among the simplest carbocations are the methenium CH
3 (a carbenium ion), methanium CH
5 (a carbonium ion), acylium ions RCO, and vinyl C
2H
3 cations.
Until the early 1970s, carbocations were called carbonium ions. This nomenclature was proposed by G. A. Olah. Carbonium ions, as originally defined by Olah, are characterized by a three-center two-electron delocalized bonding scheme and are essentially synonymous with so-called 'non-classical carbocations', which are carbocations that contain bridging C–C or C–H σ-bonds. However, others have more narrowly defined the term 'carbonium ion' as formally protonated or alkylated alkanes (CR
5, where R is H or alkyl), to the exclusion of non-classical carbocations like the 2-norbornyl cation.
In this Dossier
- ⭐ Core Definition: Carbenium ion
- 👉 Carbenium ion in the context of Carbocations
- Carbenium ion in the context of Conjugation (organic chemistry)
Carbenium ion in the context of Conjugation (organic chemistry)
In physical organic chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in a molecule, which in general lowers the overall energy of the molecule and increases stability. It is conventionally represented as having alternating single and multiple bonds. Lone pairs, radicals or carbenium ions may be part of the system, which may be cyclic, acyclic, linear or mixed. The term "conjugated" was coined in 1899 by the German chemist Johannes Thiele.
Conjugation is the overlap of one p-orbital with another across an adjacent σ bond. (In transition metals, d-orbitals can be involved.)
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