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A carbocation is an ion with a positively charged carbon atom. ... bromide. This ion is predicted to be aromatic by Hückel's rule. In 1902, ...
The arenium ion is no longer an aromatic species; however it is relatively stable due to delocalization: the positive charge is delocalized over 5 carbon atoms. Also contributing to the stability of arenium ions is the energy gain resulting from the strong C-e bond (E = electrophile). The smallest arenium ion is protonated benzene, C 6 H + 7.
The term benzylic is used to describe the position of the first carbon bonded to a benzene or other aromatic ring. For example, (C 6 H 5)(CH 3) 2 C + is referred to as a "benzylic" carbocation. The benzyl free radical has the formula C 6 H 5 CH 2 •.
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]
Two different resonance forms of benzene (top) combine to produce an average structure (bottom). In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected by the stabilization of conjugation alone.
Substitution reactions in organic chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical, and whether the substrate is aliphatic or aromatic. Detailed understanding of a reaction type helps to ...
Clar's rule states that for a benzenoid polycyclic aromatic hydrocarbon (i.e. with only hexagonal rings), the resonance structure with the largest number of disjoint aromatic π-sextets is the most important to characterize its chemical and physical properties. Such resonance structure is called the Clar structure. In other words, a polycyclic ...
Hyperconjugation can be used to rationalize a variety of chemical phenomena, including the anomeric effect, the gauche effect, the rotational barrier of ethane, the beta-silicon effect, the vibrational frequency of exocyclic carbonyl groups, and the relative stability of substituted carbocations and substituted carbon centred radicals, and the thermodynamic Zaitsev's rule for alkene stability.