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Benzene, Aromaticity, and Benzene Derivatives
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Hückel’s rule states that for planar, monocyclic hydrocarbons containing completely conjugated sp2-hybridized atoms, the presence of (4n+2) π-electrons leads to aromaticity (n is an integer in the series 0, 1, 2, 3, etc.).
Chemical Bond II: Molecular Orbitals
Published in Franco Battaglia, Thomas F. George, Understanding Molecules, 2018
Franco Battaglia, Thomas F. George
Hückel’s 4n + 2 rule for deciding on the aromaticity of a compound (meaning by that its strong stability and its reactivity, better prone to substitution reactions on the ring rather than addition reactions with rupture of the alternate double bonds or even the ring itself) extends to cycles containing atoms different than carbon (heterocyclic compounds), such as pyrrol, furan, or thiophene, in which the heteroatom lone pair contributes in the counting in Hückel’s rule (see Figure 7.23).
Organic superalkalis with closed-shell structure and aromaticity
Published in Molecular Physics, 2018
Benzene (C6H6), a prototype six-membered ring, is the building block of aromatic organic species. Aromaticity is a distinguished feature of species, which leads to energy reduction and a variety of unusual chemical and physical properties [1] such as bond-length equalisation, unusual reactivity, characteristic spectroscopic features, etc. Aromatic rings are significantly stabilised due to complete delocalisation of π-electrons, which reduces their reactivity toward addition reactions. For instance, benzene possesses very large ionisation energy (IE) and no positive electron affinity. This is why the whole chemistry of benzene is based on substitution reactions in which an atom or group usually replaces hydrogen attached to the ring. The substitution causes to significantly affect the chemical reactivity of the ring as noticed in many studies [2–4]. This may result in reducing the IE or increasing the electron affinity of the substituted rings. The increase in electron affinity by substitution at H-atoms (ligands) as well as C-atoms (core) in benzene has already been reported by Jena and co-workers [5–7]. Here, we study the substitution of lithium (Li) on benzene and its higher analogues such as naphthalene (C10H8), anthracene (C14H10) and coronene (C24H12) replacing all H-atoms. Few polylithium organic compounds have already been synthesised experimentally including C6Li6 [8,9].
The effect of the hydrogen fluoride chain on the aromaticity of C6H6 in the C6H6···(HF)1–4 complexes
Published in Molecular Physics, 2018
Hamidreza Jouypazadeh, Hossein Farrokhpour, Mohammad Solimannejad
The concept of aromaticity was introduced for the first time to explain the high stability and low reactivity of the compounds containing aromatic cycles in their structures [1]. The aromaticity can be defined as a result of the electron delocalisation in a closed cycle which leads to the energy stabilisation [2]. The intermolecular interactions involving the aromatic compounds have a main role in the understanding of biological and chemical processes, especially in the drug design and new materials with special functionality [3]. Although there are many published works in the literature on the aromaticity of the compounds [4], there are limited studies in the literature on the effect of intermolecular interaction on the aromaticity [5–8]. Miao et al. performed a systematic study on the aromaticity of borazine and its fluoroderivatives in the cation–π and anion–π interactions [5]. In another study, Rodríguez-Otero et al. studied the change in the aromaticity of benzene, pyrrol, triazine and hexafluorobenzene due to the cation–π and anion–π interactions using nucleus-independent chemical shift (NICS) methodology [6]. Foroutan-Nejad studied the aromaticity of C6H6 in the presence of an aluminium cluster (Al4) [2–7]. Recently, Sánchez-Sanz investigated the effect of π–π stacking interaction on the aromaticity in the polycyclic aromatic hydrocarbon/nucleobase complexes [8]. Also, Bloom and Wheeler studied the effect of aromaticity on cation–π, anion–π and π–stacking interactions [9].