Polycyclic aromatic hydrocarbons are drawn with fused rings to represent shared pi-electron delocalization.
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Retrieved reference literature establishes that aromatic compounds feature rings depicted with alternating bonds or circles to signify electron delocalization, and that polycyclic aromatic hydrocarbons are composed of fused rings.
We theoretically investigated the nitrogen substitution effect on the molecular structure and π-electron delocalization in linear nitrogen-substituted polycyclic aromatic hydrocarbons (N-PAHs). Based on the optimized molecular structures and magnetic field-induced parameters of fused bi- and tricyclic linear N-PAHs, we found that the local π-electron delocalization of subcycles (e.g., mono- and bicyclic constituent moieties) in linear N-PAHs is preserved, despite deviation from ideal structures of parent monocycles. The introduction of a fused five-membered ring with a pyrrolic N atom (N-5MR) in linear N-PAHs significantly perturbs the π-electronic condition of the neighboring fused six-membered ring (6MR). Monocyclic pyrrole exhibits substantial bond length alternations, strongly influencing the π-electronic systems of both the fused N-5MR and 6MR in linear N-PAHs, depending on the location of shared covalent bonds. A fused six-membered ring with a graphitic N atom in an indolizine moiety cannot generate monocyclic π-electron delocalization but instead contributes to the formation of polycyclic π-electron delocalization. This is evidenced by bifurcated diatropic ring currents induced by an external magnetic field. In conclusion, the satisfaction of Hückel’s 4n + 2 rule for both mono- and polycycles is crucial for understanding the overall π-electron delocalization. It is crucial to consider the unique characteristics of the three types of substituted N atoms and the spatial arrangement of 5MR and 6MR in N-PAHs.
Aromatic compound
An aromatic compound, or arene,[1][2] is a chemical compound that has a specific ring-like structure that gives it increased chemical stability. These compounds are called "aromatic" because many of them have sweet or pleasant smells. Benzene is the simplest aromatic compound. The aromatic ring is often depicted as alternating double and single bonds between carbon atoms; this is a simplification. Formally, the electrons in the ring are shared across all the carbon atoms: this is called delocalization, and is why aromatic rings are so stable. Aromatic rings are also depicted as a circle drawn inside a ring of single bonds. Hückel's rule predicts whether or not a ring will be aromatic by counting the number of electrons and atoms in the ring. Aromatic rings are not limited to carbon; in heteroarenes, at least one carbon atom is replaced by another atom such as oxygen, nitrogen, or sulfur.[3] Compounds with more than one aromatic ring are called polycyclic arenes.
Polycyclic aromatic hydrocarbon
Three representations of hexabenzocoronene, a polycyclic aromatic hydrocarbon. Top: standard line-angle schematic, where carbon atoms are represented by the vertices of the hexagons and hydrogen atoms are inferred. Middle: ball-and-stick model showing all carbon and hydrogen atoms. Bottom: atomic force microscopy image.
A polycyclic aromatic hydrocarbon (PAH) is any member of a class of organic compounds that is composed of multiple fused aromatic rings. Most are produced by the incomplete combustion of organic matter—by engine exhaust fumes, tobacco, incinerators, in roasted meats and cereals, or when biomass burns at lower temperatures as in forest fires. The simplest representative is naphthalene, having two aromatic rings, and the three-ring compounds anthracene and phenanthrene. PAHs are uncharged, non-polar and planar. Many are colorless. Many of them are also found in fossil fuel deposits such as coal and in petroleum. Exposure to PAHs can lead to different types of cancer, fetal development complications, and cardiovascular issues.
Polycyclic aromatic hydrocarbons are discussed as possible starting materials for abiotic syntheses of materi
# Why are arenes with conjoined benzene rings drawn as they are?
Tags: organic-chemistry, aromatic-compounds, structural-formula
- Score: 19
- Views: 1797
- Answers: 3
- Answered: yes
- Asked by: Rory (785 rep)
- Asked: 2012-04-27
- Edited: 2020-06-10
- Site: chemistry
## Question
Whilst we are taught to represent benzene as below (A) due to its delocalised electrons, however when two benzene rings share carbons (e.g. naphtalene) it seems to be more commonly represented in textbooks as two conjugated rings (B). Whilst I realise that the result is the same, what is the advantage gained by drawing them like this rather than (C)? Is it simply a matter of clarity?
A:
B:
C:
Whilst draing those in Marvin I wondered if it was as the delocalisation between the shared carbons isn't shown? I.e. it looks like the electrons are delocalised across both rings separately rather than as one big ring?
## Answers
### Answer by F'x (score: 17 [ACCEPTED])
Questions about why we represent things in one way or another are hard to answer in general, because they appeal to one’s sense of taste… de gustibus non est disputandum. Here, I want to state the position and the reasoning of IUPAC on this
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