Hosoya polynomials of general spiro hexagonal chains

Filomat ◽  
2014 ◽  
Vol 28 (1) ◽  
pp. 211-215 ◽  
Author(s):  
Xianyong Li ◽  
Xiaofan Yang ◽  
Guoping Wang ◽  
Rongwei Hu
Keyword(s):  
Organic Chemistry ◽  
Benzene Ring ◽  
Spiro Compounds

Spiro hexagonal chains are a subclass of spiro compounds which are an important subclass of Cycloalkynes in Organic Chemistry. This paper addresses general spiro hexagonal chains in which every hexagon represents a benzene ring, and establishes the formulae for computing the Hosoya polynomials of general spiro hexagonal chains.

scholarly journals Ring Contraction Reactions of a Non-Benzenoid Aromatic Cation and a Neutral Homoaromatic System into Benzene Derivatives

2021 ◽  
Author(s):  
Demelza Lyons ◽  
An Huy Dinh ◽  
Nhan Nu Hong Ton ◽  
Reece Crocker ◽  
Binh Khanh Mai ◽  
...  
Keyword(s):  
Organic Chemistry ◽  
Benzene Ring ◽  
Benzene Derivatives ◽  
Ring Contraction ◽  
Chemistry Research ◽  
Synthetic Utility ◽  
Aromatic Ions ◽  
Benzyl Halides ◽  
Tropylium Salts ◽  
Ring Contraction Reaction

Aromaticity is one of the most intriguing concepts in organic chemistry. Simple and extended benzenoid aromatic systems have been very well established in undergraduate textbooks, and there are also mentions of non-benzenoid aromatic structures such as cyclopropenium, cyclopentadienide and cycloheptatrienylium (tropylium) ions. However, the structural relationship and the comparison of stabilization energy of such aromatic ions to benzene ring have been rarely studied and remained an underexplored area of advanced organic chemistry research. To contribute some insights into this topic, we focused on the chemical transformation, namely a ring contraction reaction, of the tropylium ion to benzene ring in this work. With an approach combining computational studies with experimental reactions, we also aim to turn this transformation into a synthetically useful tool. Indeed, this work led to the development of a new synthetic protocol, which involved an oxidative ring-contraction of tropylium ion, to formally introduce the phenyl ring onto a range of organic structures. Furthermore, the homoaromatic cycloheptatrienyl precursors of tropylium salts used in these reactions can also be rearranged to valuable benzhydryl or benzyl halides, enriching the synthetic utility of this ring-contraction protocol.

Learning from Molecules in Distress

2012 ◽  
Author(s):  
Roald Hoffmann ◽  
Henning Hopf
Keyword(s):  
Organic Chemistry ◽  
Water Molecule ◽  
Benzene Ring ◽  
Functional Groups ◽  
Optical Isomers ◽  
Chemical Structures ◽  
Comb Structure ◽  
The One ◽  
Average Position ◽  
As If

From the time we first got an inkling of the geometries and metrics of molecules, the literature of organic chemistry has contained characterizations of molecules as unstable, strained, distorted, sterically hindered, bent and battered. Such molecules are hardly seen as dull; on the contrary, they are perceived as worthwhile synthetic goals, and their synthesis, or evidence of their fleeting existence, acclaimed. What is going on here? Why this obsession with abnormal molecules? Is this molecular science sadistic at its core? Let’s approach these questions, first describing what is normal for molecules, so we can define the deviance chemists perceive. After a digression into the anthropomorphic language chemists generally use, and the psychology of creation in science, we will turn to the underlying, more serious concern: “What is the value of contemplating (or creating) deviance within science?” As many as 366,319 different eicosanes (C20H42) are conceivable, not counting optical isomers. And an enumeration of the components of a reasonably constrained universe of all compounds with up to 11 C, N, O, F atoms comes to >26 million compounds. An important feature of the chemical universe is that the tree of possible structures is denumerable. At the same time, the playground of chemical structures is subject to systematic elaboration, through the decoration of an underlying skeleton by functional groups of some stability. Very quickly a multitude turns into a universe. Of structure, and of function. Thinking of these molecules as fixed, rigid structures is natural—don’t they look like olive and toothpick assemblages, prettied up by computer rendering? And one can certainly get a long way in organic chemistry in the classical, mechanical mode. But the atoms in a molecule move continually, deviating, oscillating, as if held by springs, around an average position. The honey-comb structure of the benzene ring (a molecular tile, seemingly ever so flat and rigid as the one on your bathroom floor) has become an icon of chemistry just as the angled water molecule. Yet that tile is not rigid, it moves—and one can see the deformations/deviations by looking at its vibrational (what a telling name!) spectrum.

Extension and revision of the nomenclature for spiro compounds

1999 ◽  
Vol 71 (3) ◽  
pp. 531-558 ◽  
Author(s):  
G. P. Moss
Keyword(s):  
Organic Chemistry ◽  
Spiro Compounds ◽  
Alternative Methods ◽  
Ring Systems

Spiro ring systems have two or more rings linked by one common atom. Several different methods are used to name such systems. Rules A-41, A-43, B-10 and B-12 (Nomenclature of Organic Chemistry, 1979) describe the basics of how to name these compounds. The alternative methods in rules A-42 and B-11 are abandoned.This document describes the nomenclature in greater detail and extends it to cover branched polyspiro systems and compounds where three rings have one common spiro atom. A new notation, based on the von Baeyer method of naming spiro systems where all components are monocyclic, allows both unbranched and branched polyspiro systems to be named without ambiguity. It also enables the names to be readily interpreted.

The Li Synthesis of Daphenylline

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Organic Chemistry ◽  
Free Radical ◽  
Herbal Medicine ◽  
South Asia ◽  
Benzene Ring ◽  
Chinese Herbal Medicine ◽  
Pig Liver ◽  
Pig Liver Esterase ◽  
Liver Esterase ◽  
Trees And Shrubs

The genus Daphniphyllum consists of 25–30 species of evergreen trees and shrubs of south Asia. The leaves and roots are widely used in Chinese herbal medicine. About 250 alkaloids, many with complex polycyclic structures, have been isolated from these species. Of these, daphenylline 3 is unique in incorporating a benzene ring. Ang Li of the Shanghai Institute of Organic Chemistry envisioned (Nature Chem. 2013, 5, 679) a route to 3 based on the diastereoselective intramolecular Michael cyclization of 1 to 2. Following the work of Piers (J. Org. Chem. 1996, 61, 8439), the preparation of 1 began with the Birch reduction of 4, followed by hydrolysis. Epoxidation followed by elimination and acetylation led to the racemic acetate 5. Hydrolysis with pig liver esterase left one enantiomer of the acetate, that was transesterified with methoxide to give 6 in high ee. Mitsunobu coupling of 6 with the o-nitrobenzenesulfonamide 7 gave 8. After some experimentation, selective α¢-silylation was effected with TBDPSOTf, setting the stage for gold-catalyzed Conia cyclization to 9. Deprotection of the amine fol­lowed by acylation with 10 gave 1, that cyclized smoothly to 2 as a 10:1 ratio of diastereomers. The arene of 3 was constructed by converting 2 into the corresponding vinyl tri­flate. Pd-mediated coupling with 11 gave 12. Under irradiation with strict exclusion of oxygen, 12 cyclized to the dihydro aromatic, that on warming with DBU in the pres­ence of air was oxidized to 13. To close the last ring of 3, the ketone 13 was further oxidized to the enone 14. Desilylation of 14 followed by exposure to Ph3P/I2 gave the iodide 15, that was cyclized under reductive free radical conditions to 16. The hydrogenation of 16 under Pd catalysis delivered the incorrect diastereomer, perhaps because migration to the endocyclic alkene preceded reduction. This problem was solved by using the Crabtree Ir catalyst. Modified Krapcho decarbomethoxylation then gave 17, that was reduced to daphenylline 3.

Electron Microscopic and Isozyme Study of a Case of Ochronosis

1972 ◽  
Vol 30 ◽  
pp. 88-89
Author(s):  
Jay W. Cha ◽  
Perry J. Melnick
Keyword(s):  
Benzene Ring ◽  
Enzyme System ◽  
Homogentisic Acid ◽  
Degenerative Changes ◽  
Acid Oxidase ◽  
Electron Microscopic ◽  
Tyrosine Metabolism ◽  
Collagenous Tissues

Hereditary ochronosis in very few cases has been examined electron microscopically or histochemically. In this disease homogentisic acid, a normal intermediary of tyrosine metabolism, forms in excessive amounts. This is believed to be due to absence or defective activity of homogentisic acid oxidase, an enzyme system necessary to break the benzene ring and to further break it down to fumaric and acetoacetic acids. Ochronotic pigment, a polymerized form of homogentisic acid, deposits mainly in mesenchymal tissues. There has been a question whether the pigment originates from the collagenous tissues, or deposits passively, where in contrast to melanin it induces degenerative changes.

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