Diamagnetic anisotropy of some organic molecules

1964 ◽  
Vol 256 (1073) ◽  
pp. 357-387 ◽  
Keyword(s):  
Compact Group ◽  
Aromatic Compounds ◽  
Organic Molecules ◽  
Heavy Atom ◽  
Molecular Shape ◽  
Aliphatic Chain ◽  
Aliphatic Compounds ◽  
Diamagnetic Anisotropy ◽  
Molecular Anisotropy ◽  
Bond Character

The diamagnetic anisotropies of crystals of aromatic and aliphatic compounds, mostly of known structure, have been measured, and the principal molecular susceptibilities deduced from these and the molecular orientations. In a few cases where the absolute susceptibility is not known with certainty, the molecular anisotropy may, nevertheless, be calculated with a good degree of accuracy. The molecular susceptibilities and anisotropy are related to the molecular shape and constitution, and to the bond character; and in the case of aromatic compounds they are strongly influenced by substitution, which, in general, markedly decreases the anisotropy. This decrease varies not only with the nature of the substituents (heavy atom, compact group or aliphatic chain) but with their positions on the nucleus. This may give some information concerning the effect of substitution on conjugation, especially when correlated with changes in bond lengths and angles.

scholarly journals Diamagnetic anisotropy of organic molecules

1939 ◽  
Vol 171 (947) ◽  
pp. 541-568 ◽  
Keyword(s):  
Fatty Acids ◽  
Refractive Index ◽  
Aromatic Compounds ◽  
Organic Molecule ◽  
Organic Molecules ◽  
Diamagnetic Susceptibility ◽  
Positive Sign ◽  
Magnetic Birefringence ◽  
Unsaturated Alcohols ◽  
Diamagnetic Anisotropy

The large positive value of the magnetic birefringence (Cotton-Mouton effect) of aromatic compounds led (Raman and Krishnan 1927) to the deduction, subsequently verified, that these compounds must possess pronounced molecular diamagnetic anisotropy, in addition to their already well-known optical anisotropy. The sign of the magnetic birefringence is very significant (Bhagavantam 1929). The positive sign indicates that, for uniaxial or approximately uniaxial molecules, the direction of maximum diamagnetic susceptibility is one of minimum optical polarizability, that is, of least refractive index. This is strikingly true of aromatic compounds, but must also be true of other classes of compound which show positive magnetic birefringence, such as ketones, fatty acids, esters of fatty acids and unsaturated alcohols. Very little information is as yet available concerning the magnetic anisotropy of these classes of organic molecule, measurements having been confined almost entirely to the aromatic compounds.

Reductive Dehalogenation of Environmental Contaminants: A Critical Review

1989 ◽  
Vol 24 (2) ◽  
pp. 299-322 ◽  
Author(s):  
R. M. Baxter
Keyword(s):  
Hydrogen Atom ◽  
Aromatic Compounds ◽  
Reductive Dechlorination ◽  
Halogen Atom ◽  
Environmental Contaminants ◽  
Methanogenic Bacteria ◽  
Photochemical Reactions ◽  
Reductive Dehalogenation ◽  
Iron Porphyrins ◽  
Aliphatic Compounds

Abstract It is generally recognized that reductive processes are more important than oxidative ones in transforming, degrading and mineralizing many environmental contaminants. One process of particular importance is reductive dehalogenation, i.e., the replacement of a halogen atom (most commonly a chlorine atom) by a hydrogen atom. A number of different mechanisms are involved in these reactions. Photochemical reactions probably play a role in some instances. Aliphatic compounds such as chloroethanes, partly aliphatic compounds such as DDT, and alicyclic compounds such as hexachlorocyclohexane are readily dechlorinated in the laboratory by reaction with reduced iron porphyrins such as hematin. Many of these are also dechlorinated by cultures of certain microorganisms, probably by the same mechanism. Such compounds, with a few exceptions, have been found to undergo reductive dechlorination in the environment. Aromatic compounds such as halobenzenes, halophenols and halobenzoic acids appear not to react with reduced iron porphyrins. Some of these however undergo reductive dechlorination both in the environment and in the laboratory. The reaction is generally associated with methanogenic bacteria. There is evidence for the existence of a number of different dechlorinating enzymes specific for different isomers. Recently it has been found that many components of polychlorinated biphenyls (PCBs), long considered to be virtually totally resistant to environmental degradation, may be reductively dechlorinated both in the laboratory and in nature. These findings suggest that many environmental contaminants may prove to be less persistent than was previously feared.

scholarly journals Chiroptical activity of hydroxycarboxylic acids with implications for the origin of biological homochirality

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Jana Bocková ◽  
Nykola C. Jones ◽  
Uwe J. Meierhenrich ◽  
Søren V. Hoffmann ◽  
Cornelia Meinert
Keyword(s):  
Amino Acids ◽  
Lactic Acid ◽  
Organic Molecules ◽  
Building Blocks ◽  
Aliphatic Chain ◽  
Monocarboxylic Acids ◽  
Hydroxycarboxylic Acids ◽  
Polarised Light ◽  
Suitable Target ◽  
Anisotropy Spectra

AbstractCircularly polarised light (CPL) interacting with interstellar organic molecules might have imparted chiral bias and hence preluded prebiotic evolution of biomolecular homochirality. The l-enrichment of extra-terrestrial amino acids in meteorites, as opposed to no detectable excess in monocarboxylic acids and amines, has previously been attributed to their intrinsic interaction with stellar CPL revealed by substantial differences in their chiroptical signals. Recent analyses of meteoritic hydroxycarboxylic acids (HCAs) – potential co-building blocks of ancestral proto-peptides – indicated a chiral bias toward the l-enantiomer of lactic acid. Here we report on novel anisotropy spectra of several HCAs using a synchrotron radiation electronic circular dichroism spectrophotometer to support the re-evaluation of chiral biomarkers of extra-terrestrial origin in the context of absolute photochirogenesis. We found that irradiation by CPL which would yield l-excess in amino acids would also yield l-excess in aliphatic chain HCAs, including lactic acid and mandelic acid, in the examined conditions. Only tartaric acid would show “unnatural” d-enrichment, which makes it a suitable target compound for further assessing the relevance of the CPL scenario.

Löschung der Perylen-Fluoreszenz durch Ag+ -Ionen / Quenching of the Perylene Fluorescence by Ag+-Ions

1983 ◽  
Vol 38 (6) ◽  
pp. 698-700 ◽  
Author(s):  
H. Dreeskamp ◽  
A. Läufer ◽  
M. Zander
Keyword(s):  
Triplet State ◽  
Dynamic Process ◽  
Aromatic Compounds ◽  
Heavy Atom ◽  
Silver Ions ◽  
Intersystem Crossing ◽  
Fluid Solution ◽  
Long Wavelength ◽  
Wavelength Emission ◽  
Atom Effect

The fluorescence of perylene in fluid solution (λ0.0 = 440 nm) is quenched by silver ions in a dynamic process according to a Stern-Volmer kinetics (kq = 2 · 109 [1 • mol-1 · sec-1], in ethanol at 295 K). Simultaneously an unstructured long-wavelength emission (λmax ≈ 470 nm) appears which we assign to a perylene/Ag+ exciplex. A similar emission is observed when other polvcyclic aromatic compounds (PAC) are used, whose fluorescence as in the case of perylene is not easily quenched in an external heavy atom effect by iodopropane (kq ≦ 106). In these cases the excited PAC/Ag+ complex is long-lived enough to emit fluorescence since the intersystem crossing to the triplet system is slow due to the absence of an energetically favorable accepting triplet state

Address of the President Lord Todd at the anniversary meeting, 30 November 1976

1977 ◽  
Vol 352 (1671) ◽  
pp. 451-462
Keyword(s):  
Protein Interactions ◽  
Complex Analysis ◽  
Organic Molecules ◽  
Heavy Atom ◽  
Vitamin B ◽  
Protein Protein Interactions ◽  
X Ray Crystallography ◽  
Polypeptide Chains ◽  
Complex Organic

The Copley Medal is awarded to Professor Dorothy M. C. Hodgkin, O. M., F. R. S. Professor Dorothy Hodgkin is distinguished for her research on the structure of complex organic molecules by the method of X-ray crystallography. She was among the first to appreciate the importance of heavy-atom phase-determining methods and these she used to effect the first complete determination of the stereochemistry of a sterol derivative in her analysis of cholesteryl iodide. The same powerful method of analysis and in particular her extraordinary gift of being able to interpret correctly the complex, partially resolved and often misleading electron density patterns that are first obtained, have been responsible for her success in elucidating the structures of many other important natural products, especially penicillin and vitamin B 12 . This last is by far the most beautiful and complex analysis which has yet been completed in this field and it is of fundamental importance to chemical science. In recent years Professor Hodgkin’s main interest has been devoted to the structure of insulin, on which she has been working on and off since 1935. Carried out with characteristic precision, this work has become a mine of stereochemical information relating to contacts between polypeptide chains and is of great significance for our interpretation of protein-protein interactions.

scholarly journals Bright persistent luminescence from pure organic molecules through a moderate intermolecular heavy atom effect

2017 ◽  
Vol 8 (9) ◽  
pp. 6060-6065 ◽  
Author(s):  
Pengchong Xue ◽  
Panpan Wang ◽  
Peng Chen ◽  
Boqi Yao ◽  
Peng Gong ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Heavy Atom ◽  
Persistent Luminescence ◽  
Phosphorescence Lifetime ◽  
Heavy Atom Effect ◽  
Atom Effect

A 6-(4-bromophenoxy)hexyl group linked to carbazole gives crystals that exhibit strong white photoluminescence with an efficiency of 72.6%, a ΦP of 39.5%, and a phosphorescence lifetime of 200 ms.

Molecular Shape Selectivity for Polycyclic Aromatic Compounds on a Core–Shell Octadecylsilica Stationary Phase at Subambient Column Temperatures

2013 ◽  
Vol 76 (15-16) ◽  
pp. 921-927 ◽  
Author(s):  
Takafumi Kimura ◽  
Hatsuichi Ohta ◽  
Koichi Wada ◽  
Kiyokatsu Jinno ◽  
Ikuo Ueta ◽  
...  
Keyword(s):  
Stationary Phase ◽  
Aromatic Compounds ◽  
Shape Selectivity ◽  
Molecular Shape ◽  
Polycyclic Aromatic Compounds ◽  
Core Shell ◽  
Polycyclic Aromatic

Notizen: Zur Lumineszenz von aromatischen Verbindungen mit Schweratom-Substituenten in unterschiedlichen Bindungssituationen / On the Luminescence of Aromatic Compounds with Heavy Atom Substituents in Different Bonding Situations.

1979 ◽  
Vol 34 (7) ◽  
pp. 909-910 ◽  
Author(s):  
G.-P. Blümer ◽  
M. Zander
Keyword(s):  
Electron Density ◽  
Aromatic Compounds ◽  
Heavy Atom ◽  
Electronic System ◽  
Chlorine Atoms ◽  
Heavy Atom Effect ◽  
Inductive Effects ◽  
Atom Effect

Compounds like III(4,9,10,11,12,13,13-Heptachloro-8b,9,12,12a-tetrahydro-9,12-methano-benzo[e]pyrene) are ex­amples for systems with heavy atom substituents in two different bonding situations. The halogen directly connected with the 7-electronic system causes an internal heavy atom effect whilst the halogens isolated from the .7-system by aliphatic carbons produce a “quasi external” heavy atom effect. The observation that the internal heavy atom effect in III is weaker than in halo phenanthrenes is explained with the lower electron density in the phenanthrene unit of III compared to phenanthrene. this lower electron density being a result of field and inductive effects of the peripherically arranged chlorine atoms.

Address of the President Lord Todd at the Anniversary Meeting, 30 November 1976

1977 ◽  
Vol 196 (1122) ◽  
pp. 1-12
Keyword(s):  
Protein Interactions ◽  
Complex Analysis ◽  
Organic Molecules ◽  
Heavy Atom ◽  
Vitamin B ◽  
Protein Protein Interactions ◽  
X Ray Crystallography ◽  
Polypeptide Chains ◽  
Complex Organic

The Copley Medal is awarded to Professor Dorothy M. C. Hodgkin, O. M., F. R. S. Professor Dorothy Hodgkin is distinguished for her research on the structure of complex organic molecules by the method of X-ray crystallography. She was among the first to appreciate the importance of heavy-atom phase-determining methods and these she used to effect the first complete determination of the stereochemistry of a sterol derivative in her analysis of cholesteryl iodide. The same powerful method of analysis and in particular her extraordinary gift of being able to interpret correctly the complex, partially resolved and often misleading electron density patterns that are first obtained, have been responsible for her success in elucidating the structures of many other important natural products, especially penicillin and vitamin B 12 . This last is by far the most beautiful and complex analysis which has yet been completed in this field and it is of fundamental importance to chemical science. In recent years Professor Hodgkin’s main interest has been devoted to the structure of insulin, on which she has been working on and off since 1935. Carried out with characteristic precision, this work has become a mine of stereochemical information relating to contacts between polypeptide chains and is of great significance for our interpretation of protein-protein interactions.

Intramolecular heavy-atom effect in the photophysics of organic molecules

2005 ◽  
Vol 48 (3) ◽  
pp. 231-253 ◽  
Author(s):  
Konstantin N Solov'ev ◽  
Elena A Borisevich
Keyword(s):  
Organic Molecules ◽  
Heavy Atom ◽  
Heavy Atom Effect ◽  
Atom Effect
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