Showing papers on "Substituent published in 1970"

Nuclear magnetic resonance spectroscopy. Carbon-13 chemical shifts in norbornyl derivatives

Abstract: The ^(13)C chemical shifts for a number of norbornyl derivatives have been obtained in natural abundance. The compounds studied were the series of methylnorbornanes, methylnorbornenes, methyl-2-norbornanones, methyl-2,2-difluoronorbornanes, and a variety of exo- and endo-2-substituted norbornanes. The observed shifts have been interpreted in terms of inductive, bond length, and steric effects. The ɑ- and β-substituent effects are shown to be dependent on the extent of substitution at both the α and β carbon atoms and changes in bond lengths have been used to rationalize the shift changes. Steric interactions between the endo-2 and endo-6 positions, and the exo-2 and syn-7 positions have been shown to generate important chemical- shift changes and these changes can be used as a semiquantitative measure of steric interactions in norbornyl derivatives. Studies with electron-withdrawing groups have revealed a new long-range cmr y effect produced by exo-2 substituents on C-6. These shifts appear to provide a sensitive and quantitative measure of the electronic demands of a neighboring group as a function of stereochemistry. The substituent shifts obtained from the monosubstituted derivatives have been used to predict the shifts of each of the 1- and 3-methyl-2-norbornanols. The agreement between observed and calculated values is generally good and supports the general approach. Several ^(13)C-^(13)C coupling constants for norbornane, nortricyclene, and quadricyclene are reported and interpreted in terms of the s character of the C-C bonds.

Advances in Imidazole Chemistry

Abstract: Publisher Summary This chapter reviews the developments in imidazole chemistry and discusses condensed imidazoles (such as benzimidazole, purines, etc), and compounds containing reduced imidazole rings The methods for the syntheses of the imidazole ring system are also presented Physical properties of imidazole and its derivatives such as dipole moments; melting points, boiling points, and solubilities; acid and basic strength; crystal structure; UV spectra; IR and Raman spectra; NMR spectra; mass spectrometry; electron spin resonance; optical rotatory dispersion and polarography; chromatography; thermodynamic data; and quantum mechanical calculations are described In addition, the chemical properties such as structure; aromatic character and reactivity; electrophilic substitution reactions; nucleophilic attack; reactions involving radicals; reactions of substituents on ring carbon atoms; reactions of substituents on ring nitrogen atoms; and miscellaneous properties of imidazole and its derivatives are illustrated Most of the reactions and properties of 1-substituted imidazoles have been discussed Apart from the utilization of the readily removable benzyl substituent in synthetic procedures leading to 2-substituted imidazoles, perhaps the most exciting advances have stemmed from the reactions of the 1 -acylimidazoles (imidazolides), which are extremely reactive in such nucleophilic reactions as hydrolysis and alcoholysis

Nuclear Magnetic Resonance Spectroscopy. Carbon-13 Spectra of Some Inositols and Their O-Methylated Derivatives

Abstract: The ^(13)C nmr spectra of some inositols and their partially O-methylated derivatives are tabulated and discussed. Methods of assignment are detailed. A system of empirical constants which can be used to estimate the spectra of the carbons of these ring systems is derived. The substituent effects are noted to conform generally to the notion that steric or proximity effects are very important sources of chemical-shift differences in these systems.

Catechol O-Methyltransferase: III. m- and p-O-Methylation of Catecholamines and Their Metabolites

Abstract: In vitro, O-methylation of physiological substrates of catechol O-methyltransferase (EC 2.1.1.6) such as (nor)epinephrine, dopamine, 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxymandelic acid, 3,4-dihydroxyphenylethanol, 3,4-dihydroxyphenylglycol, 3,4-dihydroxybenzoic acid, N-acetyldopamine, N-acetylnorepinephrine, and 3,4-dihydroxyphenylalanine affords mixtures of m- and p-O-methyl derivatives. The extent of p-methylation relative to m-methylation is low with substrates containing an ionized moiety in the ring substituent, i.e., amino acids, acids, and amines, and increases as the polar (hydrophilic) character of the ring substituent is decreased. With a nonpolar substituent, as in 4-ethylcatechol, the ratio of meta to para products is 1:1. The results suggest the presence of a nonpolar region in the catechol-binding site of catechol O-methyltransferase which militates against binding of polar substrates in the orientation necessary for p-methylation, which nonpolar substrates would appear to bind in a random fashion, resulting in the formation of nearly equal amounts of m- and p-O-methylated products. No change in the meta:para ratios was observed during more than 400-fold purification of catechol O-methyltransferase, suggesting that only one enzyme is involved in both m- and p-O-methylation.

Unsaturated quaternary monomers and polymers

Abstract: This invention is concerned with monoethylenically unsaturated acid ester monomers, such as those of acrylic or methacrylic acid, containing a quaternary ammonium halide group having a substituent on the quaternary nitrogen atom of the formula -CH2CH(OH)CH2X wherein X is chlorine, bromine or iodine. It is also concerned with addition polymers of such monomers, and methods of producing the monomers and polymers. The monomers and polymers are stable at acid pH values, although capable of reacting with other reactants for the hydroxyl and/or halide group. At alkaline pH values, they become self-reactive and the polymers crosslink themselves by slow reaction at room temperature. However, the reaction becomes quite rapid on heating.

Mixed ester-metal salts and lubricants and fuels containing the same

Abstract: LUBRICATING AND FUEL COMPOSITIONS COMPRISING A MAJOR AMOUNT OF A LUBRICATING OIL AND A MINOR PROPORTION OF AN ESTER DERIVATIVE OF A HYDROCARBON-SUBSTITUTED SUCCINIC ACID WHEREIN THE HYDROCARBON SUBSTITUENT CONTAINS AT LEAST ABOUT FIFTY ALIPHATIC CARBON ATOMS, THE SUBSTITUENT BEING FURTHER CHARACTERIZED BY HAVING NO MORE THAN ABOUT 5% OLEFINIC LINKAGES THEREIN BASED ON THE TOTAL NUMBER OF CARBON-TO-CARBON COVALENT LINKAGES IN THE SUBSTITUENT. THE ESTERS INCLUDE THE ACIDIC ESTERS, DIESTERS, MIXED ESTER-METAL SALTS, AND MIXTURES OF THESE WHEREIN THE ESTER MOIETY IS DERIVED FROM MONOHYDRIC AND POLYHYDRIC ALCOHOLS, PHENOLS, NAPTHTHOLS, AND THE LIKE.

Distortions of the π‐Electron System in Substituted Benzenes

Abstract: The factors leading to substituent effects on the electron distribution in aromatic molecules are discussed, particular attention being paid to the π-electron system. IR spectroscopy has proved an extremely useful probe in this field of study. Substituent d-orbital participation and the relevance of the π-inductive effects are also considered.

Studies on the antibacterial and antifungal properties of 1,4-naphthoquinones.

Abstract: 1. New halogenated 1,4-naphthoquinones were synthesized and together with other known 1,4-naphthoquinones, were screened for antibacterial activity by a turbidimetric method, and for antifungal activity by the diffusion method on agar plates. 2. The half-wave potentials and the influence on the oxidative phosphorylation of some of these compounds were determined. 3. 2-chloro-3,2′-chloro-ethyl-1,4-naphthoquinone (half-wave potential=-187 mV) was the most active compound, completely inhibiting cell respiration. 4. While the natural active naphthoquinones, vitamin K and ubiquinones, possess, as substituent, the electron repelling methyl group, the microbiologically active 1,4-naphthoquinones are substituted, in the quinone moiety, with electron attracting groups such as OH or Cl. 5. The half-wave potentials can give only an initial indication of the activity of the compounds studied; a good correlation, on the contrary, can be found between the ultraviolet spectra of such compounds and their activity which seems to depend on the ability of active compounds to exist in an extensively conjugated structure and to form hydrogen bonds.

Some cyclic tetra-amines and their metal-ion complexes. Part VI. The crystal structure of acetato-C-rac-(5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane)nickel(II) perchlorate

Abstract: The structure of acetato-C-rac-(5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane)nickel(II) perchlorate has been investigated by single-crystal three-dimensional X-ray methods. The blue prismatic crystals are monoclinic, space group P21/c, with a= 9·39, b= 30·67, c= 9·57 A, β= 119·3°, Z= 4. The structure was solved by Patterson and Fourier syntheses, and refined by least-squares methods to a final R of 0·120 for the 2753 visually estimated independent reflexions.The cyclic tetra-amine is folded, with the four secondary amine groups co-ordinated to adjacent octahedral sites of the nickel (II) ion. The acetate ion functions as a symmetric chelate, occupying the two remaining sites. The cyclic tetra-amine is the C-rac-modification, and both pairs of asymmetric nitrogens also have the racemic arrangement, but the pairs are of opposite helicity.The relative energies of the 36 configurations of the co-ordinated 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane macrocycles, arising from the pair of asymmetric carbon centres and two pairs of asymmetric nitrogen centres, are discussed in terms of the conformational energies of the chelate ring systems and methyl substituent interaction energies.The space-group determination of cis-oxalato-C-rac-(5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane)cobalt(III) perchlorate is also reported: Pccn, with a= 16·03, b= 9·61, c= 15·12 A, Z= 4.

Die Rolle des Siliciumatoms als Carbanion‐Substituent in Phosphor‐Yliden

Abstract: Die kurzlich entdeckte stabilisierende Wirkung von Silylsubstituenten auf die Carbanion-Funktion von Phosphor-Yliden ist nicht in den sterischen Effekten der R3Si-Gruppen be-grundet. Die hier beschriebene Synthese von Yliden mit der wenig raumerfullenden H3Si-Gruppe (14–16) schliest diese Moglichkeit sicher aus und beweist damit die Bedeutung eines elektronischen Effekts. Die Gegenuberstellung C/Si-analoger Ylide zeigt eine verstarkte Ubernahme der Carbanionladung durch die Siliciumatome an, die zwar der einfachen Elektro-negativitatsbeziehung (C > Si) widerspricht, mit anderen Bindungskonzepten (pπdπ oder elektrostatische Wechselwirkung zwischen freien und bindenden Elektronenpaaren) aber ausgezeichnet ubereinstimmt. Die in den Tabb. 1 und 2 aufgefuhrten Verbindungen wurden analytisch und spektroskopisch in ihrer Zusammensetzung und Konstitution gesichert. The Effect of the Silicon Atom as a Carbanion Substituent in Phosphorus Ylids The recently discovered stabilizing effect exerted on the carbanionic function of phosphorus ylids by silyl substituents is not due to a steric effect of the bulky R3Si groups. The preparation of ylids containing the simple silyl group H3Si (14–16) reported here clearly rules out steric influence as the stabilizing factor and thereby shows the importance of electronic effects. Comparative studies of C/Si analogous ylids suggest a delocalization of the carbanionic charge to silicon. This is inconsistent with simple electronegativity considerations, but in excellent agreement with expectations derived from other concepts of bonding (e. g. pπdπ or electrostatic interaction of lone and bonding pairs of electrons). The new compounds compiled in Tables 1 and 2 have been characterized by analytical and spectroscopic procedures.

Group IVB metalloidal substituent effects by fluorine-19 resonance

Abstract: Possible effects of substituents of the MR type (M = a group IVB metalloid, R = CH or CH) attached to an aryl system are evaluated and tested by examination of F substituent chemical shifts (SCS) of appropriate m- and p-fluorophenyl and 4,4′-fluorobiphenyl systems. (The extent to which a substituent electronically perturbs the C–F neighborhood is indicated by the substituent chemical shift (SCS), which is defined as the difference between the chemical shift of the unsubstituted fluoroaromatic and the substituted fluoroaromatic.) The (CH)Si substituent engages in conjugative electron withdrawal in both p-fluorophenyltrimethylsilane and 4-fluoro-4′-trimethylsilylbiphenyl, while the (CH)Ge group produces net electron withdrawal in 4-fluoro-4′-trimethylgermylbiphenyl. Overall, the evidence suggests that all the M(CH) substituents participate in dπ–pπ electron withdrawal, but this may be masked by shielding mechanisms. Replacement of CH in M(CH) by electronegative groups such as phenyl and vinyl leads to more negative SCS values, since the effective electronegativity of the metalloidal center is increased. Comparisons are also drawn with results from pentafluorophenyl systems. Substituents of the type CHMR (M and R as above) produce large positive SCS values when para to fluorine, and metallomethyl substituents generally are probably quite effective ortho–para donors. The pertinence of the present results to scales of electronegativities of the group IVB metalloids is presented.

Isoxazalin-3-yl-substituted-5-nitroimidazoles

Abstract: Substituted nitroimidazoles having a 1-alkyl or hydroxyalkyl substituent; a 5-nitro substituent; and a 2-substituent, the latter being a DELTA 2-4,5-disubstituted-isoxazoline. The 4,5-substitution on the isoxazolinemoiety is a saturated alkyl ring structure. These compounds have anti-bacterial and anti-protozoal activity against human and animal trypanosomiasis and trichomoniasis.