scholarly journals Stereochemistry of the incorporation of valine methyl groups into methylene groups in cephalosporin C.

1984 ◽  
Vol 222 (3) ◽  
pp. 777-788 ◽  
Author(s):  
C P Pang ◽  
R L White ◽  
E P Abraham ◽  
D H G Crout ◽  
M Lutstorf ◽  
...  
Keyword(s):  
Side Chain ◽  
Methyl Groups ◽  
Cephalosporin C ◽  
Cephalosporium Acremonium ◽  
Methyl Group ◽  
Methylene Groups ◽  
Methylene Group

‘Chiral methyl valines’, i.e. samples of valine labelled stereospecifically in the methyl groups with 2H and 3H, were incorporated into cephalosporin C by a suspension of washed cells of Cephalosporium acremonium. Analysis by 3H n.m.r. of the cephalosporin C produced showed that the conversion of the 3-pro-S-methyl group of valine into the acetoxymethyl side-chain was a highly stereospecific process. By contrast, conversion of the 3-pro-R-methyl group into the endocyclic methylene group of the dihydrothiazine ring was shown to proceed by a non-stereospecific process.

The Rates and Products of Addition of 4-Chlorobenzenesulfenyl Chloride to a Series of Side Chain Methyl Substituted Styrenes

1974 ◽  
Vol 52 (9) ◽  
pp. 1807-1812 ◽  
Author(s):  
George H. Schmid ◽  
Dennis G. Garratt
Keyword(s):  
Steric Hindrance ◽  
Side Chain ◽  
Methyl Groups ◽  
Methyl Group

The rates of addition and the product compositions have been determined for the addition of 4-chlorobenzenesulfenyl chloride to a series of seven side chain methyl substituted styrenes in 1,1,2,2-tetrachloroethane at 25°. Unlike the addition to the corresponding series of methylated ethylenes, the effect of the methyl groups is not cumulative. The effect of the methyl groups depends upon whether or not the β-methyl group is cis to the phenyl. When it is cis, the rate of addition is decreased compared to styrene and substitution of additional methyl groups has only a small effect on the rate of addition. In compounds lacking a cis-β-methyl group the rate of addition more closely resembles that for addition to the methylated ethylenes. Steric hindrance between the cis-methyl and phenyl groups is believed to be the cause of this difference in behavior between the ethylene and styrene series.

Mechanistic studies of the reactions of 2-methylpropene with deuterium over supported metal catalysts

1989 ◽  
Vol 424 (1866) ◽  
pp. 39-56 ◽  
Keyword(s):  
Mass Spectrometry ◽  
Gas Chromatography ◽  
Metal Catalysts ◽  
Supported Metal Catalysts ◽  
Mechanistic Studies ◽  
Dissociative Mechanism ◽  
Methyl Group ◽  
Methylene Groups ◽  
Methylene Group ◽  
Supported Metal

Deuterium NMR spectroscopy, gas chromatography and mass spectrometry have been used to examine the products from the reaction of 2-methylpropene with deuterium over supported metal catalysts. The detailed information, so obtained, about the number, location and grouping of deuterium atoms in both the exchanged alkenes and the 2-methylpropanes formed by addition provided evidence about possible mechanisms. With palladium, exchange was faster than addition and the deuterium atoms were randomly distributed in the alkene, probably through a π-allyl dissociative mechanism. With platinum and rhodium, exchange occurred preferentially in the methylene groups of the alkene and the results indicated a dissociative mechanism involving adsorbed vinyl intermediates together with some intramolecular double-bond movement through a π-allyl type of species. Relatively little exchange occurred with iridium. The activities of the metals for production of alkane at 235 K were Rh > Ir > Pd > Pt but the spread was only a factor of about 20. With all metals except palladium further exchange occurred during the addition process, but this was mainly concentrated in one methyl group. This behaviour was explained in terms of mechanisms that permitted additional exchange of the methylene group of the alkene to take place during the addition process.

The stereochemistry of the incorporation of the methyl groups of ‘chiral methyl valine’ into methylene groups in cephalosporin C

1983 ◽  
pp. 723-724 ◽  
Author(s):  
Edward Abraham ◽  
Chi-Pui Pang ◽  
Robert L. White ◽  
David H. G. Crout ◽  
Max Lutstorf ◽  
...  
Keyword(s):  
Methyl Groups ◽  
Cephalosporin C ◽  
Methylene Groups

THE INFRARED ABSORPTION SPECTRA OF DEUTERATED ESTERS: III. METHYL LAURATE

1962 ◽  
Vol 40 (2) ◽  
pp. 301-320 ◽  
Author(s):  
R. Norman Jones
Keyword(s):  
Absorption Spectrum ◽  
Infrared Absorption ◽  
Carbon Disulphide ◽  
Infrared Absorption Spectrum ◽  
Methyl Laurate ◽  
Methyl Groups ◽  
Acid Chlorides ◽  
Methyl Group ◽  
Methylene Groups ◽  
Infrared Absorption Spectra

The infrared absorption spectrum of methyl laurate in carbon tetrachloride and carbon disulphide solutions has been compared with the spectra of seven derivatives deuterated in the ω-methyl group, the α-methylene groups, the carbomethoxy group, and in binary and ternary combinations of these positions. The spectra of n-dodecanes deuterated in the terminal methyl groups and of methyl laurates chlorinated in the ω-methyl and α-methylene groups have also been measured.From an analysis of these spectra, all the bands and inflections between 3100 and 700 cm−1 in the spectrum of methyl laurate can be assigned to localized group vibrations. The spectra of some related acid chlorides, alcohols, and bromides are also briefly noted.

2003 Alcan Award Lecture — Roles of the adjacent metals in the coupling of methylene groups promoted by heterobinuclear complexes of Group 8 and 9 metals

2005 ◽  
Vol 83 (8) ◽  
pp. 1043-1055 ◽  
Author(s):  
Martin Cowie
Keyword(s):  
Ambient Temperature ◽  
Key Words ◽  
Fischer Tropsch ◽  
Methyl Group ◽  
Methylene Groups ◽  
Ru Species ◽  
Methylene Group ◽  
Coupling Sequence

The reactivities of the heterobinuclear complexes, [MM′(CO)4(dppm)2][X] (MM′ = RhOs, RhRu, IrRu; dppm = µ-Ph2PCH2PPh2; X– = BF4–, CF3SO3–) with diazomethane are reported. The RhOs species reacts to give three products of methylene-group incorporation, depending on the temperature; at –80 °C the methylene bridged product, [RhOs(CO)4(µ-CH2)(dppm)2][X], is formed exclusively, at ambient temperature only [RhOs(η1-C3H5)(CH3)(CO)3(dppm)2][X], having the allyl group bound to Rh and the methyl group bound to Os, is obtained, while at intermediate temperatures [RhOs(η1:η1-C4H8)(CO)3(dppm)2][X], having the butanediyl fragment chelating on Os, is generated. Based on labeling studies a mechanism is proposed rationalizing formation of the different products. Under the same range of conditions the Rh/Ru and Ir/Ru species yield only the methylene bridged products, [MM′(CO)4(µ-CH2)(dppm)2][X] (MM′ = RhRu, IrRu). A rationalization for the different reactivities observed and a description of the roles of the different metals in coupling of the methylene groups are presented. Attempts to model key intermediates in the methylene coupling sequence promoted by the Rh/Os complexes, through coupling of methylene groups with ethylene or alkynes, are described. Key words: heterobinuclear, rhodium/osmium, rhodium/ruthenium, iridium/ruthenium, methylene coupling, Fischer–Tropsch, alkyne insertions, bimetallic cooperativity.

The Normal Paraffins Revisited

1990 ◽  
Vol 5 (2) ◽  
pp. 93-100 ◽  
Author(s):  
R. D. Heyding ◽  
K. E. Russell ◽  
T. L. Varty ◽  
D. St-Cyr
Keyword(s):  
Nearest Neighbor ◽  
Methyl Groups ◽  
Monoclinic Symmetry ◽  
Crystal Forms ◽  
Hydrocarbon Chains ◽  
Chain Axis ◽  
Methylene Groups ◽  
In Trans ◽  
Methylene Group ◽  
Long Chain

The low temperature modifications of the normal paraffins n-CnH2n+2crystallize in three groups (Broadhurst, 1962). The structure is triclinic for n even, 6 < n < 26 (Muller and Lonsdale, 1948; Nyburg and Luth, 1972); orthorhombic for n odd, 11 < n < 39 (Smith, 1953; Teare, 1959); and monoclinic for n even, 28 < n < 36 (Shearer and Vand, 1956). In all of these structures the hydrocarbon chains are linear and in trans configuration. The chains are parallel to one another, the terminal methyl groups forming the surfaces of lamella which are more or less perpendicular to the chain axis. For n < ca.36, it is apparently the interlamellar interaction between end methyl groups which dictates the symmetry. For longer chains the structure is usually orthorhombic and comparable to the structure of highly crystalline polyethylenes. Chains do not fold (as they undoubtedly do in polyethylenes) unless n is greater than 102 (Bidd and Whiting, 1985; Ungar and Keller, 1986).The several crystal forms differ in the manner in which the nearest neighbor chains are related to one another. In the triclinic lattices the packing is such that a triclinic sublattice containing one methylene group is evident. In the other modifications the sublattice is orthorhombic and contains four methylene groups. If the overall symmetry is orthorhombic the long chain axes are perpendicular to the interlamellar surface; the x and y translations, perpendicular to the long axis, are common to both cells. If the nearest neighbor chains are displaced by two or four methylene groups along the chain axis, overall monoclinic symmetry results (Sullivan and Weeks (1970)).

Hydrogenolysis of nitrogen-containing compounds on a cobalt-molybdenum catalyst

1979 ◽  
Vol 44 (1) ◽  
pp. 85-98 ◽  
Author(s):  
Mirko Černý
Keyword(s):  
Nitrogen Atom ◽  
Methyl Groups ◽  
Molybdenum Catalyst ◽  
Methyl Group ◽  
Cobalt Molybdenum Catalyst ◽  
Methylene Groups ◽  
Methyl Derivatives ◽  
Nitrogen Containing Compounds

A sulphidized cobalt-molybdenum catalyst on Al2O3 has been used to study hydrogenolysis of pyridine, piperidine, quinoline and their methyl derivatives. In reaction mixtures were identified the compounds which contribute to the knowledge of the mechanism of hydrogenolysis. The cleavage of 2-methylpiperidine ring takes place between the nitrogen atom and the methylene groups and not between the nitrogen atom and the carbon substituted with the methyl group. The amount of hydrogenolysis products decreases in the series pyridine, 2-methylpyridine, 2,6-dimethylpyridine and 2,4,6-trimethylpyridine, i.e. with the increasing number of the methyl groups bonded to the ring.

scholarly journals Effect of side-chain length in lignin model compound on MnO2 oxidation: comparison of oxidations between C6-C2- and C6-C1-type compounds

2021 ◽  
Vol 67 (1) ◽  
Author(s):  
Shirong Sun ◽  
Tomoya Yokoyama
Keyword(s):  
Isotope Effects ◽  
Aromatic Nucleus ◽  
Side Chain ◽  
Direct Oxidation ◽  
Initial Oxidation ◽  
Methyl Group ◽  
Lignin Model Compound ◽  
Oxidation Rates ◽  
Kinetic Isotope ◽  
Lignin Model

AbstractMonomeric C6-C2-type lignin model compounds with a p-hydroxyphenyl (H), guaiacyl (G), syringyl (S), or p-ethylphenyl (E) nucleus (1-phenylethanol derivatives) were individually oxidized by MnO2 at a pH of 1.5 and room temperature. The results were compared with those of the corresponding C6-C1-type benzyl alcohol derivatives obtained in our recent report to examine the effect of the presence of the β-methyl group on the oxidation. The presence decelerated the oxidation regardless of the type of aromatic nucleus, although it did not change the order of the oxidation rates: G > S >> H > E. This deceleration results from the steric factor of the β-methyl group in the C6-C2-type compounds. The MnO2 oxidations of the corresponding C6-C2-type compounds deuterated at their α-(benzyl)positions showed that the magnitudes of the kinetic isotope effects are smaller than those observed in the oxidations of the corresponding C6-C1-type compounds, regardless of the type of aromatic nucleus. These smaller magnitudes suggest that the presence of the β-methyl group shifts the initial oxidation mode of MnO2 from direct oxidation of the benzyl position to one-electron oxidation of the aromatic nucleus. Only the S-type compounds afforded products via degradation of the aromatic nuclei.

Net charges and valence AO's in the methylamines; the hydrogen basis set and the properties of nitrogen

1985 ◽  
Vol 63 (7) ◽  
pp. 1487-1491 ◽  
Author(s):  
Giuseppe Del Re ◽  
Sándor Fliszár ◽  
Michel Comeau ◽  
Claude Mijoule
Keyword(s):  
Basis Set ◽  
Basis Sets ◽  
Methyl Groups ◽  
Extended Form ◽  
Amine Nitrogen ◽  
Methyl Group ◽  
Net Charges ◽  
Extended Basis

Net charges and valence AO's for ammonia, methylamine, dimethylamine, and trimethylamine were calculated using extended basis sets. Superposition effects, evaluated by replacing Pople's standard 6-31G* basis by an extended form in which the basis of the ammonia H atoms and of the methyl groups of trimethylamine are retained in the treatment of each molecule, indicate that the quality of the treatment of amine nitrogen atoms is strongly dependent on the number of methyl groups. A new, augmented basis is proposed for the hydrogens, which appears to be reasonably well balanced: comparison with familiar (e.g., 6-31G*) calculations illustrates in what manner the treatment of nitrogen is worsened when even just one methyl group is replaced by hydrogen unless the impoverishment of the basis is suitably taken care of.

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