Methyl-carbonyl bonds

The yields ranged from 55% for the mixture of enamines formed from morpholine and methylisopropyl ketone to 94% for the enamine formed from dimethylamine and methyl t-butyl ketone. The hindered ketone 2,5-dimethylcyclopentanone could be converted to an enamine, but the more hindered ketone, 2,6-di-t-butylcyclohexanone, was inert. White and Weingarten 43) attribute the effectiveness of titanium tetrachloride in this reaction to its ability to scavenge water and to polarize the carbonyl bond. 

It has been shown that different methods may ascribe different bond lengths to the 0-0 and C—O bonds and that the medium and substituents affect the electronic behaviors of carbonyl oxides." For example, recent computational studies (B3LYP/6-31 + G (d, p)) of carbonyl oxides, syn- and awri-methyl carbonyl oxides and dimethylcarbonyl oxides in gas and solution reveal that dipolar character increases with the number of methyl groups, and the ionic configuration is stabilized in a polar medium. These effects result in a weakened 0 0 bond and an increased double-bond character in the CO bond. ... 

Chrysin shows a similar effect which is much enhanced in tecto-chrysin, owing presumably to methylation of the 7-hydroxyl in techto-chrysin leaving only the keto-associated 5-hydroxyl free in that flavone. Opening the flavone heterocyclic ring to produce 2-hydroxychalcone leaves monophenol activity still partly suppressed because of the remaining carbonyl effect on oxidizability and H-bonding. Since the structure is relatively free to rotate about the ring-to-carbonyl bond, the suppression is less than in tectochrysin. 

Sepiolite clay (<100 mesh) was heated in air at 120°C in order to remove the zeolitic and surface bound water molecules. The partially dehydrated clay mineral was subsequently exposed to acetone vapor at room temperature for a period of four days. H and 29Si CP MAS-NMR experiments revealed that the acetone molecules penetrated into the microporous channels of the sepiolite structure. Broad line 2H NMR studies using acetone-d6 revealed that, in addition to fast methyl group rotations, the guest acetone-d6 molecules were also undergoing 2-fold re-orientations about the carbonyl bond. The presence of acetone-d6 molecules adsorbed on the exterior surfaces of the sepiolite crystals was also detected at room temperature. 

In Fig. 5b, which was obtained at 30°C, the powder pattern displays a severely distorted, intermediate rate line shape. This line shape is characteristic of both fast methyl group rotation and 2 fold molecular re-orientation about the carbonyl bond at a rate comparable to the reciprocal of the quadrupolar coupling constant ( 105 Hz). At room temperature, therefore, the acetone-d6 molecules in the microporous channels of sepiolite are able to undergo restricted re-orientations. 

The most important synthetic use of Grignard reagents and organolithium reagents is to form new carbon-carbon bonds by addition to polar multiple bonds, particularly carbonyl bonds. An example is the addition of methyl-magnesium iodide to methanal ... 

Substantial rate accelerations are observed in these systems for base hydrolysis. Thus for the ethylenediamine complex (18) rate increases of 4x 104 for GlyOEt to 1.4 x 107 for ethyl picolinate are observed.85 These rate accelerations are consistent with the formation of carbonyl-bonded species (18). The effects with methyl L-cysteinate and methyl L-histidinate are much less marked as such ligands can give mixed ligand complexes which do not involve alkoxycarbonyl donors. Thus in the case of methyl L-histidinate the complex (20) is formed. For these latter two esters only relatively small rate accelerations of 20-100 occur. For the chelate ester complexes, the ratios of kcm/kH2o fail within the range 3.8 x 109 to 3.2 x 1011. Such values for the relative nucleophilicity of water and hydroxide ion are comparable with those previously noted for copper(II) complexes.82... 

Evidence for intramolecular hydrolysis of the methyl ester (62) by metal hydroxide has been provided.329 Molecular models of the metal complex (63) indicate that when complexation with the imidazole nitrogen and the phenolic hydroxyl group occurs, it is not possible for coordination of the ester carbonyl group to occur. This point, taken in conjunction with the observed pH rate profile which shows that ionization of the M—OH2 group is associated with catalysis, eliminates metal ion activation of the carbonyl bond to intermolecular attack by OH- as a contributing factor. For base hydrolysis of (62) kOH = 2.7 x 10-2 M-1 s-1 at 25 °C. The specific rate constants for intramolecular hydrolysis by the M—OH species are 0.245 s-1 and 2 x 10-2 s-1 for the Co11 and Ni11 complexes respectively. 

The products of oxidative addition of acyl chlorides and alkyl halides to various tertiary phosphine complexes of rhodium(I) and iridium(I) are discussed. Features of interest include (1) an equilibrium between a five-coordinate acetylrhodium(III) cation and its six-coordinate methyl(carbonyl) isomer which is established at an intermediate rate on the NMR time scale at room temperature, and (2) a solvent-dependent secondary- to normal-alkyl-group isomerization in octahedral al-kyliridium(III) complexes. The chemistry of monomeric, tertiary phosphine-stabilized hydroxoplatinum(II) complexes is reviewed, with emphasis on their conversion into hydrido -alkyl or -aryl complexes. Evidence for an electronic cis-PtP bond-weakening influence is presented. 

The three equivalent protons (a) of the methyl group bonded to the carbonyl appear as a singlet of relative area 3, near 8 2.1. Methyl ketones and acetate esters characteristically give such singlets around 52.1, since there are no protons on the adjacent carbon atom. 

The singlet at 52.1 (area = 3) might be a methyl group bonded to a carbonyl group. A carbonyl group would also account for the element of unsaturation. 

Solution The IOU in this case is 1. The three-hydrogen signal at 8 2.01 is exactly where we would expect a methyl group bonded directly to an amide carbonyl (0.23 + 1.77 Table 6.2). Moreover, the two remaining hydrogens give... 

Unfortunately, none of the analogs 34, 35, 37, or (A-unsubstituted secondary amide) 36, which would mimic a rranj -olefin geometry) showed any appreciable tubulin-polymerizing or antiproliferative activity, despite the fact that preliminary NMR studies with compound (34) in DMSO/water indicate that the preferred conformation about the 12/13 A-methyl amide bond is indeed cis, that is, the methyl group and the carbonyl oxygen are located on the same side of the partial C-N double bond (cis/trans-mtio 4/l 34 may thus be considered a direct structural mimetic of Epo D). The underlying reasons for the lack of biological activity of... 

The chemistry of acetyl-CoA synthesis is thought to resemble the Monsanto process for acetate synthesis in that a metal center binds a methyl group and CO and the CO undergoes a carbonyl insertion into the methyl-metal bond. Elimination of the acetyl group is catalyzed by a strong nucleophile, iodide in the industrial process and CoA in the biochemical one. Currently, there are two views of the catalytic mechanism. 

Usually decarboxylation is accomplished by heating the acids above their melting points, often in the presence of a copper-chromium catalyst. Imidazole-4,5-dicarboxylic acid can be monodecarboxylated by heating its monoanilide imidazole- and benzimidazole-2-carboxylic acids decarboxylate very readily indeed, so readily that the carboxyl function makes a useful blocking group in metallation procedures (see Scheme 7.2.1) [3-5]. A potentially useful method of preparation of imidazole-4-carboxylic acid derivatives heats the 4,5-dicarboxylic acid (2) with acetic anhydride to form (1), which is essentially an azolide and very prone to nucleophilic attack which cleaves the nitrogen-carbonyl bond (Scheme 8.3.1). With methanol the methyl ester (3) is formed with hydrazines the 4-hydrazides (4) result [6]. 

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