Carbonyl compounds defined

After Cram had discovered the selectivities now named after him, he proposed the transition state model for the formation of Cram chelate products that is still valid today. However, his explanation for the preferred formation of Cram products was different from current views. Cram assumed that the transition state for the addition of nucleophiles to a-alkylated carbonyl compounds was so early that he could model it with the carbonyl compound alone. His reasoning was that the preferred conformation of the free a-chiral carbonyl compound defines two sterically differently encumbered half-spaces on both sides of the plane of the C=0 double bond. The nucleophile was believed to approach from the less hindered half-space. 

There have been numerous studies of the rates of deprotonation of carbonyl compounds. These data are of interest not only because they define the relationship between thermodynamic and kinetic acidity for these compounds, but also because they are necessary for understanding mechanisms of reactions in which enolates are involved as intermediates. Rates of enolate formation can be measured conveniently by following isotopic exchange using either deuterium or tritium ... 

The [2+2]-photocycloaddition of carbonyl groups with olefins (Paterno-Buchi reaction) is one of the oldest known photochemical reactions and has become increasingly important for the synthesis of complex molecules. Existing reviews have summarized the mechanistic considerations and defined the scope and limitations of this photocycloaddition73. Although this reaction likely proceeds via initial excitation of the carbonyl compound and not the excited state of the diene, the many examples of this reaction in natural product synthesis justify inclusion in this chapter. 

Reductive amination, of carbonyl compounds, 16 573 Reductive bleaching, 21 440 Reductive dechlorination defined, 3 757t Reductive dehalogenation defined, 3 757t... 

The anion can also be thought of as being formed by the addition of a hydroxide ion to the unhydrated carbonyl compound, and the following constants may be defined... 

SCHEME 8. Schematic representation for the chelate-controlled addition of an organometaUic reagent (M—R) to the carbonyl group of a chiral a-alkoxy carbonyl compound (17). Two diastere-omers 18 with different orientation of R with respect to CH2R can be obtained. The syn diastereomer is obtained when the nucleophihc attack of R takes place on the same face of the plane, defined by the carbonyl group and the R-substituted carbon atom, where CH2R is located in the chelate complex... 

Since hydrocarbon subunits (methyl, methylene and methine groups) are not polarized to a great extent, their nature can be defined by a polar substituent. The high acidity of the a-hydrogen atoms of carbonyl compounds, nitriles, sulfones, and nitroalkanes follows from polarity alternation, the carbon atoms being a donor next to the acceptor substituent. 

The Griesbaum Coozonolysis allows the preparation of defined, tetrasubsituted ozonides (1,2,4-trioxolanes) by the reaction of O-methyl oximes with a carbonyl compound in the presence of ozone. In contrast to their traditional role as intermediates in oxidative alkene cleavage, 1,2,4-trioxolanes with bulky substituents are isolable and relatively stable compounds. 

Organometallic reactions are becoming increasingly important in modern synthetic chemistry, but it is not obvious what the simple reaction dimensions would be into which such real reactions could be analyzed. Even for such a simple reaction as addition of a Grignard reagent to a carbonyl compound there are problems in picking out simple dimensions and defining a detailed... 

Reactions with dienes and carbonyl compounds did either not occur below 150°C (e.g. 2,3-dimethylbutadiene, cyclopentadiene, tetrachloro-a-pyron acetaldehyde), or were accompanied by decomposition (2,3-dicarbomethoxybutadiene, hexachlorocyclopentadiene, 1,3-diphenylisobenzofuran acrolein ). However, 1,3-dipoles reacted readily to give well-defined addition products ... 

In order to expand the worldwide market, considerable efforts are being devoted to improve the image of Madeira wine. Consequently, their characteristics have to be well defined. So, in order to define and describe the particular characteristics and the authenticity of the product, secondary metabolites of grape and wines mainly linked to a specific variety, must be deeply studied. In Madeira wine, these compounds are mainly included in the chemical classes of mono and sesquiterpenoids C13 norisoprenoid higher alcohols, ethyl esters, volatile fatty acids, carbonyl compounds, sulfur compounds, furanic compounds, lactones, and polyphenols. 

Carbonylation of organic substrates was investigated using these well defined complexes. These carbonyl compounds exhibited catalytic properties in the carbonylation of organic substrates. In particular methanol carbonylation to methyl acetate in the gas phase was successfully attempted. Mechanistic and kinetic studies of this reaction over rhodium and iridium zeolites showed the similarities between the homogeneous and the zeolite mediated reactions. Aromatic ni-tro compounds were also converted to aromatic isocyanates using similar catalytic systems. The mechanistic aspect of this reaction will be also examined. 

Optical detection of intermediates produced in the reactions of triplet carbonyl compounds with electron donors has some obvious limitations. However, the technique of CIDNP is proving particularly effective at elucidating the reaction pathways in these systems. The outstanding work of Hendriks et al. (1979) illustrates the power of the technique. Not only was the role of radical ions in the reactions of alkyl aryl ketones with aromatic amines defined but the rate constants for many of the processes determined. The technique has been used to show that trifluoracetyl benzene reacts with electron donors such as 1,4-diazabicyclo[2.2.2]octane and 1,4-dimethoxy-benzene by an electron-transfer process (Thomas et al., 1977 Schilling et al., 1977). Chemically induced dynamic electron polarisation (CIDEP) has been... 

A directed aldol reaction is a variation of the crossed aldol reaction that clearly defines which carbonyl compound becomes the nucleophilic enolate and which reacts at the electrophilic carbonyl carbon. The strategy of a directed aldol reaction is as follows ... 

Complete band assignments have been proposed for the carbonyl compounds M(CO)e (M = Cr, Mo, or W), Fe(CO)5, Ni(CO)4, and M(CO)4 (M = Co, ra = 1 M = Fe, n= 2), and normal coordinate analyses have been reported. In all these systems, the number of force constants required to define the vibrations is in excess of the number of observable frequencies thus, absolute force constants cannot be calculated. In order that an acceptable set of force constants which adequately predict the observed frequencies can be calculated, simplification of the potential energy function is necessary. 

The reactivity pattern exhibited by jS-oxycyclopropyl-a-carbonyl compounds revolves chiefly around the selective fragmentation of the C-C bond situated between the oxy and carbonyl substituents, by virtue of the possible transmission of electron density between donor and electron units. Well defined polar intermediates, that is, zwitterionic species, are likely to intervene in some cyclopropyl-carbonyl transfigurations. 

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