Carbonyl compounds theoretical studies

The ultraviolet absorption spectrum of cyclohexanone reflects the n jt transition common to all carbonyls see figure IX-E-1. The data derived from gas-phase measurements of the cross sections for cyclohexanone from two different research groups [National Center for Atmospheric Research (NCAR) and Ford Scientific Laboratories (Ford)] are in reasonable agreement (Iwasaki et al., 2008). The cyclohexanone cross sections as measured in cyclohexane solution by Benson and Kistiakowski (1942) had indicated seemingly low values (cross sections shown here is significantly less than those observed for cyclopropanone, cyclobutanone, and cyclopentanone, and in fact, all other carbonyls considered in this work. It is not obvious why these significant differences exist in the probability for the n -> 7T transition for cyclohexanone and that of the other cyclic ketones and most other carbonyl compounds. Theoretical studies will be important in defining the reasons for these differences. 

By the late 1960s, more experimental observations of partial emission in esr spectra were reported. By the early 1970s, totally emissive esr spectra were reported (13,95,96,135) in photochemical systems of organic carbonyl compounds. These studies generated much theoretical interest in CIDEP, but the mechanisms of the dynamic electron polarization in various chemical systems remained controversial for a long time. 

In a study of the deoxygenation of carbonyl compounds by atomic carbon, Dewar and coworkers (8UA2802) presented experimental and theoretical evidence that the carbonyl group can react with carbon atoms to form a carbenaoxirane. 

The importance of displacement reactions on carbonyl compounds in chemistry and biochemistry has resulted in numerous mechanistic studies. In solution, there is general acceptance of the following mechanism for addition of anionic nucleophiles which features a tetrahedral intermediate, 1, and is designated (1). However, recent experimental (2 10) and theoretical (11-17)... 

NMR spectroscopic studies f111,13C, and 31P) are consistent with the dipolar ylide structure and suggest only a minor contribution from the ylene structure.234 Theoretical calculations support this view.235 The phosphonium ylides react with carbonyl compounds to give olefins and the phosphine oxide. 

Recently, Schleyer and co-workers reported a theoretical study on the stabilities and geometries of a series of carbonyl type compounds, R2M=0 (M = C, Si, Ge, Sn, Pb R = H, CH3), and those of carbene type isomers [R(RO)M ] as shown in Table II.15 These results show that in (CH3)2 M=0 series the carbene type structure is more stable than the double bond type structure in the case of germanium, tin, and lead, unlike the case of carbon in which the double bond structure is preferred. 

While a large number of studies have been reported for conjugate addition and Sn2 alkylation reactions, the mechanisms of many important organocopper-promoted reactions have not been discussed. These include substitution on sp carbons, acylation with acyl halides [168], additions to carbonyl compounds, oxidative couplings [169], nucleophilic opening of electrophilic cyclopropanes [170], and the Kocienski reaction [171]. The chemistry of organocopper(II) species has rarely been studied experimentally [172-174], nor theoretically, save for some trapping experiments on the reaction of alkyl radicals with Cu(I) species in aqueous solution [175]. 

An extensive review of the hetero-Diels-Alder reactions of 1-oxabuta-1,3-dienes has been published. Ab initio calculations of the Diels-Alder reactions of prop-2-enethial with a number of dienophiles show that the transition states of all the reactions are similar and synchronous.Thio- and seleno-carbonyl compounds behave as superdienophiles in Diels-Alder reactions with cyclic and aryl-, methyl-, or methoxy-substituted open-chain buta-1,3-dienes.The intramolecular hetero-Diels-Alder reactions of 4-benzylidine-3-oxo[l,3]oxathiolan-5-ones (100) produce cycloadducts (101) and (102) in high yield and excellent endo/exo-selectivity (Scheme 39). A density functional theoretical study of the hetero-Diels-Alder reaction between butadiene and acrolein indicates that the endo s-cis is the most stable transition structure in both catalysed and uncatalysed reactions.The formation and use of amino acid-derived chiral acylnitroso hetero-Diels-Alder reactions in organic synthesis has been reviewed. The 4 + 2-cycloadditions of A-acylthioformamides as dienophiles have been reviewed. ... 

The mechanism of the dissociation of 1,2,3-trioxolanes to carbonyl oxides and carbonyl compounds has been studied by theoretical methods. Earlier ab initio calculations concluded that a biradical pathway and a concerted pathway were equally probable <81JA3619, 8UA3627), though it has been suggested that the transition state was not sufficiently characterized in these calculations to enable firm conclusions to be drawn from this work <91JA735>. More recent semiempirical AMI... 

These highly reactive 1,3-dipolar species readily isomerize and undergo 1,3-cycloaddition reactions in addition to their cyclization to the corresponding dioxirane. It is within this latter context that we describe the more recent theoretical studies on carbonyl oxides and their relationship to dioxiranes. As a result of the lability of carbonyl oxides much of the research on this class of compound has been of a theoretical nature ... 

Unlike olefin insertion, the reaction of aluminium alkyls with carbonyl compounds has not been studied theoretically before. The calculated barriers for addition and j -hydrogen transfer in the system Me2AlEt -I- CH2=0 are very similar (15.4 and 14.3 kcal/mol, respectively see Table 1), in accord with the close competition between the two reaction types observed experimentally. 

Friedrichsen and co-workers (135), along with Padwa, has utilized the carbonyl ylide cycloaddition to generate reactive furan moieties that can be further used in inter- or intramolecular Diels-Alder reactions to prepare aza- and carbocyclic compounds. Friedrichsen conducted a number of synthetic and theoretical studies on the reactivity, regioselectivity, and stereoselectivity of substituted furan formation and subsequent Diels-Alder reaction (Scheme 4.69). 

A number of systematic structural analyses have been described for families of saturated oxazolones. First, as mentioned previously, detailed smdies of NMR long-range coupling in 2,4-disubstimted-5(47/)-oxazolones and in 5(27/)-oxazo-lones have been reported." Similarly, detailed NMR studies of the kinetics of racemization of 2,4-disubstimted-5(47/)-oxazolones have been performed. A theoretical study of the spectral-luminescence properties of some 4-alkyl-2-phenyl-5(47/)-oxazolones has been reported and an investigation of the infrared (IR) and Raman spectra of 5(4//)-oxazolones, particularly of the carbonyl group vibration, has been reported. Electron impact mass spectra of saturated 5(47/)-oxazolones have been published. More recently this technique has been used to distinguish between the stereoisomers of some spirocyclopropane oxazolones 352 (Fig. 7.36). Finally, several studies of the HPLC behavior of 5(47/)-oxazolones complete a general view for this family of compounds. " " ... 

Theoretical studies of the addition of RMgX to carbonyl compounds 371... 

Theoretical studies of the addition of RMgX to carbonyl compounds 375 TABLE 3. Energies, dipole moments and geometries of CH3CI and CHsMgCl... 

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