Phenyl-carbonyl bonds

Due to a partial 77-character, aromatic carbonyl compounds have an activation energy barrier for rotation around the phenyl-carbonyl bond, the value of which is substantially increased upon protonation.44 In para-anisaldehyde a second protonation of the methoxy group will drastically decrease their barrier. The temperature-dependent NMR spectrum will reflect both exchange processes, intra- and intermolecular, as shown in Scheme 1.1. 

Carbonyl groups are also utilized in catalytic C-C bond cleaving reactions. Under catalytic conditions, 8-quinolyl phenyl ketone 85 reacts with ethylene to give 8-quinolyl ethyl ketone 86 and styrene in quantitative yield [105]. Styrene is formed by cleavage of the phenyl-carbonyl bond, followed by ethylene insertion into the resultant phenyl-rhodium bond, and (3-hydride elimination. The accompanying formation of a rhodium-hydride complex is followed by incorporation of ethylene to furnish the ethyl ketone 86. 

In conjugated systems, steric repulsion between alkyl groups may oppose conjugation and cancel the upheld shift characteristic of the conjugated state. This can be seen for a series of acetophenones, and a dependence on the torsional angle 0 between phenyl and carbonyl bonding planes becomes obvious [73 c], e.g. ... 

The temperature dependence of the oscillation amplitudes associated with the carbonyl groups, shown in Fig. 83, is very similar to that of the aromatic carbons, indicating that the C = O groups and adjacent phenyl rings are involved in correlated motions. Such a conclusion is consistent with the quasi-conjugated character exhibited by the phenyl-amide bond. 

Ionic initiators are much more specific toward the type of monomer and can initiate polymerization in some cases where radical initiation is ineffective (cyclic, vinyl ether, or allylic monomers). Monomers suitable for anionic initiation are those with an electron-withdrawing substituent attached to the double bond (phenyl, carbonyl, etc.). The reaction consists... 

The mass spectra of certain metal carbonyl complexes of triphenyl-phosphine and l,2-bis(diphenylphosphino)ethane (Pf-Pf) have been investigated 48>. Besides the usual stepwise loss of carbonyl groups, cleavage of the phosphorus-carbon bond occurs. Thus triphenylphosphine complexes exhibit cleavage of the phenyl-phosphorus bond after all carbonyl groups are lost. The 1,2- bis(diphenylphosphino)ethane complexes (e.g. (Pf-Pf)[W(CO)5]2 and (Pf-Pf)M(CO)4) exhibit elimination of the ethylene bridge between two phosphorus atoms. 

Figure 9.15. Effect of substituents of the carbonyl bond, (a) Inductive effect. X H, OH, OR, halogen, (b) Resonance effect, Y NH2, NHR, NRj, phenyl...

This dimer when treated with iodine produced 7r-C5H5Fe[P(OPh)3]2l, whose structure was proved by the formation of [7r-C5H5Fe(CO)2]2 under the action of CO. Apart from the latter carbonyl, a deeper colored compound was formed whose properties and elemental analysis were close to those of the carbonyl. The compound was thought to be the isomer of the carbonyl, but the X-ray analysis showed that the carbon of one of the phenyls was bonded in a striking manner to a carbon of the cyclopentadienyl (445). 

The X-ray structure determination of 2-diazo-l,2-diphenylethan-l-one ( azibenziP, 5.14) was accomplished by von Schnering et al. (1986). Relative to l,4-bis(diazo)-butane-2,3-dione longer CN and NN bonds (134.3 and 112.4 pm, respectively), a shorter carbonyl bond (120.8 pm) and a remarkably longer C(l) - C(2) bond (147.3 pm) were reported. The two phenyl groups are configurated (E) to each other. 

Sterically, acetophenone is bulkier around the carbonyl carbon. This renders the carbon less accessible for nucleophilic addition. Thermodynamically, the ketone-carbonyl bond is stronger, about 3 kcal, than the aldehyde-carbonyl bond. Thus, the addition at the acetophenone carbonyl carbon is much less favorable. Therefore, the predominant product is phenylethenyl phenyl ketone. 

Cabon-carbon double- and triple-bond-containing substrates sometimes react with double bond-containing isocyanates to undergo the Diels-Alder reaction. For example, phenyl-carbonyl isocyanate reacts with ethoxyacetylene to give the [4+2] cycloadduct 491. ... 

Cycloadditions The [4+2] cycloaddition reactions of carbodiimides with phenyl-carbonyl isocyanate, phenylcarbonyl isothiocyanate and thiocarbamoyl isothiocyanate have been discussed above. In the dimerization reactions the functional carbodiimides react as both the diene and the dienophile. Unsaturated carbodiimides, generated in situ, can be trapped with N=N bond- or C=N bond-containing substrates. 

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