Carbonyl substituent groups

Indirect evidence in support of both explanations for the dispersive kinetics of P decay comes from analysis of Ha" in reaction centres in the phototrapped state PHa"Qa = involving optical and magnetic resonance measurements at different temperatures and after different illumination times (M,h et al., 1999, 1998 Tiede et al., 1987). These experiments have shown that the Ha BPhe can adopt more than one conformation, and in particular that the 2-acetyl carbonyl substituent group adopts different conformations relative to the plane of the BPhe macrocycle depending on experimental conditions (M,h et al., 1999, 1998). Recent results from FTIR... 

Hence, ,re -excited states generally lie lower than 7i,7i -excited states involving the same re orbital. In aromatic molecules, n-orbitals are most often encountered in nitrogen heteroatoms and in carbonyl-substituent groups. The n-orbital is usually an sp2 hybrid directed in the plane of the aromatic ring and therefore at right angles to the re- and re - orbitals. 

In most cases the frequencies of substituent groups attached to these heterocycles differ little from those observed for their benzenoid counterparts. The only notable exception is the spectral behaviour of carbonyl groups attached to position 2. These have attracted much attention as they frequently give rise to doublets, and occasionally multiplets. In the case of (34), (35) (76JCS(P2)l) and (36) (76JCS(P2)597) the doublets arise from the presence of two conformers (cf. Section 3.01.5.2), whereas for the aldehydes (37) the doublets are... 

Table 8.6. Relative Stabilization of Carbonyl Compounds by Substituent Groups"...

In ketones having propyl or longer alkyl groups as a carbonyl substituent, intramolecular hydrogen abstraction can be followed by either cleavage of the bond between the a and P carbon atoms or by formation of a cyclobutanol ... 

When a carbonyl group is bonded to a substituent group that can potentially depart as a Lewis base, addition of a nucleophile to the carbonyl carbon leads to elimination and the regeneration of a carbon-oxygen double bond. Esters undergo hydrolysis with alkali hydroxides to form alkali metal salts of carboxylic acids and alcohols. Amides undergo hydrolysis with mineral acids to form carboxylic acids and amine salts. Carbamates undergo alkaline hydrolysis to form amines, carbon dioxide, and alcohols. 

Results for these CEBEs are presented in Table 1. As can be seen, for the carvone variants I-V the various substitutions have absolutely no effect at the carbonyl C=0 core, and are barely significant at the chiral center that lies between the carbonyl and substituent groups in these molecules. Only upon fluorine substitution at the tail (molecule VI) does the C=0 CEBE shift by one-half of an electronvolt the second F atom substitution adjacent to the C=0 in the difluoro derivative, VII contributes a further 0.6-eV shift. This effect can be rationalized due to the electron-withdrawing power of an F atom. Paradoxically, it is these fluorine-substituted derivatives, VI, VII, that arguably produce b curves most similar to the original carvone conformer, I, yet they are the only ones to produce a perturbation of the ground-state electron density at the C li core. This contributes further evidence to suggest that, at least for the C li... 

Some enamine alkylation reactions are shown in Scheme 1.10. Entries 1 and 2 are typical alkylations using reactive halides. In Entries 3 and 4, the halides are secondary with a-carbonyl substituents. Entry 5 involves an unactivated primary bromide and the yield is modest. The reaction in Entry 6 involves introduction of two groups. This... 

Some examples of IMDA reactions are given in Scheme 6.5. In Entry 1 the dienophilic portion bears a carbonyl substituent and cycloaddition occurs easily. Two stereoisomeric products are formed, but both have the cis ring fusion, which is the stereochemistry expected for an endo TS, with the major diastereomer being formed from the TS with an equatorial isopropyl group. 

The most optimistic response to this situation is to claim that the force constant — t-bond order relationship is still valid, but that the reference points need to be changed V(CO)e itself is then a possible reference compound (76). The relationship can then only be quantified by using calculated orbital populations for the reference species, and can only be tested by more extended comparisons between calculated bond order and observed force constant. Precisely this test has been apphed to a whole group of substituted and unsubstituted octahedral carbonyls of groups VI and VII, the substituents in every case being hahde (77). The data used in fact were not force constants, but Cotton-Krainhanzel parameters this does not actually matter, since no reference molecules were used at all. Excellent agreement was found with an expression. 

Intermediate I contains the tricyclic skeleton of longifolene, shorn of its substituent groups, but containing carbonyl groups suitably placed so that the methyl groups at C-2 and C-6 and the C-ll methylene can eventually be introduced. The retro synthetic step I = II corresponds to an intramolecular aldol condensation. However, II clearly is strained relative to I, so II (with OR=OH) should open to I. 

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