Inductive effect carbonyl substituents

If both substituents on a C=0 bond are carbon or heavier atoms and bond angles are normal ( 120 ") then carbonyl frequency shifts can be related directly to mesomeric and inductive effects which account for the change in force constants of C=0 bonds and substituent single bonds. In the inductive effect, electronegative substituents (like Cl) raise C==0 frequencies by reducing the weight of carbonyl bond weakening resonance forms... 

The addition of water to the carbonyl group in aqueous solutions can lead to the formation of hydrates. The reactions and stability of hydrates depend primarily on the inductive effect of substituents. Hydration of formaldehyde readily yields methylene glycol (methanediol), which polymerises to linear oligomers and also to polymers known as paraformaldehyde. Hydrates of a-dicarbonyl and a-hydroxycarbonyl compounds spontaneously dimerise into various cyclic 1,4-dioxanes (see Figure 4.62). These hydrates are intermediates of other a-dicarbonyl and a-hydroxycarbonyl compounds in the oxidation-reduction reactions and precursors of carboxylic acids. Dialkyl ketones do not form hydrates. 

Carboxylic acids are weak acids and m the absence of electron attracting substituents have s of approximately 5 Carboxylic acids are much stronger acids than alcohols because of the electron withdrawing power of the carbonyl group (inductive effect) and its ability to delocalize negative charge m the carboxylate anion (resonance effect)... 

In transforming bis-ketone 45 to keto-epoxide 46, the elevated stereoselectivity was believed to be a consequence of tbe molecular shape — tbe sulfur ylide attacked preferentially from tbe convex face of the strongly puckered molecule of 45. Moreover, the pronounced chemoselectivity was attributed to tbe increased electropbilicity of the furanone versus the pyranone carbonyl, as a result of an inductive effect generated by tbe pair of spiroacetal oxygen substituents at tbe furanone a-position. ... 

Effect of substituents of the carbonyl bond, (a) Inductive effect, X = H, OH,... 

Another important site of structural variation in cephalosporins is C(3) (Table 5.4.J). Electron-withdrawing substituents at C(3) such as a Cl-atom or a MeO group increase base-catalyzed hydrolysis of cephalosporins by both resonance and inductive effects [92], For cephalosporins carrying 3-methylene-linked substituents with leaving group ability (e.g., acetate, thiol, or pyridine), it has been postulated that a concerted expulsion of the substituent facilitates the nucleophilic attack on the /3-lactam carbonyl group [104][105]. However, there are also arguments for a stepwise process in which the ex-... 

On the assumption that all the reported aldehyde first ionization potentials refer to the oxygen lone-pair electrons Cook (1958) has classified the effect of substituents into two classes, A and B, according to whether inductive or resonance effects predominate. Two different linear correlations (Fig. 14) were found between ionization potential and the carbonyl stretching frequency. Anomalies were noted for diacetyl, benzaldehyde and mesityl oxide, ascribed in the last instance to noncoplanarity interfering with resonance. It seems more likely, however, that in these cases the first ionization potential refers to 7r-electrons and higher values for the lone-pair electrons (as yet undetermined) might remove the anomalies. 

If there is a suitable electron-withdrawing substituent, hydrate formation may be favoured. Such a situation exists with trichloroacetaldehyde (chloral). Three chlorine substituents set up a powerful negative inductive effect, thereby increasing the 8- - charge on the carbonyl carbon and favouring nucleophilic attack. Hydrate formation is favoured, to the extent that chloral hydrate is a stable solid, with a history of use as a sedative. 

Infrared spectra were used for investigations on tautomerism and isomerism. The frequencies of the carbonyl stretching bands seem to depend on mesomerism and inductive effects with respect to the positions of the carbonyl group and the substituents at the triazolopyrimidine system [77HC(30)179]. 

Since the carbonyl group has gone in R2C(OH)CN, we would expect very little effect from any of these substitutents. There can t be any conjugation, and inductive effects on the distant 0 atom will be small. What effect would an inductively withdrawing substituent have on the equilibrium for cyanohydrin formation ... 

Since tJtiis reaction is an equilibrium, the amount of cyanohydrin formed from any given carbonyl compound will depend on the relative stabilities of the carbonyl compound itself and the product. There can be many substituents X on a carbonyl compound R.CO.X, such as Cl, Me, NH2, Ph, OEt, H. Some have inductive effects, some conjugate with the carbonyl group. Some stabilise RCOX making it less reactive. Others activate it towards nucleophilic attack. Arrange the compounds RCOX, where X can be the substituents listed above, into an order of reactivity towards a nucleophile. 

The electron withdrawing inductive effects of the fluorine substituents render the carboxonium ion 3 more electrophilic than carboxonium ion 2, and consequently it reacts with benzene. Thus, the electrophilic reactivity of the carbonyl group can be greatly enhanced by Brpnsted or Lewis acid solvation and by substitution with electron withdrawing groups. 

Hydrogen abstraction by triplet carbonyl compounds has been the most widely studied excited state reaction in terms of structural variations in reactants. Consequently, the most detailed structure-reactivity relationships in photochemistry have been developed for hydrogen abstraction. These correlations derive from studies of both bimolecular reaction and intramolecular reactions. The effects of C—H bond strength and the inductive and steric effects of substituents have been analyzed. The only really quantitative comparisons between singlets and triplets and between n,n and 71,71 states have been provided by studies of photoinduced hydrogen abstractions. 

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