863. Infrared spectra and polar effects. Part VII. Dipolar effects in α-halogenated carbonyl compounds

Bellamy, L. J.; Williams, R. L.

doi:10.1039/jr9570004294

Cited by 128 publications

(23 citation statements)

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“…A series of papers have investigated the rotation isomerism of α-haloketones using Raman [ 11 ], IR [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ] and NMR [ 24 , 25 ] spectroscopy. Although α-haloketones can exist as two stereoisomers [ 11 ], it has been established, however, that the steric repulsion between the Cl-atom and O-atom, in the liquid state, is much less than that between Cl-atom and an alkyl group.…”

Section: Molecular Structures and Spectral Propertiesmentioning

confidence: 99%

The Chemistry of α-Haloketones and Their Utility in Heterocyclic Synthesis

2003

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Section: Molecular Structures and Spectral Propertiesmentioning

confidence: 99%

The Chemistry of α-Haloketones and Their Utility in Heterocyclic Synthesis

2003

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“…Analogy with halogeno-and cyano-acetic esters (10,14) suggests conformer I with R1 = Ph and For personal use only.…”

Section: Discussion ( a ) Stretching Frequenciesmentioning

confidence: 99%

The Carbonyl-Stretching Vibration of Arylaliphatic Esters

Bowden¹,

Chapman²,

Shorter³

1963

Can. J. Chem.

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The infrared spectra in the carbonyl-stretching region of certain arylaliphatic esters, RCOOkIe, have been examined. The stretching frequencies and absorption intensities are presented and are discussed in terms of polar and a-mass effects and thc occurrencc of conformational isomers. IXTKODCCTIOSAs carbonyl vibrations are considered rarely to be perturbed by coupling with other vibrations, the corresponding absorption band and its variation with structure has been widely studied. Several factors may affect this vibration, of which the most important, for the present work, are polar, a-mass, and steric effects.Thompson and his co-worliers (I) have suggested that the force constant is primarily determined by the relative contributions of the canonical structures I , 11, 111, and IV to the structure of the carbonyl group. The relative importance of these structures is determined by the ability of X and Y either to interact with the carbonyl bond (cf. I11 and IV), or to alter the relative contributions of I and I1 by an electrostatic effect (i.e. inductive or direct field). Since the value of the frequency indicates the energy needed to produce a dipolar state, a reduction in the part played by structures 11, 111, and IV will increase the frequency.The effect on the frequency of increasing the irlass of a-substituents is significant for small masses but reaches a limit for group X or Y in XYC=O with higher masses (e.g., Halford (2) considers the effects to be constant above about 27 atomic weight units for X or Y). Substitution of deuterium for a-hydrogen atoms in esters or ketones has been found to give fairly large a-mass effects (3).A reduction in the X-C-Y intervalency angle in X-CO-Y will increase the frequency as has been observed for the carbonyl vibrations of strained ring ketones (4, cf, ref. 2). In the absence of any change in the steric environment of the motion, successful correlations have been obtained of the carbonyl frequencies of substituted ethyl benzoates and acetophenones with substituent constants of the Hammett type (5). Similar correlations involving the carbonyl-stretching frequencies of substituted aliphatic esters and ketones have been made with varying success. Correlations of doubtful value for intensities, due to the narrow range of intensities covered and the small number of substituents involved (B), have also been attempted.A number of investigators have observed the splitting of the carbonyl bands of ketones 'Present address:

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“…Of 56 reaction series common to both treatments, Bekkum, Verkade and Wepster find 34% having correlation coefficients better than 0.998, 77% better than 0.99 and 89% better than 0.98; while Jaff6, for these reaction series, finds 29% better than 0.99, 59% better than 0.98, but none better than 0.998, in fact only 6% of the 371 reactions covered shorn this high precision. That this marked improvement is due to the removal of deviations due to variable p-substituent influences is shown by the computation of sigmavalues for other m-substituents (Table IV, numbers [11][12][13][14][15][16][17][18][19]. The standard deviations obtained are no larger than might be expected and do not greatly exceed those for substituents "H" and "p-NOn" (Table V) calculated from reaction series correlated using the primary values of these substituents.…”

Section: The Substituent Parametersmentioning

confidence: 99%