Oxygen-17 NMR studies of substituent and hydrogen-bonding effects in substituted acetophenones and benzaldehydes

Amour, Thomas E. St.; Burgar, M.; Valentine, B.; Fiat, D.

doi:10.1021/ja00395a023

Cited by 111 publications

(34 citation statements)

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“…p * transition for acetone-water solutions [316] or for acetone in different solvents [317]. Similar trends have also been observed in a variety of para-substituted acetophenones [318] (Fig. 47), however, it has been suggested that such trends may be fortuitous, since the transition energy depends upon the balance of several effects associated with both p-donation and r-withdrawal [319].…”

Section: Empirical Correlations [256]supporting

confidence: 67%

Oxygen-17 NMR spectroscopy: Basic principles and applications (Part I)

Gerothanassis

2010

Progress in Nuclear Magnetic Resonance Spectroscopy

126

107

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Section: Empirical Correlations [256]supporting

confidence: 67%

Oxygen-17 NMR spectroscopy: Basic principles and applications (Part I)

Gerothanassis

2010

Progress in Nuclear Magnetic Resonance Spectroscopy

126

107

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“…2 kJ mol -1 below the corresponding values for the 4-methoxy analogue. 14 The decrease in the dimerization energy determined for 4-ethoxybenzaldehyde relative to the reported for the 4-methoxy derivative is in consonance with two other pieces of experimental evidence for the formation of C-H‚‚‚O hydrogen bonds: when 4-ethoxy is compared to 4-methoxybenzaldehyde, the former displays a smaller split between the free and bonded ν CdO bands (10 vs 14 cm -1 , respectively) and a smaller increase of the 17 O NMR chemical shift upon dilution (12 vs 15 ppm). Since the ethoxy group has a lower electron donor character than the methoxy group, it is reasonable to conclude that the presence of electron donor substituents is important for the formation of C-H‚‚‚O bonds in aldehydes, probably due to the increase of the electron density in the vicinity of the carbonyl oxygen atom.…”

Section: Discussionsupporting

confidence: 55%

“…Figure 6 shows the concentration dependence of the 17 17 O chemical shift of substituted benzaldehyde derivatives has been reported to move to higher field upon intra-or intermolecular hydrogen bonding. [18][19][20] In the case of 4-methoxybenzaldehyde, a 15 ppm shielding was previously observed for the carbonyl oxygen atom upon hydrogen bonding.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Evidence of C−H···O Hydrogen Bonds in Liquid 4-Ethoxybenzaldehyde by NMR and Vibrational Spectroscopies

2001

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Raman, FTIR, and NMR (both 13 C and 17 O) spectroscopies are used in a complementary way in order to study the occurrence of C-H‚‚‚O intermolecular hydrogen bonds in liquid 4-ethoxybenzaldehyde (4EtOB). Additional information concerning the structure of the possible dimers is obtained through ab initio calculations, at the B3LYP/6-31G* level. The strongest evidences of the presence of C-H‚‚‚O hydrogen bonds in the liquid phase arise from the temperature and solvent intensity dependence of the two bands observed in the ν CdO region of the vibrational spectra, as well as from the shift to low magnetic field detected for the carbonyl 17 O NMR peak at higher dilutions. Further evidence is gathered from the changes observed in the ν C-H vibrational modes, the 1 J CH concentration dependence detected in the NMR spectra, and ab initio results. The experimental observations are consistent with the decrease of the C-H bond length upon hydrogen-bonding, as predicted for the nonstandard blue-shifting hydrogen bonds. Ab initio calculations predict several possible structures for the dimeric species, with nearly identical energies. The calculated dimerization energy is within the -5.1 to -6.5 kJ mol -1 range, considering both basis set superposition error and zero-point vibrational energy corrections, in agreement with the obtained experimental ∆H value of -5.7 ( 0.5 kJ mol -1 .

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“…A further strong support for the hydrogen-bonded interactions is the significant decrease of the line width of the corresponding peaks, compared to the peak at 315.3 ppm. 26,27 This effect is attributed to the strong shielding of the 17 O nucleus, resulting from the increase of the electron density due to the decrease of the bond order. The reported resonances (315.3, 294.6, and 276.2 ppm) must be attributed to three different conformers interchanging at a slow rate.…”

Section: Resultsmentioning

confidence: 99%