17O NMR spectroscopy: Geometric effects on intramolecular hydrogen bonding in rigid carbonyl systems

Photophysical Properties of Intramolecular Charge-Transfer Excited Singlet State of Aminofluorenone Derivatives

“…The former group has an amino group in the ortho or para position to the carbonyl group, and the latter has an amino group in the meta position to the carbonyl group. They have a similar infrared absorption of the carbonyl group, 17 O NMR chemical shifts of the carbonyl oxygen,17a and 1 H NMR chemical shifts of the amino proton 18 within each group. The classification of aminofluorenones in the excited singlet state is interesting.…”

“…Furthermore, intramolecular hydrogen bond of 1AF in the ground state was discussed by Baumstark et al with 17 O NMR; the chemical shifts of the carbonyl oxygen of 1AF were not so deshielded by the amino hydrogen compared with 3AF, and this result was significantly different from other typical intramolecular hydrogen-bonded compound such as hydroxyacetophenone 25 and 1AAQ 17b. The intramolecular hydrogen bond of 1AF was concluded to be weak because of the long distance between the carbonyl oxygen and the amino hydrogen 17b. Possibilities other than the simple explanation involving an intramolecular hydrogen bond should be further considered.…”

“…1AF has too long a distance between the carbonyl group and the amino hydrogen to form a strong hydrogen bond. 17b, Srivatsavoy et al reported that molecules having intersystem crossing as the dominant mode of deactivation showed small isotope effects such as those of 1-(acetylamino)-9,10-anthraquinone (1.3) and 1,5-diamino-9,10-anthraquinone (1.6), while the molecules having internal conversion as the dominant mode of deactivation showed a large isotope effect such as those of 1AAQ (8.3) and 1-(methylamino)-9,10-anthraquinone (6.5) . Furthermore, intramolecular hydrogen bond of 1AF in the ground state was discussed by Baumstark et al with 17 O NMR; the chemical shifts of the carbonyl oxygen of 1AF were not so deshielded by the amino hydrogen compared with 3AF, and this result was significantly different from other typical intramolecular hydrogen-bonded compound such as hydroxyacetophenone 25 and 1AAQ 17b. The intramolecular hydrogen bond of 1AF was concluded to be weak because of the long distance between the carbonyl oxygen and the amino hydrogen 17b.…”

17O chemical shifts and deuterium isotope effects on13C chemical shifts of intramolecularly hydrogen-bonded compounds

“…9 Hydrogen bonding has been shown to inÑuence Cx17O chemical shifts,10h25 and the e †ect has been described in terms of the acidity of the donor,23 the basicity of the acceptor,23 a twist of the acceptor group16 and in-plane distortions. 17,18 The OH chemical shifts of intramolecularly hydrogen-bonded phenols vary somewhat, 14,17,19h21 and recent data for indane-1, 3-diones show larger variations in enols. 22 Steric e †ects could also play a role.9 17O chemical shifts show a large dispersion10 in general and have therefore been used to estimate equilibrium constants of tautomeric systems such as b-diketones.26h28 One problem in using 17O chemical shifts in tautomeric systems is to obtain proper limiting 17O chemical shifts.…”

Carbonyl Groups as Molecular Valves to Regulate Chloride Binding to Squaramides

“…The N−H signal for 4 in CHCl 3 was found to be significantly upfield (10.4 ppm) relative to 1 and 2 (11.2 and 11.3 ppm, respectively) as well as the constrained anthraquinone squaramide 5 (12.6 ppm). This suggests a considerably weakened intramolecular hydrogen bond in the fluorenone squaramide 4 relative to 1 , 2 , and 5 . However, despite the weakened intramolecular hydrogen bonding, no chloride-induced spectral changes in CHCl 3 were detected for 4 , thereby underscoring the requirement for carbonyl reorientation.…”