Photoisomerization of the enol form of 1,3-dicarbonyl compounds

Veierov, D.; Bercovici, T.; Fischer, Ernst Otto; Mazur, Yehuda; Yogev, Amnon

doi:10.1021/ja00450a053

Cited by 46 publications

(40 citation statements)

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“…This approach is reasonable since the extinction coefficients of the CE and NCE form are comparable. 9 However, as the dynamics of the formation of the photoproduct are supposably not completed in the experimentally accessible time window the uncertainty in the NCE product percentages is larger than the difference found for different excitation wavelengths. Note that before the division, the value of ΔAbs was averaged over 10 delay times for both initial bleach signal (first 10 steps of delay following the temporal pump−probe overlap) and final photoproduct signal (last 10 steps of delay).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…8 The scenario upon absorption of UV light is a different one in liquids, where rotamerization is the dominant channel while tautomerization remains limited. Flash photolysis experiments on a number of β-diketones at room temperature 9,12−14 corroborated that UV irradiation breaks the intramolecular H-bond of the CE form, eventually leading to formation of NCE conformers. These structural changes are reversible, since the less stable photoproducts (NCE conformers) convert back to the most stable CE form, to a minor extent to the diketone form or into a mixture of both.…”

Section: ■ Introductionmentioning

confidence: 96%

“…C o m p o u n d s l i k e β -d i k e t o n e s o f t y p e R−C(O)−CH 2 −C(O)−R, where R = H, CH 3 , have drawn continuous attention from chemists and physicists of different research areas because of the pronounced keto−enol tautomerism that is observable (and exploitable) in the gas 5,8 and the liquid phase 6,9 and even in isolated cryogenic matrices. 7,10 The reason for the stabilization of the enolic form is an intramolecular H-bond, coupled with a π-electronic delocalization over the O−C−C−C−O pseudocycle (see Scheme 1).…”

Section: ■ Introductionmentioning

confidence: 99%

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Ultrafast UV-Induced Photoisomerization of Intramolecularly H-Bonded Symmetric β-Diketones

et al. 2014

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In photoinduced molecular reaction dynamics, the effects of electronic charge redistribution can lead to multiple pathways that are determined by the nature of the initial structures involved and the environment the molecule of interest is studied in. The β-diketones are a common example of this complexity. They show keto−enol tautomerism that is almost totally shifted toward the enolic form. However, compared to the gas phase, the photochemistry proceeds completely differently by virtue of the solvent environment for these compounds, which are used in commercial sunscreen agents due to a high absorption in the ultraviolet (UV) and fast deactivation processes. We disclose these dynamics by investigating three symmetrical β-diketones in various solvents. To observe these effects on an ultrafast time scale directly in the UV spectral region where the relevant electronic transitions take place, we have developed and employed femtosecond transient absorption with detection capability in the deep UV. Our studies confirm that electronic excitation of the chelated enol form does not lead to any ultrafast photochemistry other than proton transfer followed by rotamerization. The formation of the nonchelated conformers takes place on a picosecond time scale through a dark state, whereas the recovery to the stable chelated enol form is a comparably slow process. ■ INTRODUCTIONDerivatives of β-diketones are of great importance in diverse research fields by virtue of several remarkable chemical features that lead to a variety of applications. 1 For example, they are widely employed as chelating agents due to their binding affinity for transition metals, 1 or they are even contained in commercial sunscreen products 2−4 owing to the fast deactivation processes after ultraviolet (UV) irradiation. The most prominent property of β-diketones is their keto−enol tautomerism that is shifted almost totally toward the enolic form. 5−7 With structural similarities to relevant biomolecules and photochromic substances on the one hand, and the molecules' own versatility in combination with their structural simplicity on the other hand, small β-diketones are prototypical candidates for a systematic study of the photoinduced processes and the subsequent deactivation channels upon which the wide applicability of β-diketones is based.C o m p o u n d s l i k e β -d i k e t o n e s o f t y p e R−C(O)−CH 2 −C(O)−R, where R = H, CH 3 , have drawn continuous attention from chemists and physicists of different research areas because of the pronounced keto−enol tautomerism that is observable (and exploitable) in the gas 5,8 and the liquid phase 6,9 and even in isolated cryogenic matrices. 7,10 The reason for the stabilization of the enolic form is an intramolecular H-bond, coupled with a π-electronic delocalization over the O−C−C−C−O pseudocycle (see Scheme 1). The two simplest and smallest structures exhibiting the central six membered ring closed by the intramolecular Hbond in the chelated enol (CE) form are the compounds malonaldehyde (M...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 96%

Section: ■ Introductionmentioning

confidence: 99%

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Ultrafast UV-Induced Photoisomerization of Intramolecularly H-Bonded Symmetric β-Diketones

et al. 2014

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“…The population of keto and enol depends on many factors, such as the solvent polarity , temperature (Burdett and Rogers, 1966), and the presence of UV irradiation (Coussan et al, 2003;Veierov et al, 1973Veierov et al, , 1977. For example, in aliphatic hydrocarbon solvents, including n-hexane, n-heptane, cyclohexane, and benzene, AA exists predominantly in the chelated enol (Veierov et al, 1977), while the keto form predominates in aqueous solutions due to the strong intermolecular hydrogen bonding with water .…”

Section: Introductionmentioning

confidence: 99%

Fate and implication of acetylacetone in photochemical processes for water treatment

Zhang

2016

Water Research

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“…(9), V=Ax 4 +Bx 2 (9) which describes one-dimensional curves of the double minimum type used in representing hydrogen bonds. Isotopic redistribution of HFAA with ButOH/ButOD in acetonitrile was measured and the concentrations determined spectroscopically at 2650-3000 nm ~2°).…”

Section: Ioxl 8 ~X = [Hx] Aqmentioning

confidence: 99%

The composition, structure and hydrogen bonding of the β-diketones

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Proton transfer and hydrogen bonding are two aspects of the chemistry of hydrogen that respectively govern the behaviour and structure of many molecules, both simple and complex, from water to DNA. The fl-dicarbonyls exhibit both of these features, and in ways which have singled them out for detailed study for many years. They provide the best known examples of keto --,~ enol tautomerism, with the advantage of slow proton transfer and high concentrations of the enol tautomers in most cases. These enols are stabilized by intramolecular OHO hydrogen bonds which at various times have been thought of as being centred, linear hydrogen bonds that are somehow incorporated into the delocalised zt system to give "aromatic" systems. Research involving structural, spectroscopic and computational techniques has deepened our understanding of these compounds and changed our picture of them. The hydrogen bonding is surprisingly strong, surprising since it is neither centred, nor linear, nor involved in the ring's delocalized bonding, although it is certainly coupled to it. This review deals with controversies that have surrounded the fl-dicarbonyls and discusses the current view that the enol tautomers are a double-minimum potential well with a low energy barrier. The review ends with a brief took at the fl-thioxoketones, which provide an analogous system based on a heteronuclear SHO hydrogen bond in the enol or enethiol tautomer.

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Photoisomerization of the enol form of 1,3-dicarbonyl compounds

Cited by 46 publications

References 3 publications

Ultrafast UV-Induced Photoisomerization of Intramolecularly H-Bonded Symmetric β-Diketones

Ultrafast UV-Induced Photoisomerization of Intramolecularly H-Bonded Symmetric β-Diketones

Fate and implication of acetylacetone in photochemical processes for water treatment

The composition, structure and hydrogen bonding of the β-diketones

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