On Electron Pair Rearrangements in Photochemical Reactions: 1,3-Cyclohexadiene Ring Opening

2021 ◽  
Author(s):  
Cristian Guerra ◽  
Leandro Ayarde-Henríquez ◽  
Mario Duque-Noreña ◽  
Eduardo Chamorro
Keyword(s):  
Ring Opening ◽  
Electron Pair ◽  
Photochemical Reactions

Organic Sulfur Mechanisms. 17. A Brief Study of the Photolysis of an Unsaturated Cyclic Sulfone

1975 ◽  
Vol 53 (23) ◽  
pp. 3656-3659 ◽  
Author(s):  
J. F. King ◽  
E. G. Lewars ◽  
D. R. K. Harding ◽  
R. M. Enanoza
Keyword(s):  
Free Electron ◽  
Ring Opening ◽  
Electron Pair ◽  
Heterocyclic Ring ◽  
Organic Sulfur ◽  
Free Electron Pair

Photolysis of 3-phenyl-2H-thiopyran 1,1-dioxide (3) in methanol gives a mixture of 3-phenyl-5-methoxy-5,6-dihydro-2H-thiopyran 1,1-dioxide (4) and methyl 4-phenyl-2,4-pentadiene-1-sulfonate (5). Formation of 5 shows that the photochemical ring opening of cyclohexadienic sulfonyl compounds (1) does not require an atom bearing a free electron pair in the heterocyclic ring, and therefore argues in favor of a mechanism involving cycloreversion to the sulfene (1 → 2).

scholarly journals Structural dynamics of photochemical reactions probed by time-resolved photoelectron spectroscopy using high harmonic pulses

2016 ◽  
Vol 194 ◽  
pp. 147-160 ◽  
Author(s):  
Ryo Iikubo ◽  
Taro Sekikawa ◽  
Yu Harabuchi ◽  
Tetsuya Taketsugu
Keyword(s):  
Photoelectron Spectroscopy ◽  
Ring Opening ◽  
Potential Energy Surfaces ◽  
High Harmonic ◽  
Photochemical Reactions ◽  
Photoelectron Spectra ◽  
Time Resolved ◽  
Photon Excitation ◽  
Energy Surfaces ◽  
Sigma Bond

Femtosecond ring-opening dynamics of 1,3-cyclohexadiene (CHD) in gas phase upon two-photon excitation at 400 nm (=3.1 eV) was investigated by time-resolved photoelectron spectroscopy using 42 nm (=29.5 eV) high harmonic photons probing the dynamics of the lower-lying occupied molecular orbitals (MOs), which are the fingerprints of the molecular structure. After 500 fs, the photoelectron intensity of the MO constituting the CC sigma bond (σCC) of CHD was enhanced, while that of the MO forming the C–C sigma bond (σCC) of CHD was decreased. The changes in the photoelectron spectra suggest that the ring of CHD opens to form a 1,3,5-hexatriene (HT) after 500 fs. The dynamics of the σCC and σCC bands between 200 and 500 fs reflects the ring deformation to a conical intersection between the 21A and 11A potential energy surfaces prior to the ring-opening reaction.

scholarly journals Heteroaromatic N-Oxides in Asymmetric Catalysis: A Review

Molecules ◽  
2020 ◽  
Vol 25 (2) ◽  
pp. 330 ◽  
Author(s):  
Zuzanna Wrzeszcz ◽  
Renata Siedlecka
Keyword(s):  
Oxygen Atom ◽  
Asymmetric Catalysis ◽  
Michael Addition ◽  
Ring Opening ◽  
Electron Pair ◽  
Optically Active ◽  
High Affinity ◽  
Nitroaldol Reaction ◽  
Electronic Environments ◽  
Powerful Electron

An increasing interest in the synthesis and use of optically active pyridine N-oxides as chiral controllers for asymmetric reactions has been observed in the last few years. Chiral heteroaromatic N-oxides can work as powerful electron-pair donors, providing suitable electronic environments in the transition state formed within the reaction. The nucleophilicity of the oxygen atom in N-oxides, coupled with a high affinity of silicon to oxygen, represent ideal properties for the development of synthetic methodology based on nucleophilic activation of organosilicon reagents. The application of chiral N-oxides as efficient organocatalysts in allylation, propargylation, allenylation, and ring-opening of meso-epoxides, as well as chiral ligands for metal complexes catalyzing Michael addition or nitroaldol reaction, can also be found in the literature. This review deals with stereoselective applications of N-oxides, and how the differentiating properties are correlated with their structure. It contains more recent results, covering approximately the last ten years. All the reported examples have been divided into five classes, according to the chirality elements present in their basic molecular frameworks.

Reaction Mechanisms

2016 ◽  
Author(s):  
Richard M. Pagni
Keyword(s):  
Eighteenth Century ◽  
Reaction Mechanisms ◽  
Ring Opening ◽  
Photochemical Reactions ◽  
Related Question ◽  
Quantum Mechanical ◽  
Thermally Induced ◽  
Modern Chemistry ◽  
Ring Opening Reactions ◽  
Opening Up

AFTER I HAD BEEN in graduate school for several months, I decided to work in a group that studied photochemical reactions, those that are initiated by ultraviolet or visible light. My research advisor was interested in discovering new reactions and deducing experimentally how they occurred—the reaction mechanism. I remember my first group meeting where the topic of discussion was the ring-opening of cyclobutenes (compounds with four carbon atoms in a ring opening up to form compounds with no rings). I still recall people describing the potential ways in which the ring-openings occurred as domino and antidomino (today called conrotatory and disrotatory). Thermally induced reactions, that is, those initiated by heat, occurred one way and photochemically induced reactions, the other. Even though these reactions had been studied thoroughly, the reaction mechanisms were considered incomplete because nobody could explain the dichotomy between the thermally- and photochemically induced reactions. Why these reactions occurred in the manner they did was unknown. When quantum mechanical explanations were later proposed to explain the ring-opening reactions, the reaction mechanisms might be said to be complete, although the related question of the cause of the reactions—in other words, why they happen at all—still had to be addressed. Reaction mechanisms consist in more than merely knowing the pathways by which reactants are converted into products. Until all related questions are answered satisfactorily, a mechanism may be considered incomplete. The evolution of modern chemistry from its origin in the late eighteenth century to its present day power and sophistication is remarkable (Brock 1992, Greenberg 2000, Bensaude-Vincent and Simon 2008, Chalmers 2011). Space limitations preclude more than a very brief summer of this history; references are included for the interested reader. Oxidation was weaned from its alchemical origins and the first elements and gases synthesized during the early decades of modern chemistry (Smartt Bell 2005, Thorpe 2007, Holmes 2008, Jay 2009). Additional elements were then discovered and their properties measured and compared (Scerri 2007). Methodology, laboratory technique, and apparatus were developed to carry out these new tasks, primarily in the nineteenth century (Faraday 1960, Buckingham 2004).

A Stereochemical and Kinetic Study of the Conversion of Methyl Cyclopropyl Ketones to 4,5-Dihydrofurans

1973 ◽  
Vol 51 (10) ◽  
pp. 1487-1493 ◽  
Author(s):  
Donald Edward McGreer ◽  
James William McKinley
Keyword(s):  
Kinetic Study ◽  
Ring Opening ◽  
Photochemical Reactions ◽  
Order Reaction ◽  
Ring Closure ◽  
Hydrogen Shift ◽  
First Order ◽  
Bond Rotation ◽  
Cyclopropyl Ketones ◽  
Cis And Trans

The thermal and photochemical conversion of (1R*,2R*,3S*), (1S*,2R*,3S*), and (1S*,2R*,3R*)-1-acetyl-1,2-dimethyl-3-phenylcyclopropane (1, 2, and 3) to cis- and trans-2,3,4-trimethyl-5-phenyl-4,5-dihydrofurans has been studied. Concurrent with this reaction is an equilibration of 1, 2, and 3, a thermal ring opening of 1 by a 1,5-hydrogen shift, and a cyclopropane-to-propene type reaction under the photochemical conditions. The dihydrofuran from 1 and 2 by the thermal and photochemical conditions is 97% trans- and 3% cis- corresponding to predominant retention at the migrating carbon. The dihydrofuran formed from 3 by the thermal and photochemical reaction is 85% cis- and 15% trans- again corresponding to predominant retention. A kinetic study of the rearrangement of 1-acetyl-1-methyl-2-phenylcyclopropane to 1,2-dimethyl-5-phenyl-4,5-dihydrofuran provides Ea of 48.1 kcal/mol and log A of 14.9 for this first order reaction in the temperature range of 255–288 °C.It is concluded that the thermal and photochemical reactions occur by a non-concerted process through a common 1,3-diradical intermediate in which bond rotation and ring closure steps are competitive.

scholarly journals Time-resolved high-harmonic spectroscopy of ultrafast ring-opening of 1,3-cyclohexadiene

2019 ◽  
Vol 205 ◽  
pp. 09017
Author(s):  
Keisuke Kaneshima ◽  
Yuki Ninota ◽  
Taro Sekikawa
Keyword(s):  
Ring Opening ◽  
High Harmonic ◽  
Harmonic Signal ◽  
Photochemical Reactions ◽  
Photon Absorption ◽  
Nuclear Dynamics ◽  
Time Resolved ◽  
Two Photon Absorption ◽  
Two Photon ◽  
Bond Rearrangement

We report, to the best of our knowledge, the first time-resolved high-harmonic spectroscopy (TR-HHS) study of a chemical bond rearrangement. We investigate the transient change of the high-harmonic signal from 1,3-cyclohexadiene (CHD), which undergoes ring-opening and isomerizes to 1,3,5-hexatriene (HT) upon photoexcitation. By associating the variation in the harmonic yield to the changes in the electronic state and vibrational frequencies of the molecule due to isomerization, we find that the CHD excited via two-photon absorption of 3.1 eV photons isomerizes to HT, i.e., ring-opening occurs, around 400 fs after the excitation. The present results demonstrate that TR-HHS, which can track both electronic and nuclear dynamics, is a powerful tool for studying ultrafast photochemical reactions.

Amino-functional polyethers: versatile, stimuli-responsive polymers

2020 ◽  
Vol 11 (24) ◽  
pp. 3940-3950 ◽  
Author(s):  
Patrick Verkoyen ◽  
Holger Frey
Keyword(s):  
Ring Opening ◽  
Review Article ◽  
Stimuli Responsive ◽  
New Class ◽  
Stimuli Responsive Polymers ◽  
Responsive Polymers

Amino-functional polyethers have emerged as a new class of “smart”, i.e. pH- and thermoresponsive materials. This review article summarizes the synthesis and applications of these materials, obtained from ring-opening of suitable epoxide monomers.

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