Cyclobutanes and Cyclobutenes from Photochemical Cleavage of Some Bicyclo[3.2.0]heptan-2-ones

2009 ◽  
Vol 62 (2) ◽  
pp. 101 ◽  
Author(s):  
Leiv K. Sydnes ◽  
Doan Van Ha
Keyword(s):  
Allyl Alcohol ◽  
Hydrogen Abstraction ◽  
Type I ◽  
Mercury Lamp ◽  
Methyl Group ◽  
Primary Products ◽  
Norrish Type ◽  
Photochemical Cleavage ◽  
Isomeric Mixtures ◽  
Better Than

Irradiation of solutions of cyclopent-2-enone or 3-methylcyclopent-2-enone and allyl alcohol with light from a medium-pressure mercury lamp through a Pyrex filter with a cut-off at 295 nm furnishes excellent yields of isomeric mixtures of substituted bicyclo[3.2.0]heptan-2-ones as the primary products. Both enones give predominantly the head-to-head isomer with exo stereochemistry. The primary products turn out to be photolabile and undergo Norrish type I cleavage followed by hydrogen abstraction, but the outcome is influenced by the presence of a methyl group at C5. In the absence of such a methyl group the C1–C2 bond is cleaved, to give rise to two cyclobutenyl aldehydes in better than 90% combined yield; when a methyl group is attached at C5 both C–C bonds to the carbonyl group are broken and a mixture of cyclobutyl aldehydes and ketenes are formed in close to quantitative combined yield.

Photolysis of 4-Methyl 3-Hexanone and 2-Methoxy 3-Pentanone in Hydrocarbon Solution

1971 ◽  
Vol 49 (8) ◽  
pp. 1310-1314 ◽  
Author(s):  
L. P-Y. Lee ◽  
B. McAneney ◽  
J. E. Guillet
Keyword(s):  
Quantum Yield ◽  
Hydrogen Abstraction ◽  
Type I ◽  
Type Ii ◽  
Cage Effect ◽  
Predominant Type ◽  
Norrish Type ◽  
Hydrocarbon Solution ◽  
Membered Transition State ◽  
Made In

Studies of the photolysis of 4-methyl 3-hexanone and the iso-electronic 2-methoxy 3-pentanone have been made in hydrocarbon solution using light of wavelength 313 nm. The latter compound gives only Norrish type II products with a quantum yield of 0.19 ±.01. The former gives a predominance of type I products with a total quantum yield of 0.23 ±.01 and the quantum yield for type II is reduced to 0.10 ±.01. The predominant type I reaction appears to involve α-scission to give an ethyl and a 2-methyl butyryl radical, which suggests a "cage effect". It is suggested that the reason for the suppression of the type I reaction in 2-methoxy 3-pentanone is the greater ease of γ-hydrogen abstraction due to the presence of the oxygen atom in a six-membered transition state.

Modification of photochemical reactivity through the use of clathrates: the Norrish type I and type II reactions in Dianin's compound

1985 ◽  
Vol 63 (10) ◽  
pp. 2719-2725 ◽  
Author(s):  
P. C. Goswami ◽  
Paul de Mayo ◽  
N. Ramnath ◽  
G. Bernard ◽  
N. Omkaram ◽  
...  
Keyword(s):  
Inclusion Complexes ◽  
Hydrogen Abstraction ◽  
Photochemical Reactions ◽  
Type I ◽  
Type Ii ◽  
Guest Molecules ◽  
Photochemical Reactivity ◽  
Norrish Type ◽  
Restricted Environment ◽  
Dianin's Compound

Dianin's compound (4-p-hydroxyphenyl-2,2,4-trimethylchroman) serves as host in a series of well-defined clathrate inclusion complexes with eleven linear, as well as branched chain, phenyl alkyl ketone guest molecules, chosen for their ability to undergo the Norrish type I and type II photochemical reactions in solution. The photochemical reactivity of the guest ketones within the clathrate cavity was determined by irradiation of the inclusion complexes in the solid state. The results were compared to the photoreactivity of the ketones in polar as well as nonpolar liquid media. In general, the inclusion complex medium brings about an enhancement of type I over type II reactivity and causes an increase in type II fragmentation compared to type II cyclization. This change in reactivity is interpreted as resulting from the relatively restricted environment of the clathrate cavity coupled with the greater motion required for the type II process (γ-hydrogen abstraction) compared to the type I reaction (α-cleavage), as well as from the greater steric requirements for type II cyclization (cyclobutanol formation) as compared to type II cleavage (1,4-hydroxybiradical scission).

scholarly journals Non-adiabatic dynamic of atmospheric unimolecular photochemical reactions of 4,4-difluoro-crotonaldehyde using TD-DFT and TSH approaches

2021 ◽  
Author(s):  
Pedro J Castro Pelaez ◽  
Satoshi Maeda ◽  
Keiji Morokuma
Keyword(s):  
Degrees Of Freedom ◽  
Hydrogen Abstraction ◽  
Electronic States ◽  
Photochemical Reactions ◽  
Type I ◽  
Excitation Energies ◽  
Geometrical Structures ◽  
Photochemical Processes ◽  
Norrish Type ◽  
Global Reaction

Photochemical reactions of small molecules occur upon irradiation by ultraviolet or visible light, and they are a very important and controversial chemical process in the Earth’s atmosphere because they impact our quality of life and health. Small-unsaturated carbonyl compounds play an important role in the chemistry of the polluted troposphere. The fluorinated aldehydes are very reactive under the sunlight driving to species that trigger more atmospheric reactions. This paper is focused on a theoretical study of the photochemistry of difluoro-crotonaldehyde using static and dynamic calculations by combination of Global Reaction Route mapping (GRRM) and Trajectory Surface Hopping (TSH) approach. The static analysis of the electronic and geometrical structures at the critical points allowed to rationalize the possible pathways that interconnect the stationary and crossing points in order to get a map of the unimolecular photochemical reactions which take place. The time evolution of the electronic states and the degrees of freedom enabled the identification of the requirements to follow the most probable deactivation pathways. This article reports the unimolecular deactivation pathways after the electronic excitation of the trans and cis isomers. In both cases, the excitation energies were calculated and compared with the analogous in the crotonaldehyde in order to elucidate the effect of fluorine atoms on the electronic structure and stabilities. After the initial excitations to the ππ* excited states, the main deactivation channels follow non-adiabatic pathways via S/S conical intersections. Ultrafast processes leading to the early activation of the S govern the decay of the difluoro-crotonaldehyde. Depending on the nature of the S state before the crossing with the S, the system can follow several reaction pathways. The main photochemical processes observed were the cis-trans isomerization, the Norrish type I reaction (α-cleavage), Norrish type II reaction (γ-hydrogen abstraction) and fluorine photodissociation. The time scale, the molecular deformations and the electronic states implied for the different photochemical processes, as well as how these compete with the photophysical deactivation are discussed.

CIDNP Studies of Hydrogen Abstraction by Aroyl Radicals in Norrish Type I Processes

1977 ◽  
Vol 32 (6) ◽  
pp. 674-677 ◽  
Author(s):  
C. Bak ◽  
K. Praefcke ◽  
K. A. Muszkat ◽  
M. Weinstein
Keyword(s):  
Free Radical ◽  
Hydrogen Abstraction ◽  
Type I ◽  
Benzoic Acids ◽  
Hydrogen Atoms ◽  
Norrish Type

The abstraction of hydrogen atoms by benzoyl radicals in the photolyses of 2,2′-dihalogeno-benzil dimethylketals and of S-p-tolyl esters of substituted thio benzoic acids was investigated by the CIDNP technique. The present study supports previous conclusions that in the absence of scavengers the formyl H atoms of the benzaldehydes thus formed originate from cyclohexadienyl-like free radical precursors.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

The photochemical reactivity of some benzoylthiophenes. IV. The effect of an adjacent methyl group on the excited state reactivity of 3-benzoylthiophene

1978 ◽  
Vol 56 (15) ◽  
pp. 1970-1984 ◽  
Author(s):  
D. R. Arnold ◽  
C. P. Hadjiantoniou
Keyword(s):  
Hydrogen Abstraction ◽  
Thiophene Ring ◽  
Emission Spectra ◽  
Photochemical Reactions ◽  
Triplet States ◽  
Photochemical Reactivity ◽  
Methyl Group ◽  
State Diagrams ◽  
Phosphorescence Emission ◽  
Intramolecular Hydrogen

The electronic absorption and phosphorescence emission spectra and the photochemical reactivity of several methyl-3-benzoylthiophenes (2- and 4-methyl-3-benzoylthiophene (1, 2), 2,5-dimethyl-3-benzoylthiophene (3), and 3-(2-methylbenzoyl)thiophene (4)) have been studied. Partial state diagrams have been constructed. The lowest energy absorption in hexane solution in every case is the carbonyl n → π* transition. The two lowest triplet states of these ketones are close in energy and, in fact, the nature of the emitting triplet (n,π* or π,π*) depends upon the position of methyl substitution and upon the solvent. The photochemical reactions studied include intramolecular hydrogen abstraction (revealed by deuterium exchange in the adjacent methyl group upon irradiation in perdeuteriomethanol solution), photocycloaddition of dimethyl acetylenedicarboxylate to the thiophene ring, and photocycloaddition of isobutylene to the carbonyl group. Generalizations, potentially useful for predicting photochemical reactivity of these and other aromatic ketones are summarized.

Non-malignant gall bladder perforation: Our experience from an institution-based retrospective analysis of 25 cases

2021 ◽  
pp. 004947552110365
Author(s):  
Abhijeet Kumar ◽  
Nirmal Prasad Shah ◽  
Narendra Pandit ◽  
Suresh Prasad Sah ◽  
Rakesh Kumar Gupta ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Gall Bladder ◽  
Clinical Presentation ◽  
Gallbladder Perforation ◽  
Type I ◽  
Computed Tomography Scan ◽  
Duration Of Hospital Stay ◽  
Symptoms And Signs ◽  
Tomography Scan ◽  
Better Than

Gallbladder perforation still continues to perplex surgeons; 25 such patients diagnosed either pre- or intra-operatively and managed at our institute over the last 10 years period were analysed. Only eight were diagnosed pre-operatively, while a large majority (17) had a wrong initial working diagnosis. Symptoms and signs were variable. No blood investigation was specific. A computed tomography scan was generally better than ultrasound in detecting the perforation. All our cases were managed operatively with no mortality and a mean duration of hospital stay of 6.8 days. Most perforations were extra-hepatic (84%) and those of Niemeier’s type I (52.2%). Because of its varied clinical presentation, gallbladder perforation is often an intra-operative diagnosis, but early intervention carries a good outcome.

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