Synthetic Applications of Intramolecular Insertion in Arylcarbenes. I. o-Alkylphenylcarbenes and 1-(o-Alkylphenyl)ethylidenes

1979 ◽  
Vol 32 (1) ◽  
pp. 89 ◽  
Author(s):  
WD Crow ◽  
H McNab
Keyword(s):  
Hydrogen Atom ◽  
Gas Phase ◽  
Chain Length ◽  
Membered Ring ◽  
Ring Formation ◽  
Ortho Position ◽  
Methyl Group ◽  
Alkyl Chains ◽  
Out Of Plane

A series of phenylcarbenes and 1-phenylethylidenes, substituted in the ortho-position by alkyl chains of 1-4 carbon atoms, has been generated in the gas phase and pyrolysed at 250-750°/0.05-0.10 mm. Apart from o-tolylcarbene, the phenylcarbenes show efficient insertion to form five- and six-membered rings, the former predominating. In the phenylethylidenes, Bamford-Stevens insertion into the adjacent methyl group competes with cyclization to an extent which decreases with chain length. At the same time, five-membered ring formation is greatly increased over six-membered ring formation, due to facilitation of out-of-plane twisting of the carbene atom. The mechanistic implications of the results are discussed in terms of an angular approach of the carbene p-orbital to the hydrogen atom under attack.

Synthetic Applications of Intramolecular Insertion in Arylcarbenes. II. o-Alkoxy-, Dialkylamino- and Alkylthio-phenylcarbenes

1979 ◽  
Vol 32 (1) ◽  
pp. 99 ◽  
Author(s):  
WD Crow ◽  
H McNab
Keyword(s):  
Transition State ◽  
Gas Phase ◽  
Membered Ring ◽  
Ring Formation ◽  
High Yield ◽  
Side Chains ◽  
Ortho Position ◽  
Carbene Insertion ◽  
Donor Capacity

A series of phenylcarbenes, substituted in the ortho-position by alkoxy, dialkylamino and alkylthio side chains containing up to three carbon atoms, has been generated in the gas phase and pyrolysed at 250-750�/0.05-0.20mm. Carbene insertion occurs in moderate to high yield to give the appropriate five-and six-membered heterocyclics, the former predominating. The regioselectivity of the carbene insertion (five-membered ring us six-membered ring) is highest in the case of the alkoxy and dialkylamino compounds, where six-membered-ring formation is relatively minor; in the case of the alkylthiophenylcarbenes, the selectivity in favour of the smaller ring is, by comparison, small. The reasons for this are discussed in terms of the geometry of the transition state and the donor capacity of the heteroatom.

Radiation and Radiationless Processes in 2,3-Pentanedione; Phosphorescence Lifetime in the Gas Phase

1971 ◽  
Vol 49 (7) ◽  
pp. 987-993 ◽  
Author(s):  
A. W. Jackson ◽  
A. J. Yarwood
Keyword(s):  
Hydrogen Atom ◽  
Triplet State ◽  
Gas Phase ◽  
Ground State ◽  
Hydrogen Atom Abstraction ◽  
Intersystem Crossing ◽  
Phosphorescence Lifetime ◽  
Gaseous State ◽  
Methyl Group ◽  
Intramolecular Hydrogen

Fluorescence and phosphorescence are observed when 2,3-pentanedione in the gaseous state is excited at 365, 405, and 436°nm. The phosphorescence lifetime has been investigated as a function of temperature (298 to 363 °K) and concentration of the diketone (0.5 to 90 × 10−4 M). A mechanism that explains the experimental data is proposed. Apart from the radiative process and an intersystem crossing to the ground state, the triplet state 2,3-pentanedione molecules are removed by two other processes. One is a unimolecular reaction with a rate constant of 1 × 1011 exp (−11.0/RT) s−1 (consistent with an intramolecular hydrogen atom abstraction), and the other is an interaction with ground state molecules. The photochemistry of the triplet state of 2,3-pentanedione is compared with that of biacetyl to consider the effect of substitution of a hydrogen atom by the methyl group on the radiationless processes in diketones.

Catalytic Synthesis of Cyclic Guanidines via Hydrogen Atom Transfer and Radical-Polar Crossover

2020 ◽  
Author(s):  
Shunya Ohuchi ◽  
Hiroki Koyama ◽  
Hiroki Shigehisa
Keyword(s):  
Hydrogen Atom ◽  
Functional Group ◽  
Hydrogen Atom Transfer ◽  
Catalytic Synthesis ◽  
Membered Ring ◽  
Biologically Active ◽  
Atom Transfer ◽  
Powerful Method ◽  
Protective Groups ◽  
The Common

A catalytic synthesis of cyclic guanidines, which are found in many biologically active compounds and natu-ral products, was developed, wherein transition-metal hydrogen atom transfer and radical-polar crossover were employed. This mild and functional-group tolerant process enabled the cyclization of alkenyl guanidines bearing common protective groups, such as Cbz and Boc. This powerful method not only provided the common 5- and 6-membered rings but also an unusual 7-membered ring. The derivatization of the products afforded various heterocycles. We also investigated the se-lective cyclization of mono-protected or hetero-protected (TFA and Boc) alkenyl guanidines and their further derivatiza-tions.

2-Deoxyribose Radicals in the Gas Phase and Aqueous Solution. Transient Intermediates of Hydrogen Atom Abstraction from 2-Deoxyribofuranose

2005 ◽  
Vol 70 (11) ◽  
pp. 1769-1786 ◽  
Author(s):  
Luc A. Vannier ◽  
Chunxiang Yao ◽  
František Tureček
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Atom ◽  
Gas Phase ◽  
Computational Study ◽  
Hydrogen Atom Abstraction ◽  
Oh Radical ◽  
Free Energies ◽  
Intramolecular Hydrogen ◽  
Solvation Free Energies ◽  
Transient Intermediates

A computational study at correlated levels of theory is reported to address the structures and energetics of transient radicals produced by hydrogen atom abstraction from C-1, C-2, C-3, C-4, C-5, O-1, O-3, and O-5 positions in 2-deoxyribofuranose in the gas phase and in aqueous solution. In general, the carbon-centered radicals are found to be thermodynamically and kinetically more stable than the oxygen-centered ones. The most stable gas-phase radical, 2-deoxyribofuranos-5-yl (5), is produced by H-atom abstraction from C-5 and stabilized by an intramolecular hydrogen bond between the O-5 hydroxy group and O-1. The order of radical stabilities is altered in aqueous solution due to different solvation free energies. These prefer conformers that lack intramolecular hydrogen bonds and expose O-H bonds to the solvent. Carbon-centered deoxyribose radicals can undergo competitive dissociations by loss of H atoms, OH radical, or by ring cleavages that all require threshold dissociation or transition state energies >100 kJ mol-1. This points to largely non-specific dissociations of 2-deoxyribose radicals when produced by exothermic hydrogen atom abstraction from the saccharide molecule. Oxygen-centered 2-deoxyribose radicals show only marginal thermodynamic and kinetic stability and are expected to readily fragment upon formation.

The photoinduced addition of acetone to 1,7-dimethyltricyclo[4.1.0.02,7]Heptane. Hydrogen atom abstraction from an activated methyl group

1984 ◽  
Vol 25 (29) ◽  
pp. 3051-3054 ◽  
Author(s):  
Paul G. Gassman ◽  
John L. Smith
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Atom Abstraction ◽  
Methyl Group

Molecular orbital structures of sulfones

1982 ◽  
Vol 60 (6) ◽  
pp. 730-734 ◽  
Author(s):  
Russell J. Boyd ◽  
Jeffrey P. Szabo
Keyword(s):  
Crystal Structure ◽  
Gas Phase ◽  
Molecular Orbital ◽  
Geometry Optimization ◽  
Membered Ring ◽  
Molecular Orbital Calculations ◽  
Bond Lengths ◽  
Comparison With Experiment ◽  
The Difference

Abinitio molecular orbital calculations are reported for several cyclic and acyclic sulfones. The geometries of XSO2Y, where X, Y = H, F, or CH3 are optimized at the STO-3G* level. Similar calculations are reported for the smallest cyclic sulfone, thiirane-1,1 -dioxide, as well as the corresponding sulfoxide, thiirane-1-oxide, and the parent sulfide, thiirane. Where comparison with experiment is possible, the agreement is satisfactory. In order to consider the possibility of substantial differences between axial and equatorial S—O bonds in the gas phase, as observed in the crystal structure of 5H,8H-dibenzo[d,f][1,2]-dithiocin-1,1-dioxide, STO-3G* calculations are reported for a six-membered ring, thiane-1,1-dioxide, and a model eight-membered ring. Limited geometry optimization of the axial and equatorial S—O bonds in the chair conformations of the six- and eight-membered rings leads to bond lengths of 1.46 Å with the difference being less than 0.01 Å.

Ring formation via β-keto ester dianions

1977 ◽  
Vol 55 (6) ◽  
pp. 996-1000 ◽  
Author(s):  
Phaik-Eng Sum ◽  
Larry Weiler
Keyword(s):  
Membered Ring ◽  
Ring Formation ◽  
Methyl Acetoacetate ◽  
Keto Ester ◽  
Keto Esters

The reaction of α,ω-dihalides with the dianion of methyl acetoacetate gives a mixture of mono- and bisalkylated products. The monoalkylated products can be cyclized via the monoanion to cyclic β-keto esters with a seven- or eight-membered ring. Alternatively these monoalkylated products can be cyclized via the dianion to γ-cyclopentyl- or γ-cyclohexyl-β-keto esters.

Gas-Phase Infrared Spectroscopy of Substituted Cyanobutadiynes: Roles of the Bromine Atom and Methyl Group as Substituents

ChemPhysChem ◽  
2016 ◽  
Vol 17 (7) ◽  
pp. 1018-1024 ◽  
Author(s):  
M. Merced Montero-Campillo ◽  
Otilia Mó ◽  
Manuel Yáñez ◽  
Abdessamad Benidar ◽  
Cédric Rouxel ◽  
...  
Keyword(s):  
Infrared Spectroscopy ◽  
Gas Phase ◽  
Bromine Atom ◽  
Methyl Group

Five vs Six Membered-Ring PAH Products from Reaction of o-Methylphenyl Radical and two C3H4 Isomers

2021 ◽  
Author(s):  
Oisin J Shiels ◽  
Matthew Brian Prendergast ◽  
John Savee ◽  
David L Osborn ◽  
Craig A. Taatjes ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Membered Ring ◽  
Gas Phase Reactions

Gas-phase reactions of the o-methylphenyl (o-CH3C6H4) radical with the C3H4 isomers allene (H2C=C=CH2) and propyne (HCºC-CH3) are studied at 600 K and 4 Torr (533 Pa) using VUV synchrotron photoionisation mass spectrometry,...

scholarly journals Impact of molecular structure on secondary organic aerosol formation from aromatic hydrocarbon photooxidation under low NO<sub><i>x</i></sub> conditions

2016 ◽  
Author(s):  
L. Li ◽  
P. Tang ◽  
S. Nakao ◽  
D. R. Cocker III
Keyword(s):  
Molecular Structure ◽  
Chemical Composition ◽  
Aromatic Hydrocarbon ◽  
Chain Length ◽  
Aromatic Hydrocarbons ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Ortho Position ◽  
Aerosol Formation ◽  
The Impact

Abstract. The molecular structure of volatile organic compounds (VOC) determines their oxidation pathway, directly impacting secondary organic aerosol (SOA) formation. This study comprehensively investigates the impact of molecular structure on SOA formation from the photooxidation of twelve different eight to nine carbon aromatic hydrocarbons under low NOx conditions. The effects of the alkyl substitute number, location, carbon chain length and branching structure on the photooxidation of aromatic hydrocarbons are demonstrated by analyzing SOA yield, chemical composition and physical properties. Aromatic hydrocarbons, categorized into five groups, show a yield order of ortho (o-xylene and o-ethyltoluene) > one substitute (ethylbenzene, propylbenzene and isopropylbenzene) > meta (m-xylene and m-ethyltoluene) > three substitute (trimethylbenzenes) > para (p-xylene and p-ethyltoluene). SOA yields of aromatic hydrocarbon photooxidation do not monotonically decrease when increasing alkyl substitute number. The ortho position promotes SOA formation while the para position suppresses aromatic oxidation and SOA formation. Observed SOA chemical composition and volatility confirm that higher yield is associated with further oxidation. SOA chemical composition also suggests that aromatic oxidation increases with increasing alkyl substitute chain length and branching structure. Further, carbon dilution theory developed by Li et al. (2015a) is extended in this study to serve as a standard method to determine the extent of oxidation of an alkyl substituted aromatic hydrocarbon.

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