The C6H5N energy surface. III. Isomerization processes and intramolecular trapping in picolylcarbenes

1975 ◽  
Vol 28 (8) ◽  
pp. 1741 ◽  
Author(s):  
WD Crow ◽  
AN Khan ◽  
MN Paddon-Row
Keyword(s):  
Gas Phase ◽  
Energy Surface ◽  
Methyl Groups ◽  
Ring Contraction ◽  
Isomerization Process ◽  
Major Process ◽  
Isomerization Processes

The synthesis is reported of a series of 5-(methyl-2-, -3- and -4- pyridyl)tetrazoles from the corresponding picolinecarbonitriles. These compounds are used as gas phase generators for the corresponding picolylcarbenes at 600�/0.05 mm. The normal isomerization process in arylcarbenes are interrupted in some cases by intramolecular trapping by the methyl groups, resulting in the first reported syntheses of cyclobuta-[b] and -[c]pyridines. The major process competing with this is that of nitrogen-extrusion to give tolylnitrenes, which then undergo ring contraction to form methyl-cyclopentadienecarbonitriles. The relative yields from these and other processes are used to deduce the preferred isomerization pathways in picolylcarbenes. In methyl-2- pyridylcarbenes there is almost exclusive insertion into the 2,3-bond, leading to the tolylnitrenes. The 3- and 4-pyridylcarbenes, however, show a tendency for the carbene centre to oscillate over the 3-, 4- and 5-positions of the ring with slower leakage to the 2-position.

The C6H5N energy surface. IV. Isotopic labelling studies in phenylnitrene isomerizations

1975 ◽  
Vol 28 (8) ◽  
pp. 1755 ◽  
Author(s):  
WD Crow ◽  
MN Paddon-Row
Keyword(s):  
Nitrogen Atom ◽  
Energy Level ◽  
Gas Phase ◽  
Energy Surface ◽  
Product Formation ◽  
Isotopic Labelling ◽  
Phenyl Azide ◽  
Ring Contraction ◽  
Isomerization Processes

Gas phase pyrolysis of phenyl azide gives rise to aniline, cyclopentadienecarbonitrile and pyridine as isomerization products from phenylnitrene. Isotopic labelling studies (14C, 13C) are used to examine the isomerization processes which occur in phenylnitrene prior to product formation. ��� At the lowest energy level of the intermediate little or no label randomization occurs and aniline evidently arises from hydrogen capture at this stage. Higher levels of the intermediate involve a cycloperambulatory motion of the nitrene nitrogen atom, followed by ring contraction to cyclo- pentadiene-1-carbonitrile. The pyridine formed possibly arises from a ring-expanded intermediate, which may not have undergone the cycloperambulation of the nitrene nitrogen atom. � The aniline and cyanocyclopentadiene derived from 5- pyridyltetrazole pyrolysis appear to exhibit very similar behaviour to those from phenyl azide as far as isotopic migration is concerned.

The C7H6 energy surface: phenylcarbene and 2-Methylene-3,5-cyclohexadienylidene - A duality of mechanism

1973 ◽  
Vol 26 (8) ◽  
pp. 1705 ◽  
Author(s):  
WD Crow ◽  
MN Paddon-Row
Keyword(s):  
Gas Phase ◽  
Energy Surface ◽  
Ring Contraction ◽  
Factors Affecting ◽  
Tracer Techniques ◽  
13C Tracer

The conversion of phenylcarbene (1) into fulvenallene (17) and ethynylcyclo-pentadiene (18) on gas-phase pyrolysis has been examined by 13C-tracer techniques. Complete randomization of all seven carbon atoms has been shown to precede ring contraction. The result is consistent with a pool of intermediates [cycloheptatrienylidene (19) and bicyclo[4,1,0]hepta-2,4,6-triene (21)], interconverting rapidly through tautomerism and concomitant H-shifts. Dimerization, intramolecular trapping, and ring contraction constitute the major exits from this pool. ��� Gas-phase thermolysis of indazole generates the same products (17)/(18) and in this case the mechanism has been investigated by the intramolecular trapping in 1-deutero-3-methylindazole to yield deuterostyrenes. Two pathways are revealed, proceeding respectively through phenylcarbene and 2-methylene-3,5-cyclohexadienyl-idene (36); factors affecting the latter pathway are discussed.

Gas phase pyrolysis of annelated pyrazoles: a duality of mechanism in aromatic ring contraction

1972 ◽  
Vol 13 (22) ◽  
pp. 2235-2238 ◽  
Author(s):  
W.D. Crow ◽  
A.R. Lea ◽  
M.N. Paddon-Row
Keyword(s):  
Gas Phase ◽  
Aromatic Ring ◽  
Ring Contraction

Kinetics and dynamics study of the OH + C2H6 → H2O + C2H5 reaction based on an analytical global potential energy surface

2020 ◽  
Vol 22 (26) ◽  
pp. 14796-14810 ◽  
Author(s):  
C. Rangel ◽  
M. Garcia-Chamorro ◽  
J. C. Corchado ◽  
J. Espinosa-Garcia
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Gas Phase ◽  
Energy Surface ◽  
Hydrogen Abstraction ◽  
Ethane Molecule ◽  
Abstraction Reaction ◽  
Kinetics And Dynamics ◽  
Oppenheimer Approximation ◽  
Hydrogen Abstraction Reaction

To describe the gas-phase hydrogen abstraction reaction between the hydroxyl radical and the ethane molecule, an analytical full-dimensional potential energy surface was developed within the Born–Oppenheimer approximation.

scholarly journals Effect of additional side groups on the vibrational frequencies of benzoquinone molecules

BIBECHANA ◽  
2016 ◽  
Vol 14 ◽  
pp. 66-76
Author(s):  
Nabin Kumar Raut ◽  
Hari Prasad Lamichhane
Keyword(s):  
Ir Spectra ◽  
Gas Phase ◽  
Vibrational Frequencies ◽  
The Other ◽  
Methyl Groups ◽  
Computational Investigation ◽  
Strongly Coupled ◽  
Solvent Phase ◽  
Other Hand

The present work enumerates detailed computational investigation into the IR spectra in gas phase and in solvent of 1, 4- Benzoquinone family (benzoquinone (BQ), duroquinone (DQ), plastoquinone (PQ), ubiquinone (UQ), and dimethoxy dimethyl benzoquinone (MQo)). In  the spectra of BQ, PQ, and DQ, we observed separate intense carbonyl (C=O) and C=C bands respectively around 1730 cm-1 (intense), 1645 cm-1 (weak). On the other hand, for UQ and MQo, three prominent bands around 1652, 1703, and 1733 cm-1 were observed, where two C=O modes were uncoupled but one of the carbonyl is strongly coupled with C=C vibrations. The additional methyl groups downshift the intense carbonyl bands and upshift C=C mode frequencies. The carbonyl modes further downshifted in the solvent phase calculation.BIBECHANA 14 (2017) 66-76

Full-dimensional analytical potential energy surface describing the gas-phase Cl + C2H6 reaction and kinetics study of rate constants and kinetic isotope effects

2018 ◽  
Vol 20 (6) ◽  
pp. 3925-3938 ◽  
Author(s):  
Cipriano Rangel ◽  
Joaquin Espinosa-Garcia
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Gas Phase ◽  
Energy Surface ◽  
Isotope Effects ◽  
Hydrogen Abstraction ◽  
System P ◽  
Abstraction Reaction ◽  
Analytical Potential ◽  
Oppenheimer Approximation

Within the Born–Oppenheimer approximation a full-dimensional analytical potential energy surface, PES-2017, was developed for the gas-phase hydrogen abstraction reaction between the chlorine atom and ethane, which is a nine body system.

scholarly journals Enthalpies of Combustion and Formation of Severely Crowded Methyl-Substituted 1,3-dioxanes. The Magnitudes of 2,4- and 4,6-diaxial Me,Me-Interactions and the Chair–2,5-twist Energy Difference

Molecules ◽  
2020 ◽  
Vol 25 (12) ◽  
pp. 2762 ◽  
Author(s):  
Kalevi Pihlaja ◽  
Henri Kivelä ◽  
Pirjo Vainiotalo ◽  
William V. Steele
Keyword(s):  
Gas Phase ◽  
Chair Conformation ◽  
Energy Difference ◽  
Enthalpies Of Formation ◽  
Methyl Groups ◽  
Chair Form ◽  
Twist Form

Enthalpies of combustion of 2,2-trans-4,6- (1) and 4,4,6,6-tetramethyl- (2) and 2,4,4,6,6- (3) and 2,2,4,4,6-pentamethyl-1,3-dioxanes (4) were determined to estimate their enthalpies of formation in the gas phase. By comparing the latter with the corresponding enthalpies estimated based on the various bond–bond interactions allowed to determine the chair–2,5-twist energy difference (ΔHCT = 29.8 kJ mol–1) for 1 since C-13 shift correlations indicate that it escapes to the 2,5-twist form where the 2-methyl groups are isoclinal and 4- and 6-methyl groups pseudoequatorial to avoid syn-axial interactions. Compounds 2 and 3 in turn give the values 21.0 and 21.6 kJ mol–1 for the 4,6-diaxial Me,Me-interaction. Finally compound 4, which retains the chair conformation to avoid pseudoaxial interactions in the twist forms gives the value 19.5 kJ mol–1 for the 2,4-diaxial Me,Me-interaction indicating that its chair form appears to be somewhat deformed.

Quantum-Chemical Investigations on the Structural Variability of Anion–π Interactions

2014 ◽  
Vol 69 (7) ◽  
pp. 339-348 ◽  
Author(s):  
Verena Moha ◽  
Michael Giese ◽  
Richard Moha ◽  
Markus Albrecht ◽  
Gerhard Raabe
Keyword(s):  
Gas Phase ◽  
Aromatic Ring ◽  
Energy Surface ◽  
Electrostatic Energy ◽  
Dispersion Energy ◽  
Substitution Pattern ◽  
Energy Of Interaction ◽  
Electron Withdrawing Group ◽  
Energy Surfaces ◽  
Structural Versatility

The structural versatility of anion-p interactions was investigated computationally. Employing quantum-chemically optimized structures of a series of C6H6-nFn/Br- complexes and the Coulomb law together with the London formula to calculate the electrostatic and the dispersion energy of the interaction between the anion and the π-system led to the result that up to the number of n = 2 due to a significantly repulsive electrostatic energy of interaction the dispersion energy is not sufficient to stabilize such structures in the gas phase where the anion is located above the plane defined by the aromatic ring. The energy surfaces resulting from the interaction of bromide anions with isolated arenes bearing varying numbers of fluorine atoms in different positions of the aromatic ring also show a pronounced dependency on the subsitution pattern of the aromatic system. Depending on the nature of the electron withdrawing group and its position, the energy surface can have a sharply defined energetically low minimum, in which the anion is ‘fixed’. Other substitution patterns result in very flat energy surfaces, and even a surface with more than two local minima within the scanned area was found. Thus, our study reveals the reason for the experimentally observed structural versatility depending on the substitution pattern in the solid state.

Sign in / Sign up

Export Citation Format

Share Document