Trimethylenemethane. Activation energy for the ring closure of a 1,3 diradical

1977 ◽  
Vol 99 (19) ◽  
pp. 6438-6440 ◽  
Author(s):  
Paul Dowd ◽  
Mudan Chow
Keyword(s):  
Activation Energy ◽  
Ring Closure

Reactions of methyl-substituted Hex-5-enyl and Pent-4-enyl radicals

1983 ◽  
Vol 36 (3) ◽  
pp. 545 ◽  
Author(s):  
ALJ Beckwith ◽  
CJ Easton ◽  
T Lawrence ◽  
AK Serelis
Keyword(s):  
Activation Energy ◽  
Kinetic Data ◽  
Ring Closure ◽  
Cyclic Transition ◽  
Transition Complexes

Relative and absolute kinetic data have been determined for ring closure of methyl-substituted hex-5-enyl radicals: 2-methyl- (10a), 3-methyl-(4a), 4-methyl-(5a), 2,2-dimethyl-(10c), 3,3-dimethyl-(4c) and 4,4-dimethyl-hex-5-enyl (5c) radicals, generated by interaction of tributylstannane with the corresponding bromides (1a)-(3a) and (1c)-(3c). Each radical undergoes regiospecific or highly regioselective 1,5-cyclization more rapidly than does the unsubstituted radical (4d). The rate enhancements, which arise mainly from lowering of the activation energy, can be rationalized in terms of the gem-dimethyl effect. 1,5-Ring closures of monosubstituted species are stereoselective: 2-methyl- and 4-methyl-hex-5-enyl radicals (10a) and (5a) give mainly trans products, whereas 3-methylhex-4- enyl radical gives mainly the cis. This behaviour reflects the effect of the substituent on the stabilities of cyclic transition complexes in chair-like conformations. Ring closure of 2,2-dimethylpent-4-enyl radical or of 3,3-dimethylpent-4-enyl radical (19) could not be detected.

A Theoretical and Experimental Investigation of the Kinetics of Ring Closure of the 3-Methyl-3-azahex-5-enyl Radical

1995 ◽  
Vol 48 (12) ◽  
pp. 2047 ◽  
Author(s):  
EW Della ◽  
AM Knill
Keyword(s):  
Activation Energy ◽  
Experimental Investigation ◽  
Force Field ◽  
Activation Barrier ◽  
Ring Closure ◽  
Force Field Calculations ◽  
Arrhenius Parameters ◽  
A Value ◽  
Kinetics Of

Evaluation of the Arrhenius parameters for ring closure of the 3-methyl-3-azahex-5-enyl radical is reported. Cyclization of the radical is found to occur with high regioselectivity giving the exo -trig product exclusively with an activation energy of 22 kJ mol-1 and log A value of 11.1. The experimental activation barrier compares favourably with that determined by force field calculations which predict a value of 21 kJ mol-1. The 3-methyl-3-azahex-5-enyl radical is therefore found to undergo ring closure some 70 times faster than the parent hex-5-enyl radical, in accord with predictions based upon geometrical considerations.

Implications of the final ring closure to 10b-aza-10c-borapyrene for aryl–alkyne ring-closing mechanisms

2017 ◽  
Vol 95 (4) ◽  
pp. 357-362 ◽  
Author(s):  
Joseph A. Jaye ◽  
Benjamin S. Gelinas ◽  
Grant M. McCormick ◽  
Eric H. Fort
Keyword(s):  
Activation Energy ◽  
Functional Groups ◽  
Isotopic Labeling ◽  
Ring Closure ◽  
Synthetic Methods ◽  
Reaction Conditions ◽  
Fused Ring ◽  
Reaction Proceeds ◽  
Efficient Construction ◽  
Alternate Mechanism

Through a combined computational and isotopic labeling study, it has been observed that the activation energy for the aryl–alkyne ring closure of the azaborine containing 4-ethynyl-4a-aza-4b-boraphenanthrene is dramatically lower, and it appears to proceed via an alternate mechanism than that of its hydrocarbon analog. This catalyst-free reaction proceeds at modest reaction conditions compared with traditional pyrolytic synthetic methods and holds promise for the efficient construction of fused ring systems containing azaborine functional groups that may not be accessible in the purely hydrocarbon form.

Formation of Ring A in the Biosynthesis of Hopanoids from Squalene. A Density Functional Study

2004 ◽  
Vol 69 (1) ◽  
pp. 261-266 ◽  
Author(s):  
B. Andes Hess
Keyword(s):  
Activation Energy ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Ring Closure ◽  
Functional Study ◽  
Chair Conformer ◽  
Density Functional Study ◽  
Concerted Reaction

Density functional calculations were carried out on the ring closure of the 2,6-dimethyloct-6-en-2-yl cation to a chair conformer of the 1,2,3,3-tetramethylcyclohexyl cation as a model for the first step in the biosynthetic cyclization of squalene to the triterpene hopanoids. The concerted reaction was found to have an activation energy of 4.6 kcal/mol and to be exothermic by 11.5 kcal/mol.

High Temperature n- and p-type Doped Microcrystalline Silicon Layers Grown by VHF PECVD Layer-by-Layer Deposition

2003 ◽  
Vol 762 ◽  
Author(s):  
A. Gordijn ◽  
J.K. Rath ◽  
R.E.I. Schropp
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
High Temperatures ◽  
Continuous Wave ◽  
Hydrogen Plasma ◽  
Silicon Layer ◽  
Dark Conductivity ◽  
High Deposition Rate ◽  
Layer By Layer ◽  
Microcrystalline Silicon

AbstractDue to the high temperatures used for high deposition rate microcrystalline (μc-Si:H) and polycrystalline silicon, there is a need for compact and temperature-stable doped layers. In this study we report on films grown by the layer-by-layer method (LbL) using VHF PECVD. Growth of an amorphous silicon layer is alternated by a hydrogen plasma treatment. In LbL, the surface reactions are separated time-wise from the nucleation in the bulk. We observed that it is possible to incorporate dopant atoms in the layer, without disturbing the nucleation. Even at high substrate temperatures (up to 400°C) doped layers can be made microcrystalline. At these temperatures, in the continuous wave case, crystallinity is hindered, which is generally attributed to the out-diffusion of hydrogen from the surface and the presence of impurities (dopants).We observe that the parameter window for the treatment time for p-layers is smaller compared to n-layers. Moreover we observe that for high temperatures, the nucleation of p-layers is more adversely affected than for n-layers. Thin, doped layers have been structurally, optically and electrically characterized. The best n-layer made at 400°C, with a thickness of only 31 nm, had an activation energy of 0.056 eV and a dark conductivity of 2.7 S/cm, while the best p-layer made at 350°C, with a thickness of 29 nm, had an activation energy of 0.11 V and a dark conductivity of 0.1 S/cm. The suitability of these high temperature n-layers has been demonstrated in an n-i-p microcrystalline silicon solar cell with an unoptimized μc-Si:H i-layer deposited at 250°C and without buffer. The Voc of the cell is 0.48 V and the fill factor is 70 %.

White- and Brown-Rice Supplementation Improves Insulin Tolerance, Brown Fat Activation, Energy Expenditure, and Changes the Gut Microflora in Diet-Induced Obesity

Diabetes ◽  
2018 ◽  
Vol 67 (Supplement 1) ◽  
pp. 1897-P
Author(s):  
HISASHI YOKOMIZO ◽  
ATSUSHI ISHIKADO ◽  
TAKANORI SHINJO ◽  
KYOUNGMIN PARK ◽  
YASUTAKA MAEDA ◽  
...  
Keyword(s):  
Activation Energy ◽  
Energy Expenditure ◽  
Brown Rice ◽  
Brown Fat ◽  
Gut Microflora ◽  
Diet Induced Obesity ◽  
Insulin Tolerance

Activation energy of relaxation processes in chalcogenide glasses

2013 ◽  
Vol 34 (0) ◽  
pp. 59-63
Author(s):  
А. А. Горват ◽  
В. М. Кришеник ◽  
А. Е. Кріштофорій ◽  
В. В. Мінькович ◽  
О. А. Молнар
Keyword(s):  
Activation Energy ◽  
Chalcogenide Glasses ◽  
Relaxation Processes
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