Reactions of N-(arylsulfonoxy)-N-alkylbenzylamines with sodium methoxide-methanol. Steric effect on the structure of the imine-forming transition state

1991 ◽  
Vol 113 (10) ◽  
pp. 3920-3924 ◽  
Author(s):  
Bong Rae Cho ◽  
Sang Yong Pyun
Keyword(s):  
Transition State ◽  
Sodium Methoxide ◽  
Steric Effect

The Influence of the 2-Alkoxy Group and of C-5 Substituents on the Direction of Reductive Cleavage of 2-Alkoxytetrahydrofurans by AlH2Cl in Ether Solution

1972 ◽  
Vol 50 (10) ◽  
pp. 1502-1512 ◽  
Author(s):  
P. C. Loewen ◽  
Miss L. P. Makhubu ◽  
R. K. Brown
Keyword(s):  
Transition State ◽  
Alkyl Group ◽  
Steric Effect ◽  
Bond Cleavage ◽  
Alkoxy Group ◽  
Ring Cleavage ◽  
Relative Ease ◽  
Ether Solution ◽  
A Minor ◽  
Minor Extent

The AlH2Cl hydrogenolysis of ether solutions of 2-alkoxytetrahydrofurans in which the alkoxy group is either CH3O, C2H5O, i-C3H7O, or t-C4H9O, gives only those products resulting from ring C—O bond cleavage. However, substituents at C-5 of 2-methoxytetrahydrofuran exert a strong effect on the ratio of ring to exo C—O bond cleavage. Thus, alkyl (electron donor) groups at C-5 promote an increase in the amount of exo cleavage, the proportion increasing from 62.5 to 100% as the C-5 alkyl group is changed from CH3 to t-C4H9. In contrast, electron withdrawing substituents, CH3OCH2— and C6H5, at C-5 favor ring cleavage to the extent of 93 and 84% respectively.The results are interpreted in terms of the influence that these substituents exert through their electronic properties on the relative ease of attainment of the transition state leading to either ring C—O or exo C—O bond cleavage. However, evidence is provided to show that the bulk steric effect of these substituents also controls, though to a minor extent, the proportion of ring to exo cleavage.

Primary isotope effects and mechanism of base initiated β-elimination reactions of di-(p-nitrophenyl)fluoroethanes

1977 ◽  
Vol 55 (10) ◽  
pp. 1696-1700 ◽  
Author(s):  
Jan Kurzawa ◽  
Kenneth T. Leffek
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Elimination Reactions

The second-order rate constants have been determined for the β-elimination reactions of 2,2-di-(p-nitrophenyl)-1,1,1-trifluoroethane, 2,2-di-(p-nitrophenyl)-1-fluoroethane, and their β-deuterated analogues with sodium methoxide in methanol. The primary isotope effects and activation parameters for these reactions are reported. It is suggested that the trifluoro-compound reacts via the pre-equilibrium carbanion mechanism (ElcB)R and that the monofluoro compound follows the E2 mechanism via a carbanion-like transition state.

Kinetic solvation steric effect at the transition state of reaction between trichlorocobaltate(II) and chloride ions in N,N-dimethylformamide and dimethyl sulfoxide

2005 ◽  
Vol 119 (1-3) ◽  
pp. 177-182 ◽  
Author(s):  
Yasuhiro Umebayashi ◽  
Nobuyuki Shigeta ◽  
Yue Zhang ◽  
Morito Komiya ◽  
Yu-ichi Murakami ◽  
...  
Keyword(s):  
Transition State ◽  
Dimethyl Sulfoxide ◽  
Steric Effect ◽  
Chloride Ions

The reinvestigation of the kinetics of the reactions of fluorodi(4-nitrophenyl)ethanes with sodium methoxide in methanol

1982 ◽  
Vol 60 (13) ◽  
pp. 1696-1701 ◽  
Author(s):  
Kenneth T. Leffek ◽  
Grzegorz Schroeder
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Elimination Reaction ◽  
Methoxide Ion ◽  
Dimerization Reaction ◽  
Multistep Reaction ◽  
Kinetics Of

The procedure previously described for the preparation of 1-fluoro-2,2,-di(4-nitrophenyl)ethane actually yields 1,1,2-tri-(4-nitrophenyl)ethane. 1-Fluoro-2,2-di(4-nitrophenyl)ethane has been prepared and rate constants, isotope effects, and activation parameters for the β-elimination reaction with methoxide ion in methanol are reported. These parameters indicate a concerted E2 mechanism, with a fairly symmetrical transition state. The subsequent dimerization reaction of the olefin product to yield 1,1,3,3-tetra(4-nitrophenyl)butene-1 is described.The reaction of 1,1,1-trifluoro-2,2-di(4-nitrophenyl)ethane with methoxide ion in methanol has been reinvestigated and the reaction of the first product 1,1-difluoro-2,2-di(4-nitrophenyl)ethylene with excess methoxide, to give di(4-nitrophenyl)ketene dimethylacetal in a multistep reaction, is reported.

A DFT study of Zr-S rotational barriers of (η5-C5H5)2Zr(Cl)(SR); the origin of an inverse steric effect

2001 ◽  
Vol 79 (5-6) ◽  
pp. 809-816 ◽  
Author(s):  
P K Das ◽  
Susan Stanislav Alguindigue ◽  
Michael T Ashby
Keyword(s):  
Low Temperature ◽  
Transition State ◽  
Ground State ◽  
Steric Effect ◽  
Rotational Transition ◽  
The Other ◽  
Steric Interaction ◽  
Rotational Barriers ◽  
State Orientation ◽  
Thiolate Ligand

We have previously reported the experimental rotational barriers about the M–S bonds of 16e– bent metallocene monothiolates (η5-C5H5)2Zr(Cl)(SR) (R = CH3, CH2CH3, CH(CH3)2, C(CH3)3] (1a–d): 32, 33, 35, and 26 kJ mol–1, respectively. The ground-state orientation about the Zr–S bonds of 1 that maximizes S(pπ) [Formula: see text] M(dπ) bonding (Cl-Zr-S-R [Formula: see text] 90°) also maximizes Cp « R (Cp = η5-C5H5) steric interaction, whereas the rotational transition-state orientation (Cl-Zr-S-R [Formula: see text] 0°) is one that minimizes S(pπ) [Formula: see text] M(dπ) bonding and maximizes Cl « R steric interaction. Deviation from a ground-state orientation that is ideal for S(pπ ) [Formula: see text] M(dπ ) bonding might be expected as the size of the R-group and Cp « R steric interaction increases. The present study employs hybrid density function computational methods to reproduce the experimental rotational barriers. The computational rotational barriers decrease in the order 1a (R = CH3) > 1b (R = CH2CH3) > 1c (R = CH(CH3)2) at low temperature. However, opposing enthalpic factors reverse this trend at higher temperatures. The aberrant trend (unexpectedly low rotational barrier) that is observed for the 1d (R = C(CH3)3) derivative is due to dominant ground-state steric (enthalpic) effects. We conclude the thiolate ligand of 1d is misdirected in the ground-state with respect to the other thiolate derivatives.Key words: misdirected ligands, metallocene, thiolate, structure, bonding, dynamics.

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