Degenerate transesterification of 3,5-dimethylphenolate/3,5-dimethylphenyl esters in weakly polar, aprotic solvents. Reactions of aggregates and complex-induced proximity effects

1991 ◽  
Vol 113 (9) ◽  
pp. 3451-3458 ◽  
Author(s):  
L. M. Jackman ◽  
M. M. Petrei ◽  
B. D. Smith
Keyword(s):  
Proximity Effects ◽  
Aprotic Solvents

Heterocyclic Ambident Nucleophiles. V. Alkylation of Benzimidazoles

1993 ◽  
Vol 46 (8) ◽  
pp. 1177 ◽  
Author(s):  
JR Howell ◽  
M Rasmussen
Keyword(s):  
Transition State ◽  
Electrostatic Field ◽  
Alkyl Halides ◽  
Proximity Effects ◽  
Aprotic Solvents ◽  
Control Factors ◽  
Transition State Structures

Alkylation of 5-substituted benzimidazole anions with a variety of primary alkyl halides in both protic and aprotic solvents showed only small regioselectivity , with a slight preference for reaction at N1 for 5-nitro and N3 for 5-methoxy systems. With 4-substituted benzimidazole anions, alkylation gave more divergent results with the N1 to N3 regioselectivity varying between 100:0 and 29:71. These alkylation patterns are interpreted as deriving from an interplay of electrostatic, thermodynamic, steric and associative control factors within the variable SN2 transition state structures involved. In the 4-substituted series, proximity effects, both electrostatic field and steric non-bonded, are clearly dominant.

Processing cost and its consequences

2016 ◽  
Vol 39 ◽  
Author(s):  
William O'Grady
Keyword(s):  
Word Order ◽  
Proximity Effects ◽  
Processing Cost

AbstractI focus on two challenges that processing-based theories of language must confront: the need to explain why language has the particular properties that it does, and the need to explain why processing pressures are manifested in the particular way that they are. I discuss these matters with reference to two illustrative phenomena: proximity effects in word order and a constraint on contraction.

ANALYSIS OF PROXIMITY EFFECTS BETWEEN SPIN SINGLET AND SPIN TRIPLET SUPERCONDUCTORS

1978 ◽  
Vol 39 (C6) ◽  
pp. C6-481-C6-483 ◽  
Author(s):  
K. Scharnberg ◽  
D. Fay ◽  
N. Schopohl
Keyword(s):  
Proximity Effects ◽  
Spin Singlet ◽  
Spin Triplet

Solvation of ions by dipolar aprotic solvents and water. A CNDO/2 study

1985 ◽  
Vol 50 (11) ◽  
pp. 2493-2508 ◽  
Author(s):  
Petr Kyselka ◽  
Zdeněk Havlas ◽  
Ivo Sláma
Keyword(s):  
Binary Mixtures ◽  
Quantum Chemical ◽  
Chemical Method ◽  
Molecular Structures ◽  
Dimethyl Sulphoxide ◽  
Ternary Mixtures ◽  
Aprotic Solvents ◽  
Quantum Chemical Method ◽  
Solvation Of Ions ◽  
Dipolar Aprotic Solvents

Solvation of Li+, Be2+, Na+, Mg2+, and Al3+ ions has been studied in binary mixtures with dimethyl sulphoxide, dimethylformamide, acetonitrile and water, and in ternary mixtures of the organic solvents with water. The CNDO/2 quantum chemical method was used to calculate the energies of solvation, molecular structures and charge distributions for the complexes acetonitrile...ion (1:1, 2:1, 4:1), dimethyl sulphoxide...ion (1:1), dimethylformamide...ion (1:1), and acetonitrile (dimethyl sulphoxide, dimethylformamide)...ion...water (1:1:1).

Oxidation of (1-hydroxybenzyl)ferrocene and its derivatives substituted in phenyl ring with bis(triphenylsilyl) chromate

1982 ◽  
Vol 47 (12) ◽  
pp. 3375-3380 ◽  
Author(s):  
Jaroslav Holeček ◽  
Karel Handlíř ◽  
Milan Nádvorník ◽  
Milan Vlček
Keyword(s):  
Linear Dependence ◽  
Rate Constants ◽  
Oxidation Rate ◽  
Phenyl Ring ◽  
Equilibrium Constants ◽  
Aprotic Solvents ◽  
Protonation Equilibrium ◽  
Oxidation Of Alcohols ◽  
Hammett Σ Constants ◽  
Sulphuric Acid Medium

Kinetics have been studied of oxidation of (1-hydroxybenzyl)ferrocenes substituted in phenyl ring with bis(triphenylsilyl) chromate in benzene solutions as well as protonation of these alcohols in sulphuric acid medium. Logarithms of the oxidation rate constants (kobs, 20-40 °C) and those of the protonation equilibrium constants (KR+, 25 °C) show linear dependence on the Hammett σ constants, the ρ constant values being -0.86 to -0.40 and -2.50, respectively. These negative values suggest that the both processes are influenced by the same effects and confirm the mechanism proposed earlier for oxidation of alcohols with ferrocenyl substituent by action of bis(triphenylsilyl) chromate in aprotic solvents.

1H and 13C NMR spectra of 2,2’-disubstitutedtrans-azobenzenes suitable for preparation of metallized azo dyes

1991 ◽  
Vol 56 (10) ◽  
pp. 2160-2168 ◽  
Author(s):  
Josef Jirman
Keyword(s):  
Nmr Spectra ◽  
Electron Pair ◽  
Phenyl Group ◽  
Aprotic Solvents ◽  
1H And 13C Nmr ◽  
Predominant Form ◽  
Rapid Equilibrium ◽  
Dipolar Aprotic Solvents ◽  
Free Electron Pair ◽  
C Nmr

The 1H and 13C NMR spectra have been measured of six trans-azobenzenes substituted at 2 and 2’ positions with substituents favourable for complex formation with a metal (OH, NH2, NHCOCH3, COOH). From the standpoint of NMR such substituted trans-azobenzenes are present in solution in a rapid equilibrium following from rotation around the bond between C-1 of phenyl group and N atom of azo linkage. The predominant form has the substituent in the syn-position with respect to the free electron pair of the nearer azo nitrogen atom. The equilibrium is affected by dipolar aprotic solvents (such as hexadeuteriodimethyl sulfoxide) by decreasing the presence of the predominant form by 1 to 11%.

Proximity and conformation effects in 29Si and 13C NMR spectra of di-ortho substituted trimethylsiloxybenzenes

1990 ◽  
Vol 55 (8) ◽  
pp. 2027-2032 ◽  
Author(s):  
Jan Schraml ◽  
Robert Brežný ◽  
Jan Čermák
Keyword(s):  
Benzene Ring ◽  
13C Nmr ◽  
Proximity Effect ◽  
Nmr Spectra ◽  
Methoxy Group ◽  
Chemical Shifts ◽  
Proximity Effects ◽  
13C Nmr Spectra ◽  
Methoxy Groups ◽  
C Nmr

29Si and 13C NMR spectra of five 4-substituted 2,6-dimethoxytrimethylsiloxybenzenes were studied with the aim to elucidate the nature of the deshielding proximity effects observed in the spectra of ortho substituted trimethylsiloxybenzenes. The sensitivity of 29Si chemical shifts to para substitution is in the studied compounds essentially the same as in mono ortho methoxytrimethylsiloxybenzenes. The deshielding proximity effect of the ìsecondî methoxy group is somewhat smaller than that of the ìfirstî group. The present results indicate that the two methoxy groups assume coplanar conformations with the benzene ring and are turned away from the trimethylsiloxy group which is not in the benzene plane. It is argued that in mono ortho methoxytrimethylsiloxybenzenes the two substituent groups adopt the same conformations as in the compounds studied here.

The excited state behaviors of 3-(benzo[d]thiazol-2-yl)-2-hydroxy-5-methoxybenzaldehyde system in aprotic solvents

2021 ◽  
pp. 111280
Author(s):  
Junyu Li ◽  
Shiquan Feng ◽  
Xuechao Feng ◽  
Jie Wu ◽  
Liancai Xu
Keyword(s):  
Excited State ◽  
Aprotic Solvents
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