Taft equation in the light of NBO computations. Introduction of a novel polar computational substituent constant scale for alkyl groups

Substituted Terminal Alkyl Groups and Their Prospects in Liquid Crystal Chemistry

Molecular Crystals and Liquid Crystals ◽

10.1080/00268948608084954 ◽

1986 ◽

Vol 131 (3) ◽

pp. 353-360 ◽

Cited By ~ 1

Author(s):

Maged Osman

Keyword(s):

Liquid Crystal ◽

Crystal Chemistry ◽

Alkyl Groups

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Electrochemical Vicinal Difluorination of Alkenes: Sustainable, Scalable, and Amenable to Electron-rich Substrates

10.26434/chemrxiv.9974687 ◽

2019 ◽

Author(s):

Sayad Doobary ◽

Alexi Sedikides ◽

Henry caldora ◽

Darren poole ◽

Alastair Lennox

Keyword(s):

Bioactive Compounds ◽

Hypervalent Iodine ◽

Electrochemical Generation ◽

Oxidative Decomposition ◽

Alkyl Groups ◽

Rich Functionality

Fluorinated alkyl groups are important motifs in bioactive compounds, positively influencing pharmacokinetics, potency and F conformation. The oxidative difluorination of alkenes represents an H important strategy for their preparation, yet current methods are limited in their alkene-types and tolerance of electron-rich, readily oxidized functionalities, as well as in their scalability. Herein, we report a method for the difluorination of a number of unactivated alkene-types that is tolerant of electron-rich functionality, giving products that are otherwise unattainable. Key to success is the electrochemical generation of a hypervalent iodine mediator (in the presence of nucleophilic fluoride and HFIP) using an ‘ex-cell’ approach, which avoids the oxidative decomposition of the substrate. The more sustainable conditions give good to excellent yields of product in up to decagram scales<br>

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Molecular Engineering of Liquid Crystal Polymers by Living Polymerization. 13. Synthesis and Living Cationic Polymerization of 4-((S(-)-2- Methyl-1-Butyl)Oxycarbonyl)-4'-(omega-Oxyalkyl-1-Vinyl Ether)Biphenyl with Undecanyl and Hexyl Alkyl Groups

10.21236/ada235791 ◽

1991 ◽

Author(s):

V. Percec ◽

Q. Zheng ◽

M. Lee

Keyword(s):

Liquid Crystal ◽

Vinyl Ether ◽

Cationic Polymerization ◽

Living Polymerization ◽

Molecular Engineering ◽

Liquid Crystal Polymers ◽

Living Cationic Polymerization ◽

Alkyl Groups

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Alkyl 1-[2-(oxido anion)-, 3-, 4-, 5-alkyl substituted]phenyl ketyl radicals

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19791731 ◽

1979 ◽

Vol 44 (6) ◽

pp. 1731-1741 ◽

Cited By ~ 6

Author(s):

Andrej Staško ◽

Ľubomír Malík ◽

Alexander Tkáč ◽

Vladimír Adamčík ◽

Eva Maťašová

Keyword(s):

Electron Donor ◽

Unpaired Electron ◽

Grignard Reagents ◽

Slight Effect ◽

Benzene Nucleus ◽

Alkyl Groups ◽

Splitting Constant

Reactions of R2,R3-alkyl substituted 2-hydroxybenzenecarboxylic acids 2-HO-C6H2R2-COOH with Grignard reagents R1MgBr in the presence of nickel give stable aryl alkyl ketyl radicals 2-O--R2-, R3-C6H2-CO--R1 where R1 = CH3, C2H5, C2D5, n-C3H7 and R2,R3 = CH3, C2H5, i-C3H7, t-C4H9. The β protons of ketyl group are equivalent (splitting constant 1.25 mT) and non-equivalent (splitting constants within 0.5 to 1.5 mT) for R1 = methyl and other alkyl groups, respectively. Interaction of the γ protons with the unpaired electron was only observed in the case of R1 = n-propyl (splitting constants about 0.07 mT). The substituents R1 have but slight effect on values of splitting constants of the protons in R2,R3 and vice versa. Also splitting constants of the benzene nucleus (a4H = 0.55 mT, a6H = 0.44 mT) are only slightly affected by the substituents R1,R2,R3, which indicates dominant electron-donor effect of the oxido-anion group eliminating the relatively smaller contributions of the alkyl substituents.

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Chemometric Analysis of Substituent Effects. VIII. Alternative Interpretation of Substituent Effects (AISE)

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19951502 ◽

1995 ◽

Vol 60 (9) ◽

pp. 1502-1528 ◽

Cited By ~ 12

Author(s):

Oldřich Pytela

Keyword(s):

Multiple Bond ◽

Substituent Effects ◽

Alternative Interpretation ◽

Class I ◽

Reaction Centre ◽

Correlation Equations ◽

Class Iii ◽

Substituent Constant ◽

Chemical Models ◽

The Individual

Alternative interpretation of substituent effects (AISE) starts from the presumption that a substituent only possesses a single property described by a single substituent constant. This property is transmitted to the reaction centre by three different ways depending on the interaction type in the triad reaction centre - basic skeleton - substituent. For interpretation it is substantial whether or not the substituent has p electrons at the atom adjacent to the basic skeleton. If it has none, the substituent belongs to class I and operates only by its basic effect described by the mentioned single substituent constant. Substituents of class II possess a free electron pair at the atom adjacent to the basic skeleton, and those of class III have a multiple bond between the first and the second atoms which is polarized in the direction from the basic skeleton. Substituent effects in class I are described by a substituent constant identical with σI constant. Substituents in classes II and III show additional effects proportional to the same constant. Hence, a separate treatment of substituent effects in the individual classes provides three straight lines intersecting in a common point. Mathematically, the description of substituent effects in this approach is expressed by a family of lines with a single explaining variable. The point of intersection, which is referred to as the iso-effect point, is not identical with the classic standard substituent - hydrogen - but is near to CN substituent. The approach given has the advantage of adopting a single substituent constant whose scale can be adjusted relatively precisely. Its drawback (like in the case of the correlation equations derived from the principle of separation of substituent effects) lies in a more extensive set of substituents needed for a correlation. The AISE principle has been applied to 318 series of experimental data describing effects of 32 substituents in a large variety of chemical models (aliphatic, alicyclic, aromatic, heteroaromatic, with or without direct conjugation between reaction centre and substituent) in both chemical reactions and equilibria. A comparison with two other correlation relations with two and three substituent constants for interpretation of substituent effects based on the principle of separation of the individual substituent effects showed that the closeness of AISE based correlations is comparable with that of the correlation equations currently used. It was somewhat less successful in the models with direct conjugation between reaction centre and substituent but the AISE principle can be used even in these cases.

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Chemometric Analysis of Substituent Effects. VII. Inductive Effect as a Basic Substituent Effect. Isoeffect Substituent Constant

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19951316 ◽

1995 ◽

Vol 60 (8) ◽

pp. 1316-1332 ◽

Cited By ~ 5

Author(s):

Oldřich Pytela ◽

Aleš Halama

Keyword(s):

Inductive Effect ◽

Chemical Shifts ◽

Quantitative Description ◽

Substituent Effects ◽

Intersection Point ◽

Chemometric Analysis ◽

Reaction Centre ◽

Substituent Constant ◽

Modified Method ◽

Substituted Benzoic Acids

The paper deals with chemometric analysis of the inductive effect. The notion of inductive effect is discussed, and unambiguous definitions are given for the notions of triad: reaction centre-basic skeleton-substituent, and the therewith connected definitions of inductive effect. For a quantitative description of inductive effect 7 types of chemical models were selected including noncyclic compounds, cyclic, and bicyclic compounds, derivatives of quinuclidine, 3-substituted benzoic acids, sulfonamides and pyridines. Altogether 139 sets of experimental data from literature have been used including altogether 1 294 points (9.3 points per set, 5 points at least) reflecting substituent effects of 34 substituents. It has been found that for a standard model the dissociation of substituted bicycloalkanecarboxylic acids only is satisfactory, all the other models reflecting also the mesomeric effects to variable extent (up to 10%). A distinctly different substitution behaviour was observed with 19F and 13C NMR chemical shifts of 4-substituted 1-fluoro- or 1-methylbicyclo[2.2.2]octanes. The earlier suggested model of substituent effects based on different way of transmission of substituent effects (3 classes) has been used for separating the inductive and mesomeric effects: it is mathematically presented as a set of straight lines with the intersection point at the so-called isoeffect substituent constant. Using the modified method of conjugated deviations a chemometric scale has been created for the inductive effect which agrees very well with the conventional scales given in literature; the only differences were observed for F and CH=O substituents (which are overestimated and underestimated, respectively, in literature). In the context given the inductive effect appears as a fundamental quantity forming a basis for quantitative description of other effects transferred by electrons.

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Kinetics of the Imidazolium Ring-Opening of mRNA 5'-cap Analogs in Aqueous Alkali

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc20060567 ◽

2006 ◽

Vol 71 (4) ◽

pp. 567-578 ◽

Cited By ~ 2

Author(s):

Alicja Stachelska ◽

Zbigniew J. Wieczorek ◽

Janusz Stępiński ◽

Marzena Jankowska-Anyszka ◽

Harri Lönnberg ◽

...

Keyword(s):

Electrostatic Interaction ◽

Ring Opening ◽

Nucleophilic Attack ◽

Amino Groups ◽

Hydroxide Ion ◽

Methyl Group ◽

Structural Modifications ◽

Alkyl Groups ◽

Imidazolium Ring ◽

Kinetics Of

Second-order rate constants for the hydroxide-ion-catalyzed imidazolium ring-opening of several mono- and dinucleosidic analogs of mRNA 5'-cap have been determined. Intramolecular stacking of the two nucleobases in the dinucleosidic analogs, m7GpppN (m7G = 7-methylguanosine, N = 5'-linked nucleoside), and electrostatic interaction between the N-alkylated imidazolium ring and phosphate moiety have been shown to shield the m7G moiety against the nucleophilic attack of hydroxide ion. In addition, the effect of methylation of the nucleobase amino groups and replacement of the 7-methyl group with other alkyl groups have been studied. The influence of all the structural modifications studied turned out to be modest, the cleavage rates of the most and least reactive analogs (with the exception of non-phosphorylated nucleosides) differing only by a factor of 5.

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