Participation of Alkoxy Groups in Reactions of Acetals: Violation of the Reactivity/Selectivity Principle in a Curtin-Hammett Kinetic Scenario

The self-assembly of foldamers into macrocycles is a simple approach to non-biological higher-order structure. Previous work on the co-assembly of ortho-phenylene foldamers with rod-shaped linkers has shown that folding and self-assembly affect each other; that is, the combination leads to new emergent behavior, such as access to otherwise unfavorable folding states. To this point this relationship has been passive. Here, we demonstrate control of self-assembly by manipulating the foldamers’ conformational energy surfaces. A series of o-phenylene decamers and octamers have been assembled into macrocycles using imine condensation. Product distributions were analyzed by gel-permeation chromatography and molecular geometries extracted from a combination of NMR spectroscopy and computational chemistry. The assembly of o-phenylene decamers functionalized with alkoxy groups or hydrogens gives both [2+2] and [3+3] macrocycles. The mixture results from a subtle balance of entropic and enthalpic effects in these systems: the smaller [2+2] macrocycles are entropically favored but require the oligomer to misfold, whereas a perfectly folded decamer fits well within the larger [3+3] macrocycle that is entropically disfavored. Changing the substituents to fluoro groups, however, shifts assembly quantitatively to the [3+3] macrocycle products, even though the structural changes are well-removed from the functional groups directly participating in bond formation. The electron-withdrawing groups favor folding in these systems by strengthening arene–arene stacking interactions, increasing the enthalpic penalty to misfolding. The architectural changes are substantial even though the chemical perturbation is small: analogous o-phenylene octamers do not fit within macrocycles when perfectly folded, and quantitatively misfold to give small macrocycles regardless of substitution. Taken together, these results represent both a high level of structural control in structurally complex foldamer systems and the demonstration of large-amplitude structural changes as a consequence of a small structural effects.

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α-Alkoxyalkyl Triphenylphosphonium Salts: Synthesis and Reactions

Current Organic Chemistry ◽

10.2174/1385272823666190926092242 ◽

2019 ◽

Vol 23 (16) ◽

pp. 1738-1755

Author(s):

Humaira Y. Gondal ◽

Zain M. Cheema ◽

Abdul R. Raza ◽

Ahmed Abbaskhan ◽

M. I. Chaudhary

Keyword(s):

Carbonyl Compounds ◽

Claisen Rearrangement ◽

Alder Reaction ◽

Coupling Reactions ◽

Phosphonium Salts ◽

Organic Transformations ◽

Enol Ethers ◽

Wide Range ◽

Synthetic Methodologies ◽

Alkoxy Groups

Following numerous applications of Wittig reaction now functionalized phosphonium salts are gaining attention due to their characteristic properties and diverse reactivity. This review is focused on α-alkoxyalkyl triphenylphosphonium salts: an important class of functionalized phosphonium salts. Alkoxymethyltriphenylphosphonium salts are majorly employed in the carbon homologation of carbonyl compounds and preparation of enol ethers. Their methylene insertion strategy is extensively demonstrated in the total synthesis of a wide range of natural products and other important organic molecules. Similarly enol ethers prepared thereof are important precursors for different organic transformations like Diels-Alder reaction, Claisen rearrangement, Coupling reactions, Olefin metathesis and Nazarov cyclization. Reactivity of these α-alkoxyalkylphosphonium salts have also been studied in the nucleophilic substitution reactions. A distinctive application of this class of phosphonium salts was recently reported in the phenylation of carbonyl compounds under very mild conditions. Synthesis of structurally diverse alkoxymethyltriphenylphosphonium salts with variation in alkoxy groups as well as counter anions are reported in literature. Here we present a detailed account of different synthetic methodologies for the preparation of this unique class of quaternary phosphonium salts and their applications in organic synthesis.

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The effects controlling the oxygen basicity in alkoxysilanes (RO)nSi(CH3)4-n. The mutual polarizability effect of alkoxy groups attached to silicon

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19790750 ◽

1979 ◽

Vol 44 (3) ◽

pp. 750-755 ◽

Cited By ~ 5

Author(s):

Josef Pola ◽

Marie Jakoubková ◽

Václav Chvalovský

Keyword(s):

Regression Analysis ◽

Linear Regression ◽

Electronic Effect ◽

Linear Regression Analysis ◽

Effect Of Substituents ◽

Relative Basicity ◽

Polarizability Effect ◽

Alkoxy Groups ◽

Individual Series

Relative basicity of the oxygen in alkoxysilanes (RO)nSi(CH3)3-n having n = 1-4 and various electrondonating and electronwithdrawing groups R measured as Δν(OH) of phenol due to its interaction with these compounds in CCl4 is shown to be chiefly controlled by the electronic effect of substituents R. Linear regression analysis of the Δν(OH) vs n relatioship for individual series (RO)nSi(CH3)4-n suggests the operation of the polarizability effect of RO groups becoming more important with increasing electronwithdrawing nature of R.

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Boundary Friction of ZDDP Tribofilms

Tribology Letters ◽

10.1007/s11249-020-01389-4 ◽

2020 ◽

Vol 69 (1) ◽

Author(s):

Jie Zhang ◽

Mao Ueda ◽

Sophie Campen ◽

Hugh Spikes

Keyword(s):

Friction Coefficient ◽

Group Structure ◽

Boundary Friction ◽

Considerable Proportion ◽

Base Oil ◽

Characteristic Boundary ◽

Long Duration ◽

Structure Boundary ◽

Alkoxy Groups ◽

20 Nm

AbstractThe frictional properties of ZDDP tribofilms at low entrainment speeds in boundary lubrication conditions have been studied in both rolling/sliding and pure sliding contacts. It has been found that the boundary friction coefficients of these tribofilms depend on the alkyl structure of the ZDDPs. For primary ZDDPs, those with linear alkyl chains give lower friction those with branched alkyl chain ZDDPs, and a cyclohexylmethyl-based ZDDP gives markedly higher friction than non-cyclic ones. Depending on alkyl structure, boundary friction coefficient in rolling-sliding conditions can range from 0.09 to 0.14. These differences persist over long duration tests lasting up to 120 h. For secondary ZDDPs, boundary friction appears to depend less strongly on alkyl structure and in rolling-sliding conditions stabilises at ca 0.115 for the three ZDDPs studied. Experiments in which the ZDDP-containing lubricant is changed after tribofilm formation by a different ZDDP solution or a base oil indicate that the characteristic friction of the initial ZDDP tribofilm is lost almost as soon as rubbing commences in the new lubricant. The boundary friction rapidly stabilises at the characteristic boundary friction of the replacement ZDDP, or in the case of base oil, a value of ca 0.115 which is believed to represent the shear strength of the bare polyphosphate surface. The single exception is when a solution containing a cyclohexylethyl-based ZDDP is replaced by base oil, where the boundary friction coefficient remains at the high value characteristic of this ZDDP despite the fact that rubbing in base oil removes about 20 nm of the tribofilm. XPS analysis of the residual tribofilm reveals that this originates from presence of a considerable proportion of C-O bonds at the exposed tribofilm surface, indicating that not all of the alkoxy groups are lost from the polyphosphate during tribofilm formation. Very slow speed rubbing tests at low temperature show that the ZDDP solutions give boundary friction values that vary with alkyl group structure in a similar fashion to rolling-sliding MTM tests. These variations in friction occur immediately on rubbing, before any measurable tribofilm can develop. This study suggest that ZDDPs control boundary friction by adsorbing on rubbing steel or tribofilm surfaces in a fashion similar to organic friction modifiers. However it is believed that, for primary ZDDPs, residual alkoxy groups still chemically bonded to the phosphorus atoms of newly-formed polyphosphate/phosphate tribofilm may also contribute to boundary friction. This understanding will contribute to the design of low friction, fuel efficient crankcase engine oils. Graphical Abstract

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Silicon-functionalized silyl enol ethers. Part 2. Silyl enol ethers bearing stereogenic silicon atoms and chiral alkoxy groups: the effect of these groups upon the facial selectivity of the epoxidation of an enol double bond

The Journal of Organic Chemistry ◽

10.1021/jo00239a057 ◽

1988 ◽

Vol 53 (4) ◽

pp. 920-923 ◽

Cited By ~ 17

Author(s):

Robert D. Walkup ◽

Nihal U. Obeyesekere

Keyword(s):

Double Bond ◽

Enol Ethers ◽

Silyl Enol Ethers ◽

Facial Selectivity ◽

Alkoxy Groups

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ChemInform Abstract: Fluoride Salts-Alcohols-Alumina as Reagents for Nucleophilic Substitution of Chlorine Atoms for Alkoxy Groups in 2,3- Dichlorosubstituted Juglones, Naphthazarines, and Quinizarines.

ChemInform ◽

10.1002/chin.199531111 ◽

2010 ◽

Vol 26 (31) ◽

pp. no-no

Author(s):

V. PH. ANUFRIEV ◽

V. L. NOVIKOV

Keyword(s):

Nucleophilic Substitution ◽

Chlorine Atoms ◽

Alkoxy Groups ◽

Fluoride Salts

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Liquid Crystalline Properties of 4,4and#39;-methylenebis(N-(4-Alkanoxybenzylidene)aniline): Synthesis, Characterization, and Theoretical study

Journal of the chemical society of pakistan ◽

10.52568/000822/jcsp/41.06.2019 ◽

2019 ◽

Vol 41 (6) ◽

pp. 1107-1107

Author(s):

Mohammed Taha Yaseen and Abdullah Hussein Kshash Mohammed Taha Yaseen and Abdullah Hussein Kshash

Keyword(s):

Liquid Crystalline ◽

Theoretical Study ◽

Basis Set ◽

Spectroscopic Techniques ◽

Benzene Nucleus ◽

Crystal Properties ◽

Ft Ir ◽

Alkoxy Groups ◽

Gaussian Program ◽

Mesomorphic Properties

The paper presents six homologues series of Schiff bases ether compounds distinguished by the length of terminal alkoxy groups which substituted on a side benzene nucleus. The above structures were demonstrated through the use of spectroscopic techniques, like FT- IR and 1H-NMR. Polarized hot stage optical microscopy was used to study both mesomorphic properties and phase transitions. The results showed that out of the six compounds only three (B2, B3 and B4) were pure (marble) nematic mesophase, while no liquid crystal properties for (B5, B6 and B7) compounds. The theoretical study for the electronic structures was intended to study the effects of alkyl chain length on the electronic structure by using Gaussian program, DFT and 6-31G as basis set. The theoretical results indicate that there is no effect to the terminal substituted alkoxy groups on the HOMO energies but there is an effect on LUMO energies through decreasing energy for the prepared compounds.

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