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Substituent

About: Substituent is a research topic. Over the lifetime, 42877 publications have been published within this topic receiving 516716 citations. The topic is also known as: side chain & side group.


Papers
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Journal ArticleDOI
TL;DR: A family of Group 4 post-metallocene catalysts, supported by fluorine-functionalized tridentate ligands with the fluorine substituent in the locality of the metal center, is described and for the first time, the contentious C-H...F-C interaction has been characterized by a neutron diffraction study.
Abstract: A family of Group 4 post-metallocene catalysts, supported by fluorine-functionalized tridentate ligands with the fluorine substituent in the locality of the metal center, is described. For the first time, the contentious CH⋅⋅⋅FC interaction has been characterized by a neutron diffraction study, which has allowed the position of the hydrogen atoms to be accurately determined. The nature of the weak intramolecular CH⋅⋅⋅FC contacts in these complexes in solution and the solid state was probed by using multinuclear NMR spectroscopy in tandem with neutron and X-ray crystallography. Evidence is presented to demonstrate that the spectroscopic CH⋅⋅⋅FC coupling occurs “through-space” rather than “through-bond” or by M⋅⋅⋅F coordination. The titanium catalysts exhibit excellent activities and high co-monomer incorporation in olefin polymerization. The observed intramolecular CH⋅⋅⋅FC interactions are important with regards to potential applications in polyolefin catalysis because they substantiate the proposed ortho-F⋅⋅⋅H(β) ligand–(polymer chain) contacts derived from DFT calculations for the remarkable fluorinated phenoxyimine Group 4 catalysts. Compared with agostic and co-catalyst⋅⋅⋅metal contacts, weak attractive noncovalent interactions between a polymer chain and a judiciously designed “active” ligand is a new concept in polyolefin catalysis.

78 citations

Journal ArticleDOI
TL;DR: In this article, the side-chains of meta-and para-substituted benzenes of the type XC6H4COZ have been measured and the reverse inductive contribution observed is explained in terms of a π-polarization mechanism.
Abstract: 13 C Substituent chemical shifts of the carbonyl sites in the side-chains of meta- and para-substituted benzenes of the type XC6H4COZ have been measured. Analysis of this data using the dual substituent parameter method shows that inductive effects are predominant. The reverse inductive contribution observed is explained in terms of a π-polarization mechanism. Critical support for this mechanism is obtained from additional series where the carbonyl is complexed with Lewis acids. The concepts of ‘extened’ and ‘localized’π-polarization are discussed.

78 citations

Journal ArticleDOI
TL;DR: In this article, the free energy of inclusion complexation has been shown to increase linearly to a certain limit with extending chain length or ring size of the guests, giving unit increments per methylene (dΔG°/dNC).
Abstract: Novel α- and/or β-cyclodextrin benzoates (2α, 2β), methyl phthalate (3β), tethered benzamide (4β) and 2-naphthoate (5β) have been synthesized. The complex stability constants (Ks) of these cyclodextrin derivatives with a series of acyclic and cyclic hydrocarbons, and alcohols have been determined in water to reveal the role of the hydrophilic group in the guest molecule, and to evaluate the individual contribution of weak interactions involved in inclusion complexation by cyclodextrin. The free energy of complexation (–ΔG°) increases linearly to a certain limit with extending chain length or ring size (NC) of the guests, giving unit increments per methylene (–dΔG°/dNC). Interestingly, the unit increment obtained is independent of the host’s size or substituent introduced, but is a critical function of the guest type. Thus, a remarkably large –dΔG°/dNC value of 5.4 kJ mol–1 has been obtained for the cycloalkane series, whereas much smaller, but conventional, values have been recorded for cycloalkanols (3.3 kJ mol–1), alkanes (3.1 kJ mol–1) and alkanols (2.7 kJ mol–1). No significant isotope effects on Ks are observed when deuterated cyclohexane is complexed with the same cyclodextrins. Similarly, there is no significant effect when deuterated water is used as solvent. Moderate enantioselectivities of up to 2.0 are obtained with some chiral guests.

78 citations

Patent
02 Feb 1999
TL;DR: In this article, a thermally-sensitive polymer with a pH-sensitive substituent was used to provide liposomes that are pH sensitive, yet are also stable in serum.
Abstract: This invention relates to the field of liposomes In particular, this invention provides novel liposomes that are pH-sensitive, yet are also stable in serum The liposomes are complexed with a molecule comprising a thermally-sensitive polymer showing lower critical solution temperature behavior in aqueous solutions, said thermally-sensitive polymer bearing a hydrophobic substituent and a pH sensitive substituent, wherein said hydrophobic substituent is less than 10 kD and which pH sensitive substituent remains ionizable following said covalent bonding to said thermally-sensitive polymer, and whose pH sensitive does not depend on cleavage of the covalent bond to said thermally-sensitive polymer The invention further relates to methods of conferring pH sensitivity upon liposomes by complexing the liposomes with such molecules

78 citations

Patent
13 Feb 1986
TL;DR: In this article, the UV-absorbing compound of formula (I) is defined as a polyester composition useful in formed articles such as beverage bottles and having condensation reacted therein at least one UV absorbing compound, wherein X is hydroxyl, carboxy, carbalkoxy, substituted carbalkoxoxy, or acyloxy.
Abstract: Polyester compositions useful in formed articles such as beverage bottles and having condensation reacted therein at least one UV-absorbing compound of formula (I), wherein X is hydroxyl, carboxy, carbalkoxy, substituted carbalkoxy, or acyloxy; Y is cyano, carbamyl, substituted carbamyl, aryl, acyl, alkylsulfonyl, substituted alkylsulfonyl, phenylsulfonyl, or substituted phenylsulfonyl; R is selected from -alkylene-O-alkylene-, -alkylene-S-alkylene-, -alkylene-N(-SO2alkyl)-alkylene-, straight or branched chain alkylene or such alkylene substituted with an X substituent; and R1 is hydrogen or 1-3 groups selected from alkyl, alkoxy and halogen.

78 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023660
20221,273
2021568
2020787
2019753
2018858