Density functional theory (DFT) calculations of the nucleophilic addition of allyltrimethylsilane to selected oxocarbenium ions accounted for the dramatic reduction in diastereoselectivity observed when five-membered ring acetals become constrained by effects of ring fusion. This chapter describes carbocation reactions, SN reactions forming CC bonds, SN reactions forming CY bonds and nucleophilic attack at elements other than carbon. ![]() This chapter contains sections titled: Carbocation Reactions SN Reactions Forming C–C Bonds Allyl and Vinyl Systems Small-Ring Systems SN Reactions Forming C–Y Bonds Allyl and Vinyl Systems Small-Ring Systems Nucleophilic Attack at Elements Other than Carbon References A review of recent progress in catalytic functionalization of tertiary alcohols to fully substituted carbon centres using carbon or heteroatom-based nucleophiles has included application of asymmetric reactions to natural product synthesis. Experimental evidence points toward an ionic mechanism, since the more electron‐rich thiophenyl‐substituted substrates reacted faster. Only minor amounts of side products were observed in the reaction mixtures. Cyclobutyl‐substituted propargylic alcohols gave the corresponding propargyl ether substituted products in 40 to 55% isolated yields (40 to 45 ☌, around 16 h reaction time), and no rearrangement of the cyclobutyl unit was observed. Cyclopropyl‐substituted propargylic alcohols bearing a thiophenyl substituent gave the corresponding cyclopropyl‐substituted propargylic ethers in 27 to 56% isolated yields (45 ☌, 2 h reaction time), where the cyclopropyl unit did not rearrange. After 2 h reaction time at 40 ☌ in CH 2 Cl 2 and 3 to 5 mol% catalyst load, aromatic, cyclopropyl‐substituted propargylic alcohols gave rearranged, conjugated ene‐yne products as single isomers in 35 to 73% isolated yields. The alcohol nucleophiles and the propargylic alcohols were employed in a nearly equimolar amount and no further additives were required. The effect of the xylitol functionalization in monomers was evidenced by their viscosity, whereas for polymers, the dielectric constant was evaluated.Ĭommercial ferrocenium hexafluorophosphate (PF 6 ) and ferrocenium boronic acid hexafluoroantimonate (SbF 6 ) were found to be efficient catalysts for the etherification of terminal, tertiary, cyclopropyl‐substituted propargylic alcohols through nucleophilic substitution with primary and secondary alcohols. All of the structures were characterized by 1H NMR, FT-IR, DSC and TGA. ![]() Fully bio-resourced polymers were obtained by thermal curing in which the ELO-Xyl-50% monomer was crosslinked by a reaction between epoxy residues (50%) and the primary hydroxyls of pendant xylitol at 180☌ for 90 min, whereas the ELO-Xyl-100% monomer was mixed with ELO in stoichiometrically molar proportions and cured at 200☌ for 120 min. Using N-methyl-2-pyrrolidone (NMP) as the solvent, the ZnCl2 catalyst amount, time and temperature were studied to achieve these functionalizations. Epoxidized linseed oil obtained by a chemoenzymatic method was first reacted with xylitol by a nucleophilic opening of the epoxy rings with one of the primary hydroxyl groups from xylitol, reaching a partial 50% (ELO-Xyl-50%) and a complete 100% (ELO-Xyl-100%) functionalization. For example, the epoxy ring opening can be a mechanism for anomalous photoluminescent (PL) quenching of GO dispersions in alkaline conditions.Novel xylitol-functionalized epoxidized linseed oil (ELO) polyols were synthesized. Thus, the reversible epoxy formation should be an important part of our understanding of reactivity and properties of GO. A high concentration of basal plane epoxides is a remarkable feature of GO. Our experimental results indicate that an irreversible epoxy formation observed in base-treated GO under flux conditions is due to the decomposition of the vic-diol groups formed by epoxy ring opening in alkaline solutions. We suggest that unique properties of GO including stability of the carbocation and fast proton migration on the surfaces enable the unusual pH-driven epoxide ring opening/closing reactions. In the present study, we have discovered reversible epoxide opening/closing reactions in GO upon alkaline and acid treatments, respectively, under ambient conditions. Oxygen functional groups (OFGs) in graphene oxide (GO) are responsible for the unique optical, electrical, magnetic as well as ionic, liquid and gaseous transport properties.
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