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Pillararene
Pillararenes are macrocycles composed of hydroquinone or dialkoxybenzene units (5 to 10) linked in the para position by methylene bridges. They are structurally similar to the cucurbiturils and calixarenes that play an important part in host–guest chemistry. The first pillararene was the five membered dimethoxypillar rene. History 1,4-Dimethoxypillar rene, the first pillararene, was reported in 2008 by Tomoki Ogoshi ''et al.'' They catalyzed the condensation of 1,4-dimethoxybenzene and paraformaldehyde using a Lewis acid to obtain 1,4-dimethoxypillar rene (DMpillar rene). The methoxy groups of DMpillar rene were then deprotected using boron tribromide and removed to give pillar rene. Ogoshi and Kanai decided naming the new family of host macrocycles "pillararene", since they are cylindrical or pillar-like in shape and composed of aromatic or "arene" moieties.1 Chemists often refer to them as "pillarenes" orally as this is easier to pronounce and remember. It is pertinent to men ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calixarenes
A calixarene is a macrocycle or cyclic oligomer based on a methylene-linked phenols. With hydrophobic cavities that can hold smaller molecules or ions, calixarenes belong to the class of cavitands known in host–guest chemistry. Nomenclature Calixarene nomenclature is straightforward and involves counting the number of repeating units in the ring and including it in the name. A calix rene has 4 units in the ring and a calix rene has 6. A substituent in the meso position Rb is added to the name with a prefix C- as in C-methylcalix rene The word calixarene is derived from the Greek calix or chalice because this type of molecule resembles a vase (or cup) and from the word arene that refers to the aromatic building block. Synthesis Calixarenes are generally produced by condensation of two components: an electron-rich aromatic compound, classically a 4-substituted phenol, and an aldehyde, classically formaldehyde. *The scope for the aromatic component is broad diverse. The key at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cucurbituril
In host-guest chemistry, cucurbiturils are macrocyclic molecules made of glycoluril () monomers linked by methylene bridges (). The oxygen atoms are located along the edges of the band and are tilted inwards, forming a partly enclosed cavity (cavitand). The name is derived from the resemblance of this molecule with a pumpkin of the family of Cucurbitaceae. Cucurbiturils are commonly written as cucurbit 'n''ril, where ''n'' is the number of glycoluril units. Two common abbreviations are CB 'n'''', or simply CB''n''. These compounds are particularly interesting to chemists because they are suitable hosts for an array of neutral and cationic species. The binding mode is thought to occur through hydrophobic interactions, and, in the case of cationic guests, through cation-dipole interactions as well. The dimensions of cucurbiturils are generally on the ~10 Å size scale. For instance, the cavity of cucurbit ril has a height ~9.1 Å, an outer diameter ~5.8 Å, and a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macrocycles
Macrocycles are often described as molecules and ions containing a ring of twelve or more atoms. Classical examples include the crown ethers, calixarenes, porphyrins, and cyclodextrins. Macrocycles describe a large, mature area of chemistry. Synthesis The formation of macrocycles by ring-closure is called macrocylization. Pioneering work was reported for studies on terpenoid macrocycles. The central challenge to macrocyclization is that ring-closing reactions do not favor the formation of large rings. Instead, small rings or polymers tend to form. This kinetic problem can be addressed by using high-dilution reactions, whereby intramolecular processes are favored relative to polymerizations. Some macrocyclizations are favored using template reactions. Templates are ions, molecules, surfaces etc. that bind and pre-organize compounds, guiding them toward formation of a particular ring size. The crown ethers are often generated in the presence of an alkali metal cation, whic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
