Synthetic requirements

The fundamental mechanisms of free radical reactions were considered in Chapter 11 of Part A. Several mechanistic issues are crucial in development of free radical reactions for synthetic applications.285 Free radical reactions are usually chain processes, and the lifetimes of the intermediate radicals are very short. To meet the synthetic requirements of high selectivity and efficiency, all steps in a desired sequence must be fast in comparison with competing reactions. Owing to the requirement that all the steps be fast, only steps that are exothermic or very slightly endothermic can participate in chain processes. Comparison between addition of a radical to a carbon-carbon double bond and addition to a carbonyl group can illustrate this point. 

However, the particular synthetic requirements in the preparation of conjugated polymers have thus far severely limited the number of similarly hierarchically structured examples. Pu et al. reported different types of conjugated polymers with fixed main-chain chirality containing binaphthyl units in their backbone which exhibited, for example, nonlinear optical activity or were used as enantioselective fluorescent sensors [42—46]. Some chirally substituted poly(thiophene)s were observed to form helical superstructures in solution [47-51], Okamoto and coworkers reported excess helicity in nonchiral, functional poly(phenyl acetylenejs upon supramolecular interactions with chiral additives, and they were able to induce a switch between unordered forms as well as helical forms with opposite helical senses [37, 52, 53]. 

In summary, a wide variety of methods are available to prepare enantiopure Reissert-type adducts. Depending on the synthetic requirements, the use of chiral auxiliaries, enantioselective catalysis or chiral reagents may be the most suitable option. 

Hawker and Frechet525 via convergent attachment of preformed poly(benzyl ether) dendrons 4 to a poly-benzyl ester) monomer, 238. Continuation of the poly(benzyl ester) synthesis followed by coupling to a triphenolic core afforded the layered dendrimer 241. The primary synthetic requirement for the two different monomers is that the outermost dendritic layers must be chemically inert to the coupling and... 

Due to the synthetic requirement for sufficiently C—H acidic starting materials most of the bispidine compounds described above have a keto group in the 9-position (i.e., most of the ligands discussed in this chapter are bispidine-... 

Research into the biological activity of phytochemicals has a long history. Initially, the focus was on natural product chemistry, with degradation studies providing a basis for structure determination that was confirmed by elegant multistage synthesis. Many key reactions of organic chemistry were first developed out of the specific synthetic requirements of this area. 

There are a variety of different types of particle that can be synthesized using microfluidics and the exact fluidic format used defines the flow characteristics of the synthesis environment which needs to be carefully matched to the synthetic requirements of each particle type. Broadly speaking, the main particle types of interest include monodisperse microgels, metal nanoparticles and nanocrystals, core-shell particles, microemulsions, and microcapsules. Typically these particles should be homogeneous in size and are composed either of an organic polymer matrix or a metal or metal mixture at the micron or nanometer scale. In addition to these simple particle architectures, we may also consider more complex particles composed of multiple layers or components such as core-shell particles or using a central cavity to encapsulate small molecules, proteins, or other particles, and these are called microcapsules. 

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