Building construction, alternative approaches

An alternative approach to constructing designs for estimating second-order models is to consider building a design from those constructed for the first-order model. In Section 2.2.1, we discussed the use of fractional factorial designs to estimate the coefficients of the first-order model. It was noted that a fractional factorial design of resolution V would yield... 

Weak interaction potentials can be constructed specihc to a single system, such as the dimer of two molecules of water or the trimer of hydrogen huoride. They may contain terms that correspond to the usual contributing elements and may incorporate cooperative effects. In any case, the objective is a potential that is expressed in terms of geometrical parameters of the specihc system as a whole. The alternative approach is to construct potentials with parameters tied to the molecule building blocks. This alternate approach imposes a type of constraint in that functional forms used to represent a surface must rehect the types of parameters. The contributing element of permanent moment interactions is... 

An alternative approach for tunable singlemode operation is to build an external cavity. In this case, a FP laser is placed into an optical cavity, and the wavelength is tuned by using a dispersive element, such as a grating. The wavelength can be tuned continuously over many wave-numbers (20-50 cm" ) by rotating the grating. The linewidth depends on the construction of the external cavity and its stability and is usually less than 1 MHz. 

An alternative and much more flexible approach is represented hy the STAR file format [L48, 149, which can be used for building self-describing data files. Additionally, special dictionaries can be constructed, which specify more precisely the contents of the eorresponding data files. The two most widely used such dictionaries (and file formats) arc the CIF (Crystallographic Information File) file format [150] - the International Union of Crystallography s standard for representation of small molecules - and mmCIF [151], which is intended as a replacement for the PDB format for the representation of macromolecular structures,... 

This reaction is particularly suitable for the preparation of the Wieland-Miescher ketone 96, a very useful building block for construction of a broad variety of biologically active compounds such as steroids, terpenoids, and taxol. On the basis of the proline-catalyzed approach described above Barbas et al. recently reported an optimized procedure for formation of the chiral Wieland-Miescher ketone, 96 [105]. It has been shown that this synthesis (which comprises three reactions) can be performed as a one-pot synthesis. The desired product is obtained in 49% yield with enantioselectivity of 76% ee (Scheme 6.43). Here L-proline functions as an efficient catalyst for all three reaction steps (Michael-addition, cydiza-tion, dehydration). It is also worth noting that although many other amino adds and derivatives thereof were tested as potential alternative catalysts, L-proline had the best catalytic properties for synthesis of 96. This result emphasizes the superior catalytic properties of proline reported after previous comparative studies by the Hajos group [100, 101]. 

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