Space other selection schemes

Scheme 5 accounts for the observation in Eq. (206). At first, the bulky aluminum reagent occupies a less-hindered space of the substrate so that an incoming nucleophile should approach the ketone from its superficially more-hindered side (i.e., by axial attack). The change in selectivity here has been considered to arise from a steric control, rather than transmetallation of the Grignard reagent to an aluminumate complex before the addition. Other selective reactions based on the same notion have also been developed [451-453]. 

To date, two specific phase-space optical-pumping schemes have been demonstrated. One uses a two-photon Raman transition and the other is based on the velocity-selective coherent population-trapping (VSCPT) effect. 

Most schemes that have been proposed to propel starships involve plasmas. Schemes differ both in the selection of matter for propulsion and the way it is energi2ed for ejection. Some proposals involve onboard storage of mass to be ejected, as in modem rockets, and others consider acquisition of matter from space or the picking up of pellets, and their momentum, which are accelerated from within the solar system (184,185). Energy acquisition from earth-based lasers also has been considered, but most interstellar propulsion ideas involve nuclear fusion energy both magnetic, ie, mirror and toroidal, and inertial, ie, laser and ion-beam, fusion schemes have been considered (186—190). 

The catalytic test reaction, the acylation of 2-methox)maphthalene (2MN), distinguishes between the inner and outer surfaces by means of product selectivity. Absorption experiments under the same reaction conditions show that the linear ketone product 2-acetyl-6-methoxynaphthalene (2AC) can pass through the 12-ring channels of beta whereas the other product l-acetyl-2-methoxynaphthalene (lAC) is too bulky to enter into any zeolite except Y. Once formed, lAC is unstable in the presence of acids and can deacylate to give the starting material (see reaction scheme 1). Since 1 AC can only form outside the micropore space of zeolite beta, the yield can be used as a measure of the catalytic activity on the external surface, although high yields can be expected because the 1-position is the most favoured for electrophilic attack. 

There are of course many other possible ways to select the Cl space. For example, it is possible to generalize the RAS scheme to allow for more flexible Cl spaces work along these lines is presented later. In contrast, it is also possible to make the Cl selection process essentially random. A recent paper by Greer discusses the unusual strategy of selecting CSFs using a Monte Carlo algorithm.103... 

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