Secondary partial yield

The partial yield of electrons in an energy window AE at a fixed final state energy E, as a function of photon energy, where E is fixed at < 5eV so that only secondary electrons are measured, is referred to as partial yield spectroscopy. When E > 5eV, although the technique is experimentally identical, it is used to study initial state and excitonic effects and is known as constant final state spectroscopy. 

Fig. IZ The appearance potential spectra in the vicinity of the Co 2p core levels for samples as indicated (Horn et al. 1988). Plotted is the derivative of the total secondary-electron yield as a function of incident electron energy, (i) The non-superconducting YBajCujO, does not give any signature of Cu (3d ) configuration in Cu 2p region, (ii) The spectrum of PrBajCUjOT is partially obscured by Pr 3d peaks, but it is evident that if Cu 2p features were as large as in superconducting YBajCujO, they would be visible, (iii) The YBa2Cu30, exhibits characteristic 2p APS peaks of Cu (3d ) configuration.

In some cases products of rearrangement are obtained either partially or exclusively on treatment of Grignard reagents with epoxides. Thus, reaction of the 2/ ,3/ -epoxide (14) with methyl Grignard reagent affords a mixture of two epimeric secondary A-nor alcohols (15) in 80% yield and the tertiary hydroxy compound, 2a-methyl-5a-cholestan-2/f-ol (16) in 15 % yield. ... 

According to Quinkert, photoexcited cyclic ketones may be transformed to open-chain unsaturated carboxylic acids in the presence of molecular oxygen. This reaction may compete efficiently with a-cleavage and secondary transformations thereof. Thus, both stereo iso meric 17-ketones (109) and (110) yield as much as 20% of the unsaturated acid (111) when irradiated in benzene under a stream of oxygen. This photolytic autoxidation has been used notably for partial syntheses of naturally occurring unsaturated 3,4-seco-acids from 3-oxo triterpenes (for references, see ref. 72). 

It will be observed that most syntheses yield pyrylium salts in which positions 2,4, and 6 are substituted. Since according to formulas Ib-lc these positions have a partial positive charge, it can readily be understood why electron-donating substituents (hydroxy, alkoxy, alkyl, or aryl) in these positions stabilize the pyrylium salts. Only three pyrylium salts which do not have substituents in either a-position have been reported and few unsubstituted in y or in one a-position they are less stable toward hydrolysis, and in the case of perchlorates they explode more easily, than 2,4,6-trisubstituted compounds. In fact, the former are secondary, the latter tertiary carbonium ions. This fact also explains why the parent compound (1) was prepared only in 1953. 

Among the tasks remaining is the replacement of the C-16 hydroxyl group in 16 with a saturated butyl side chain. A partial hydrogenation of the alkyne in 16 with 5% Pd-BaS04 in the presence of quinoline, in methanol, followed sequentially by selective tosylation of the primary hydroxyl group and protection of the secondary hydroxyl group as an ethoxyethyl ether, affords intermediate 17 in 79% overall yield from 16. Key intermediate 6 is formed in 67 % yield upon treatment of 17 with lithium di-n-butylcuprate. 

Enantiomerically pure alkylboranes arc known to be excellent reagents for asymmetric reduction but they can also be used to generate enantiomerically pure /V-borylimines by partial reduction of nitriles. Addition of organolithium and Grignard reagents to these compounds affords secondary carbinamines in moderate to good yield but low enantioselectivity13,14. The best results reported so far are shown below. 

Then, following the appropriate steps (i.e., partial differentiation of the Lagrange function) and solving the resulting set of six simultaneous equations, values are obtained for the appropriate levels of X and X2, to yield an optimum in vitro time of 17.9 mm (Lo%). The solution to a constrained optimization program may depend heavily on the constraints applied to the secondary objectives. 

---