Yield sections

Many [2 + 2] photocycloadditions have not been assigned a definitive mechanism, but they serve well as synthetic methods. Thiones add vinyl ethers to give thietanes in very good yields (Section 5.14.4.1.2), and interesting wavelength-stereochemistry relations were found in the photoaddition of 2-adamantanone to dicyanoethylene (Section 5.14.4.1.2). Diheterocyclobutanes can also be prepared by [2 + 2] photocycloadditions (Section 5.13.3.3). 

The major product obtained from the reaction of TeCU with (McsSijsN is determined by the stoichiometry. When approximately equimolar amounts of the two reagents in THF are used the dimeric cluster TceNs (stabilized by coordination to four TeCU molecules) is obtained in high yields (Section 5.2.8). When the same reaction is carried out in acetonitrile with a molar ratio of 2 1, followed by treatment of the product with AsFs in SO2, [Tc4N2Cl8][AsF6]2 is obtained Section The dication [Tc4N2Cl8] in this salt is the dimer of the hypothetical tellurium(IV) imide [Cl3Te-N=TeCl]. ... 

In all of the above preparations the lithium exchange step was conducted in ether. The use of a mixed ether-THF solvent system would probably improve the yields (Section VI,H, 1). 

The Mannich reaction has been used to synthesize numerous heterocyclic nitramine explosives. Adolph and Cichra prepared a number of A-heterocycles containing ferf-butyl A-blocking groups. The nitrolysis of these f-butyl groups provides the corresponding A-nitro derivatives in excellent yields (Section 5.6.2.2). Some of the nitramine products from these reactions are powerful, energetic explosives with attractive properties. 

The 2,4- and 2,5-dinitrothiophenes are prepared by direct nitration of mononitrothio-phenes. Nitration of 2-nitrothiophene with nitric acid and sulfuric acid at 10 °C gives 2,5-dinitrothiophene, with only traces of 2,4-dinitrothiophene. Similar treatment of 3-nitrothiophene gives the 2,4-dinitrothiophene in good yield (Section 3.14.2.4). 

Reaction of Mes -arsaalkyne 92 with [W(CO)sTHF] yields the antiaromatic free lA3,3A3-diarsete ditungsten complex 93 in low yield (Section 2.20.9.3) <1996CC631>. 

Ditungsten complexes If of l,2-dihydro-lA3,2A3-diphosphetes are accessible in 25-27% yield by direct [2+2] cycloaddition reactions of diphosphene ditungsten compound 82 and several alkynes at elevated temperatures <1997OM2506>. Alternatively If and related species 117 are obtained from W(CO)s-stabilized phosphirenes 119a and 119b by insertion of transient phosphinidene complex PhPW(CO)s 118a in 47% yield (Section 2.20.10) <1997OM4501>. 

The concept of efficiency could also be used for the absorption step however, because an absorption step is also a process, it is more convenient to use quantum yield (Section III.B.4). 

It has been reported by Denmaric et al. that aldehyde hydrazones react smoothly with oi]ganocerium reagents to give addition products in good to high yields (Section 1.8.2.6). ... 

NaOH. Since the organic layer and the water layer are immiscible, the base in the aqueous phase does not come into contact with chloroform in the or c phase, and there is no reaction. If, however, a small amount of ben h ethylammonium chloride is added, an immediate reaction occurs. The ( roform reacts with NaOH to generate dichlorocarbene, which adds to thee hexene double bond to give a dichlorocyclopropane in 11% yield (Section 74... 

Determine the percentage yield of a reaction from its calculated theoretical yield and its measured actual yield (Section 2.6, Problems 49 and 50). 

The third protocol for exhaustive methylation includes exploitation of the Me2S04-Na2C03-H20 system and is especially suitable for polyamines with low NH-acidity. Obviously, alkylation in this case proceeds by means of a quatemization-deprotonation sequence. The reaction occurs in a two-phase mode at room temperature and provides remarkably high yields (Section n.B.l). 

It has been shown that the fetal adrenal can convert progesterone and pregnenolone into cortisol in substantial yield (Sections 4.2.1 and 4.2.2), and, notably, Solomon (S25), after perfusion of fetuses with proges-terone-4- C, has isolated radioactive corticosterone and cortisol from the... 

The fracture behaviour of some tough plastics can be inconsistent. For example, polycarbonate sometimes fails by yielding, but, on other occasions, a crack initiates and brittle fracture follows (Fig. 9.5). The explanation lies in the analysis of localised yielding. Section 8.2.4 showed that the indentation pressure could be three times the uniaxial compression yield stress. The yield stress can change by a similar factor during localised tensile deformation. 

Hydrogen peroxide is a more selective reagent and can convert pyrrole itself into a tautomeric mixture of pyrrolin-2-ones in good yield (section 13.17.1). 

Ketones are much more resistant to oxidation than are aldehydes. For example, ketones are not normally oxidized by chromic acid or potassium permanganate. In fact, these reagents are used routinely to oxidize secondary alcohols to ketones in good yield (Section 8.2F). 

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