Inverted configuration

To collect the holes from the front subcell, the p-type material is deposited on the active layer. This is not a trivial step because the polymer active layer surface is hydrophobic and a p-type material spincoated from an aqueous solution or dispersion such as PEDOTrPSS will not form a uniform layer because of de-wetting. Different strategies have been developed to solve this challenge. Kouijzer et al used a mild nitrogen plasma treatment on the P3HT ICBA active layer and PEDOTrPSS (PHIOOO) diluted with an alcohol to improve the wetting. A similar approach has been adopted 

The n-type layer in the inverted configuration had mostly been ZnO, until Kippelen et al. introduced ethoxylated polyethylenimine (PEIE), which is deposited from water and 2-methoxyethanol on a thermally annealed PEDOTrPSS to give a coating of only a few nanometers. This layer induces a modification of the work function of the PEDOTrPSS at the top surface from 4.9 to 3.6 eV, enabling selective electron collection. The effect is thought to originate from a molecular dipole and interface dipole.  

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Partial but not complete loss of optical activity m S l reactions probably results from the carbocation not being completely free when it is attacked by the nucleophile Ionization of the alkyl halide gives a carbocation-hahde ion pair as depicted m Figure 8 8 The halide ion shields one side of the carbocation and the nucleophile captures the carbocation faster from the opposite side More product of inverted configuration is formed than product of retained configuration In spite of the observation that the products of S l reactions are only partially racemic the fact that these reactions are not stereospecific is more consistent with a carbocation intermediate than a concerted bimolecular mechanism... 

Evidently, since there is no appreciable rate acceleration, this participatimi is not very strong at the transition state. Nevertheless, the participation is strong enough to control stereochemistry. When mote nucleophilic solvents are used (e.g., acetic acid), participation is not observed, and the product is 100% of inverted configuration. 

The final step is the nucleophilic displacement of the oxyphosphonium group by the carboxylate anion via a SN2-mechanism, yielding ester 3 with inverted configuration at the stereogenic center, and triphenylphosphine oxide. A hydrolysis of the ester 3 will leave the new configuration unchanged, and yield the inverted alcohol 4 ... 

The kinetics and stereochemical data definitely point to a transient aziridinone of inverted configuration 2 among the further potential intermediates (Fig. 5). Reactions of aziridinone 2 with a nucleophile would allow the crucial bond of the product Ifl to form through a second inversion (overall retention). This pathway... 

Evidence for this mechanism is as follows The addition of pyridine to the mixture of alcohol and thionyl chloride results in the formation of alkyl halide with inverted configuration. Inversion results because the pyridine reacts with ROSOCl to give ROSONC5H5 before anything further can take place. The Cl freed in this process now attacks from the rear. The reaction between alcohols and thionyl chloride is second order, which is predicted by this mechanism, but the decomposition by simple heating of ROSOCl is first order. ... 

The reaction results in inverted configuration at C-2. Of course, the product can also revert to the starting material by the same pathway, so a mixture of epoxy alcohols is generally obtained. 

Scheme 19 Inverted configuration indicated by the dihedral angle (99.5°) together with selected bond length and bond angle...

The disila- 52 [48, 49] and digermabridged 53 [50] were synthesized and their X-ray analyses were performed. The inversion angle of 38.8° for 52 and extremely long M-M (M=Si, Ge) bond lengths were observed (Scheme 21). The inverted configuration was consistent with both the NMR data and the simulation. 

Bertrand and Santelli (89) have investigated the hydrolysis, under apparently heterogeneous conditions, of 4,5-hexadien-2-yl tosylate, 114, and 4-methyl4,5-hexadien-2-yl tosylate, 115. After 90 min at 80°, 114 upon steam distillation yields a mixture consisting of 3% hydrocarbon 67% of cis- and rrans-2-methylcyclopropyl methyl ketone, 116 and 30% of 4,5-hexadien-2-ol, 117. When optically active 114 was treated under similar conditions, the resulting rrans-2-methylcyclopropyl methyl ketone had an inverted configuration at the reaction center, whereas the dienol 117 was found to be racemic (90). This... 

By modification of the elegant method of preparation of optically active sulfinates previously reported by Mikolajczyk and coworkers , an efficient stereospecific method for the conversion of readily available optically active sulfinamides to optically active sulfinates of inverted configuration at the sulfinyl function, has been recently reported by Hiroi and coworkers . The same authors subsequently reported the thermal rearrangement of several optically active cis- and trans-y-substituted allylic p-toluenesulfinates to optically active chiral sulfones with high stereoselectivity. For example, trans and cis (S)-( — )-crotyl p-toluenesulfinates rearranged to optically active (S)-(-l-)- and (R)-( — )-a-methylallyl p-tolyl sulfone, respectively (equation 19). 

In the inverted configuration the feed is charged to the reflux drum and then continuously added to the top of the column. The inverted column seems to be better suited for cases in which the products are to be recovered at high purity from a feed low in light components, whereas the regular column appears to be best for cases in which the products are to be recovered at high purity from a feed rich in light components. 

Sulfonate esters also can be prepared under Mitsunobu conditions. Use of zinc tosylate in place of the carboxylic acid gives a tosylate of inverted configuration. 

Rg. 5 (a) Potential function rad energy levels as functions of die normal coordinate Q(Ai) (b) Structure of the ammonia molecule in its two equivalent inverted configurations. 

The inverted configuration of Fig. 1.31 (b) reduces the contribution of the photoelectron current, extending the range to about 10-10 torr. 

Reactions of the corresponding tosylates with Me3SnLi proceeded in low yield, but products of inverted configuration were produced. The cis and trans chlorides led to extensive loss of configuration at carbon with a slight preference for inversion. 

Inversion of configuration.1 The configuration of a secondary alcohol (2) can be inverted by reaction with dicyclohexylcarbodiimide (1) to form an isourea ether (3), which is allowed to react, without isolation, with formic acid with formation of the ester 4 with inverted configuration. 

Thus D-(+)-2 chlorobutane is converted to 2. butanol by aqueous base and the product has inverted configuration ... 

It is also known (Mikolajczyk et al., 1976) that treatment of an optically active sulfinamide with an alcohol in the presence of two moles of strong acid as catalyst results in the formation of optically active sulfinate esters of inverted configuration (152), although the degree of stereoselectivity depends on the... 

In case of optically active alkyl halides, the product formed as a result of Sn2 mechanism has the inverted configuration as compared to the reactant. This is because the nucleophile attaches itself on the side opposite to the one where the halogen atom is present. When (-)-2-bromooctane is allowed to react with sodium hydroxide. (+)-octan-2-ol is formed with the -OH group occupying the position opposite to what bromide had occupied. 

Reaction of the appropriate alkene with 1 equiv of tellurium tetrachloride in chloroform or acetonitrile gives a 2-chloroalkyltellurium trichloride adduct in a high yield (see Section 3.5.1.2). Reduction of this adduct with aqueous sodium sulphide results in the instantaneous separation of elemental tellurium and formation of the starting alkenes which, in most cases, exhibit an inverted configuration (with relevant variations depending on the solvent and olefin used). The proposed mechanism involves an intermediate epitelluride. 

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