Very low-temperature processing

For very low temperature processing a caustic solution of two powerful developing agents, such as amidol and pyrocatechin, may be required, as used in Kodak SD-22. 

Examine the transition state for the hydride shift. Calculate the barrier from the more stable initial carbocation. Is the process more facile than typical thermal rearrangements of neutral molecules (.05 to. 08 au or approximately 30-50 kcal/mol) Is the barrier so small (<.02 au or approximately 12 kcal/mol) that it would be impossible to stop the rearrangement even at very low temperature Where is the positive charge in the transition state Examine atomic charges and the electrostatic potential map to tell. Is the name hydride shift appropriate If not, propose a more appropriate name. 

Under high applied electric fields, electrons can surmount a potential barrier even at very low temperatures. This process is based on field-induced tunneling of the charge carriers across potential barrier. The probability for the tunneling depends strongly on the height and the width of the potential barrier. 

Trimethylsilylepoxides can be prepared by an addition-cyclization process. Reaction of chloromethyltrimethylsilane with sec-butyllithium at very low temperature gives an a-chloro lithium reagent that leads to an epoxide on reaction with an aldehyde or ketone.291... 

Arylcopper intermediates can be generated from organolithium compounds, as in the preparation of cuprates.95 These compounds react with a second aryl halide to provide unsymmetrical biaryls in a reaction that is essentially a variant of the cuprate alkylation process discussed on p. 680. An alternative procedure involves generation of a mixed diarylcyanocuprate by sequential addition of two different aryllithium reagents to CuCN, which then undergo decomposition to biaryls on exposure to oxygen.96 The second addition must be carried out at very low temperature to prevent equilibration with the symmetrical diarylcyanocuprates. 

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