Fragmentation of 2,2,2-triphenylethoxychlorocarbene: evidence for ultrafast fragmentation-rearrangement in excited diazirines.
[reaction: see text] Photolysis of 3-(2,2,2-triphenylethoxy)-3-chlorodiazirine gives 2,2,2-triphenylethoxychlorocarbene which fragments with 1,2-phenyl migration and loss of CO and Cl(-) to yield the 1,1,2-triphenylethyl cation and thence 1,1,2-triphenylethene by proton loss. However, ps and fs laser flash photolysis provides evidence that up to 25% of the alkene product stems from carbocation that arises directly from excited diazirine rather than from the carbene.
Substituted diphenylmethyl cations. Part I. Acid–base equilibria
The ionisation of several alkyldiphenylmethanols in sulphuric acid is examined. Evidence is presented which confirms the conjecture that where possible equilibrium in these systems exists between carbonium ion and olefin. α-Substitution in the alkyl group is shown to strongly destabilise the carbonium ion through steric effects on solvation and on the planarity necessary for resonance. It is also shown that internal ‘solvation’ by a hydroxysubstituent in the alkyl group causes an unusually high slope for a plot of log (ionisation ratio)versus–HR.
STUDIES IN ISO-UREAS AND ISO-UREIDES: I. SOME NEW ISO-UREAS; SALTS AND ACYL DERIVATIVES
In this investigation a series of new iso-urea ethers has been prepared by the general reaction of addition of alcohols to cyanamide in the presence of dry hydrogen chloride. Where the hydrochlorides of the iso-ureas were difficult to isolate and purify, conversion to the salicylates gave excellent results. The new iso-ureas were further characterized by condensing them with methyl malonate to form iso-urea salts of 2-alkoxy-barbituric acids, from which the acids themselves could be easily liberated by the addition of dilute mineral acid. A few open-chain acyl derivatives were also prepared.