The ionisation (Ar2CHCl + BC13 v=± Ar2CH+BCi;) and dissociation (Ar2CH+BCi;
^=*Ar2CH+ + BCl^) equilibria of diarylmethyl chlorides i n boron trichloride/
dichloromethane solution have been studied by conductimetry, photometry
and *H NMR spectroscopy. Small differences i n the UV-vis spectra of diarylcarbenium
tetrachloroborates, which have been observed i n solutions of low
and high tetrachloroborate concentration, can be attributed to the formation
of 1 :1 ion-pairs i n the more concentrated solutions. Low temperature calorimetry
was used to determine the heats of addition of diarylcarbenium tetrachloroborates
to 2~methyl-1 -pentene (Ar2CH+BCi; + H2C=CRRT ArjCH-CHj-CRR'Cl
+ BC13), and it is estimated that the standard free enthalpy of t h i s reaction
is greater than 0 for systems with pKR+ > -2.6. Kinetic studies have shown
that paired and unpaired diarylcarbenium tetrachloroborates exhibit identical
reactivity towards alkenes. A rationalisation for the different situation
in carbocationic and carbanionic polymerisation i s presented. The rate
constants for the initiation of isobutene, styrene and isoprene polymerisation
by diarylcarbenium ions have been determined, and it is shown, how propagation
rate constants can be estimated from linear free energy relationships