In the reaction of styrene with chlorine, the added bromide ions were mostly incorporated into the adduct, giving a bromo chloro compound. Tetrabutylammonium dichlorobromate(1–) was found to be an efficient bromochlorinating agent. The reactions of 2-butenes and stilbenes were completely anti stereospecific.

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The bromochlorination of phenyl- and alkyl-substituted acetylenes with tetrabutylammonium dichlorobromate(1−) (1) in dichloromethane was found to be anti-stereospecific and nonregiospecific (regiospecific in the case of phenylacetylene). Whereas the addition of molecular bromine chloride (2) to phenyl-substituted acetylenes was found to give nonstereospecific and regiospecific adducts, the reaction of alkyl-substituted acetylenes gave anti-stereospecific and nonregiospecific adducts. These results suggest that the addition of 1 involves an attack of chloride ion to a three-centered π-complex in the product-forming stage, and that the addition of 2 to phenyl-substituted acetylenes involves a vinyl cation intermediate (but a bridged bromonium ion intermediate in the case of alkyl-substituted acetylenes).

The PIES and UPS spectra of xanthone (1a), thioxanthone (1b), and selenoxanthone (1c) were measured, together with those of the corresponding xanthene (2a), thioxanthene (2b), and selenoxanthene (2c). Ab initio MO calculations were performed with the 6-311+G(d,p) basis sets at the DFT (B3LYP) level on 1a − c and 2a − c. The results of the measurements and of the MO calculations explained well the striking difference in the reactivity of the compounds, especially for 1c versus 2c. The ionization potentials (IP) of π6(n) (HOMO), n(p z ) (π2(n) for 1a and 2a), and n(p y ) were in the order IP(1a) > IP(1b) > IP(1c) and IP(2a) > IP(2b) > IP(2c). The IP of the xanthones were larger than those of the corresponding xanthenes. The IP of n(p z ) of 1c was demonstrated to be larger than those of 2b and PhSPh (3b), which showed that 1c was less reactive than 2b and 3b toward electrophiles. These results accounted for the reactivity of 1c to give a molecular complex (MC) with bromine similar to the case of the MC structure of the sulfide dibromides. The relative intensity of PIES of HOMO in 1c was smaller than that in 2c. The electron density outside the molecular surface of the orbital of 1c must be smaller than that of 2c, due to the strong electron-withdrawing carbonyl group in 1c, which was supported by the calculated natural populations at the chalcogen atoms of the compounds.

The regioselectivity of the addition of molecular bromine chloride to alkenes is dependent on both the steric and electronic effects of the alkyl substituent. In contrast, the regioselectivity of the addition of dichlorobromate (1−) ion to alkenes is controlled mainly by the steric effect of the substituent.