Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The oxygen relative basicity of di-n-butylboronous anhydride ((n-C₄H₉)₂B)₂O, ethyl di-n-butylboronite (n-C₄H₉)₂BOC₂H₅ and some orthoborates (RO)₃B having electrondonating and electronwithdrawing groups R was measured from the IR spectra of hydrogen bonds of phenol interacting with these compounds in CCl₄ and analysed by means of the Taft equation. The substituent electronic effect of (n-C₄H₉)₂B- and (RO)₂B-groups attached to the oxygen of the-OR and -OB= moieties has been estimated asa more electronwithdrawing than that of structurally alike R₂Z- and (RO)₂Z-groups having Z = CH and SiCH₃ and is discussed in terms of the vacant 2p orbital of the boron and a weak, if any, mutual polarizability effect of the alkoxy groups in orthoborates. The trimethylsiloxy group in trimethylsilyl borate possesses reduced electronwithdrawing ability compared to that in ((CH₃)₃SiO)₃SiCH₃ as a consequence of its great polarizability.