Pseudohalides. Part III. Infrared, ultraviolet, and proton magnetic resonance spectra of boron isocyanates and isothiocyanates
- 1 January 1967
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc. A
- p. 854-860
- https://doi.org/10.1039/j19670000854
Abstract
The infrared spectra of thirty-seven iso- and isothio-cyanatoboranes, having one, two, or three isocyanate or iso-thiocyanate groups attached directly to the boron atom, have been recorded in the region 5000–400 cm.–1. From the frequency, intensity, and shape of the absorption band associated with the asymmetric stretching motion of the –NCX (X = O or S) functions, the iso-structure (B–NCX) is proposed for all the compounds. The -NCO and –NCS asymmetric stretching vibrations fall at 2273 ± 30 and 2089 ± 31 cm.–1, respectively, for the two classes of compound. From the frequencies of other vibrational modes [v(N–H), v(B–N), v(B–O), and v(C–N)], conclusions are drawn as to the relative electron-attraction (-l effect) and effectiveness in π-bond formation (+M effect) to boron of halogens and pseudohalogens (–NCO and –NCS). Full assignments are proposed for (OCNBNH)3, (SCNBNH)3, (OCNBNMe)3, (SCNBNMe)3, (MeO)2BNCO, and (MeO)2BNCS. Ultraviolet spectra of isothiocyanatoboranes show absorption maxima 250 ± 5 mµ(log ε= 2·7 ± 0·5), whilst the isocyanatoborane chromophore does not absorb in the range 220–350 mµ. Proton magnetic resonance spectra on the series (XBNEt)3 and PhB(X)NMe2 show that the relative ease of BX π-bonding is F > NCO > NCS > Cl > Br.Keywords
This publication has 0 references indexed in Scilit: