アミンボラン化合物の立体相互作用について

Chemical shifts of methyl group in amine boranes, <(CH_3)>_<3-n>H_nN･BF_3 and (CH_3)_3N･BX_3 (X = H, F, Cl, Br...) were larger than those of o-halotoluenes, o-XC_6 H_4 CH_3. It is explained by differences in steric effects between <sp>^3 bybrid in amine boranes and <sp>^2 bybrid in o-halotoluenes and by a number of methyl groups and halogen atoms. The facts that larger Van der Waals radius of halogen atoms make the B-N bond length shorter in the haloborazines B_3N_3H_3X_3 and amine boranes are explained by the steric effect based on sp^3 hybrid.