Ab initio molecular orbital calculations have been employed to study four simple oxoboron molecules, XBO (X = H, F, Cl and CH3) and their isomers XOB. Several properties of oxoborons including the geometries, rotational constants, vibrational wavenumbers, thermochemical parameters and nuclear quadrupole coupling constants have been calculated and thereby predicted using appropriate correction schemes based on available experimental data. Energy barriers for the 1,2-shifts obtained at the MP4/DZP level using MP2/DZP-geometries suggest that, while HOB and CH3OB are relatively stable with respect to unimolecular rearrangement (energy barrier of about 25 kcal mol-1), FOB and ClOB are unstable in this regard. The former have bent equilibrium structures and their energy is quite high relative to their oxoboron isomers (greater-than-or-equal-to 50 kcal mol-1). An analysis based on the Boys' localized orbitals and molecular electrostatic potentials discloses that during the 1,2-shifts, the migrating group (H or CH3) behaves essentially as a cationic species moving between two electron pairs.