We report NMR spectra of niaobenzene-d(5) recorded in the presence of strong ac electric fields using a home-built probe and electric field amplifier. Pulsed ac electric fields up to 70 kV/cm rms were used, rather than de fields, to reduce electrode corrosion, electrode polarization, electrical convection, sensitivity to impurities, electrolysis, and heating. A two-dimensional detection method was used in which fields are applied only during the variable delay associated with the indirect dimension. Tensorial interactions are partially recovered due to partial alignment of the polar molecules in the applied electric field. Molecular order parameters of order 10(-4) were observed in these experiments, in agreement with previous work, and followed the expression S-mol proportional to E-2, as expected, where the constant of proportionality describes the effects of the dielectric response of the medium. Deuterium splittings for the ortho- and paradeuterons were in the ratios expected for a 61 degrees relative angle in bond vectors. We observed a strong dependence of the order parameter on concentration: neat nitrobenzene ordered significantly more than did nitrobenzene diluted in a nonpolar solvent. Under the assumption that neat nitrobenzene forms weakly bound clusters with large effective dipole moments, we attempted to rationalize the degree of order for dilute nitrobenzene only in terms of simple electrostatic theories. Onsager's model involving spherical molecules overestimates the alignment while Scholte's adaptation of Onsager' s model for elliptical molecules achieves reasonable agreement with our data for dilute nitrobenzene.