A novel theory, based on density operator calculations, is provided for assessing the nuclear quadrupole resonance behaviour of a spin 1 (14N) subjected to a single radio-frequency pulse. It is for a powder sample in zero magnetic field for an electric field gradient tensor without symmetry. A complete set of equations is obtained for the quantities of interest. It is derived from the general Liouville–von Neumann equation and from a proper basis on which the density operator is expanded. Theoretical results, in terms of signal evolution as a function of the pulse length (nutation experiments), show that the same nutation curve is expected for the three different transitions which exist when the electric field gradient tensor is without symmetry. This latter nutation curve is, however, different from that which prevails in the case of an axially symmetric tensor, this apparent discrepancy being easily resolved on theoretical grounds. Experimental data (for NaNO2, electric field gradient tensor without symmetry) are checked against values of the radio-frequency field amplitude provided by NMR measurements performed with the same equipment. Good agreement between theory and experiment is obtained.