Single engine airplanes do not have a "Vmc." When you get cross controlled and stall/spin in a single, you just happened to reach Vs or Vso and when yaw is introduced, one wing is more stalled than the other inducing a spin.

Vmc is defined as minimum directional control speed with the critical engine inoperative. The critical engine being the one, where if it fails, causes the most heartache..I mean, biggest change in performance, handing, directional control. It only applies to Multi-Engine planes