Well with window light, you often need a reflector to get some fill light and to even out the lighting ratio. One key for exposure is the eyes. You usually want the eyes to have visble pupils rather than just being one big black ball as you have in the examples. Evening out the light would help, but the other thing is to meter the shot with careful attention to the tonal range. You can try a gray card and the camera's histogram (if shooting digital). For a person with medium skin tones, if a test shot of the gray card (fill the frame with the card), has one spike in the center, then you're pretty close to exact exposure. I often use a black/gray/white target which gives three spikes and then you can see for sure if you are clipping either the shadows or highlights.
It may also be that your conversion to B/W may have caused part of the problem, so you might post the color versions for comparison.
This photo of Brigette illustrates eyes with good pupil defintion from the rest of the eye. Of course, since this was shot with a ring light, you also have the catchlights as a rign around the pupil.