How can neck pain be avoided when doing floor ab exercises?

Hi everyone! I have a specific question for whoever can give me some tips, and I apologize if this isn’t the correct place to place it.

For the longest time, I have never been able to get an actual workout for my abs, because when I do certain ones, I have so much strain in my neck. Example exercises (performed by laying on floor on the back):

Single leg jacknife

Toe touch reaches (this and the jackknife are found in the ab portion of the 1000 calorie workout for 2 million subscribers at time 38:00 https://www.youtube.com/watch?v=PBHBhvv-Lhg)

Those are just two examples, but I can’t get anything out of them like I should because of neck pain. I’m getting a cramp just thinking about it.

Now, I’m not sure if it’s a lack of strength, or bad form while performing the exercises or what. I’m hoping to get some advise from anyone whose experienced this sort of thing as well.