The following obligations cannot be enforced specifically:
1. An obligation to render personal service.
2. An obligation to employ another in personal service.
3. An agreement to perform an act that the party has no power lawfully to perform when required to do so.
4. An agreement to procure the act or consent of the spouse of the contracting party or of any other third person.
5. An agreement, the terms of which are not sufficiently certain to make the precise act that is to be done clearly ascertainable.