The following obligations cannot be specifically enforced:
(1) an obligation to render personal service or to employ another therein;
(2) an agreement to marry or live with another;
(3) an agreement to perform an act which the party has not power to perform lawfully 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; or
(5) an agreement the terms of which are not sufficiently certain to make the precise act which is to be done clearly ascertainable.