When an alkyne is then added to the solution, an electron adds to the triple bond to yield an intermediate anion radical--a species that is both an anion (has an odd number of electrons). This anion radical is a strong base, which removes H from ammonia to give a vinylic radical. Addition of a second electron to the vinylic radical gives a vinylic anion, which abstracts a second H from ammonia to give trans alkene product