Final answer:
The major product of the reaction under Birch reduction conditions is an achiral trans alkene, due to the anti-addition mechanism favored in such reactions.
Step-by-step explanation:
The reaction described suggests the use of sodium (Na) in liquid ammonia (NH3), which is a classic Birch reduction condition. This reaction typically yields trans alkenes due to the anti-addition mechanism, where the two hydrogen atoms are added to opposite sides of the double bond.
Moreover, this reaction is stereoselective rather than stereospecific, meaning it will favor one stereoisomer over the other. Alkenes with a trans configuration are often preferred due to sterics in the transition state. Because the starting materials and the reaction conditions do not involve chiral substrates or catalysts, the product will not be chiral. Hence, the major product of this reaction will be an achiral trans alkene.