Trans-3, 4-Dirnethvlcyclobutene can open by two conrotatory paths to give either (2E, 4E)-2, 4-hexadicne or (2Z, 4Z)-2,

Question:

Trans-3, 4-Dirnethvlcyclobutene can open by two conrotatory paths to give either (2E, 4E)-2, 4-hexadicne or (2Z, 4Z)-2, 4-hexadiene. Explain why both products are symmetry-allowed, and then account for the fact that only the 2E, 4E isomer is obtained in practice.