Lowestπ orbital of 1.3- butadiene denoted 88 π orbital of π* orbital of cyclobutene cyclobutene g orbital of cyclobutene cyclobutene igure 5.5 The active valence orbitals of 1, 3-butadiene and of cyclobutene13 Lowest p orbital of 1,3- butadiene denoted p1 p2 p3 p4 p orbital of cyclobutene p* orbital of cyclobutene s orbital of cyclobutene s* orbital of cyclobutene Figure 5.5 The active valence orbitals of 1, 3- butadiene and of cyclobutene