The isomers of 3-methyl pentene-2; configurational assignment and molecular structure by electron diffraction

The two isomers of 3-methyl pentene-2 have been investigated in the vapour phase by electron diffraction. The higher boiling isomer (70.4 °C) has the E-configuration and the isomer boiling at 67.7 °C has the Z-configuration. Bond distances in the E-isomer are: r(CC) = 1.349, r(Csp²-Csp³) = 1.511, r(C-C) = 1.551, r(C-H) = 1.116 Å; in the Z-isomer: r(CC) = 1.344, r(Csp²-Csp³) = 1.508, r(C-C) = 1.553, r(C-H) = 1.114 Å. In both compounds the Csp³-Csp³ bond is at approximately right angles to the plane containing the double bond. The possibility of non-planar arrangements around the double bond is discussed.