A redetermination of the ultraviolet photoelectron spectrum of (Z)-2-methyl-1,3-pentadiene; evidence that twisted conformers predominate in the gas phase

A redetermination of the ultraviolet photoelectron spectrum of (Z)-2-methyl-1,3-pentadiene (1a) has resulted in a correction of the spectrum published by Masclet and co-workers. MMX and AM1 calculations on 1a predict that twisted s-cis conformations should be populated preferentially in the gas phase; this is in keeping with the experimentally determined -π − , π + splitting of 1.55 ± 0.05 eV.