The Molecular Structure of 4‐tert‐Butyl‐5,5‐dimethyl‐1,3‐hexadiene (1,1‐Di‐tert‐butyl‐1,3‐butadiene)

The highly strained hydrocarbon 4-tert-butyl-5,5-dimethyl-1,3-hexadiene (3) has been prepared and its molecular structure and conformation have been studied experimentally by the gas-electron diffraction method and by theoretical ab initio (HF-6-31G*) calculations. The 1,3-diene skeleton assumes an anti conformation, and the sterical strain primarily manifests itself in the following structural details: The butadiene C=C−C angle on the substituted side is larger than normal (GED: 128.2°; HF-6-31G*: 132.7°); the Z-oriented tert-butyl group is rotated to a nearly staggered position relative to the C1=C2 double bond, forming a cogwheel system together with the other tert-butyl group, which has the normal eclipsed conformation relative to C1=C2; the C1−CtBu and C−CH3 bonds are both elongated compared to those in unstrained compounds, and the formally C(sp2)−C(sp3) C1−CtBu bonds are longer than the formally C(sp3)−C(sp3) ones in the methyl groups.