Ab initio SCF-MO calculations at the 3–21G F* level with full geometry optimization were performed for cis-1-, trans-1- and 2-fluoro-1, 3-butadiene.The critical points for the rotation around the central CC bond are located and discussed. Trans-1-fluoro-butadiene has a stable gauche from (θ=40.0°), lying 9.1 kJ mol−1 above the s-trans minimum, close to the values found for butadiene itself (θ=38.1°, ΔE=10.2 kJ mol¯¹). The second stable conformer of cis-1-fluorobutadiene is a planar s-cis structure, favoured by an attractive H…F interaction. 2-fluorobutadiene displays a shallow potential curve in the s-cis configuration, with a difference of only 0.2 kJ mol¯¹ between the minimum (θ=19.2°) and the planar form.