While θ = 180 • and θ = 0 • , are clearly distinct limits for butane, it is also interesting to examine the behavior at θ = 49 • and θ = 50 • . As seen in Figure , at these dihedral angles a very small angular change results in qualitatively different transmission, with the two sharp dips present at θ = 49 • disappearing at θ = 50 • with only a single 'V' shaped dip remaining. We note here that in terms of experimental observables (eg. current and conductance) this change is not significant as the transmission is extremely low in both cases. The significance in this qualitative change in the transmission is in how sure one can be in labelling the low transmission as coming from destructive interference if we consider transmission alone, as these sharp dips are a definitive feature. We also note here that there other situations where we are confident that low transmission results from destructive interference, despite the absence of a sharp dip, for example if transport through the σ system masks destructive interference in the π transport or if we see ring current reversal in a local current picture .