Electron transfer measurements between solution redox probes and a Au electrode coated with self-assembled monolayers of symmetric and asymmetric omega-hydroxyalkane disulfides are used to probe the quantum interference between hydrocarbon chains of different lengths, While nb initio theory predicts a measurable destructive interference effect between hydrocarbon chains differing in length by a single methylene unit, electron transfer rates for the ferricyanide and horse heart cytochrome c are more consistent with rates estimated in the absence of the interference effect. The discrepancy between theory and experiment is discussed in light of possible interchain electronic coupling and phase segregation within the monolayers and limitations of the theoretical models.