Treatment of an unknown alkene with Hg(OAc)2 in H2O/THF, followed by a NaBH4 workup, produces an alcohol isomeric to one obtained by hydroboration-oxidation of the same alkene. Reduction of the alkene affords the compound C5H12, while ozonolysis yields an aldehyde, CH3CHO, as one of the products. Deduce the structure of the alkene.