Stright- or branched-chain 4-18C alkanes substd. in the omega-position by a heterocyclic residue of formula (Ia) or (Ib) are new cmpds. (where X is CH or N and Y is O or S). The new compounds have the property of accelerating dark-adaptation. This is demonstrated by results of electroretinographic studies of mice given in the specification. EXAMPLE 1-Bromohexane (17g) and 2-pyridone potassium salt (13g) are stirred 2 hrs. in refluxing EtOH, then KBr is filtered off and the filtrate concentrated in vacuo. The residue is fractionated under water-aspirator vacuum to give 1-n-hexyl-2-pyridone distilling at ca. 160 degrees C.