2,2,6,6-tetraalkyl-4-piperidyl ketones and ketals are provided, useful as stabilizers for organic polymeric materials, and having the general formula: ##STR1## wherein n are each 0 or 1 and are each the same;R is selected from the group consisting of hydrogen, alkyl having from one to about eighteen carbon atoms, and acryl ##STR2## R' being alkyl having from one to about eighteen carbon atoms; R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are selected from the group consisting of hydrogen and alkyl having from one to about eighteen carbon atoms;R.sub.6 is selected from the group consisting of hydrogen and O.sup.. ;Y is selected from the group consisting of a carbon-to-carbon bond--, oxy --O--; alkylene having from one to about three carbon atoms, and alkyl-substituted alkylene, the alkylene having from one to about three carbon atoms, the alkyl having from one to about six carbon atoms; andZ is selected from the group consisting of: ##STR3##