Described are mono-oxomethyl substituted polyhydrodimethanonaphthalene derivatives having the generic structure: ##STR1## wherein the dashed line represents a carbon-carbon single bond or a carbon-carbon double bond; wherein R.sub.1, R.sub.1 ', R.sub.1 ", R.sub.1 '", R.sub.1 "", R.sub.3, R.sub.5, R.sub.5 ', R.sub.5 ", R.sub.5 '", R.sub.5 "" and R.sub.6 represent hydrogen or methyl with the provisos:(i) at least four of R.sub.1, R.sub.1 ', R.sub.1 ", R.sub.1 '" and R.sub.1 "" are hydrogen; and (ii) at least four of R.sub.5, R.sub.5 ', R.sub.5 ", R.sub.5 '" and R.sub.5 "" represent hydrogen;and wherein Z represents one of the moieties:(i) carboxaldehyde having the structure: ##STR2## (ii) alkylene dioxy or dialkoxy methyl having the structure: ##STR3## (iii) hydroxy methyl having the structure: ##STR4## (iv) acetoxymethyl having the structure: ##STR5## and wherein R.sub.7 and R.sub.8 taken separately represent C.sub.1 -C.sub.4 lower alkyl or R.sub.7 and R.sub.8 taken together represent C.sub.2 -C.sub.4 alkylene; wherein the line represented by:[++++]is either (i) a carbon-carbon single bond when R.sub.7 and R.sub.8 taken together are C.sub.2 -C.sub.4 alkylene or (ii) no bond at all when R.sub.7 and R.sub.8 taken separately represent C.sub.1 -C.sub.4 lower alkyl. Also described are processes for preparing such mono-oxomethyl substituted polyhydrodimethanonaphthalene derivatives, and processes for using the above defined mono-oxomethyl substituted polyhydrodimethanonaphthalene derivatives for their organoleptic properties and compositions containing said mono-oxomethyl substituted polyhydrodimethanonaphthalene derivatives including perfumes, perfumed articles (such as solid or liquid anionic, cationic, nonionic or zwitterionic detergents, perfumed polymers, fabric softeners and cosmetic powders), foodstuffs, chewing gums, toothpastes, medicinal products, chewing tobaccos, smoking tobaccos and smoking tobacco articles.