Eight ethers, nine esters and one ketone were submitted to a systematic structural variation by replacing a hydrogen atom in the vicinity of the oxo function by fluorine and Me. As long as steric factors dominate, a fluorine substituent alters the olfactory properties of the parent compd. much less than a Me substituent does. However, if it occupies a position adjacent to a carbonyl group, the halogen may more profoundly affect the odor perception, presumably as a consequence of conformational changes. [on SciFinder (R)]