1. The problem is to understand the classification and examples of aliphatic heterocyclic compounds based on their shapes and heteroatoms. 2. Heterocyclic compounds are cyclic organic compounds containing at least one heteroatom (N, O, S) in the ring. 3. Aliphatic heterocyclic compounds are saturated rings without double bonds, including cyclic amines, ethers, amides, and thioethers. 4. The shapes and examples given are: - Triangle with NH: Aziridine - Triangle with O: Ethylene oxide - Triangle with S: Thiirane - Square with O: Oxetane - Square with NH: Azetidine - Square with S: Thietane - Pentagon with O: Tetrahydrofuran (THF) - Hexagon with two adjacent O atoms: 1,2-dioxane - Hexagon with two opposite O atoms: 1,4-dioxane - Pentagon with NH: Pyrrolidine - Hexagon with NH: Piperidine 5. These shapes correspond to rings of 3 to 6 members with heteroatoms placed as indicated. 6. Understanding these structures helps in recognizing the chemical and physical properties of these compounds. Final answer: Aliphatic heterocyclic compounds are classified by ring size and heteroatom type, with examples as listed above.