961.14(2)(nd)24.24. N-phenyl-N-(1-(2-phenylpropyl)piperidin-4-yl)propionamide (β-methyl fentanyl); 961.14(2)(nd)25.25. N-(2-fluorophenyl)-N-(1-phenethylpiperidin-4-yl)butyramide (ortho-fluorobutyryl fentanyl; 2-fluorobutyryl fentanyl); 961.14(2)(nd)26.26. N-(2-methylphenyl)-N-(1-phenethylpiperidin-4-yl)acetamide (ortho-methyl acetylfentanyl; 2-methyl acetylfentanyl); 961.14(2)(nd)27.27. 2-methoxy-N-(2-methylphenyl)-N-(1-phenethylpiperidin-4-yl)acetamide (ortho-methyl methoxyacetylfentanyl; 2-methyl methoxyacetyl fentanyl); 961.14(2)(nd)28.28. N-(4-methylphenyl)-N-(1-phenethylpiperidin-4-yl)propionamide (para-methylfentanyl; 4-methylfentanyl); 961.14(2)(nd)29.29. N-(1-phenethylpiperidin-4-yl)-N-phenylbenzamide (phenyl fentanyl; benzoyl fentanyl); 961.14(2)(nd)30.30. N-(1-phenethylpiperidin-4-yl)-N-phenylthiophene-2-carboxamide (thiofuranyl fentanyl; 2-thiofuranyl fentanyl; thiophene fentanyl). 961.14(2)(qz)(qz) 2-methyl AP-237 (1-(2-methyl-4-(3-phenylprop-2-en-1-yl)piperazin-1-yl)butan-1-one); 961.14(2)(rg)(rg) MPPP (1-methyl-4-phenyl-4-propionoxypiperidine); 961.14(2)(rk)(rk) MT-45 (1-cyclohexyl-4-(1,2-diphenylethyl)piperazine); 961.14(2)(vg)(vg) PEPAP (1-(2-phenylethyl)-4-phenyl-4-acetoxypiperidine);