smiles:C1=CC=NC(=C1)NC(=O)C/C(=N/O)/N

The one double bond here could take either configuration. (E) and (Z) differ in which side of the double bond the substituents sit on, and the bond cannot rotate to interconvert them.

Same atoms, joined differently. Every one of these is a separate compound with its own boiling point, smell and reactions. These are the ones PubChem has on file, which for a larger formula is fewer than the number that could exist on paper.

• Caffeine
• Enprofylline
• Isophthalyl dihydrazide
• Isocaffeine
• 2,4-Dicyano-3-methylglutaramide
• 3,9-Dihydro-1,3,8-trimethyl-1H-purine-2,6-dione
• 1-Propylxanthine
• Terephthalohydrazide
• 1-Ethyl-3-methyl-3,7-dihydro-purine-2,6-dione
• 2,4,6-Trimethyl-2,3,5,6-tetraazabicyclo[5.2.0]nona-1(7),3-diene-8,9-dione
• 1-(4-Pyridoyl)-4-methylsemicarbazide
• Isophthalamidoxime
• N1,N4-Dihydroxyterephthalimidamide
• 3-Amino-5-carbamimidamidobenzoic acid
• N-(6-acetamidopyrimidin-4-yl)acetamide
• 4-(furan-2-ylmethylamino)-2,5-dihydro-1H-1,3,5-triazin-6-one
• 3-Ethyl-1-methyl-3,7-dihydro-1H-purine-2,6-dione
• 2-(N'-hydroxycarbamimidoyl)-N-(pyridin-2-yl)acetamide
• 1-hydroxy-2-[(E)-(4-hydroxyphenyl)methylideneamino]guanidine
• 1-hydroxy-2-[(E)-(2-hydroxyphenyl)methylideneamino]guanidine
• 4,7-Dimethyl-1,4,6,7-tetrahydroimidazo[4,5-E][1,4]diazepine-5,8-dione
• 5-ethyl-7-methyl-1H-pyrazolo[3,4-d]pyrimidine-4,6(5H,7H)-dione
• 1,4-Dimethyl-4,5,7,8-tetrahydroimidazo-[4,5-E]-1,4-diazepin-5,8(6H)-dione
• 1-hydroxy-3-[(E)-(6-methyl-2-pyridinyl)methylideneamino]urea
• N-(4-(Hydrazinecarbonyl)pyridin-2-yl)acetamide
• 1-Methyl-3-(pyridine-3-carbonylamino)urea
• Cyclo(-Gly-L-His)
• 3-Isopropyl-3,7-dihydro-purine-2,6-dione
• 7-Propylxanthine
• 9-Propylxanthine
• 4-Amino-6-methyl-7,8-dihydropyrimido[5,4-f][1,4]oxazepin-5-one
• 1,2-Hydrazinedicarboxamide, N-phenyl-
• 3-Amino-1-ethylpyrazolo[4,5-c]pyridine-4,6-diol
• [4-(Carbamoylamino)phenyl]urea
• 2-(Cyanoimino)-N-formyl-1-pyrrolidineacetamide
• 1,2-Propanedione, 1-(4-imino-1,4-dihydro-1-pyridyl)-, dioxime
• 6-(3-Ethyl-1,2,4-oxadiazol-5-yl)-2,3,4,5-tetrahydropyridazin-3-one
• 4,5-dimethyl-4H,7H-(1,2,4)triazolo(1,5-a)pyrimidine-6-carboxylic acid
• 5-(methoxymethyl)-2-methyl[1,2,4]triazolo[1,5-a]pyrimidin-7(4H)-one
• 2-Amino-6,7-dimethyl-3,7-dihydropyrimido[4,5-b][1,4]oxazin-4-one
• 1-(2-hydroxyethyl)-6-methyl-2H-pyrazolo[3,4-d]pyrimidin-4-one
• 3-ethyl-7-methyl-1H-pyrazolo[1,5-a][1,3,5]triazine-2,4-dione
• Phthalohydrazide
• 6-Amino-1,3-dimethylpyrrolo[3,4-d]pyrimidine-2,4-dione
• 1,8,7-Trimethylxanthin
• 3,5,7-trimethyl-2H-pyrazolo[3,4-d]pyrimidine-4,6-dione
• 3-(Propan-2-yl)-2H-pyrazolo[4,3-d]pyrimidine-5,7(4H,6H)-dione
• 9-(2-Hydroxyethyl)-2-methyl-9H-purin-6-ol