Molecular formula
C18H21N3O3S
227 compounds have this formula on CompoundList.
- Molar mass
- 359.44g/mol
- Monoisotopic mass
- 363.1555Da
- Atoms
- 46
- Elements
- 5
- Rings plus double bonds
- 10
The formula C18H21N3O3S describes a molecule made of 18 carbon atoms, 21 hydrogen atoms, 3 nitrogen atoms, 3 oxygen atoms and 1 sulfur atom. It is written in Hill notation: carbon first, then hydrogen, then the other elements in alphabetical order. The formula tells you which atoms are present, not how they are connected, which is why several different chemicals can share it.
Elemental composition
- C Carbon × 1860.15%12.011 × 18 = 216.198 g/mol
- H Hydrogen × 215.89%1.008 × 21 = 21.168 g/mol
- N Nitrogen × 311.69%14.007 × 3 = 42.021 g/mol
- O Oxygen × 313.35%15.999 × 3 = 47.997 g/mol
- S Sulfur × 18.92%32.06 × 1 = 32.060 g/mol
Look up another formula
Compounds with the formula C18H21N3O3S
Isomers we list, best known first. Open one to see its structure, properties, safety data and suppliers.
Showing 101 to 200 of 227 compounds
![N-[4-(Cyclohexylsulfamoyl)phenyl]pyridine-4-carboxamide chemical structure, C18H21N3O3S, CAS 692762-45-1](/s/CJTMTSCSGFZGCL-UHFFFAOYSA-N.svg)
N-[4-(Cyclohexylsulfamoyl)phenyl]pyridine-4-carboxamide
CAS 692762-45-1C18H21N3O3S
![4-[5-(Morpholine-4-carbonyl)-4-phenyl-1,3-thiazol-2-yl]morpholine chemical structure, C18H21N3O3S, CAS 862391-28-4](/s/HSFJSGILTISKGG-UHFFFAOYSA-N.svg)
4-[5-(Morpholine-4-carbonyl)-4-phenyl-1,3-thiazol-2-yl]morpholine
CAS 862391-28-4C18H21N3O3S
![N-[4-(2-Methylpiperidin-1-yl)sulfonylphenyl]pyridine-3-carboxamide chemical structure, C18H21N3O3S, CAS 510739-68-1](/s/UILKNIUYRYEYHM-UHFFFAOYSA-N.svg)
N-[4-(2-Methylpiperidin-1-yl)sulfonylphenyl]pyridine-3-carboxamide
CAS 510739-68-1C18H21N3O3S
![4-Methoxy-3-methyl-N-(2-(8-methylimidazo[1,2-a]pyridin-2-yl)ethyl)benzenesulfonamide chemical structure, C18H21N3O3S, CAS 868979-20-8](/s/YTCSAMFYYUFYDN-UHFFFAOYSA-N.svg)
4-Methoxy-3-methyl-N-(2-(8-methylimidazo[1,2-a]pyridin-2-yl)ethyl)benzenesulfonamide
CAS 868979-20-8C18H21N3O3S
![2-(2,4-Dimethylphenoxy)-N-{[(4-methoxyphenyl)carbamothioyl]amino}acetamide chemical structure, C18H21N3O3S, CAS 83673-34-1](/s/ONJMZFRCKUVBKD-UHFFFAOYSA-N.svg)
2-(2,4-Dimethylphenoxy)-N-{[(4-methoxyphenyl)carbamothioyl]amino}acetamide
CAS 83673-34-1C18H21N3O3S
![5,6-Dihydro-1,4-dioxin-2-yl[4-(6-ethyl-1,3-benzothiazol-2-yl)piperazino]methanone chemical structure, C18H21N3O3S, CAS 897468-74-5](/s/CZGMUSMXFGEJEG-UHFFFAOYSA-N.svg)
5,6-Dihydro-1,4-dioxin-2-yl[4-(6-ethyl-1,3-benzothiazol-2-yl)piperazino]methanone
CAS 897468-74-5C18H21N3O3S
(E)-4-Butoxy-N-(2-oxo-2-(2-(thiophen-2-ylmethylene)hydrazinyl)ethyl)benzamide
CAS 391878-18-5C18H21N3O3S
![4-Methyl-1-(2-methylpropyl)-1H-pyrazolo[3,4-b]pyridin-6-yl 4-methylbenzene-1-sulfonate chemical structure, C18H21N3O3S, CAS 929975-56-4](/s/HRCJNECMGQKSRI-UHFFFAOYSA-N.svg)
4-Methyl-1-(2-methylpropyl)-1H-pyrazolo[3,4-b]pyridin-6-yl 4-methylbenzene-1-sulfonate
CAS 929975-56-4C18H21N3O3S
![Methyl 2-{3-[4,6-dimethyl-2-(methylsulfanyl)pyrimidin-5-yl]propanamido}benzoate chemical structure, C18H21N3O3S, CAS 924068-64-4](/s/WIBQUTDISGKBOF-UHFFFAOYSA-N.svg)
Methyl 2-{3-[4,6-dimethyl-2-(methylsulfanyl)pyrimidin-5-yl]propanamido}benzoate
CAS 924068-64-4C18H21N3O3S
![N-Benzyl-2-((1-(2-hydroxyethyl)-2-oxo-2,5,6,7-tetrahydro-1H-cyclopenta[d]pyrimidin-4-yl)thio)acetamide chemical structure, C18H21N3O3S, CAS 941887-89-4](/s/OIZZFOKYKXQPSN-UHFFFAOYSA-N.svg)
N-Benzyl-2-((1-(2-hydroxyethyl)-2-oxo-2,5,6,7-tetrahydro-1H-cyclopenta[d]pyrimidin-4-yl)thio)acetamide
CAS 941887-89-4C18H21N3O3S
Cyclopropyl(4-((3,4-dihydroisoquinolin-2(1H)-yl)sulfonyl)-3,5-dimethyl-1H-pyrazol-1-yl)methanone
CAS 943105-82-6C18H21N3O3S
N-Methyl esomeprazole
CAS 1820041-19-7C18H21N3O3S
1-(5-(1,1-Dioxidoisothiazolidin-2-yl)-2-methylphenyl)-3-(m-tolyl)urea
CAS 1203120-44-8C18H21N3O3S
![1-(Thiophen-2-ylmethyl)-3-(3,3,5-trimethyl-4-oxo-2,3,4,5-tetrahydrobenzo[b][1,4]oxazepin-7-yl)urea chemical structure, C18H21N3O3S, CAS 1170378-79-6](/s/WWPQYDFYZWZSJI-UHFFFAOYSA-N.svg)
1-(Thiophen-2-ylmethyl)-3-(3,3,5-trimethyl-4-oxo-2,3,4,5-tetrahydrobenzo[b][1,4]oxazepin-7-yl)urea
CAS 1170378-79-6C18H21N3O3S
(E)-2-Cyclopropyl-5-(1-(styrylsulfonyl)piperidin-4-yl)-1,3,4-oxadiazole
CAS 1211949-58-4C18H21N3O3S
![Benzo[d][1,3]dioxol-5-yl(4-(((1-methyl-1H-imidazol-2-yl)thio)methyl)piperidin-1-yl)methanone chemical structure, C18H21N3O3S, CAS 1428372-20-6](/s/BRUCJUBTDPDGDV-UHFFFAOYSA-N.svg)
Benzo[d][1,3]dioxol-5-yl(4-(((1-methyl-1H-imidazol-2-yl)thio)methyl)piperidin-1-yl)methanone
CAS 1428372-20-6C18H21N3O3S
![(5Z)-2-Morpholin-4-yl-5-[(4-morpholin-4-ylphenyl)methylidene]-1,3-thiazol-4-one chemical structure, C18H21N3O3S, CAS 667913-81-7](/s/PDKJSKXHMULMOM-SSZFMOIBSA-N.svg)
(5Z)-2-Morpholin-4-yl-5-[(4-morpholin-4-ylphenyl)methylidene]-1,3-thiazol-4-one
CAS 667913-81-7C18H21N3O3S
(E)-2-(4-Acetylpiperazin-1-yl)-5-(4-ethoxybenzylidene)thiazol-4(5H)-one
CAS 384795-33-9C18H21N3O3S
![(E)-5-(3-Ethoxy-4-(pentyloxy)benzylidene)thiazolo[3,2-b][1,2,4]triazol-6(5H)-one chemical structure, C18H21N3O3S, CAS 616210-90-3](/s/CQTCJZIGNPYXLE-LFIBNONCSA-N.svg)
(E)-5-(3-Ethoxy-4-(pentyloxy)benzylidene)thiazolo[3,2-b][1,2,4]triazol-6(5H)-one
CAS 616210-90-3C18H21N3O3S
![N-[4,5-Dimethyl-3-(pyridin-3-ylmethylcarbamoyl)thiophen-2-yl]oxolane-2-carboxamide chemical structure, C18H21N3O3S, CAS 895945-17-2](/s/VTDDNLUBXGXEOC-UHFFFAOYSA-N.svg)
N-[4,5-Dimethyl-3-(pyridin-3-ylmethylcarbamoyl)thiophen-2-yl]oxolane-2-carboxamide
CAS 895945-17-2C18H21N3O3S
![N-[2-(4-Methylsulfonylpiperazin-1-yl)phenyl]benzamide chemical structure, C18H21N3O3S, CAS 766523-37-9](/s/FGFVPZUQRXKMBR-UHFFFAOYSA-N.svg)
N-[2-(4-Methylsulfonylpiperazin-1-yl)phenyl]benzamide
CAS 766523-37-9C18H21N3O3S
Pyrazinecarboxamide, N-(1-hydroxy-2-(4-((3-methylbutyl)thio)phenyl)-2-oxoethyl)-
CAS 53140-58-2C18H21N3O3S
Butyl 2-(pyrazine-2-carbonylamino)-4,5,6,7-tetrahydro-1-benzothiophene-3-carboxylate
CAS 445022-45-7C18H21N3O3S
1-(Furan-2-carbonyl)-N-(4,5,6,7-tetrahydro-1,3-benzothiazol-2-yl)piperidine-4-carboxamide
CAS 887682-29-3C18H21N3O3S
- 6-Methyl-1,1-dioxo-N-(2,4,6-trimethylphenyl)-3,4-dihydro-2H-1lambda6,2,4-benzothiadiazine-3-carboxamide941877-23-2C18H21N3O3S
- (Z)-N-(2-(tert-Butyl)-5,5-dioxido-4,6-dihydro-2H-thieno[3,4-c]pyrazol-3-yl)-3-phenylacrylamide449784-83-2C18H21N3O3S
- 1-(1-(4-Ethoxyphenyl)-5-oxopyrrolidin-3-yl)-3-(thiophen-2-ylmethyl)urea894014-46-1C18H21N3O3S
- N-(2-Methoxyphenethyl)-2-(7-methyl-5-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyrimidin-3-yl)acetamide946346-10-7C18H21N3O3S
- N-(4-Methoxyphenethyl)-2-(6-methyl-5-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyrimidin-3-yl)acetamide946237-80-5C18H21N3O3S
- (E)-1-((1-(3-(Furan-2-yl)acryloyl)piperidin-4-yl)methyl)-3-(thiophen-2-yl)urea1235690-76-2C18H21N3O3S
- N-((1-(Furan-3-carbonyl)piperidin-4-yl)methyl)-2-(methylthio)nicotinamide1396748-72-3C18H21N3O3S
- Methyl 4-((2-phenylthiazole-4-carboxamido)methyl)piperidine-1-carboxylate1797793-82-8C18H21N3O3S
- N-(3-(1H-Pyrrolo[2,3-b]pyridin-1-yl)propyl)-4-methoxy-3-methylbenzenesulfonamide1797262-12-4C18H21N3O3S
- (2-(Benzo[D][1,3]dioxol-5-ylamino)thiazol-4-yl)(3,5-dimethylpiperidin-1-yl)methanone1908149-45-0C18H21N3O3S
- 5-Amino-4-[4-(3,4-dimethoxyphenyl)-1,3-thiazol-2-yl]-1-propyl-1,2-dihydro-3H-pyrrol-3-one929810-57-1C18H21N3O3S
- 5-Amino-4-[4-(4-methoxyphenyl)-1,3-thiazol-2-yl]-1-(3-methoxypropyl)-1,2-dihydro-3H-pyrrol-3-one929869-29-4C18H21N3O3S
- N-[[4-(Dimethylamino)phenyl]carbamothioyl]-3,4-dimethoxybenzamide364624-58-8C18H21N3O3S
- N-(5,5-Dioxido-2-phenyl-4,6-dihydro-2H-thieno[3,4-c]pyrazol-3-yl)cyclohexanecarboxamide681265-37-2C18H21N3O3S
- 3-Cyclohexyl-N-[4-(4-nitrophenyl)-1,3-thiazol-2-yl]propanamide544689-50-1C18H21N3O3S
- 1-(Furan-2-ylmethyl)-4-(2-oxo-2-pyrrolidin-1-ylethyl)sulfanyl-6,7-dihydro-5H-cyclopenta[d]pyrimidin-2-one1003254-24-7C18H21N3O3S
- 4-(Cyclopentylsulfamoyl)-N-(pyridin-3-ylmethyl)benzamide898657-79-9C18H21N3O3S
- N-{4-[(2-Methylpiperidin-1-yl)sulfonyl]phenyl}pyridine-4-carboxamide932855-48-6C18H21N3O3S
- N-(3,5-Dimethoxyphenyl)-2-(3-phenylpropanoyl)hydrazinecarbothioamide667443-05-2C18H21N3O3S
- N-(1,3-Benzodioxol-5-ylmethyl)-2-{[6-methyl-2-(propan-2-yl)pyrimidin-4-yl]sulfanyl}acetamide924122-33-8C18H21N3O3S
- 3-[(Methylsulfonyl)amino]phenyl 4-phenylpiperazinyl ketone928956-43-8C18H21N3O3S
- N-(2H-1,3-Benzodioxol-5-yl)-2-[(1-cyclohexyl-1H-imidazol-2-yl)sulfanyl]acetamide946319-88-6C18H21N3O3S
- N-(4-{[(2-Methoxyethyl)carbamoyl]methyl}phenyl)-2-(methylsulfanyl)pyridine-3-carboxamide1060316-75-7C18H21N3O3S
- 1-(1-(2-Methoxyacetyl)-1,2,3,4-tetrahydroquinolin-7-yl)-3-(thiophen-2-ylmethyl)urea1203293-07-5C18H21N3O3S
- 1-{[2-(4-Methoxyphenyl)-4-methyl-1,3-thiazol-5-yl]carbonyl}-4-piperidinecarboxamide1282122-26-2C18H21N3O3S
- 1-(2-Butoxy-4,5-dimethylbenzenesulfonyl)-1H-1,2,3-benzotriazole1087640-80-9C18H21N3O3S
- N-(3-(6-(Methylsulfonyl)pyridazin-3-yl)phenyl)cyclohexanecarboxamide946226-16-0C18H21N3O3S
- Rabeprazole-d3934295-30-4C18H21N3O3S
- 2-[Acetyl(cyclopropyl)amino]-N-(2-methoxybenzyl)-4-methyl-1,3-thiazole-5-carboxamide1190293-26-5C18H21N3O3S
- N-[5-(Azepane-1-carbonyl)-1-methyl-2-oxo-1,2-dihydropyridin-3-yl]thiophene-2-carboxamide1203147-62-9C18H21N3O3S
- N-(2-Isobutyryl-1,2,3,4-tetrahydroisoquinolin-7-yl)pyridine-3-sulfonamide1207028-77-0C18H21N3O3S
- 1-(4-(2-Morpholino-2-oxoethyl)phenyl)-3-(thiophen-2-ylmethyl)urea1210281-10-9C18H21N3O3S
- Phenyl 4-((3-(thiophen-2-yl)ureido)methyl)piperidine-1-carboxylate1235662-76-6C18H21N3O3S
- N-(5-Cyclopropyl-1,3,4-thiadiazol-2-yl)-4-(4-methoxyphenyl)tetrahydro-2H-pyran-4-carboxamide1324084-30-1C18H21N3O3S
- 3-(3-(Thiophen-2-yl)ureido)cyclohexyl phenylcarbamate1351646-84-8C18H21N3O3S
- N-(2-(4-Isopropylthiazol-2-yl)ethyl)-2-(3-oxo-3,4-dihydro-2H-benzo[b][1,4]oxazin-2-yl)acetamide1630873-07-2C18H21N3O3S
- 4-Methyl-N-(pyridin-3-ylmethyl)-3-pyrrolidin-1-ylsulfonylbenzamide603971-66-0C18H21N3O3S
- 2-[[2-(3-Methoxyphenyl)-7,7-dimethyl-5,8-dihydropyrano[4,3-d]pyrimidin-4-yl]sulfanyl]acetamide902021-77-6C18H21N3O3S
- N-(4-Ethoxyphenyl)-2-[(2-oxo-5,6,7,8-tetrahydro-1H-quinazolin-4-yl)sulfanyl]acetamide1001519-95-4C18H21N3O3S
- 1-{[3-(Propan-2-yl)-4-propoxyphenyl]sulfonyl}-1H-benzotriazole941261-96-7C18H21N3O3S
- 2-(4-(4-Methoxyphenyl)piperazin-1-yl)-2-oxo-N-(thiophen-2-ylmethyl)acetamide941962-82-9C18H21N3O3S
- N1-(2-hydroxyethyl)-N2-(2-(indolin-1-yl)-2-(thiophen-2-yl)ethyl)oxalamide898424-09-4C18H21N3O3S
- 2-(7-Ethyl-5-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyrimidin-3-yl)-N-(4-methoxybenzyl)acetamide953229-89-5C18H21N3O3S
- 2-(7-Ethyl-5-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyrimidin-3-yl)-N-(2-methoxybenzyl)acetamide953008-44-1C18H21N3O3S
- 2-{7-Ethyl-5-oxo-2H,3H,5H-[1,3]thiazolo[3,2-a]pyrimidin-3-yl}-N-[(3-methoxyphenyl)methyl]acetamide952994-80-8C18H21N3O3S
- 2-(6,7-Dimethyl-5-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyrimidin-3-yl)-N-(4-methoxybenzyl)acetamide953017-16-8C18H21N3O3S
- 1-((1-(4-Methoxyphenyl)-5-oxopyrrolidin-3-yl)methyl)-3-(thiophen-2-ylmethyl)urea946351-82-2C18H21N3O3S
- Methyl 5-methyl-2-{[(4-phenylpiperazin-1-yl)carbonyl]amino}thiophene-3-carboxylate777874-82-5C18H21N3O3S
- N-(2,3-Dihydro-1,4-benzodioxin-6-yl)-4-(furan-2-ylmethyl)piperazine-1-carbothioamide724758-16-1C18H21N3O3S
- 2-((6-(3-Methoxyphenyl)pyridazin-3-yl)thio)-N-((tetrahydrofuran-2-yl)methyl)acetamide893989-50-9C18H21N3O3S
- 2-((1-(2-(Azepan-1-yl)-2-oxoethyl)-1H-indol-3-yl)sulfonyl)acetonitrile894016-79-6C18H21N3O3S
- N-Methyl-4-(2-oxopyrrolidin-1-yl)-N-(2-(pyridin-4-yl)ethyl)benzenesulfonamide919666-30-1C18H21N3O3S
- 1,1-Dimethylethyl 1,3,4,5,7,8-hexahydro-4-oxo-3-phenyl-2-thioxopyrido[4,3-d]pyrimidine-6(2H)-carboxylate1016975-27-1C18H21N3O3S
- N-(3-(6-(Ethylsulfonyl)pyridazin-3-yl)phenyl)cyclopentanecarboxamide946202-31-9C18H21N3O3S
- N-[4-({[2-(4-Methoxyphenyl)ethyl]carbamoyl}methyl)-1,3-thiazol-2-yl]cyclopropanecarboxamide921802-23-5C18H21N3O3S
- 1-Benzyl-3-(1-methanesulfonyl-1,2,3,4-tetrahydroquinolin-7-yl)urea1203317-38-7C18H21N3O3S
- 1-(1-(Ethylsulfonyl)-1,2,3,4-tetrahydroquinolin-6-yl)-3-phenylurea1203104-04-4C18H21N3O3S
- 1-(3-(1,1-Dioxidoisothiazolidin-2-yl)phenyl)-3-phenethylurea1203077-84-2C18H21N3O3S
- 1-Benzyl-3-(5-(1,1-dioxidoisothiazolidin-2-yl)-2-methylphenyl)urea1203083-48-0C18H21N3O3S
- 1-(5-(1,1-Dioxidoisothiazolidin-2-yl)-2-methylphenyl)-3-(p-tolyl)urea1203238-35-0C18H21N3O3S
- 2-(1,1-Dioxidotetrahydrothiophen-3-yl)-N-(o-tolyl)-2,4,5,6-tetrahydrocyclopenta[c]pyrazole-3-carboxamide1105231-31-9C18H21N3O3S
- (4-(1H-Pyrrol-1-yl)phenyl)(4-(cyclopropylsulfonyl)piperazin-1-yl)methanone1226428-30-3C18H21N3O3S
- N-(2-Hydroxy-2-(naphthalen-1-yl)ethyl)-1,3,5-trimethyl-1H-pyrazole-4-sulfonamide1448031-08-0C18H21N3O3S
- N1-(2-hydroxy-2-(1-methylindolin-5-yl)ethyl)-N2-(thiophen-2-ylmethyl)oxalamide1706124-44-8C18H21N3O3S
- 1-(2-Cyclopropyl-6,7-dihydropyrazolo[1,5-a]pyrazin-5(4H)-yl)-3-(phenylsulfonyl)propan-1-one2034507-43-0C18H21N3O3S
- N-(4-(Furan-3-yl)benzyl)-2-isopropyl-1-methyl-1H-imidazole-4-sulfonamide2034603-01-3C18H21N3O3S
- 4-(Benzylsulfonyl)-N-(pyridin-3-yl)piperidine-1-carboxamide2034388-21-9C18H21N3O3S
- 2-(1,1-Dioxidotetrahydrothiophen-3-yl)-N-(m-tolyl)-2,4,5,6-tetrahydrocyclopenta[c]pyrazole-3-carboxamide2310157-51-6C18H21N3O3S
- 2-(1,1-Dioxidotetrahydrothiophen-3-yl)-N-(p-tolyl)-2,4,5,6-tetrahydrocyclopenta[c]pyrazole-3-carboxamide2310157-28-7C18H21N3O3S
- 6-Cyclopropyl-3-{2-oxo-2-[4-(thiophen-3-yloxy)piperidin-1-yl]ethyl}-3,4-dihydropyrimidin-4-one2034562-24-6C18H21N3O3S
- (1R,5S)-8-((2,3-Dihydrobenzofuran-5-yl)sulfonyl)-3-(1H-pyrazol-1-yl)-8-azabicyclo[3.2.1]octane2320886-75-5C18H21N3O3S
- 1-[2-Methoxy-4-methyl-5-(propan-2-yl)benzenesulfonyl]-5-methyl-1H-1,2,3-benzotriazole2419420-11-2C18H21N3O3S
- 4-Butoxy-N-({imidazo[1,2-A]pyridin-2-YL}methyl)benzene-1-sulfonamide868972-18-3C18H21N3O3S
- N-[4-(Azepan-1-ylsulfonyl)phenyl]pyridine-3-carboxamide875108-72-8C18H21N3O3S
- N-[(1,3-Dioxaindan-5-yl)methyl]-3-[4,6-dimethyl-2-(methylsulfanyl)pyrimidin-5-yl]propanamide930674-81-0C18H21N3O3S
- 2-[(5,6-Diethoxy-1H-benzimidazole-2-sulfinyl)methyl]aniline107562-88-9C18H21N3O3S
Frequently asked questions
What is the molar mass of C18H21N3O3S?
The molar mass of C18H21N3O3S is 359.44 g/mol, calculated from standard atomic weights for 18 carbon atoms, 21 hydrogen atoms, 3 nitrogen atoms, 3 oxygen atoms and 1 sulfur atom. The monoisotopic mass is 363.1555 Da.
How many compounds have the formula C18H21N3O3S?
CompoundList lists 227 compounds with the molecular formula C18H21N3O3S, including N-[4-(Cyclohexylsulfamoyl)phenyl]pyridine-4-carboxamide, 4-[5-(Morpholine-4-carbonyl)-4-phenyl-1,3-thiazol-2-yl]morpholine, N-[4-(2-Methylpiperidin-1-yl)sulfonylphenyl]pyridine-3-carboxamide. Compounds that share a formula are isomers. They contain the same atoms arranged differently, so their properties, uses and prices can be very different.
What is the degree of unsaturation of C18H21N3O3S?
C18H21N3O3S has a degree of unsaturation of 10. That is the total number of rings and pi bonds (a double bond counts as one, a triple bond as two) in any structure with this formula.