摩熵化学
数据库官网
小程序
打开微信扫一扫
首页 分子通 化学资讯 化学百科 反应查询 关于我们
请输入关键词
历史搜索
    热门化合物HOT
    • 喹啉
    • 水杨醛
    • 二溴甲烷
    • 谷胱甘肽
    • L-乳酸
    • 苯巴比妥
    • 辣椒碱
    • 非那明
    • 百草枯
    • 联苯烯
    首页 分子通 字母
    按分子首字母查询
    按分子CAS号查询
    中文名称 英文名称 CAS号 化学式 结构式图片
    —— (E)-5-acetamido-4-oxo-6-phenylhex-2-enoic acid —— C14H15NO4
    (E)-5-acetamido-4-oxo-6-phenylhex-2-enoic acid
    —— (E)-N,N-dimethyl-3-[2-(4-methylpyridin-2-yl)pyridin-4-yl]prop-2-en-1-amine —— C16H19N3
    (E)-N,N-dimethyl-3-[2-(4-methylpyridin-2-yl)pyridin-4-yl]prop-2-en-1-amine
    —— E-7-(4-methoxyphenyl)hept-4-enoic acid amide —— C14H19NO2
    E-7-(4-methoxyphenyl)hept-4-enoic acid amide
    —— Ethyl 1-(1-hydroxy-2-oxopropyl)-5-oxopyrrolidine-2-carboxylate —— C10H15NO5
    Ethyl 1-(1-hydroxy-2-oxopropyl)-5-oxopyrrolidine-2-carboxylate
    —— ethyl 5-[(hydroxyamino)methylideneamino]-1-methylpyrazole-4-carboxylate —— C8H12N4O3
    ethyl 5-[(hydroxyamino)methylideneamino]-1-methylpyrazole-4-carboxylate
    —— E-7-phenylhept-4-enoic acid amide —— C13H17NO
    E-7-phenylhept-4-enoic acid amide
    —— Ethyl 2-methyl-2-prop-2-enylcyclopropane-1-carboxylate —— C10H16O2
    Ethyl 2-methyl-2-prop-2-enylcyclopropane-1-carboxylate
    —— (E)-4-(benzenesulfinyl)-2-methylbut-2-en-1-ol —— C11H14O2S
    (E)-4-(benzenesulfinyl)-2-methylbut-2-en-1-ol
    —— E-5-(2-Bromovinyl)cytosine —— C6H6BrN3O
    E-5-(2-Bromovinyl)cytosine
    —— (E,3R)-1-sulfanyldec-5-en-3-ol —— C10H20OS
    (E,3R)-1-sulfanyldec-5-en-3-ol
    —— (E)-N-[3-[2-[2-[3-[[(E)-heptadec-8-enoyl]amino]propyl-[(E)-octadec-9-enoyl]amino]ethyl-[(Z)-octadec-9-enoyl]amino]ethyl-[(E)-octadec-9-enoyl]amino]propyl]octadec-9-enamide —— C99H185N5O5
    (E)-N-[3-[2-[2-[3-[[(E)-heptadec-8-enoyl]amino]propyl-[(E)-octadec-9-enoyl]amino]ethyl-[(Z)-octadec-9-enoyl]amino]ethyl-[(E)-octadec-9-enoyl]amino]propyl]octadec-9-enamide
    —— (E)-3-[1-[(2R,4S,5R)-5-[[bis(4-methoxyphenyl)-phenylmethoxy]methyl]-4-[2-cyanoethoxy-[di(propan-2-yl)amino]phosphanyl]oxyoxolan-2-yl]-2,4-dioxopyrimidin-5-yl]-N-[6-[[4-[[4-(dimethylamino)phenyl]diazenyl]phenyl]sulfonylamino]hexyl]prop-2-enamide —— C62H76N9O11PS
    (E)-3-[1-[(2R,4S,5R)-5-[[bis(4-methoxyphenyl)-phenylmethoxy]methyl]-4-[2-cyanoethoxy-[di(propan-2-yl)amino]phosphanyl]oxyoxolan-2-yl]-2,4-dioxopyrimidin-5-yl]-N-[6-[[4-[[4-(dimethylamino)phenyl]diazenyl]phenyl]sulfonylamino]hexyl]prop-2-enamide
    —— (E)-N-[[(2S,4R)-1-[2-(2,4-difluorobenzoyl)benzoyl]-4-[2-methylpropyl-[(2-phenylphenyl)methyl]amino]pyrrolidin-2-yl]methyl]-3-[4-[(Z)-(2,4-dioxo-1,3-thiazolidin-5-ylidene)methyl]phenyl]prop-2-enamide;4-methylbenzenesulfonic acid —— C56H52F2N4O8S2
    (E)-N-[[(2S,4R)-1-[2-(2,4-difluorobenzoyl)benzoyl]-4-[2-methylpropyl-[(2-phenylphenyl)methyl]amino]pyrrolidin-2-yl]methyl]-3-[4-[(Z)-(2,4-dioxo-1,3-thiazolidin-5-ylidene)methyl]phenyl]prop-2-enamide;4-methylbenzenesulfonic acid
    —— ethyl 3-[[4-[4-[(Z)-N'-ethoxycarbonylcarbamimidoyl]phenyl]-1,3-thiazol-2-yl]-[1-(2-ethoxy-2-oxoethyl)piperidin-4-yl]amino]propanoate;methyl (2S)-2-(2-chlorophenyl)-2-(6,7-dihydro-4H-thieno[3,2-c]pyridin-5-yl)acetate;sulfuric acid —— C43H55ClN6O12S3
    ethyl 3-[[4-[4-[(Z)-N'-ethoxycarbonylcarbamimidoyl]phenyl]-1,3-thiazol-2-yl]-[1-(2-ethoxy-2-oxoethyl)piperidin-4-yl]amino]propanoate;methyl (2S)-2-(2-chlorophenyl)-2-(6,7-dihydro-4H-thieno[3,2-c]pyridin-5-yl)acetate;sulfuric acid
    —— (E)-2-[2-[1-[1-[1-[1-[1-[2-[(6-chloro-2-methoxyacridin-9-yl)amino]propoxy]propan-2-yloxy]propan-2-yloxy]propan-2-yloxy]propan-2-yloxy]propan-2-ylamino]-2-oxoethyl]icos-4-enoic acid —— C54H86ClN3O9
    (E)-2-[2-[1-[1-[1-[1-[1-[2-[(6-chloro-2-methoxyacridin-9-yl)amino]propoxy]propan-2-yloxy]propan-2-yloxy]propan-2-yloxy]propan-2-yloxy]propan-2-ylamino]-2-oxoethyl]icos-4-enoic acid
    —— (E)-N-[[(2S,4R)-4-[benzhydryl(2-methylpropyl)amino]-1-[2-(2,4-difluorobenzoyl)benzoyl]pyrrolidin-2-yl]methyl]-3-[4-[(Z)-(2,4-dioxo-1,3-thiazolidin-5-ylidene)methyl]phenyl]prop-2-enamide —— C49H44F2N4O5S
    (E)-N-[[(2S,4R)-4-[benzhydryl(2-methylpropyl)amino]-1-[2-(2,4-difluorobenzoyl)benzoyl]pyrrolidin-2-yl]methyl]-3-[4-[(Z)-(2,4-dioxo-1,3-thiazolidin-5-ylidene)methyl]phenyl]prop-2-enamide
    —— ethyl 3-[2-[4-[2-[4-[(2R)-6,15-dibromo-13-chloro-4-azatricyclo[9.4.0.03,8]pentadeca-1(11),3(8),4,6,12,14-hexaen-2-yl]piperidin-1-yl]-2-oxoethyl]piperidin-1-yl]-2-oxoethyl]-5-methylimidazole-4-carboxylate —— C35H40Br2ClN5O4
    ethyl 3-[2-[4-[2-[4-[(2R)-6,15-dibromo-13-chloro-4-azatricyclo[9.4.0.03,8]pentadeca-1(11),3(8),4,6,12,14-hexaen-2-yl]piperidin-1-yl]-2-oxoethyl]piperidin-1-yl]-2-oxoethyl]-5-methylimidazole-4-carboxylate
    —— Ethyl 2-[[2-[5-[benzenesulfonyl-[(1-methylpiperidin-2-yl)methyl]amino]-2-[(4-carbamimidoylphenyl)methyl]benzimidazol-1-yl]acetyl]amino]acetate;dihydrochloride —— C34H43Cl2N7O5S
    Ethyl 2-[[2-[5-[benzenesulfonyl-[(1-methylpiperidin-2-yl)methyl]amino]-2-[(4-carbamimidoylphenyl)methyl]benzimidazol-1-yl]acetyl]amino]acetate;dihydrochloride
    —— Ethyl 2-amino-5-[[3-benzylsulfanyl-1-[(2-hexadecoxy-2-oxo-1-phenylethyl)amino]-1-oxopropan-2-yl]amino]-5-oxopentanoate —— C41H63N3O6S
    Ethyl 2-amino-5-[[3-benzylsulfanyl-1-[(2-hexadecoxy-2-oxo-1-phenylethyl)amino]-1-oxopropan-2-yl]amino]-5-oxopentanoate
    —— (E)-4-[2-hydroxy-2-[3-hydroxy-4-[(4E,6E,12E,14E)-10-hydroxy-3-methoxy-7,9,11,13,15-pentamethyl-16-oxo-1-oxacyclohexadeca-4,6,12,14-tetraen-2-yl]pentan-2-yl]-5-methyl-6-propan-2-yloxan-4-yl]oxy-4-oxobut-2-enoic acid —— C39H60O11
    (E)-4-[2-hydroxy-2-[3-hydroxy-4-[(4E,6E,12E,14E)-10-hydroxy-3-methoxy-7,9,11,13,15-pentamethyl-16-oxo-1-oxacyclohexadeca-4,6,12,14-tetraen-2-yl]pentan-2-yl]-5-methyl-6-propan-2-yloxan-4-yl]oxy-4-oxobut-2-enoic acid
    —— ethyl 2-[5-[(2R,3S,4R,5R)-5-[6-(2,2-diphenylethylamino)-2-(2-piperidin-1-ylethylamino)purin-9-yl]-3,4-dihydroxyoxolan-2-yl]tetrazol-2-yl]acetate —— C35H43N11O5
    ethyl 2-[5-[(2R,3S,4R,5R)-5-[6-(2,2-diphenylethylamino)-2-(2-piperidin-1-ylethylamino)purin-9-yl]-3,4-dihydroxyoxolan-2-yl]tetrazol-2-yl]acetate
    —— Ethyl 4-[1-[4-[benzoyl(methyl)amino]-3-(3,4-dimethoxyphenyl)butyl]-4-phenylpiperidine-4-carbonyl]morpholine-2-carboxylate —— C39H49N3O7
    Ethyl 4-[1-[4-[benzoyl(methyl)amino]-3-(3,4-dimethoxyphenyl)butyl]-4-phenylpiperidine-4-carbonyl]morpholine-2-carboxylate
    —— Ethyl 2-[5-[[1-[4-[4-(3,4-dichlorophenyl)piperazin-1-yl]-4-oxobutyl]-2-[(4-fluorophenyl)methylsulfanyl]-4-oxopyrimidin-5-yl]methyl]-2-oxopyrimidin-1-yl]acetate —— C34H35Cl2FN6O5S
    Ethyl 2-[5-[[1-[4-[4-(3,4-dichlorophenyl)piperazin-1-yl]-4-oxobutyl]-2-[(4-fluorophenyl)methylsulfanyl]-4-oxopyrimidin-5-yl]methyl]-2-oxopyrimidin-1-yl]acetate
    —— (E)-3-(furan-2-yl)-N-(3-morpholin-4-ylpropyl)-2-[(2-phenylacetyl)amino]prop-2-enamide —— C22H27N3O4
    (E)-3-(furan-2-yl)-N-(3-morpholin-4-ylpropyl)-2-[(2-phenylacetyl)amino]prop-2-enamide
    —— (E)-3-(furan-2-yl)-N-(3-morpholin-4-ylpropyl)-2-[(2-phenylacetyl)amino]prop-2-enamide;(1E)-N-[1-(2-hydroxy-2-phenylethyl)piperidin-1-ium-1-yl]ethanimidate —— C37H49N5O6
    (E)-3-(furan-2-yl)-N-(3-morpholin-4-ylpropyl)-2-[(2-phenylacetyl)amino]prop-2-enamide;(1E)-N-[1-(2-hydroxy-2-phenylethyl)piperidin-1-ium-1-yl]ethanimidate
    —— ethyl (E)-3-[4-carbamimidoyl-2-[2-[[4-(1-ethanimidoylpiperidin-4-yl)oxybenzoyl]amino]ethoxy]phenyl]prop-2-enoate;2,2,2-trifluoroacetic acid —— C30H36F3N5O7
    ethyl (E)-3-[4-carbamimidoyl-2-[2-[[4-(1-ethanimidoylpiperidin-4-yl)oxybenzoyl]amino]ethoxy]phenyl]prop-2-enoate;2,2,2-trifluoroacetic acid
    —— ethyl (2S)-2-amino-5-[[(2R)-3-[2-[bis(2-chloroethyl)carbamoyloxy]ethylsulfonyl]-1-[(2-ethoxy-2-oxoethyl)amino]-1-oxopropan-2-yl]amino]-5-oxopentanoate —— C21H36Cl2N4O10S
    ethyl (2S)-2-amino-5-[[(2R)-3-[2-[bis(2-chloroethyl)carbamoyloxy]ethylsulfonyl]-1-[(2-ethoxy-2-oxoethyl)amino]-1-oxopropan-2-yl]amino]-5-oxopentanoate
    —— ethyl 4-[[3-cyano-4-[(2R)-2-hydroxy-3-[(2-methyl-1-naphthalen-2-ylpropan-2-yl)amino]propoxy]phenyl]-methylsulfamoyl]benzoate —— C34H37N3O6S
    ethyl 4-[[3-cyano-4-[(2R)-2-hydroxy-3-[(2-methyl-1-naphthalen-2-ylpropan-2-yl)amino]propoxy]phenyl]-methylsulfamoyl]benzoate
    —— Ethyl 18-fluoro-17-[3-[(2-methylpropan-2-yl)oxycarbonylamino]pyrrolidin-1-yl]-21-oxo-5,15-dioxa-1-azahexacyclo[14.7.1.02,14.04,12.06,11.020,24]tetracosa-2(14),3,6,8,10,12,16(24),17,19,22-decaene-22-carboxylate —— C33H30FN3O7
    Ethyl 18-fluoro-17-[3-[(2-methylpropan-2-yl)oxycarbonylamino]pyrrolidin-1-yl]-21-oxo-5,15-dioxa-1-azahexacyclo[14.7.1.02,14.04,12.06,11.020,24]tetracosa-2(14),3,6,8,10,12,16(24),17,19,22-decaene-22-carboxylate
    —— (E)-but-2-enedioic acid;methyl N-[1-[4-(3,4-difluorophenoxy)butyl]piperidin-4-yl]-N-methyl-N'-(4-methylphenyl)carbamimidothioate —— C29H37F2N3O5S
    (E)-but-2-enedioic acid;methyl N-[1-[4-(3,4-difluorophenoxy)butyl]piperidin-4-yl]-N-methyl-N'-(4-methylphenyl)carbamimidothioate
    —— (E)-N-[6-[2-(5-bromopyrimidin-2-yl)oxyethoxy]-5-(4-methylphenyl)pyrimidin-4-yl]-2-phenylethenesulfonamide —— C25H22BrN5O4S
    (E)-N-[6-[2-(5-bromopyrimidin-2-yl)oxyethoxy]-5-(4-methylphenyl)pyrimidin-4-yl]-2-phenylethenesulfonamide
    —— Ethyl 7-[methyl-[2-[[2-[4-[(4-phenylphenyl)methoxy]phenyl]acetyl]amino]ethyl]amino]heptanoate;hydrochloride —— C33H43ClN2O4
    Ethyl 7-[methyl-[2-[[2-[4-[(4-phenylphenyl)methoxy]phenyl]acetyl]amino]ethyl]amino]heptanoate;hydrochloride
    —— ethyl N-[3-[4-[(5-formyl-4-methoxy-2-phenylimidazol-1-yl)methyl]phenyl]-5-(2-methylpropyl)thiophen-2-yl]sulfonylcarbamate —— C29H31N3O6S2
    ethyl N-[3-[4-[(5-formyl-4-methoxy-2-phenylimidazol-1-yl)methyl]phenyl]-5-(2-methylpropyl)thiophen-2-yl]sulfonylcarbamate
    —— ethyl 4-[(3S)-3-ethoxycarbonyl-5-oxo-4-[(1-pyridin-4-ylpiperidin-4-yl)methyl]cyclohexyl]sulfonylbenzoate —— C29H36N2O7S
    ethyl 4-[(3S)-3-ethoxycarbonyl-5-oxo-4-[(1-pyridin-4-ylpiperidin-4-yl)methyl]cyclohexyl]sulfonylbenzoate
    —— (E)-(S)-2-((2R,3R,4S,5R,6S)-3,4,5-Tris-benzyloxy-6-methoxy-tetrahydro-pyran-2-ylmethyl)-octa-1,5,7-trien-4-ol —— C36H42O6
    (E)-(S)-2-((2R,3R,4S,5R,6S)-3,4,5-Tris-benzyloxy-6-methoxy-tetrahydro-pyran-2-ylmethyl)-octa-1,5,7-trien-4-ol
    —— Ethyl 2-(naphthalen-1-ylsulfonylamino)-3-[[4-[3-oxo-3-(1,4,5,6-tetrahydropyrimidin-2-ylamino)propyl]benzoyl]amino]propanoate —— C29H33N5O6S
    Ethyl 2-(naphthalen-1-ylsulfonylamino)-3-[[4-[3-oxo-3-(1,4,5,6-tetrahydropyrimidin-2-ylamino)propyl]benzoyl]amino]propanoate
    —— Ethyl 1-(6-bromo-13-chloro-4-azatricyclo[9.4.0.03,8]pentadeca-1(11),3(8),4,6,12,14-hexaen-2-yl)-4-(2-pyridin-3-ylacetyl)piperazine-2-carboxylate —— C28H28BrClN4O3
    Ethyl 1-(6-bromo-13-chloro-4-azatricyclo[9.4.0.03,8]pentadeca-1(11),3(8),4,6,12,14-hexaen-2-yl)-4-(2-pyridin-3-ylacetyl)piperazine-2-carboxylate
    —— (E)-but-2-enedioic acid;N-[5-methyl-8-(4-methylpiperazin-1-yl)-1,2,3,4-tetrahydronaphthalen-2-yl]-4-morpholin-4-ylbenzamide —— C31H40N4O6
    (E)-but-2-enedioic acid;N-[5-methyl-8-(4-methylpiperazin-1-yl)-1,2,3,4-tetrahydronaphthalen-2-yl]-4-morpholin-4-ylbenzamide
    —— ethyl (E)-7-amino-7-oxo-4-[[2-[6-oxo-2-phenyl-5-(phenylmethoxycarbonylamino)pyrimidin-1-yl]acetyl]amino]hept-2-enoate —— C29H31N5O7
    ethyl (E)-7-amino-7-oxo-4-[[2-[6-oxo-2-phenyl-5-(phenylmethoxycarbonylamino)pyrimidin-1-yl]acetyl]amino]hept-2-enoate
    —— (E,4S)-4-[[(2R)-2-(2-adamantyloxycarbonylamino)-3-(1H-indol-3-yl)-2-methylpropanoyl]amino]-5-phenylpent-2-enoic acid —— C34H39N3O5
    (E,4S)-4-[[(2R)-2-(2-adamantyloxycarbonylamino)-3-(1H-indol-3-yl)-2-methylpropanoyl]amino]-5-phenylpent-2-enoic acid
    —— (E)-3-[4-[[1-[[1-cyclohexyl-2-(furan-3-yl)benzimidazole-5-carbonyl]amino]-2-ethenylcyclopropanecarbonyl]amino]phenyl]prop-2-enoic acid —— C33H32N4O5
    (E)-3-[4-[[1-[[1-cyclohexyl-2-(furan-3-yl)benzimidazole-5-carbonyl]amino]-2-ethenylcyclopropanecarbonyl]amino]phenyl]prop-2-enoic acid
    —— ethyl 2-[(2-carbamimidoyl-3,4-dihydro-1H-isoquinolin-7-yl)oxy]-2-[4-(1-carbamimidoylpiperidin-4-yl)oxyphenyl]acetate;dihydrochloride —— C26H36Cl2N6O4
    ethyl 2-[(2-carbamimidoyl-3,4-dihydro-1H-isoquinolin-7-yl)oxy]-2-[4-(1-carbamimidoylpiperidin-4-yl)oxyphenyl]acetate;dihydrochloride
    —— ethyl N-[3-[(4-methylphenyl)sulfonylamino]propyl]-N-[3-[(4-methylphenyl)sulfonyl-(2-methylprop-2-enyl)amino]propyl]carbamate —— C27H39N3O6S2
    ethyl N-[3-[(4-methylphenyl)sulfonylamino]propyl]-N-[3-[(4-methylphenyl)sulfonyl-(2-methylprop-2-enyl)amino]propyl]carbamate
    —— [(E)-[4-[(8S,11R,13S,14S,17S)-17-methoxy-13-methyl-3-oxo-17-(propoxymethyl)-1,2,6,7,8,11,12,14,15,16-decahydrocyclopenta[a]phenanthren-11-yl]phenyl]methylideneamino] methylsulfanylformate —— C32H41NO5S
    [(E)-[4-[(8S,11R,13S,14S,17S)-17-methoxy-13-methyl-3-oxo-17-(propoxymethyl)-1,2,6,7,8,11,12,14,15,16-decahydrocyclopenta[a]phenanthren-11-yl]phenyl]methylideneamino] methylsulfanylformate
    —— [(E)-[4-[(8S,11R,13S,14S,17S)-17-(3-hydroxyprop-1-ynyl)-17-methoxy-13-methyl-3-oxo-1,2,6,7,8,11,12,14,15,16-decahydrocyclopenta[a]phenanthren-11-yl]phenyl]methylideneamino] ethylsulfanylformate —— C32H37NO5S
    [(E)-[4-[(8S,11R,13S,14S,17S)-17-(3-hydroxyprop-1-ynyl)-17-methoxy-13-methyl-3-oxo-1,2,6,7,8,11,12,14,15,16-decahydrocyclopenta[a]phenanthren-11-yl]phenyl]methylideneamino] ethylsulfanylformate
    —— [(E)-[4-[(8S,11R,13S,14S,17S)-17-(chloromethyl)-17-ethoxy-13-methyl-3-oxo-1,2,6,7,8,11,12,14,15,16-decahydrocyclopenta[a]phenanthren-11-yl]phenyl]methylideneamino] methylsulfanylformate —— C30H36ClNO4S
    [(E)-[4-[(8S,11R,13S,14S,17S)-17-(chloromethyl)-17-ethoxy-13-methyl-3-oxo-1,2,6,7,8,11,12,14,15,16-decahydrocyclopenta[a]phenanthren-11-yl]phenyl]methylideneamino] methylsulfanylformate
    —— (E)-N-[4-(3-bromoanilino)-7-methoxyquinazolin-6-yl]-4-(2-ethoxymorpholin-4-yl)but-2-enamide —— C25H28BrN5O4
    (E)-N-[4-(3-bromoanilino)-7-methoxyquinazolin-6-yl]-4-(2-ethoxymorpholin-4-yl)but-2-enamide
    —— Ethyl 2-[6-[benzenesulfonyl(methyl)amino]-2-[(4-carbamimidoylphenyl)methyl]benzimidazol-1-yl]acetate —— C26H27N5O4S
    Ethyl 2-[6-[benzenesulfonyl(methyl)amino]-2-[(4-carbamimidoylphenyl)methyl]benzimidazol-1-yl]acetate
    —— (E)-7-[(1R,2R,3R,5S)-6,6-dimethyl-3-[[[5-(2-methylpyrrol-1-yl)sulfonylthiophene-2-carbonyl]amino]methyl]-2-bicyclo[3.1.1]heptanyl]hept-5-enoic acid —— C27H36N2O5S2
    (E)-7-[(1R,2R,3R,5S)-6,6-dimethyl-3-[[[5-(2-methylpyrrol-1-yl)sulfonylthiophene-2-carbonyl]amino]methyl]-2-bicyclo[3.1.1]heptanyl]hept-5-enoic acid
    —— (E)-7-[(1R,2S,3S,5S)-6,6-dimethyl-3-[(5-thiophen-3-ylsulfonylthiophene-2-carbonyl)amino]-2-bicyclo[3.1.1]heptanyl]hept-5-enoic acid —— C25H31NO5S3
    (E)-7-[(1R,2S,3S,5S)-6,6-dimethyl-3-[(5-thiophen-3-ylsulfonylthiophene-2-carbonyl)amino]-2-bicyclo[3.1.1]heptanyl]hept-5-enoic acid