Cov dej tsis ua haujlwm (Anhydrides) yog qee qhov muaj cov pa oxygen kom tshem tawm ib lossis ntau cov lwg me dej, qhov seem. Feem ntau, kev tiv thaiv cov kab mob yog ib qho molecule ntawm cov kua qaub, thiab cov kua qaub anhydride ntawm cov kua qaub yog tsim los ntawm kev poob ncaj qha ib cov qauv ntawm cov dej, thiab lub siab ntawm cov kua-txiav txim siab nyob rau hauv cov kua qaub anhydride tseem tsis hloov. Cov organic acid yog tsim los ntawm cov tshuaj tiv thaiv lub cev qhuav dej ntawm ob lub lwg ntawm cov kua qaub lossis ntau lub cev ntawm cov kua qaub. Tsuas yog cov pa oxygen thiaj li muaj dej ua kom tsis muaj cev. Anaerobic acid tsis muaj qhov ntxaum tsis txaus.
Kev txiav txim siab rau lub cev feem ntau tuaj yeem suav tau tias yog cov oxides tsim los ntawm cov dej qab ntsev (anhydrides ntawm cov organic acids tsis yog oxides). Ntau tus tuaj yeem muaj peev xwm nrog dej los tsim cov thawj kua qaub. Raws li lub cev ntawm cov kua qaub, nws muaj peev xwm muab faib ua: (1) Anhydride ntawm inorganic acid, uas tau tsim los ntawm kev shrinkage ntawm ib lossis ob lub kua qaub. Piv txwv li, cov pa roj carbon (acid) anhydride yog carbon dioxide CO2, nitric (acid) anhydride yog dinitrogen pentoxide N2O5. (2) Tshuaj tiv thaiv kab mob ua kom tsis haum cov organic acid, ib qho tsim los ntawm cov hws ntawm ob lub monobasic acid lwg me lossis ib qho dibasic acid molecule. Txawm hais tias nws tsis yog oxide, nws tseem hu ua anhydride. Piv txwv, acetic anhydride (CH3CO) 2O, phthalic anhydride C8H4O3 thiab lwm yam.