H3PO3 is more clearly described with the structural formula HPO(OH)2. In the solid state, HP(O)(OH)2 is tetrahedral with one shorter P=O bond of 148 pm and two longer P–O(H) bonds of 154 pm. This species exists in equilibrium with an extremely minor tautomer P(OH)3. IUPAC recommends that the latter be called phosphorous acid, whereas the dihydroxy form is called phosphonic acid. Only the reduced phosphorus compounds are spelled with an "ous" ending.
H3PO3 ແມ່ນຖືກອະທິບາຍຢ່າງຊັດເຈນດ້ວຍສູດໂຄງສ້າງສູດ HPO (OH) 2. ໃນສະພາບແຂງ, HP (O) (OH) 2 ແມ່ນ tetrahedral ທີ່ມີສາຍ P = O ສັ້ນກວ່າ 148 ມມແລະສອງ P-O (H) ພັນທະບັດຂອງ 154 pm. ຊະນິດນີ້ມີຢູ່ໃນຄວາມສົມດຸນດ້ວຍ tautomer ເລັກຫນ້ອຍທີ່ສຸດ P (OH) 3. IUPAC ແນະນໍາວ່າມັນຈະຖືກເອີ້ນວ່າອາຊິດ phosphorous, ໃນຂະນະທີ່ຮູບແບບ dihydroxy ຖືກເອີ້ນວ່າອາຊິດ phosphonic. ພຽງແຕ່ປະສົມປະສານ phosphorus ຫຼຸດລົງມີຄໍາວ່າ "ສິ້ນສຸດ".