Progesterone, which regulates cyclical changes in the endometrium of the uterus and maintains a pregnancy The letters α and β[18] denote absolute stereochemistry at chiral centers—a specific nomenclature distinct from the R/S convention[19] of organic chemistry to denote absolute configuration of functional groups, known kakım Cahn–Ingold–Prelog priority rules. The R/S https://www.northwestu.edu/?URL=https://tr.wikipedia.org/wiki/Vitamin