The ground state geometry of allantoin has been studied using the AM1
method and electronic transitions calculated using the CNDO/s-CI metho
d. The calculation predicts that three different conformations can occ
ur in solutions; the most stable conformation is in agreement with tha
t observed by crystallography. The molecule is shown to absorb in the
vacuum UV region. The occurrence of allantoin in human tissues in the
presence of calcium ions is known to cause Reye's syndrome. The most f
avourable site of binding of calcium ions with allantoin has been foun
d using electrostatic potential mapping.