The Z/E iminol forms formohydroxamic acids (HX(OH)NHOH where X=C, Si, Ge, Sn and Pb) have been investigated in the gas phase using B3LYP density functional theory at B3LYP/6-31++G(d,p) level of theory.The barrier to the rotation of Z to the more stable isomer E is significant in C, Si and Ge structures, whereas in Sn and Pb the Ztautomer is more stable than E. The highest energy point is TS1-2, which lies 46.35 kcal/mol above the E isomer 2.The rate constant for tautomeric interconversion lies between 5.62´10-14 and 2.23´109 s-1. The 3®4 interconversion exhibits the highest rate constant for the tautomeric interconversion. The equilibrium constant for interconversion of tautomer 1 to 2 is 4.45´106. The solvent effect on formohydroxamic acid showed that the DG1- 2values are 0.37, 0.70, 0.58, 0.85, 1.97 and -9.07 kcal/mol, in DMSO, methanol, acetone, THF, cyclohexane and in gas phase respectively.