The energy of a 10-S-3 hypervalent, i.e., N-S-N, bond was theoretically determined to be 60.6 kcal/mol using bond energy density analysis with the density functional theory. Upon rotation of the pyrimidine ring of a sulfurane compound, the hypervalent bond is broken. The total energy of the system changes by 15.7 kcal/mol. The broken N-S bond is destabilized by 56.5kcal/mol, while another is stabilized by 44.2kcal/mol. The results support previous experimental data.