We have previously reported that, whereas conventional density functional theory (DFT) functionals have provided poor calculations on the alkane isodesmic reaction energy and isomerization reaction energy of organic molecules that include C, N, and O atoms, our developed long-range corrected (LC)- and LC including Gaussian attenuation (LCgau)-DFT + local response dispersion (LRD) functionals, which can accurately calculate inter- and intramolecular weak interactions, give accurate isomerization energies on these reactions. In this work, we found that B3LYP-D3, LC-ωPBE-D3, and ωB97XD, known for their good descriptions of weak interaction calculations, fail to reproduce the isomerization reaction energies of the molecules that include the S atom, such as methyl-thiourea, ethyl-thiourea, and propyl-thiourea. In contrast, LC- and LCgau-BOP+LRD functionals provide isomerization reaction energies that are very close to those produced by highly accurate wave function methods. These results show that an accurate description of the intramolecular weak interaction between the alkyl group and the S atom, unlike in the case of urea, is significant to reproduce the correct energy of the molecules with an alkyl group and S atom.