Abstract The crystal and molecular structure of 2H-and 2-(p-tolylamino)-5, 6-dimethylthieno [2, 3-d] pyrimidin-4-ones was investigated by X-ray diffraction. In crystals, the tautomeric form with a localized N (1)= C (2) bond is realized. A comparative analysis of the two structures using the literature data is given to examine the conjugation effect on the geometrical parameters of a pseudoaromatic pyrimidine system.
![5,6-dimethyl-2-methylsulfanyl-3H-thieno[2,3-d]pyrimidin-4-one Structure](https://image.chemsrc.com/caspic/479/53074-16-1.png)