We substituted the t-but group on Cβ position of 4-amino-3-penten-2-one, APO. The aminoketone form of ,-Unsaturated--ketoenamines are more stable than iminoketone and iminoenol forms [1-2]. From the theoretical point of view, by considering the torsion of methyl groups with respect to together and chelated ring, 4 aminoketone forms can be drawn for 2,2-dimethyl-5-amino-4-hexen-3-one, DMAHO, molecule. All the mentioned forms of DMAHO have been optimized at the B3LYP level, using 6-311++G** basis set. Some selected optimized structural parameters, related to intramolecular hydrogen bond (IHB), of DMAHO and APO are collected in Table 1. According to this table 1, the N…O and O…H distances decrease, while the OHN bond angle and N-H bond length increase. Therefore, the IHB strength of DMHAO is more than that of APO. The AIM results confirm that the IHB in DMHAO is stronger than that in APO. This result is in agreement with the EHB for DMHAO molecule, which is obtained by the AIM method. The EHB values are 9.20 and 7.67 kcal/mol, in DMHAO and APO, respectively

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