Conventional and Unconventional Intramolecular Hydrogen Bonding in some Beta-diketones

Abstract

This study presents our view of unconventional and conventional intramolecular hydrogen bonds (HBs) for some beta-diketones theoretically and experimentally. According to our results, the groups such as Phenyl and t-But in beta positions increase and CF3 group decrease IHB strength, respectively. For better understanding of the substitution effects, the compounds with similar and different substitutions compared to each other experimentally and theoretically. Comparison between theoretical and experimental results, EHB and OH, show, by adding one substitution, these parameters change, which by adding another similar substitution, these changing approximately doubled. This conclusion achieved for DMPD, with phenyl and t-But groups in beta positions. Whereas, TFBA, with phenyl and CF3 groups, and TFDMHD, with CF3 and t-But groups in beta positions, don't follow this achievement. The 1HNMR chemical shifts for the stable cis-enol forms of the mentioned compounds have been calculated at different levels with various basis sets in CHCl3 as solvent by using PCM method. For the most beta-diketones, the 6-311G** and 6-311++G** basis sets, in all our calculated levels, are in better agreement with the experimental results. According to AIM results, unconventional hydrogen bonding created in some beta-diketones, which have Ph group. The strength of this hydrogen bonding for these compounds are same and about 2 kcal/mol.