Study of H/D exchange rates to derive the strength of intramolecular hydrogen bonds in halo substituted organic building blocks: An NMR spectroscopic investigation

Intramolecular Hydrogen Bonding Involving Organic Fluorine: NMR Investigations Corroborated by DFT-Based Theoretical Calculations

“…The plot of integral areas of NH 2 peaks as a function of time, for unsubstituted and ortho -halosubstituted benzamides (2-fluoro, 2-chloro, 2-bromo, 2-iodo) are compared in Figure 42 . Similar results for meta - and para -substituted derivatives have also been obtained [ 169 ].…”

“…Consequent to significant difference in electronegativity (EN) and size among halogens, the strength of hydrogen bonds, steric hindrance and electronic effects [ 168 ] by these groups would also be substantially different. Hence the electronic effect, size effect and the effect of organic fluorine involved intramolecular HB on H/D exchange using 1 H-NMR spectroscopic techniques has also been explored in the different halo substituted anilines and benzamides [ 169 ]. The chemical structures of all the investigated molecules are reported in Figure 40 .…”

“…The nature of the substituents dictated the H/D rate constants and they were different for different substituents. It has been observed that when all the physical parameters were kept unchanged for any of the investigated molecules, the results could be reproduced with high degree of accuracy within the experimental error [ 169 ]. There is a perfect match of graphical plots obtained from integral intensity of the labile protons peaks as a function of time, carried out for different samples at different times for 2-fluorobenzamide.…”

Retention of strong intramolecular hydrogen bonds in high polarity solvents in binaphthalene–benzamide derivatives: extensive NMR studies

“…In the number of previous studies reported from our group, the 1h J FH disappeared in a high polarity solvent DMSO-d 6 . 16,29 Interestingly in the present study the strength of N-H/F-C HB is so strong that it gets weakened but does not get completely ruptured even in pure solvent DMSO-d 6 . Such an unusual behaviour has been reported earlier in monosaccharides, inositols and ginkgolides 48 where the strength of HB has been correlated to the value of 1h J HF .…”

“…It has been previously reported that the rate of H/D exchange depends on both the strength of HB as well as electronic effects of the substituents. 28,29 When the deuterated solvent is present in excess, this exchange phenomenon is known to follow the pseudo rst order kinetics. This concept has been exploited in the present study for monitoring the rate of exchange of labile hydrogen atom with the deuterium of the solvent to extract information on the relative strengths of HB.…”