NMR Measurements of Intramolecular Hydrogen Bonding in 1,3-Disiloxanediols and 1,6-Diols

Methanol titrations of partially deuterated diols dissolved in non-polar solvents such as CD2Cl2 and C6D6 provide 1H NMR measurements of OH/OD isotope shifts, diagnostic for the presence or absence of intramolecular hydrogen bonds under increasing protic solvent conditions. Understanding how intramolecular OH/OH bonds respond to solvent perturbations is important for advancing models of non-covalent interactions in catalysis. While conformationally rigid 1,3- and 1,4-diols have been extensively studied, the behavior of systems with labile intramolecular hydrogen bonds remains unexplored. A series of 1,6 diols (1-3) were synthesized from 2-adamantanone (4) and structurally confirmed via ¹H NMR and GCMS. These compounds, models for distal hydrogen bonds, were titrated with deuterated methanol to track isotope shifts indicative of relatively weak, non-persistent OH/OH interactions. These 1,6-diols act differently than rigid diols, whose intramolecular OH/OH hydrogen bonds persist in the presence of excess methanol. Specifically, these 1,6-diols exhibit a positive, non-persistent isotope shift mapped alongside the mole ratio of CD3OD/diol. Similar experiments are underway involving 1,3-disiloxanediols for a comparative analysis (7 – 8).