Quantitative Measurement of Cooperativity in H-Bonded Networks

Abstract

Cooperative H-bonding interactions are a feature of supramolecular networks involving alcohols. A family of phenol oligomers, in which the hydroxyl groups form intramolecular Hbonds, was used to investigate this phenomenon. Chains of intramolecular H-bonds were characterized using nuclear magnetic resonance (NMR) spectroscopy in solution and X-ray crystallography in the solid state. The phenol oligomers were used to make quantitative measurements of the effects of the intramolecular interactions on the strengths of intermolecular H-bonding interactions between the H-bond donor on the end of the chain and a series of H-bond acceptors. Intramolecular H-bonding interactions in the chain increase the strength of a single intermolecular H-bond between the terminal phenol and quinuclidine by up to 14 kJ mol −1 in the n-octane solution. Although the magnitude of the effect increases with the length of the H-bonded chain, the first intramolecular H-bond has a much larger effect than subsequent interactions. H-bond cooperativity is dominated by pairwise interactions between nearest neighbors, and longer range effects are negligible. The results were used to develop a simple model for cooperativity in H-bond networks using an empirical parameter κ to quantify the sensitivity of the H-bond properties of a functional group to polarization. The value of κ measured in these systems was 0.33, which means that formation of the first H-bond increases the polarity of the next H-bond donor in the chain by 33%. The cumulative cooperative effect in longer H-bonded chains reaches an asymptotic value, which corresponds to a maximum increase in the polarity of the terminal H-bond donor of 50%.

Cooperativity and intermolecular hydrogen bonding in donor‐acceptor complexes of phenol and polyhydroxybenzenes

“…Analogous damping effects on the acidities of tertiary alcohols, [ 8 ] sulfonic acids [ 9a ] and hydroxy‐1,4‐benzoquinone [ 9b ] derivatives with 1,3‐diol chains have been reported, and the cumulative cooperative effect on the reactivity of phenolic 1,5‐diol chains with amines fits a simple damping equation. [ 11 ] It is pertinent to consider how the behaviour of hydroxybenzenes compares with this well‐established pattern of cooperativity.…”

“…Complexation of tertiary amines with a 1,5‐diol, 1,5,9‐triol, 1,5,9,14‐tetrol series, based on repeating phenol motifs separated by methylene groups, has been investigated. [ 11 ] NMR‐NOESY spectra revealed an interaction between the methylene groups close to the nitrogen atom in quinuclidine and the hydrogen atom ortho to the H 1 O group to which the nitrogen is hydrogen‐bonded. In our calculations this same phenomenon is expressed by a topological hydrogen bond between the methyl hydrogens of trimethylamine and the same aromatic hydrogen atom for compounds 2‐4 , but not 1 (Figure 3).…”

“…Many theoretical studies, notably of long chains of small molecules, such as water, [ 2 ] methanol, [ 2b,3 ] aldehydes [ 2b,4 ] and amides, [ 5 ] describe positive cooperativity in intermolecular hydrogen bonding. More complex molecules with fewer hydrogen bonds, usually between HO groups in 1,2‐polyols, [ 6 ] 1,3‐polyols [ 6–10 ] and phenolic 1,5‐polyols, [ 11 ] display cooperative intramolecular hydrogen bonding. The view that the stability and other important features of carbohydrates, where there are 1,2‐diol chains, were due to long‐range cooperativity, has been criticised, [ 12 ] and other explanations advanced.…”

“…[17] It has been suggested that this anomaly could be attributed to polarisation effects and the low intramolecular O … H-O bond angles, as well as intramolecular hydrogen bonding. [11,17] The present study seeks to explain these different cooperative effects by means of DFT calculations of the binding energies, HO proton NMR shifts, and geometries of some complexes of 1, 2, 3 and 4 (Scheme 1) with various hydrogen-bond acceptors (HBA). In the Quantum Theory of Atoms in Molecules (QTAIM) a topological hydrogen bond is characterised by the existence of a bond critical point (BCP).…”

The surface site interaction point approach to non-covalent interactions

“…9). 72,[126][127][128] Polarisation has also been shown to affect aromatic interactions. 129 The magnitude of these allosteric effects is likely to depend on the nature of interacting partners, so a treatment that goes beyond pairwise interactions is required to describe this phenomenon.…”