Hydrogen Bonding in Liquid Alcohols

Licentiate thesis, 2012

Hydrogen bonded (H-bonded) materials, such as water, alcohols, sugars, and even DNA, are extremely important for biology, as well as chemical industry. Alcohols are used as solvents in paints, in perfumes, as cleaners, anti-freezers, or as an alternative to petrol in combustion engines. In medicine, the polymeric alcohol polyethylene glycol, PEG, is used in a process called pegylation, where PEG chains are attached to drugs or therapeutic proteins. Pegylation can prolong the medicines half life in the body, as well as aid in making the drug water soluble. Crucial in most of the applications are the effects the H-bonds have on the physical properties of the liquid and its functionality. H-bonds are intermolecular bonds, with a bond strength corresponding to ∼ 10 times the kinetic energy of the molecule at room temperature. In alcohols and water, this leads to a transient H-bond network, where molecules leaves and joins the networks at picosecond timescales. H-bonding is responsible for intriguing properties, both structural and dynamic. The most well known “anomaly”, is probably the density maximum water exhibits at 4◦ C, but also alcohols have unusual properties, caused by H- bonding, such as the so called Debye process seen in dielectric spectra of mono alcohols. To better understand the effect H-bonds have in different materials, it is im- portant to know what the H-bonded structures look like. This thesis is concerned with the H-bonding structure in some of the simplest H-bonding material: small molecule alcohols. To investigate the structure of the H-bonded clusters we use a combinations of experimental, computational, and theoretical methods. The clusters we have found have a tree-like topology, and a broad distribution of cluster sizes.