Research on Hydrogen Bonds and Conformations of n-Pentanol under High Pressure

Hydrostatic pressure is a very important physical parameter. Application of hydrostatic pressure to molecular systems can adjust the distances and forces of the molecules and atoms, which can result in new structure and conformation change. Normal alkanols H(CH2)(n)OH are among the simplest substituted organic matters, in which a single OH group replaces a hydrogen atom at the end of the aliphatic chain. Normal alcohols are held together by the interplay between the hydrogen bond and the alkyl chain, and are called hydrogen bonded liquids. Hydrogen bonds are far weaker, so application of hydrostatic pressure to hydrogen-bonded organic molecules can compress hydrogen bonds. Large modifications can be observed in hydrogen bonds, including breakage and rearrangement. The changes in hydrogen bonds can lead to variations of crystal structures and symmetry, which will affect the properties of materials. N-pentanol (C5H12O) is short chain alcohol. It is simple in structure, but it can be a typical representative of alkyl chain organic compounds. However, the properties researches on n-pentanol under high pressure are scarce, especially studies on the conformational changes and hydrogen bonds under pressure have not been reported. So it is necessary to investigate n-pentanol at higher pressure, which is helpful to probe more information. Raman and IR spectroscopy are common spectral measurement techniques in high pressure research. They are useful for observing and providing interesting insights into the changes of the molecule. They are crucial tools, in studying structures, conformations and hydrogen bonds. Thus, in this paper, hydrogen-bonding and phase transitions of n-pentanol (C5H12O) have been investigated under high pressure usingRaman and Infrared spectroscopy. The high pressure Raman and IR spectrum have been collected as a function of high pressure to 12. 0 GPa by using the diamond anvil cell (DAC). The experiment results have been discussed in section 3. In the first part, the Raman spectrum of n-pentanol have been measured under high pressure. The Raman spectrum showed that the characteristic peaks become sharpened, characteristic peaks split and new modes appear at 3. 2 GPa. These results indicated that n-pentanol might experience a liquid to solid transition at 3. 2 GPa. In the second part, the influence of high pressure on conformational behavior of n-pentanol has been analyzed. N-pentanol has two characteristic conformers, including TTTt conformer and GTTt conformer. The changes of characteristic peaks with pressure have been studied. The data analysis showed that conformational change between trans and gauche is observed accompanied by the phase transitions. It was concluded that the gauche conformation is the main form in the liquid n-pentanol and the trans conformation in solid state. In the last part, the effect of high pressure on hydrogen-bond of n-pentanol has been investigated. The red shift of O-H stretching modes indicates that the H-bond is strengthened with increasing in pressure. The O-H stretching modes split into multiple peaks, which implied that new clusters and hydrogen bonding network of n-pentanol have formed. With the pressure increasing, the cluster structure of n-pentanol has become more stable and bigger. These results suggested that hydrogen bond is sensitive to pressure and plays an important role in promoting the stability of n-pentanol crystal structure. The high-pressure study on n-pentanol can provide a theoretical basis for the study of physical and chemical properties of similar or complex molecular systems.