Study On Structural Changes Of Typical Unsaturated Organic Compounds Under High Pressure

Unsaturated organic compounds widely found in nature.Since an unsaturated bond,they have special properties.This paper focuses on the structural changes of two typical unsaturated organic compounds under high pressure.1?Study on the Structural Change of Crotonic Acid under High PressureCrotonic acid is a typical ?,?-site unsaturated fatty acid materials.Crotonic acid has carbon–carbon and carbon–oxygen double bonds.It has special chemical structure.It can be used to prepare for fungicides,plasticizer and pharmaceutical intermediates materials.In this paper,the in situ high pressure Raman spectra of crotonic acid were measured,and the phase transition information of the material was obtained by the frequency shift-pressure curve.The information about intermolecular hydrogen bond was also obtained according to the change of the relative intensity.And it provides the spectral basis for the judgment of the material structure.Crotonic acid is chemically stable at atmospheric pressure to 14 GPa.According to the Raman frequency shift-pressure curve of crotonic acid,it can be seen that all spectral bands are nearly linearly moving in the direction of high wave number as the pressure increases.At about 6 GPa,the slopes of frequency shift-pressure curves have abrupt changes.And the first order phase transition exists near 6 GPa.The intensity ratio of 688cm^-1 and 695cm^-1 is exponentially related to the pressure in the process of pressurization.We think this is related to the new structure of crotonic acid.A new hydrogen bond structure is formed between the molecules under the high pressure.Due to the external pressure,the intermolecular interaction is enhanced.The intermolecular hydrogen bonds change from simple to complex.So the crotonic acid changes from dimer structure to the multimeric structure.2?Study on the Structural Change of TCNQ under High PressureCharge-transfer organic compounds have potential technological application in molecular electronics,and one of the most popular electron acceptor compounds is TCNQ.TCNQ molecule is planar structure and contains ? electrons.When the distance between molecules is reduced,? electrons overlap will increases,whichcan present a high conductivity.It is benefit for the study on complexes with TCNQ and electronic transfer process by research on TCNQ.So the high-pressure research would be meaningful.In this paper,we measured the high pressure Raman spectra of TCNQ up to about24 GPa.In this range,the Raman spectra of TCNQ are irreversible.According to the frequency shift-pressure curve of TCNQ,it is inferred that TCNQ undergoes phase transition around 2.3 GPa.The Fermi resonance phenomenon between the fundamental frequency modes induced by the pressure is observed in phase 2.And we simply explain the causes of the Fermi resonance phenomenon.In the process of pressurization,hydrogen bonding is enhanced,and the TCNQ change to a multimeric structure.We also obtained the relationship between intensity and pressure,and relationship between frequency difference and pressure.The energy difference and the natural frequency difference are increased,the coupling coefficient decreases in pressurization.