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Questions and Answers
What was the original term used by Eilhard Mitscerlich to describe the phenomenon of chemically identical salts having different forms?
What was the original term used by Eilhard Mitscerlich to describe the phenomenon of chemically identical salts having different forms?
What was the significance of Wilhelm Ostwald's contribution to the study of polymorphism?
What was the significance of Wilhelm Ostwald's contribution to the study of polymorphism?
What was the advantage of the polarized light microscope over the traditional microscope?
What was the advantage of the polarized light microscope over the traditional microscope?
What was the primary application of the hot stage microscope in the study of polymorphism?
What was the primary application of the hot stage microscope in the study of polymorphism?
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What is the modern technique used to determine the enthalpy of polymorphic transitions?
What is the modern technique used to determine the enthalpy of polymorphic transitions?
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Who was the first to demonstrate methods to induce crystal phase changes and summarize the findings on the nature of polymorphism?
Who was the first to demonstrate methods to induce crystal phase changes and summarize the findings on the nature of polymorphism?
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What is the primary purpose of using x-ray crystallography in studying polymorphs?
What is the primary purpose of using x-ray crystallography in studying polymorphs?
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What type of vibrational modes are revealed by terahertz and low frequency Raman spectroscopies?
What type of vibrational modes are revealed by terahertz and low frequency Raman spectroscopies?
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What is the main advantage of combining computational methods with vibrational spectroscopy techniques?
What is the main advantage of combining computational methods with vibrational spectroscopy techniques?
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What is the primary goal of crystal structure prediction?
What is the primary goal of crystal structure prediction?
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What type of spectroscopy is sensitive to changes in hydrogen bonding patterns?
What type of spectroscopy is sensitive to changes in hydrogen bonding patterns?
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What is the main difference between polymorphs of a compound?
What is the main difference between polymorphs of a compound?
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Study Notes
X-ray Crystallography
- X-ray crystallography is commonly used to study the crystal structure of polymorphs.
- Both single crystal x-ray diffraction and powder x-ray diffraction techniques are used to obtain measurements of the crystal unit cell.
- Each polymorph of a compound has a unique crystal structure, resulting in different x-ray diffraction patterns.
Vibrational Spectroscopic Methods
- Vibrational spectroscopic methods, such as infrared (IR) spectroscopy, terahertz spectroscopy, and Raman spectroscopy, are used to investigate polymorphism.
- Mid-frequency IR and Raman spectroscopies are sensitive to changes in hydrogen bonding patterns.
- Terahertz and low frequency Raman spectroscopies reveal vibrational modes resulting from intermolecular interactions in crystalline solids.
Computational Methods
- Computational chemistry is used in combination with vibrational spectroscopy techniques to understand the origins of vibrations within crystals.
- The combination of techniques provides detailed information about crystal structures, similar to what can be achieved with x-ray crystallography.
- Crystal structure prediction is a technique that uses computational chemistry to model the formation of crystals and predict the existence of specific polymorphs of a compound.
Early Records of Polymorphism
- Eilhard Mitscerlich and Jöns Jacob Berzelius are credited for their studies of phosphates and arsenates in the early 1800s.
- They measured the interfacial angles of the crystals to show that chemically identical salts could have two different forms.
- Mitscerlich originally called this discovery isomorphism.
Historical Development of Polymorphism Studies
- Wilhelm Ostwald used the measurement of crystal density to study polymorphism and expressed it in Ostwald's Ratio.
- Moritz Ludwig Frankenheim demonstrated methods to induce crystal phase changes and formally summarized his findings on the nature of polymorphism.
- The development of the microscope, particularly the polarized light microscope, enhanced observations of polymorphism.
- Otto Lehmann invented the hot stage and fitted it to a polarized light microscope, allowing crystallographers to determine melting points and observe polymorphic transitions.
Thermal Methods
- Thermal methods, such as differential scanning calorimetry (DSC), are used to observe the heat flow that occurs during phase changes such as melting and polymorphic transitions.
- DSC is used to determine the enthalpy of polymorphic transitions.
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Description
Learn about the early discoveries of polymorphism, a phenomenon where chemically identical substances can have different forms. This quiz covers the contributions of Eilhard Mitscerlich, Jöns Jacob Berzelius, and Wilhelm Ostwald to the understanding of polymorphism.
