Spectroscopy 2
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Questions and Answers

What is one of the primary pharmaceutical applications of Infrared Spectroscopy?

  • Quantitative measurement of drug concentrations
  • Qualitative fingerprint check for identity of raw materials (correct)
  • Assessment of drug stability over time
  • Kinetic study of drug interactions

Which types of transitions do molecules undergo during Infrared Spectroscopy?

  • Chemical and physical transitions
  • Thermal and structural transitions
  • Vibrational and rotational transitions (correct)
  • Electronic and magnetic transitions

How is the IR spectrum typically plotted?

  • As a percentage of absorption versus wavelength
  • As a graph of intensity versus frequency
  • As energy versus time
  • As wavenumber (cm-1) versus intensity (correct)

What underlies the origin of the IR spectrum at the molecular level?

<p>Vibrational energy associated with molecular bonds (A)</p> Signup and view all the answers

What is a useful method of sample preparation for analyzing solid samples with IR Spectroscopy?

<p>Compressing into a pellet with potassium bromide (B)</p> Signup and view all the answers

Infrared Spectroscopy is primarily used for identifying which type of molecular characteristics?

<p>Functional groups within a molecule (C)</p> Signup and view all the answers

Which statement best describes vibrational energy levels in a molecule?

<p>They are discrete and associated with molecular bonds. (A)</p> Signup and view all the answers

In which scenario would Infrared Spectroscopy not be effectively used?

<p>To analyze chemical reactions in real-time. (A)</p> Signup and view all the answers

Which type of molecular vibrations specifically absorb IR radiation?

<p>Asymmetrical vibrations (D)</p> Signup and view all the answers

What condition must be met for a molecule to absorb IR radiation?

<p>The molecule must be polarisable (D)</p> Signup and view all the answers

Which of the following statements is true regarding symmetrical molecules and IR absorption?

<p>Symmetrical molecules do not display absorbance in the IR region unless asymmetrical vibrations occur. (D)</p> Signup and view all the answers

What is the primary reason complicated compounds produce many bands in an IR spectrum?

<p>They possess multiple bonds and complex structures. (B)</p> Signup and view all the answers

Which of the following vibration modes contributes a peak close to 3756 cm-1 in an IR spectrum?

<p>Anti-symmetric stretching (C)</p> Signup and view all the answers

For which purpose is the IR spectrum commonly utilized in pharmaceutical applications?

<p>To analyze vibrational transitions of drug molecules (B)</p> Signup and view all the answers

What is typically involved in sample preparation for IR spectroscopy?

<p>Forming the sample into a thin film or pellet (A)</p> Signup and view all the answers

Which characteristic distinguishes between anti-symmetric and symmetric stretching modes?

<p>Anti-symmetric stretching results in a net dipole change. (B)</p> Signup and view all the answers

What is the main purpose of using IR spectroscopy in pharmaceuticals?

<p>To identify functional groups and confirm drug identity (C)</p> Signup and view all the answers

What characteristic of the fingerprint region makes it difficult to assign all absorption bands?

<p>The complexity of the spectrum (C)</p> Signup and view all the answers

Which bond requires the most energy to stretch according to the provided data?

<p>O-H (A)</p> Signup and view all the answers

How can solvent residues affect the purity determination of compounds using IR spectroscopy?

<p>They create additional absorption bands not seen in pure compounds (C)</p> Signup and view all the answers

Which technique is used to prepare solid samples for IR spectroscopy?

<p>Mixing with a mulling agent or KBr (B)</p> Signup and view all the answers

What information can be obtained from the peak intensities in an IR spectrum?

<p>The purity and concentration of the sample (B)</p> Signup and view all the answers

Which statement accurately describes the bond strength of C-H compared to N-H and O-H?

<p>C-H bond is the weakest among them (C)</p> Signup and view all the answers

What kind of molecular transition is primarily analyzed in IR spectroscopy?

<p>Vibrational transitions (B)</p> Signup and view all the answers

What is the significance of using the British Pharmocopoeia (BP) in pharmaceutical IR spectroscopy?

<p>It has standard IR spectra for confirming drug identity (C)</p> Signup and view all the answers

What is the primary reason for needing longer path lengths when analyzing gases with IR spectroscopy?

<p>Gases absorb less IR radiation than liquids (C)</p> Signup and view all the answers

How does the mass of an atom influence its absorption frequency in infrared spectroscopy?

<p>The lighter the atom, the higher the frequency of absorption.</p> Signup and view all the answers

What effect does bond strength have on the absorption frequency of a molecule?

<p>Stronger bonds result in higher absorption frequencies.</p> Signup and view all the answers

In the context of group frequencies, why is it important to use correlation charts for interpreting IR spectra?

<p>Correlation charts help identify specific functional groups based on their characteristic absorption frequencies.</p> Signup and view all the answers

What is the importance of absorption bands appearing at the same frequency for multiple molecules?

<p>It indicates that different molecules can possess similar functional groups, making spectral analysis complex.</p> Signup and view all the answers

How does the understanding of normal modes of vibration assist in analyzing compounds like water and carbon dioxide?

<p>It provides insight into how these molecules vibrate and absorb IR radiation, aiding in their identification.</p> Signup and view all the answers

What type of molecular vibrations can absorb infrared radiation?

<p>Only asymmetrical vibrations absorb infrared radiation.</p> Signup and view all the answers

Why do complicated compounds produce multiple bands in an IR spectrum?

<p>Complicated compounds have more than one mode of vibration, leading to many absorbance bands.</p> Signup and view all the answers

What is required for a molecule to exhibit absorbance in the IR region?

<p>A molecule must be polarisable and have asymmetrical vibrations to absorb IR radiation.</p> Signup and view all the answers

What is the main difference between symmetrical and anti-symmetric stretching?

<p>Symmetrical stretching involves equal movement of atoms in opposite directions, while anti-symmetric stretching involves unequal movements.</p> Signup and view all the answers

What role does frequency play in molecular vibrations for IR spectra?

<p>Each type of vibration corresponds to a specific frequency of radiation absorbed.</p> Signup and view all the answers

Which molecular configurations exhibit IR absorptions under normal circumstances?

<p>Asymmetrical molecules or symmetrical molecules undergoing specific bending or stretching can exhibit IR absorptions.</p> Signup and view all the answers

What is the significance of bending vibrations in relation to IR absorption?

<p>Bending vibrations can allow symmetrical molecules to absorb infrared light if they can induce a dipole.</p> Signup and view all the answers

At what wavenumbers do some common molecular vibrations occur according to the provided data?

<p>Common vibrations occur at approximately 3756 cm-1 for stretching and 1595 cm-1 for bending.</p> Signup and view all the answers

What are the two additional types of radiation-induced transitions observed in molecules during Infrared Spectroscopy?

<p>Vibrational and rotational transitions.</p> Signup and view all the answers

Explain how the energy required for vibrational transitions compares to that needed for electronic transitions.

<p>The energy required for vibrational transitions is smaller than that for electronic transitions.</p> Signup and view all the answers

What type of spectrum is produced by Infrared Spectroscopy, and what is it plotted as?

<p>Infrared Spectroscopy produces absorption spectra, which are plotted as wavenumber (cm-1).</p> Signup and view all the answers

How does the infrared spectrum assist in the identification of functional groups within a molecule?

<p>It provides characteristic absorption peaks corresponding to specific functional groups.</p> Signup and view all the answers

What molecular concepts underlie the appearance of an IR spectrum?

<p>The appearance of an IR spectrum is due to the transitions of molecules between discrete vibrational energy levels.</p> Signup and view all the answers

Describe the nature of vibrational energy levels in molecules.

<p>Vibrational energy levels are set values that only assume certain discrete levels within electronic states.</p> Signup and view all the answers

What is one of the primary roles of Infrared Spectroscopy in the pharmaceutical industry?

<p>To perform qualitative fingerprint checks for the identity of raw materials.</p> Signup and view all the answers

In terms of sample states, what types of samples can Infrared Spectroscopy analyze?

<p>Infrared Spectroscopy can analyze samples in solid and semi-solid states, such as creams and tablets.</p> Signup and view all the answers

What is the frequency range associated with the fingerprint region in an IR spectrum?

<p>The fingerprint region is typically between 1500 and 400 cm-1.</p> Signup and view all the answers

Which bond requires the least amount of energy to stretch, as indicated by the provided bond strength data?

<p>The C-H bond requires the least energy to stretch.</p> Signup and view all the answers

In IR spectroscopy, what happens when a molecule has a symmetrical structure?

<p>Symmetrical molecules generally do not absorb IR radiation effectively.</p> Signup and view all the answers

What is the significance of the British Pharmocopoeia (BP) in IR spectroscopy for pharmaceuticals?

<p>The BP provides standard IR spectra of compounds for comparison to ensure drug authenticity.</p> Signup and view all the answers

How do solvent residues affect the interpretation of an IR spectrum concerning purity?

<p>Solvent residues can introduce additional absorption peaks not found in a pure compound.</p> Signup and view all the answers

What role does the group frequency region (4000 – 1500 cm-1) play in IR spectroscopy?

<p>This region is associated with stretching vibrations of diatomic units.</p> Signup and view all the answers

Why is it challenging to assign all absorption bands in the fingerprint region?

<p>The complexity and unique patterns in this region make precise assignments difficult.</p> Signup and view all the answers

What method is typically used to prepare solid samples for IR spectroscopy?

<p>Solid samples are often ground to a paste and mixed with a mulling agent like nujol.</p> Signup and view all the answers

What can be inferred about the strength of an O-H bond based on its bond energy compared to C-H and N-H?

<p>The O-H bond is stronger than both N-H and C-H bonds.</p> Signup and view all the answers

What is required for a molecule to exhibit IR absorption?

<p>A molecule must have a changing dipole moment during vibration.</p> Signup and view all the answers

Flashcards

IR spectroscopy

A technique that analyzes the vibrational energy of bonds in molecules using infrared light.

Group frequency region

The region in an IR spectrum (4000-1500 cm⁻¹) where stretching vibrations of diatomic units are usually found.

Fingerprint region

The region in an IR spectrum (1500-400 cm⁻¹) characterized by complex patterns of absorption bands, used for confirming structures.

Bond stretching

A vibrational mode of molecules where atoms vibrate along the bond axis, giving characteristic absorptions in IR spectra.

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Bond strength (kJ/mol)

The amount of energy required to break a chemical bond.

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IR frequency

The frequency of infrared light absorbed by a bond, related to the bond strength.

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Sample preparation (liquids)

Techniques for preparing liquid samples for IR analysis, such as spreading a drop between IR plates.

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Sample preparation (solids)

Methods for preparing solid samples for IR analysis, including grinding, mulling, and KBr pellet techniques.

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British Pharmacopoeia (BP)

Standard reference for drug identification and analysis, using IR spectra.

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IR Analysis (impurities)

Using IR spectroscopy to detect and quantify impurities in a sample by observing differing absorption bands.

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Infrared Spectroscopy

A technique that analyzes the absorption of infrared radiation by molecules to identify functional groups and bonds.

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Vibrational Transitions

Changes in the vibrational energy levels of molecules, caused by absorption of infrared radiation.

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IR Spectrum

A plot of the amount of infrared radiation absorbed by a molecule versus wavenumber(cm-1).

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Wavenumber (cm-1)

A measurement of the frequency of infrared radiation, equivalent to the reciprocal of wavelength.

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Functional Groups

Specific groups of atoms within a molecule that determine its chemical properties and reactions.

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Electronic Transition

Changes in the electronic energy levels of molecules, as seen by UV-Vis spectroscopy.

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UV-Visible Spectroscopy

Technique analyzing electronic transitions within molecules using specific electromagnetic spectrum.

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Sample Preparation

Methods needed to put a sample in a form suitable for analysis by IR spectroscopy, including solids, semi-solids, etc

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IR radiation vs. UV

Infrared (IR) radiation has lower energy compared to ultraviolet (UV) radiation.

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Vibrational Modes

Molecules can vibrate in different ways, including stretching and bending of bonds. Each vibration corresponds to a specific energy level.

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Symmetrical vs. Asymmetrical Stretching

Symmetrical stretching involves equal movement of atoms on both sides of a bond. Asymmetrical stretching has unequal movement.

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Polarisability and IR Absorption

For a molecule to absorb IR radiation, it needs to be 'polarisable' - meaning the electron distribution can change during vibration.

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Infrared Spectrum

A graph plotting absorbance against frequency (or wavelength) of IR radiation. Each peak corresponds to a specific vibration.

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Complicated Compounds and IR

Complex molecules have many different vibrational modes, leading to multiple peaks in the IR spectrum.

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Anti-symmetric Stretching and IR Absorption

Only asymmetric stretching vibrations absorb IR radiation because they create a changing dipole moment.

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Identifying Molecules with IR Spectroscopy

By analyzing the peaks in an IR spectrum, we can identify the functional groups and structure of a molecule.

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What's UV-Vis spectroscopy used for?

UV-Vis spectroscopy studies how molecules absorb UV and visible light, causing electrons to jump to higher energy levels. This helps determine the structure and properties of molecules.

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IR spectroscopy: where does the energy go?

IR spectroscopy analyzes how molecules absorb infrared radiation, causing their bonds to vibrate. This helps identify functional groups and determine the molecule's structure.

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What makes a molecule IR active?

A molecule is IR active if its vibrations create a changing dipole moment. This means the charge distribution within the molecule changes during vibration.

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Two types of IR vibrations

Molecules can vibrate in two main ways: stretching, where the bond length changes, and bending, where the bond angle changes.

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What's the fingerprint region in IR spectroscopy?

The fingerprint region (1500-400 cm⁻¹) in an IR spectrum shows complex patterns of absorption bands unique to each molecule. It's like a fingerprint for identifying specific compounds.

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Why is IR spectroscopy important in pharmaceuticals?

IR spectroscopy is used to identify raw materials, confirm product purity, and identify functional groups in drug molecules, ensuring quality control and patient safety.

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What are some ways to prepare samples for IR analysis?

Samples can be prepared as liquids, solids, or pastes. Liquid samples can be placed between salt plates. Solids can be ground and mixed with KBr to make a pellet.

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How does IR spectroscopy reveal structure?

Different types of bonds absorb IR radiation at specific frequencies. By analyzing the peak positions in an IR spectrum, we can identify the functional groups present in a molecule and deduce its structure.

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IR radiation energy

Infrared (IR) radiation has lower energy compared to ultraviolet (UV) radiation. It causes molecular vibrations rather than electronic transitions.

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Stretching Vibrations

The vibration where atoms move along the bond axis, either symmetrically or asymmetrically.

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Bending Vibrations

The vibration where the bond angle changes, causing the molecule to bend or twist.

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Polarisability

The ability of a molecule's electron distribution to change during vibration.

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IR Absorption

For a molecule to absorb IR radiation, it must be polarisable, meaning its electron distribution changes during vibration.

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Complex Molecules and IR

Complicated molecules have many different possible vibrations, leading to numerous peaks in the IR spectrum.

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What affects IR absorption frequency?

The frequency of infrared light absorbed by a molecule is influenced by the mass of the atoms and the strength of the bond.

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How does mass affect IR frequency?

Lighter atoms vibrate at higher frequencies, resulting in a higher absorption frequency in the IR spectrum.

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How does bond strength affect IR frequency?

Stronger bonds vibrate at higher frequencies, leading to higher absorption frequencies in the IR spectrum.

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What are group frequencies?

Characteristic absorption frequencies in an IR spectrum associated with specific functional groups in a molecule.

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What are correlation charts?

Tables that list group frequencies for different functional groups, helping to interpret IR spectra and identify unknown compounds.

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Stronger Bond, Higher Frequency

Stronger bonds require more energy to stretch, resulting in absorption at higher frequencies in the IR spectrum.

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IR Spectra for Purity

IR spectra can show the presence of impurities in a compound by revealing additional absorption bands not present in a pure sample.

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IR Spectroscopy: Different Samples

IR spectroscopy is versatile and can analyze various forms of samples, including solids, liquids, and gases.

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UV and IR Energy Differences

UV-Vis spectroscopy analyzes electronic energy transitions, while IR spectroscopy studies vibrational energy changes – UV has higher energy than IR.

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Study Notes

Introduction to Organic Spectroscopy

  •  Organic spectroscopy is an introduction to pharmaceutical chemistry
  •  The lecture discusses UV-VIS and Infrared (IR) Spectroscopy.
  •  UV-VIS spectroscopy involves electromagnetic radiation between 180-780 nm interacting with molecules.
  •  Absorption of energy causes excitation of an electron to a higher energy level.
  •  IR spectroscopy uses lower energy electromagnetic radiation for vibrational and rotational transitions within molecules.
  •  IR radiation involves stretching and bending of bonds in the molecule.

Infrared Spectroscopy

  •  IR spectra are absorption spectra
  •  IR radiation has enough energy to stretch or bend bonds in molecules.
  •  The spectrum is plotted as wavenumber (cm⁻¹).
  •  IR radiation is lower energy than UV radiation.
  •  For a bond to absorb IR radiation, the bond must be polarizable.
  •  Asymmetrical vibrations are the ones that absorb IR.
  •  Symmetrical molecules don't absorb IR unless asymmetric stretching/bending is possible

Vibrational Modes

  •  Symmetrical stretch
  •  Asymmetrical stretch
  •  Bend
  •  These modes create different frequencies of radiation absorption in the IR spectrum.
  •  Complicated compounds have more than one way to vibrate, resulting in multiple absorption bands.

Regions of the IR Spectrum

  •  The intensity of light absorption changes in different parts of the region
  •  Higher frequency regions for a shorter wavelength are associated with bonds to hydrogen atoms.
  •  Lower frequency regions for a longer wavelength are associated with heavier atoms/bonds

Group Frequencies

  •  Absorption frequency depends on the mass (heavy or light atoms) and bond strength of bonded atoms in the regions.
  •  Tables or databases of group frequencies can aid in determining functional groups within molecules.
  •  One absorption band can appear at the same frequency for many different molecules.

Applications of Infrared Spectroscopy in Pharmaceuticals

  •  Qualitative tests for drugs and materials used in drug manufacturing.
  •  Identification of functional groups in molecules.
  •  Analysis of solid and semi-solid pharmaceutical forms, e.g., creams and tablets.

Sample Preparation Methods for IR Spectroscopy

  •  Liquid films: spreading a drop of liquid between IR plates
  •  Solutions: using suitable solvents and background correction with a blank solvent
  •  Solids: ground solids to a paste with a mulling agent (e.g., mineral oil) or with KBr in a mortar

British Pharmacopoeia (BP) Standards for IR Spectroscopy

  •  BP uses IR spectra of standard compounds to verify the identity of the drug.
  •  The IR spectrum of an unknown drug must exactly match the spectrum of a standard compound
  •  All peaks and intensities in the spectra should match exactly.
  •  Functional groups at specific frequencies can aid in determining purity.

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