Podcast
Questions and Answers
What does the energy of a photon relate to according to the equation E = hn?
What does the energy of a photon relate to according to the equation E = hn?
- The mass of the photon
- The frequency of the photon (correct)
- The wavelength of light
- The speed of light
What is the value of Planck's constant, which is represented by 'h' in the energy-frequency relationship?
What is the value of Planck's constant, which is represented by 'h' in the energy-frequency relationship?
- 3.00 x 10^8 J s
- 1.60 x 10^-19 J s
- 9.11 x 10^-31 J s
- 6.626 x 10^-34 J s (correct)
Which type of molecules are primarily absorbed in UV-Vis spectroscopy?
Which type of molecules are primarily absorbed in UV-Vis spectroscopy?
- Aliphatic hydrocarbons
- Ionic compounds
- Metallic compounds
- Aromatic compounds (correct)
How is the relationship between wavelength (λ) and frequency (n) best described?
How is the relationship between wavelength (λ) and frequency (n) best described?
What aspect does the spectral output of light sources affect in Spectroscopy?
What aspect does the spectral output of light sources affect in Spectroscopy?
Which type of bonds are essential for producing an absorption spectrum?
Which type of bonds are essential for producing an absorption spectrum?
What equation relates energy, frequency, and Planck's constant?
What equation relates energy, frequency, and Planck's constant?
In the UV/Vis absorption spectrum, which aspect is primarily used for drug analysis?
In the UV/Vis absorption spectrum, which aspect is primarily used for drug analysis?
The relationship between wavelength and frequency can be calculated using which equation?
The relationship between wavelength and frequency can be calculated using which equation?
What role do chromophores play in UV/Vis spectroscopy?
What role do chromophores play in UV/Vis spectroscopy?
Which property can be monitored using UV/Vis spectroscopy in pharmaceutical formulations?
Which property can be monitored using UV/Vis spectroscopy in pharmaceutical formulations?
What does the equation E = hc/λ imply about the energy of photons?
What does the equation E = hc/λ imply about the energy of photons?
Which of the following can be determined using UV/Vis spectroscopy for a drug?
Which of the following can be determined using UV/Vis spectroscopy for a drug?
How is the energy of electromagnetic radiation related to its frequency?
How is the energy of electromagnetic radiation related to its frequency?
What is the equation used to calculate the velocity of light?
What is the equation used to calculate the velocity of light?
Which statement correctly describes monochromatic radiation?
Which statement correctly describes monochromatic radiation?
How does the energy of photons in the UV region compare to those in the infrared region?
How does the energy of photons in the UV region compare to those in the infrared region?
What is the purpose of using wavenumber in infrared spectroscopy?
What is the purpose of using wavenumber in infrared spectroscopy?
What is the peak output wavelength range of sunlight?
What is the peak output wavelength range of sunlight?
Using Planck’s constant, how is energy calculated for electromagnetic radiation?
Using Planck’s constant, how is energy calculated for electromagnetic radiation?
What does the speed of light in a vacuum represent in terms of its wavelength and frequency?
What does the speed of light in a vacuum represent in terms of its wavelength and frequency?
What is the definition of a chromophore and its role in absorption?
What is the definition of a chromophore and its role in absorption?
How does extended conjugation in chromophores affect their absorption wavelength?
How does extended conjugation in chromophores affect their absorption wavelength?
In what range of the spectrum do compounds with long chromophores typically absorb, and what is the significance of this?
In what range of the spectrum do compounds with long chromophores typically absorb, and what is the significance of this?
Why do only molecules with conjugated π bonds absorb in the UV spectrum?
Why do only molecules with conjugated π bonds absorb in the UV spectrum?
What relationship exists between the structure of a chromophore and its absorption characteristics?
What relationship exists between the structure of a chromophore and its absorption characteristics?
Explain the significance of electromagnetic radiation's dual wave-particle nature in organic spectroscopy.
Explain the significance of electromagnetic radiation's dual wave-particle nature in organic spectroscopy.
Describe how conjugation affects the absorption properties of molecules in UV-Vis spectroscopy.
Describe how conjugation affects the absorption properties of molecules in UV-Vis spectroscopy.
Discuss the role of Planck's constant in the context of electromagnetic radiation energy calculations.
Discuss the role of Planck's constant in the context of electromagnetic radiation energy calculations.
What is the importance of understanding the electromagnetic spectrum when studying organic compounds?
What is the importance of understanding the electromagnetic spectrum when studying organic compounds?
How do the vectors of electric and magnetic fields in electromagnetic radiation relate to spectroscopy?
How do the vectors of electric and magnetic fields in electromagnetic radiation relate to spectroscopy?
How do you calculate the frequency of light given its wavelength?
How do you calculate the frequency of light given its wavelength?
What is the energy of a photon that has a frequency of 5.71 x 10^14 Hz?
What is the energy of a photon that has a frequency of 5.71 x 10^14 Hz?
Explain the significance of wavenumber in spectroscopy.
Explain the significance of wavenumber in spectroscopy.
What defines monochromatic radiation and how does it differ from polychromatic radiation?
What defines monochromatic radiation and how does it differ from polychromatic radiation?
Describe how the energy of ultraviolet photons compares to that of infrared photons.
Describe how the energy of ultraviolet photons compares to that of infrared photons.
What is the speed of light in a vacuum and how is it relevant to calculations involving wavelength and frequency?
What is the speed of light in a vacuum and how is it relevant to calculations involving wavelength and frequency?
What characteristics of sunlight make it a continuum source in the electromagnetic spectrum?
What characteristics of sunlight make it a continuum source in the electromagnetic spectrum?
How does the intensity of a beam relate to the energy of monochromatic radiation?
How does the intensity of a beam relate to the energy of monochromatic radiation?
What is indicated if peaks are recorded in an absorption spectrum?
What is indicated if peaks are recorded in an absorption spectrum?
In UV/Vis spectroscopy, what types of electronic features in a molecule are primarily responsible for absorption?
In UV/Vis spectroscopy, what types of electronic features in a molecule are primarily responsible for absorption?
How can UV/Vis spectroscopy aid in the quantitative analysis of drugs?
How can UV/Vis spectroscopy aid in the quantitative analysis of drugs?
What relationship can be derived from the equation E = hc/λ in terms of light absorption?
What relationship can be derived from the equation E = hc/λ in terms of light absorption?
What can UV/Vis spectroscopy reveal about the solubility and partition coefficients of drugs?
What can UV/Vis spectroscopy reveal about the solubility and partition coefficients of drugs?
Why is UV/Vis absorption significant in the monitoring of drug release from formulations?
Why is UV/Vis absorption significant in the monitoring of drug release from formulations?
What does the electromagnetic spectrum encompass in relation to UV/Vis spectroscopy?
What does the electromagnetic spectrum encompass in relation to UV/Vis spectroscopy?
What type of analysis can the UV spectrum be utilized for in drug formulation development?
What type of analysis can the UV spectrum be utilized for in drug formulation development?
What is the ground state of a molecule in the context of UV-Vis spectroscopy?
What is the ground state of a molecule in the context of UV-Vis spectroscopy?
Explain the significance of the λmax in absorption spectroscopy.
Explain the significance of the λmax in absorption spectroscopy.
What transitions are represented by n → π* and π → π* in UV-Vis spectroscopy?
What transitions are represented by n → π* and π → π* in UV-Vis spectroscopy?
What effect does conjugation have on the energy levels of HOMO and LUMO?
What effect does conjugation have on the energy levels of HOMO and LUMO?
Why are absorption bands below 210 nm typically not detected in UV-Vis spectroscopy?
Why are absorption bands below 210 nm typically not detected in UV-Vis spectroscopy?
How does the excitation of electrons occur in a molecule when exposed to UV-Vis light?
How does the excitation of electrons occur in a molecule when exposed to UV-Vis light?
Contrast the energy required for n → π* transitions with that for π → π* transitions.
Contrast the energy required for n → π* transitions with that for π → π* transitions.
What would be the expected λmax values for acetone compared to methyl vinyl ketone in UV-Vis spectroscopy?
What would be the expected λmax values for acetone compared to methyl vinyl ketone in UV-Vis spectroscopy?
Flashcards
Electromagnetic Wavelengths
Electromagnetic Wavelengths
The range of wavelengths of light, from radio waves to gamma rays.
Wave Equation (c = λν)
Wave Equation (c = λν)
The speed of light (c) equals the wavelength (λ) times the frequency (ν).
Frequency (ν)
Frequency (ν)
Number of waves that pass a point per second (Hz).
Wavelength (λ)
Wavelength (λ)
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Energy of Photon (E)
Energy of Photon (E)
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Electromagnetic Spectrum
Electromagnetic Spectrum
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Speed of Light (c)
Speed of Light (c)
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Wavenumber (σ)
Wavenumber (σ)
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Electromagnetic radiation
Electromagnetic radiation
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Photon
Photon
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Energy (E) and Frequency (n)
Energy (E) and Frequency (n)
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UV/Vis absorption spectrum
UV/Vis absorption spectrum
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Chromophore
Chromophore
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UV/Vis spectroscopy
UV/Vis spectroscopy
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Drug analysis
Drug analysis
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Wavelength
Wavelength
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Energy level transition
Energy level transition
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Conjugated systems
Conjugated systems
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The Wave Equation
The Wave Equation
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Monochromatic
Monochromatic
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Conjugated π bonds
Conjugated π bonds
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λmax
λmax
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Why do longer conjugated systems absorb at longer wavelengths?
Why do longer conjugated systems absorb at longer wavelengths?
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What makes a molecule colored?
What makes a molecule colored?
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Electronic Transitions
Electronic Transitions
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Ground State
Ground State
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Excited State
Excited State
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LUMO
LUMO
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n → π* Transition
n → π* Transition
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π → π* Transition
π → π* Transition
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UV/Vis Spectrometer
UV/Vis Spectrometer
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Absorbance Spectrum
Absorbance Spectrum
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Quantitative Drug Analysis
Quantitative Drug Analysis
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Drug Formulation
Drug Formulation
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pKa
pKa
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Dissolution Testing
Dissolution Testing
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What's the relationship between Energy (E) and Frequency (n)?
What's the relationship between Energy (E) and Frequency (n)?
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Study Notes
Introduction to Pharmaceutical Chemistry Organic Spectroscopy
- The subject matter is Pharmaceutical Chemistry, specifically Organic Spectroscopy.
- A graph displays absorbance/transmittance data against wavelength (nm) and wavenumber (cm⁻¹).
- Dr. Lynda Storey, N548 RSE, [email protected], is teaching the course.
Areas Covered
- Electromagnetic spectrum
- Ultraviolet and Visible Spectroscopy
- Infrared Spectroscopy
Learning Objectives
- Understand the origin of electromagnetic radiation
- Relate energy, frequency, and wavelength of electromagnetic radiation.
- Understand the types of molecules that absorb in UV-Vis spectroscopy.
- Understand the concepts of conjugation and chromophores.
- Explain how UV spectroscopy can indicate the presence of various structural features within molecules.
The Electromagnetic Spectrum
- Organic spectroscopy examines the interactions between molecular components and the electromagnetic spectrum.
- These interactions provide crucial insights into molecular structure.
- The spectrum encompasses a wide range of energy levels, including gamma rays, X-rays, ultraviolet, visible, infrared, radio waves, etc.
- Increasing energy corresponds to decreasing wavelength.
The Electromagnetic Spectrum (continued)
- The energy (E) of a photon is directly proportional to its frequency (ν) and inversely proportional to its wavelength (λ): E = hν = hc/λ.
- Frequency (ν) is measured in Hertz (Hz) or wavenumber (cm⁻¹).
- Wavelength (λ) is measured in meters (m) or nanometers (nm).
- Planck's constant (h) is 6.626 x 10⁻³⁴ J s.
- Electromagnetic radiation has both wave and particle properties.
Electromagnetic Spectrum (Continued)
- Electromagnetic radiation consists of waves with two perpendicular vectors (electric and magnetic).
- Wavelength is the distance between equivalent points on successive waves.
- Frequency is the number of wave cycles per second.
Electromagnetic Spectrum (Continued)
- Velocity (c) of light in a vacuum is 2.998 x 10⁸ m/s.
- The velocity of light (c) is the product of wavelength (λ) and frequency (ν): c = λν
Example Calculations
- The frequency (ν) of a 525 nm light wavelength is 5.71 x 10¹⁴ s⁻¹.
- The energy (E) of a 525 nm light wavelength is 3.78 x 10⁻¹⁹ J.
The Electromagnetic Spectrum of Light Sources
- Most light sources emit polychromatic light, containing multiple wavelengths.
- Sunlight spans a broad range of wavelengths. The peak irradiance is in the visible region (800-400 nm).
Spectral Output of the Sun
- A graph displays the relative spectral irradiance of the sun over a wide range of wavelengths.
Strength of Radiation
- The energy of monochromatic radiation depends on its frequency or wavelength; it is independent of its beam intensity.
- Photons in the UV region have higher energy than photons in the IR region. Higher energy photons equate to stronger radiation.
The Electromagnetic Spectrum (Size)
- The size of electromagnetic wavelengths range from extremely short (gamma rays, x-rays) to extremely long (radio waves).
- The example sizes of wavelengths for different categories of objects: atoms, molecules, bacteria, pinpoints, houseflies, humans, and mountains.
Ultraviolet (UV) and Visible (VIS) Spectroscopy
- UV-Vis spectroscopy investigates how molecules with conjugated double bonds absorb light in the UV (180-400 nm) and visible (400-780 nm) regions.
- Absorbed light causes electronic transitions within the molecule.
- A molecule’s ground state corresponds to its normal electronic configuration. In this state, electrons occupy orbitals having the lowest energy levels.
- Absorption of energy causes electronic transitions from ground state to excited states.
Ultraviolet (UV) and Visible (VIS) Spectroscopy (continued)
- n → π* transitions involve the promotion of a lone pair (n) electron to a higher antibonding orbital (π*).
- π →π* transitions involve promotion of a pi bonding electron to a pi antibonding orbital.
Example Calculations
- Acetone absorbs distinctly at 195 nm and 274 nm due to different electronic transitions and presence of n and π electrons in the molecules
- If a compound contains conjugated n bonds, then the absorption spectrum will be observed in the UV region of the spectrum.
- The spectrophotometer can be adapted to remove Oxygen from the sample chamber using Nitrogen gas so that the absorption spectrum of the compound can be clearly observed in a range below 210 nm in some cases.
Chromophores
- Chromophores are molecular components responsible for UV-Vis absorption features.
- The carbonyl (C=O) group acts as a chromophore in acetone.
- Conjugated π bonds (an alternating system of double bonds) determine the wavelength and position of absorption.
Chromophores (continued)
- Conjugated π systems absorb light at longer wavelengths than isolated π bonds. The stronger/ longer the π system, the longer the wavelength absorbed.
- Examples of chromophores include conjugated carbonyl compounds, aromatics, and systems with multiple conjugated double bonds (polyenes).
Visible Absorption
- Compounds with many conjugated π bonds absorb light in the visible region and hence are coloured.
- A typical example is β-carotene (orange).
Absorption of Light by Dyes
- A series of graphs showcase the absorption spectra of various dyes, encompassing the visible range.
- Each dye demonstrates distinctive absorption peaks, providing a signature for identification.
UV Spectroscopy
- To record a UV spectrum the sample needs to be dissolved in a suitable solvent and then scanned across a range of required wavelengths.
- The UV absorption peaks indicate the presence of chromophores within the molecule. By scanning across the different wavelengths we can identify specific substances and their different absorbances.
- Information regarding the chromophores present, which are responsible for absorption, is deduced, though not the exact structure/ arrangement thereof. Further analyses are required to determine this.
Quantitative Analysis of Drugs
- UV-Vis spectroscopy is crucial for drug analysis. Its applications include quantifying drugs in different formulations (e.g., without interfering excipients), determining pK values, partition coefficients, solubilities, releasing kinetics, and measuring degradation rates.
Summary
- Covered the electromagnetic spectrum, its different wavelengths, and the relationship between energy, frequency, and wavelength (E = hν = hc/λ).
- Explained that only chromophores containing conjugated π systems, double bonds, and lone pairs, absorb in the UV/Vis region.
Points to Consider
- Identify the bond types necessary for absorption spectra.
- Determine the types of bonds responsible for longer wavelengths in absorption.
- Understand the connection between energy, wavelength, frequency, and the electromagnetic spectrum.
- Apply frequency and wavelength relationships in quantitative calculations.
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