IR Spectroscopy

Understanding Color and States of Matter

• Color is a property that can be observed at the microscale.
• Microscale is the realm of very small entities such as ions and individual molecules.

Limitations of Current Technology

• Current techniques are increasingly able to observe smaller structures but may never enable us to observe real-time chemical reactions or bond changes directly due to technological constraints.

Historical Context: Alexander Fleming and Penicillin

• Fleming's discovery of penicillin was catalyzed by a historical context where bacterial infections killed more soldiers in WWI than direct wounds.
• In 1928, Fleming worked in an unconditioned lab where bacteria cultures were left exposed while he was on vacation.
• Upon his return, he observed the accidental introduction of mold which inhibited bacterial growth, ultimately leading to the discovery of penicillin.
• Originally, large-scale production of penicillin required industrial facilities, necessitating the understanding of the mold's structure through spectroscopy.

Spectroscopy: Introduction and Importance

• Spectroscopy is crucial for analyzing chemical structures and is essential in organic chemistry, particularly for identifying functional groups.
• Five main techniques are used:
  • IR Spectroscopy (to be covered)
  • NMR Spectroscopy
  • Mass Spectrometry
  • UV Spectroscopy (less frequently used)

Microscopic Analogy: Horton Hears a Who!

• Horton symbolizes the ability to perceive things at the microscale, as he can hear the tiny 'Who's' that others cannot.
• This highlights the importance of having proper tools in science to detect phenomena that are otherwise invisible.

Overview of Spectroscopy Techniques and the Electromagnetic Spectrum

• Spectroscopy techniques relate to electromagnetic waves:
  • Electromagnetic waves travel at the speed of light, but have different wavelengths and frequencies.
  • Shorter wavelengths correspond to higher frequencies and higher energy.
• Implications of these energies:
  • High energy frequencies (e.g., X-rays) can cause cellular damage, necessitating protective measures like lead aprons during dental X-rays.
  • Ultraviolet (UV) light can damage skin, leading to the use of sunscreen.
  • Infrared radiation is associated with heat and molecular vibration.
  • Radio waves are low energy, and safety precautions are unnecessary.

Molecular Vibrations and Infrared Spectroscopy

• Different forms of electromagnetic radiation elicit distinct molecular changes:
  • Infrared radiation causes molecular vibrations—either stretching or bending of bonds.
  • Key to IR spectroscopy are vibrational modes: stretches (lengthening/shortening of bonds) and bends (angle changes).
• Introduction to Hooke's Law and vibrational frequency relationships:
  • The equation relating wavelength, frequency, and the speed of light is $ext{Wavelength} imes ext{Frequency} = c$ where $c = 3 imes 10^8 m/s$
  • Energy relationship: $E = h imes ext{Frequency}$ where $h = 6.626 imes 10^{-34} ext{J} ext{s}$ (Planck's constant).

IR Spectroscopy and Signal Interpretation