Orgo 6a - 6a 13C-NMR and IR Spectroscopies(388-409 417-423...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
6a. 13C-NMR and IR Spectroscopies (388-409, 417-423, 433-437) Infrared Spectroscopy What Is EM Radiation? - Gamma rays, Xrays, ultraviolet light, visible light, infrared radiation, microwaves, and radio waves are all part of the EM spectrum. EM radiation behaves as a wave travelling at the speed of light, therefore is described in terms of its wavelength and frequency. Wavelength( λ ) is the distance between any two consecutive identical points of the wave. The frequency ( ν ) of a wave is the number of full cycles of the wave that pass a given point in a second. Wavelength and frequency are inversely proportional. νλ = c which is the velocity of light (3.00 x 10^8 m/s). An alternative way to describe electromagnetic radiation is in terms of its properties as a stream of particles called photons. The energy in a mole of photons and the frequency of radiation are related by E= h ν = h c/ λ where E is energy in kJ/mol and h is Plancks constant 3.99 x 10 -13 kJs/mol. High energy radiation corresponds to short wavelengths and vice versa. Ultraviolet light (high energy) has a shorter wavelength than infrared radiation (lower energy). What Is Molecular Spectroscopy - Organic molecules are flexible structures. All energy changes within a molecule are quantized. We can cause an atom or molecule to undergo a transition from a lower energy state to a higher energy state by irradiating it with EM radiation corresponding to the energy difference between the two levels. When the atom or molecule returns to the ground state an equivalent amount of energy is emitted. Molecular spectroscopy is the experimental process of measuring which frequencies of radiation a substance absorbs or emits and then correlating those frequencies with specific types of molecular structures. In infrared spectroscopy we irradiate a compound with infrared radiation, the absorption of which causes covalent bonds to change from a lower vibrational energy level to a higher one. Because different functional groups have different bond strengths, the energy required to bring about these transitions will vary from one functional group to another, therefore in IR spectroscopy we detect functional groups by the vibrations of their bonds. What Is Infrared Spectroscopy - The IR region of the EM spectrum covers the range from jus above the visible region to just below the microwave region. In organic chemistry we use only the middle portion of this range called the vibrational infrared region, we refer to radiation in this region by its wavenumber. The vibrational region of the IR spectrum extends from 4000 to 400cm -1 . Wavenumbers are directly proportional to energy. Atoms joined by covalent bonds are not permanently fixed in one position, but instead undergo continual vibrations relative to each other. Transitions can be induced by the absorption of radiation in the IR region of the EM spectrum. For a molecule to absorb IR radiation, the bond undergoing vibration must be polar, and its vibration must cause a periodic change in the bond dipole; the greater
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/09/2012 for the course SCIENCE 2213 taught by Professor Lee during the Spring '11 term at UWO.

Page1 / 4

Orgo 6a - 6a 13C-NMR and IR Spectroscopies(388-409 417-423...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online