CHE 202 1nd Edition Lecture 1 Key Terms From Previous Semester I 1 primary carbon attached to one other carbon 2 secondary carbon attached to two other carbons 3 tertiary carbon attached to three other carbons methyl carbon with four hydrogens II Alkyl Groups groups chains of carbons III Resonance When electrons are shared among more than one bond may be represented by one drawing while resonance is implied IV Polarity Dipole Moments Polar molecules have charges associated with them and dipole moments occur when a molecule has a charge on one end Outline of Current Lecture II Overview of Spectroscopy III Review of Waves IV Electromagnetic Spectrum Waves A Infared Region B Molecular Vibrations Current Lecture Spectroscopy Helps to determine the structure of a compound Absorption spectroscopy A type of spectroscopy that measures the amount of light absorbed by a compound The different wavelengths of light from the electromagnetic spectrum reveal different properties and give different information about the compound Four Types of Spectroscopy These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute I II III IV Infared Spectroscopy uses infared light waves a Measures the vibrations in bonds b Shows functional groups in compound c Abbreviated IR Mass Spectrometry Used to determine molecular weight and information about the possible functional groups a Breaks the compound apart b Abbreviated MS Nuclear Magnetic Resonance Used to determine the chemical surroundings of a compound as well as information on alkyl groups a Covered in Chapter 13 b Abbreviated NMR Ultraviolet Spectroscopy Involves electron activity and determining bonding in a compound a Covered in Chapter 15 b Abbreviated UV Waves Electromagnetic Spectrum I The entire electromagnetic spectrum gamma rays X rays visible light microwaves radio waves is made up of waves Waves always travel at the speed of light 3x10 10 cm sec or 3000000000 cm sec II Waves are measured in frequencies and wavelengths III a Wavelength represented by the greek letter lambda measures the distance between the high points of the wave in centimeters b Frequency represented by the greek letter nu measures the number of wave cycles that pass a certain point in a second in Hertz The Math of Waves If given either of the above variables the other can be determined Frequency and wavelength are inversely proportional because a short wavelength would lead to more cycles passing by the fixed point in a second therefore increasing the frequency a c or with a little algebra c C speed of light frequency in hertz wavelength in centimeters b Electromagnetic Waves travel in photons whose energy can be measured with the equation E h hc h planks constant 6 62x10 37 kJxsec E photon energy c The electromagnetic spectrum runs from lower frequencies longer wavelengths to higher frequencies shorter wavelengths with radio waves on the lower end and gamma rays on the higher frequency end Infared Region I Wavelengths range from 2 5x10 4 cm to 25x10 4 cm mostly reported in reciprocal centimeters cm 1 II Infared photons cause parts of a compound to vibrate based on the bonds III Wave numbers can be determined by the two following equations cm 1 1 cm 10 000 m cm m or m 10 000 m cm cm 1 Molecular Vibrations I When the photons from the infared region are introduced to a compound the bonds react with different patterns of stretching and compressing specific to that type of bond II The recorded frequencies then show differences in atomic mass and bond energy a The higher the atomic mass the lower the frequency b The higher the bond energy the higher the frequency III A nonlinear molecule has a certain number of unknown atoms represented with n and therefore has an unknown number of vibrational patterns that can be found with the equation 3n 6 IV The vibration patterns or vibrational modes include V a Symmetric stretching such as extending both arms out equally b antisymmetric stretching such as extending your right hand out while retracting your left hand in c Scissoring such as extending and raising both arms out and above your head Electric Fields and Polar Bonds a VI Bonds with dipole moments are affected by electrical fields as the energy decreases the bonds compress as the energy increases the bonds stretch Reading IR spectrum graphs a Fingerprint Regions regions of the spectrum that include the most information about the molecule for IR the region is between 600 and 1400cm 1 while the most common occur between 1600 and 3500cm 1