CHE 202 1nd Edition Lecture 4 Outline of Last Lecture I Resonance Review II Introduction to Mass Spectrometry a Overview b Fragment Patterns c Alcohol MS III Example Compound Outline of Current Lecture I Introduction to Nuclear Magnetic Resonance a Spin States II Magnetic Shielding III NMR Spectra a Analyzing Steps b Chemical Shift Current Lecture Introduction to Nuclear Magnetic Resonance Method of Spectroscopy used for determination of the structure of unknown organic compounds Analyzes the properties of nuclei o Atomic Numbers o Mass o Charges Nuclear Spin Nuclei with odd numbered atomic masses have a spin Nuclear Spin s generate Magnetic field Magnetic moment External Magnetic Field 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 Bo External Magnetic Field o Applies force used for realignment o Combination of Magnetic fields can flip the nuclear spin this absorption of energy is what the NMR records Alpha Spin o Proton aligned with magnetic field o Lower energy state Beta Spin o Proton out of alignment with magnetic field o Higher energy state Magnet Strength Changes in Energy The change in energy is related to the strength of the magnet g Gyromagnetic ration a constant per nucleus 26 753 sec 1gauss 1 for Hydrogen DE hn g h B0 2p 60MHz photon needed to flip a proton in a 14 092 gauss field Magnetic Shielding Electrons shield protect protons from the Bo external magnetic field Protons near electronegative atoms will have less shielding due to the uneven sharing of electrons Electrons create own partial induced magnetic field in a circular current o A proton with no electrons naked proton absorb at 70 459 gauss o Shielded proton absorbs at less than 70 459 gauss NMR Spectra Analyzing NMR Spectra multiple factors to consider I II III IV Numbers of peaks signals a Shows number of different types of protons Location PPM of signals a Shows amount of shielding on a proton Intensity of signals a Number of protons of each type by integration Splitting of signals a Two or more peaks connected indicate protons on adjacent nearby atoms on the same molecule Tetramethylsilane Abbreviated TMS Si surrounded with four CH3 s Used as a control standard Highly shielded Defined as 0 00ppm 0 on the spectra Chemical Shif Different positions in the NMR absorptions o Chemical Shif in ppm Shift downfield from TMS in Hz Total spectrometer frequency in MHz Uses the delta scale Table 13 3 Typical Values of Chemical Shifs will be provided for exams