The NMR Spectrometer mpi magnet RF transmitter tector recorder absorption magnet B controller magnetic field Chapter 13
Chapter 13 11 The NMR Spectrometer =>
The NMR Graph ia H H-O—C—H H less shielded more shielded lower field(downfield) higher field(upfield) increasing magnetic field strength( Bo) Chapter 13 12
Chapter 13 12 The NMR Graph =>
CH3 HaC-Si-CHa Tetramethylsilane CH3 TMS is added to the sample Since silicon is less electronegative than carbon, TMs protons are highly shielded. Signal defined as zero Organic protons absorb downfield (to the left)of the TMs signal > Chapter 13 13
Chapter 13 13 Tetramethylsilane • TMS is added to the sample. • Since silicon is less electronegative than carbon, TMS protons are highly shielded. Signal defined as zero. • Organic protons absorb downfield (to the left) of the TMS signal. => Si CH3 CH3 CH3 H3C
Chemical shift Measured in parts per million Ratio of shift downfield from TMS(Hz) to total spectrometer frequency(Hz) Same value for 60. 100 or 300 Mhz machine · Called the delta scale > Chapter 13
Chapter 13 14 Chemical Shift • Measured in parts per million. • Ratio of shift downfield from TMS (Hz) to total spectrometer frequency (Hz). • Same value for 60, 100, or 300 MHz machine. • Called the delta scale. =>
Delta scale shift downfield from TMs (in Hz) chemical shift, ppm o spectrometer frequency (in MHz) 600 Hz 480 Hz 360 Hz 240 Hz 120 Hz O HZ 109876543210 ppm s TMS 60 MHZ 3000Hz2400Hz1800Hz1200Hz600Hz0Hz 109876543210 ppm s TMS 300 MHZ
Chapter 13 15 Delta Scale =>