ch09 - Chapter 9 Nuclear Magnetic Resonance and Mass...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 9 Nuclear Magnetic Resonance and Mass Spectrometry: Tools for Structure Determination
Background image of page 1

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

View Full DocumentRight Arrow Icon
Chapter 9 2 Introduction Spectroscopy: the study of the interaction of energy with matter Energy applied to matter can be absorbed, emitted, cause a chemical change, or be transmitted Spectroscopy can be used to elucidate the structure of a molecule Examples of Spectroscopy Infrared (IR) Spectroscopy (Chapter 2) Infrared energy causes bonds to stretch and bend IR is useful for identifying functional groups in a molecule Nuclear Magnetic Resonance (NMR) Energy applied in the presence of a strong magnetic field causes absorption by the nuclei of some elements (most importantly, hydrogen and carbon nuclei) NMR is used to identify connectivity of atoms in a molecule Mass Spectrometry (MS) Molecules are converted to ions by one of several methods (including bombardment by a beam of electrons) The ions formed may remain intact (as molecular ions, M+), or they may fragment The resulting mixture of ions is sorted by mass/charge ( m/z ) ratio, and detected Molecular weight and chemical formula may be derived from the M+ and M+1 ions Molecular structure may be deduced from the distribution of fragment ions
Background image of page 2
Chapter 9 3 The Electromagnetic Spectrum Electromagnetic radiation has the characteristics of both waves and particles The wave nature of electromagnetic radiation is described by wavelength (λ29 or frequency (ν 29 The relationship between wavelength (or frequency) and energy (E) is well defined Wavelength and frequency are inversely proportional = c/ λ29 The higher the frequency, the greater the energy of the wave The shorter the wavelength, the greater the energy of the wave
Background image of page 3

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

View Full DocumentRight Arrow Icon
Chapter 9 4 NMR involves absorption of energy in the radiofrequency range
Background image of page 4
Chapter 9 5 Nuclear Magnetic Resonance (NMR) Spectroscopy The nuclei of protons ( 1 H) and carbon-13 ( 13 C), and certain other elements and isotopes, behave as if they were tiny bar magnets When placed in a magnetic field and irradiated with radio frequency energy, these nuclei absorb energy at frequencies based on their chemical environments NMR spectrometers are used to measure these absorptions Continuous-Wave (CW) NMR Spectrometers The oldest type of NMR spectrometer The magnetic field is varied as the electromagnetic radiation is kept at a constant frequency Different nuclei absorb the electromagnetic energy based on their chemical environment and produce peaks in different regions of the spectrum
Background image of page 5

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

View Full DocumentRight Arrow Icon
Chapter 9 6 Fourier Transform (FT) NMR Spectrometers The sample is placed in a constant (and usually very strong) magnetic field The sample is irradiated with a short pulse of radio frequency energy that excites nuclei in different environments all at once The resulting signal contains information about all of the absorbing nuclei at once This signal is converted to a spectrum by a Fourier transformation
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/14/2011 for the course CHEM 20A3 taught by Professor Brooke during the Spring '10 term at McMaster University.

Page1 / 47

ch09 - Chapter 9 Nuclear Magnetic Resonance and Mass...

This preview shows document pages 1 - 7. Sign up to view the full document.

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