Nuclear magnetic resonance spectroscopy презентация

Nuclear Magnetic Resonance Spectroscopy Student: Burlakov A.S. Group: fm-104 Supervisor: Chernov V.M.

SIMPLE PLAN ! THAT’S SO SIMPLE 1.Principles of molecular spectroscopy 2. Nuclear Shieldingand1H Chemical Shifts

Lets understand few things Electromagnetic Radiation – is propagated at the speed of light has properties of particles and waves the energy of a photon is proportional to its frequency

the Electromagnetic spectrum

1. Principles Electromagnetic radiation is absorbed when the energy of photon corresponds to difference in energy between two states.

What Kind of States?

The nuclei that are most useful to organic chemists are: 1H and 13C both have spin = ±1/2 1H is 99% at natural abundance 13C is 1.1% at natural abundance

Nuclear Spin

The distribution of nuclear spins is random in the absence of an external magnetic field.

An external magnetic field causes nuclear magnetic moments to align parallel and antiparallel to applied field.

Some important relationships in NMR The frequency of absorbed electromagnetic radiation is proportional to the energy difference between two nuclear spin states which is proportional to the applied magnetic field

Energy Differences Between Nuclear Spin States

The frequency of absorbed electromagnetic radiation for a particular nucleus (such as 1H) depends on its molecular environment. This is why NMR is such a useful tool for structure determination.

2. Nuclear Shielding What do we mean by "shielding?" What do we mean by "chemical shift?" An external magnetic field affects the motion of the electrons in a molecule, inducing a magnetic field within the molecule.

The induced field shields the nuclei (in this case, C and H) from the applied field. The induced field shields the nuclei (in this case, C and H) from the applied field. A stronger external field is needed in order for energy difference between spin states to match energy of rf radiation. Chemical shift is a measure of the degree to which a nucleus in a molecule is shielded. Protons in different environments are shielded to greater or lesser degrees; they have different chemical shifts.

Effects of Molecular Structure on 1H Chemical Shifts protons in different environments experience different degrees of shielding and have different chemical shifts CHCl3 d 7.3 ppm CH2Cl2 d 5.3 ppm CH3Cl d 3.1 ppm CH3F d 4.3 ppm least shielded H CH3OCH3 d 3.2 ppm CH3N(CH3)2 d 2.2 ppm CH3CH3 d 0.9 ppm CH3Si(CH3)3 d 0.0 ppm most shielded H

Conclusion A spinning charge can make us understand the structure of matter An external magnetic field affects the motion of the electrons in a molecule NMR useful tool for structure determination.

THIS IS THE END. THX FOR ATTENTION.