DETERMINACIÓN DE ESTRUCTURAS ORGÁNICAS(ORGANIC SPECTROSCOPY)

RESONANCIA MAGNÉTICA NUCLEAR

Hermenegildo García GómezHermenegildo García GómezDepartamento de QuímicaDepartamento de Química

Instituto de Tecnología QuímicaInstituto de Tecnología QuímicaUniversidad Politécnica de ValenciaUniversidad Politécnica de Valencia

46022 Valencia46022 Valencia

EE--mail: mail: hgarcia@qim.upv.eshgarcia@qim.upv.esTelephone: +34 96 387 7807 or ext. 78572/73441Telephone: +34 96 387 7807 or ext. 78572/73441

Fax: + 34 96 387 7809Fax: + 34 96 387 7809

INTRINSIC PROPERTIES OF THE MATTER

FIELD PROPERTY Gravitational Mass

Electrical Charge Magnetic Spin

PHYSICAL PROPERTIES OF FUNDAMENTAL PARTICLES

MASS / uam CHARGE SPIN Electron ~0 -1 ½ Proton 1 1 ½

Neutron 1 0 ½

PHYSICAL PROPERTIES OF A NUCLEUS

Mass ∑mass of ptoyons + ∑mass or neutrons Charge ∑number of protons (always positive)

Spin Depends on the magnetic or anti/magnetic coupling of spins

What is the spin? Intrinsic fundamental property Classical Newtonian approach

NUCLEII WITH NET SPIN

Mass Nº proton Spin

odd It does not matter 1/2, 3/2, 5/2…

even uneven 1, 3…

even even 0

A charged particle moving

What happens to a magnetic nucleus in a magnetic field

Classical view of a spin orientation on a magnetic field

Schematic of a NMR Spectrometer

NMR Spectrum

Four types of information

• Types of protons• Chemical shift• Number of protons in each type• Coupling Contast

Chemical shift

• If , h or was the variable plotted, the value willdepend on the intensity of the magnetic field

Reason:

• A scale indepedent in the magnetic field:

The numerator are normally a few HzThe denominator is MHz

is given in ppm

υυ

υγε ⋅=⋅⋅=∆ H || HEr

Standard

Standard

υυυ

δ−

= H

δ

Chemical Shift

• The “effective” magnetic field experienced at the nucleus

electron screening does not with the “external”“macroscopic” magnetic field

• Each type of proton “resonates” at a particular frequency depending on the bonding electrons.

The two main factor are:• inductive and resonance effects• anisotropy effects

HHH ef

rrr−= 0

Chemical shifts overall view

Chemical shift and anisotropy

The space around the aromatic ring is stronglyinfluenced by the induced magnetic field

Carbonyl group and anisotropy

C=C double bond and anisotropy

Coupling. Influence between neighbour nuclear spins.

Case of CH-CH

First order couplingand evolution to a combined system