Proton NMR Spectroscopy The NMR Phenomenon Most nuclei

The NMR Phenomenon • Most nuclei possess an intrinsic angular momentum, P. • Any

Which nuclei have a “spin”? • If mass # and atomic # are both

Spin states split in the presence of B 0

When a nucleus aligned with a magnetic field, B 0, absorbs radiation frequency (Rf),

NMR instruments typically have a constant Rf and a variable B 0. A proton

Energy Difference ( E) Between Two Different Spin States of a Nucleus With I=1/2

What Does an NMR Spectrum Tell You? • # of chemically unique H’s in

How many signals in the Proton NMR Spectrum?

Chemical Equivalence How many signals in 1 H NMR spectrum?

Diamagnetic Anisotropy Shielding and Deshielding

Chemical Shift is Affected by Electron Density Around Nucleus

Integral Trace How many protons give rise to each signal?

Methyl Group appears as an Upfield Doublet

Methine H Appears as a Downfield Quartet

1, 2, 2 -Trichloropropane 1 H and 13 C NMR Spectra

Slides: 66

Download presentation

Proton NMR Spectroscopy

The NMR Phenomenon • Most nuclei possess an intrinsic angular momentum, P. • Any spinning charged particle generates a magnetic field. P = [I(I+1)]1/2 h/2 p where I = spin quantum # I = 0, 1/2, 1, 3/2, 2, …

Which nuclei have a “spin”? • If mass # and atomic # are both even, I = 0 and the nucleus has no spin. e. g. Carbon-12, Oxygen-16 • For each nucleus with a spin, the # of allowed spin states can be quantized: • For a nucleus with I, there are 2 I + 1 allowed spin states. 1 H, 13 C, 19 F, 31 P all have I = 1/2 DE = g(h/2 p)Bo

Spin states split in the presence of B 0

When a nucleus aligned with a magnetic field, B 0, absorbs radiation frequency (Rf), it can change spin orientation to a higher energy spin state. By relaxing back to the parallel (+1/2) spin state, the nucleus is said to be in resonance. Hence, NMR

Presence of Magnetic Field

NMR instruments typically have a constant Rf and a variable B 0. A proton should absorb Rf of 60 MHz in a field of 14, 093 Gauss (1. 4093 T). Each unique probe nucleus (1 H perhaps) will come into resonance at a slightly different and a very small percentage of - the Rf. All protons come into resonance between 0 and 12/1, 000 (0 – 12 ppm) of the B 0.

Energy Difference ( E) Between Two Different Spin States of a Nucleus With I=1/2

What Does an NMR Spectrum Tell You? • # of chemically unique H’s in the molecule # of signals • The types of H’s that are present e. g. aromatic, vinyl, aldehyde … chemical shift • The number of each chemically unique H integration • The H’s proximity to eachother spin-spin splitting

How many signals in the Proton NMR Spectrum?