Learning Objectives Use high resolution n.m.r spectrum of simple molecules (carbon, hydrogen & oxygen) to predict The different types of proton present The relative numbers of each type of proton The number of protons adjacent to a given proton Possible structures Given a simple molecule predict features of the n.m.r spectrum. Describe the use of D 2 O to identify –OH groups

Nuclear Magnetic Resonance Spectroscopy

H H

Absorption peak corresponds to the radio frequency absorbed

Only nuclei with an odd number of nucleons (neutrons and protons) possess a magnetic spin Only nuclei with an odd number of nucleons (neutrons and protons) possess a magnetic spin 1 H (proton nmr) 13 C

The vast majority of proton NMR spectroscopy is performed on liquids. The vast majority of proton NMR spectroscopy is performed on liquids. You have a solid sample, what do you dissolve it in? You have a solid sample, what do you dissolve it in?

structure spectrum

Proton NMR Spectra

ABSORTIONABSORTION CHEMICAL SHIFT Electrons around the nucleus shield it from the applied magnetic field. Different radio-frequencies are aborbed depending on the environment of the proton. CHEMICAL SHIFT is a measure of the magnetic field experienced by protons in different environments. CHEMICAL SHIFT is measured in ppm relative to TMS, Si(CH 3 ) 4 CHEMICAL SHIFT tells us about the types of protons present

ABSORTIONABSORTION CHEMICAL SHIFT ABSORPTIONS The area under each peak is directly proportional to the number of protons responsible for the absorption These areas are most often presented as integration traces on the spectrum

Your Turn

Our Turn

Different types of proton? Relative numbers of each type of proton?

CHEMICAL SHIFT ppm Type of proton Number of protons 1.0 R-CH O-CH 2 -R 2 4.9R-O-H1 CH 3 CH 2 OH

structure spectrum CH 3 CH 2 OH Expect 3 different types of proton Expect peaks in the following ranges ppm (CH3) ppm (CH2-O) ppm (OH) Expect integration 3:2:1 Predict 3 different types of proton Number protons is in ratio 1:2:3 Assign possible types of proton to chemical shifts obtained

Learning Objectives Use high resolution n.m.r spectrum of simple molecules (carbon, hydrogen & oxygen) to predict The different types of proton present The relative numbers of each type of proton The number of protons adjacent to a given proton Possible structures Given a simple molecule predict features of the n.m.r spectrum. Describe the use of D 2 O to identify –OH groups

The number of absorption peaks tells us the number of different types of protons. The chemical shift helps us identify the type of proton. The integration values tells us the relative number of protons.

Nuclear Magnetic Resonance Spectroscopy Part 2

Learning Objectives Use high resolution n.m.r spectrum of simple molecules (carbon, hydrogen & oxygen) to predict The different types of proton present The relative numbers of each type of proton The number of protons adjacent to a given proton Possible structures Given a simple molecule predict features of the n.m.r spectrum. Describe the use of D 2 O to identify –OH groups

CHEMICAL SHIFT ppm Type of proton Number of protons 1.0 R-CH O-CH 2 -R 2 4.9R-O-H1 CH 3 CH 2 OH

why does this happen? Is it any use?

CH 3 CH 2 OH CCO What name do we give to this effect? spin coupling

CH 3 CH 2 OH CCO H H H H H H

triplet As a result of spin-spin coupling effects the signals are multiplets What causes this triplet splitting pattern? The spin-spin coupling effects from the protons on the adjacent carbon. The n+1 rule For n adjacent protons We have n+1 peaks in the multiplet 2 adjacent protons Gives a triplet

quartet The n+1 rule For n adjacent protons We have n+1 peaks in the multiplet We have quartet How many protons on the adjacent carbon?

why does signal splitting this happen? Is it any use? Spin-spin coupling Yes. It tells us the number of protons attached to the adjacent carbon.

multiplet Protons on adjacent carbon singletnone doublet One (C-H) triplet Two (CH 2 ) quadruplet Three (CH 3 )

Identifying O-H protons O-H protons can absorb at different chemical shifts, dependant upon O-H protons can absorb at different chemical shifts, dependant upon Solvent used Solvent used Concentration of solvent Concentration of solvent As a result it is difficult to identify O-H protons from chemical shifts As a result it is difficult to identify O-H protons from chemical shifts Trick D 2 O – sometimes called a “D 2 O shake” Trick D 2 O – sometimes called a “D 2 O shake”

In CCl 4 In D 2 O

Identifying O-H protons To identify O-H protons, To identify O-H protons, run the sample in a suitable solvent run the sample in a suitable solvent Re-run the sample in D 2 O Re-run the sample in D 2 O Compare spectra Compare spectra If the signal for the O-H proton dissapears in D 2 O If the signal for the O-H proton dissapears in D 2 O Evidence Evidence

Learning Objectives Use high resolution n.m.r spectrum of simple molecules (carbon, hydrogen & oxygen) to predict The different types of proton present The relative numbers of each type of proton The number of protons adjacent to a given proton Possible structures Given a simple molecule predict features of the n.m.r spectrum. Describe the use of D 2 O to identify –OH groups

Learning Objectives Use high resolution n.m.r spectrum of simple molecules (carbon, hydrogen & oxygen) to predict The different types of proton present The relative numbers of each type of proton The number of protons adjacent to a given proton Possible structures Given a simple molecule predict features of the n.m.r spectrum. Describe the use of D 2 O to identify –OH groups

Learning Objectives Use high resolution n.m.r spectrum of simple molecules (carbon, hydrogen & oxygen) to predict The different types of proton present The relative numbers of each type of proton The number of protons adjacent to a given proton Possible structures Given a simple molecule predict features of the n.m.r spectrum. Describe the use of D 2 O to identify –OH groups

Learning Objectives Use high resolution n.m.r spectrum of simple molecules (carbon, hydrogen & oxygen) to predict The different types of proton present The relative numbers of each type of proton The number of protons adjacent to a given proton Possible structures Given a simple molecule predict features of the n.m.r spectrum. Describe the use of D 2 O to identify –OH groups

Your Turn

Old Exam Questions

[8] June2007 Q7d

Jan2007

June2008 Q4d