19/12/2015 Draw the displayed formula of ethanol What would we see in an IR and in the mass spec for ethanol?

19/12/2015 Suggested timing What info about a molecule can we get using em radiation? IR task – explain what is meant by aliphatic and aromatic NMR – video (break around now deepending on timing – before or after video) Stop video at CDCl3 – ask why added, why is TMS used? Flow chart – 10 wrods or less – what do we know about nmr and how we get spectra Draw EtOH on paper, how many peaks, height of peaks? Draw propanone, propanal, propan-1-ol and propan-2-ol – go over key ideas - pleanary Pupils Answer any 3 question challenge and leave

19/12/2015 Key words Odd CDCl 3 TMS Magnetic field Radio Spin

19/12/2015 So what is NMR? A sample of the compound is spun in a magnetic field hydrogen atoms in different environments respond differently to the field each different environment of hydrogen produces a signal in a different position the area under each peak / signal is proportional to the number of hydrogens The signal can be split according to how many H’s are on adjacent atoms

19/12/2015 Look at your displayed formula for ethanol Predict how many peaks you would see in the 1 H nmr

19/12/2015 NMR of ethanol

19/12/2015

Low resolution and high resolution the signal produced indicates the number of protons on adjacent carbon atoms low resolution nmr gives 1 peak for each environmentally different group of protons LOW RESOLUTION SPECTRUM OF 1- BROMOPROPANE What do you notice about the height of each peak?

19/12/2015 Draw displayed formula for the following and sketch the predicted nmr you would see a) propan-1-ol, b) propan-2-ol, c) propanone d) propanal Can we distinguish between any of these compounds based on low resolution nmr alone?

19/12/2015 Technical bits and pieces

19/12/2015 Tetramethylsilane (CH 3 ) 4 Si PROVIDES THE REFERENCE SIGNAL The molecule contains four methyl groups attached to a silicon atom in a tetrahedral arrangement. All the hydrogen atoms are chemically equivalent.

19/12/2015 What other features should our reference have? non-toxic liquid - SAFE TO USE inert - DOESN’T REACT WITH COMPOUND BEING ANALYSED has a low boiling point - CAN BE DISTILLED OFF AND USED AGAIN all the hydrogen atoms are chemically equivalent - PRODUCES A SINGLE PEAK

19/12/2015 What other features should our reference have? twelve hydrogens so it produces an intense peak - DON’T NEED TO USE MUCH signal is outside the range shown by most protons - WON’T OBSCURE MAIN SIGNALS given the chemical shift of  = 0 the position of all other signals is measured relative to TMS

19/12/2015 Chemical shift

19/12/2015 Chemical shift each proton type is said to be chemically shifted relative to a (our) standard (usually TMS) the delta () scale is widely used as a means of reporting chemical shifts Observed chemical shift (Hz) x 10 6  = ppm (parts per million) Spectrometer frequency (Hz) the chemical shift of a proton is constant under the same conditions (solvent, temperature)

19/12/2015 Approximate chemical shifts The actual values depend on the environment  DOWNFIELD - ‘deshielding’ -COOH -CHO-CHO -C=CH- RO H - C - X H - C - H TM S

19/12/2015

Summary An nmr spectrum provides several types of information :- number of signal groups tells you the number of different proton environments chemical shift tell you the general environment of the protons peak area (integration) tell you the number of protons in each environment Multiplicity tells you how many protons are on adjacent atoms

19/12/2015 Draw displayed formula for the following and sketch the predicted nmr you would see a) propan-1-ol, b) propan-2-ol, c) propanone d) propanal Can we distinguish between any of these compounds based on low resolution nmr alone?

19/12/2015 What is high resolution NMR?

19/12/2015 High resolution gives more complex signals - doublets, triplets, quartets, multiplets HIGH RESOLUTION SPECTRUM OF 1- BROMOPROPANE The broad peaks are split into sharper signals The splitting pattern depends on the number of hydrogen atoms on adjacent atoms

19/12/2015 Challenge – can you draw the HIGH resolution NMR for a) propan-1-ol, b) propan-2-ol, c) propanone d) propanal?