Learning Guide for Chapter 5 - NMR SpectroscopyI. Introduction to NMR spectroscopy - p 1II. Distinguishing equivalent H's - p 3III. Chemical shift - p 4IV. Integration - p 7V. Spin-spin Splitting - p 9VI. Practice with NMR spectraVI. Deuterium in NMR - p 12 VII. Carbon-13 NMR- p 13I. Introduction to NMR spectroscopyTo introduce you to NMR spectroscopy, we will first compare it to IR spectroscopy.IR spectroscopyNMR spectroscopytype of light: type of light:what causes light to be absorbed: what causes light to be absorbed:what bands represent: what peaks represent:what we learn about a compound:what we learn about a compound:x-axis: x-axis:O OHIRNMROH OHWhich kind of spectroscopy can distinguish each pair of compounds?Which type of spectroscopy is more powerful?LG Ch 5 p 2What characteristic allows an atom to be detected by NMR?What elements are commonly found in organic molecules? Which are suitable for NMR?isotopes:element:NMR?A typical proton NMR spectrum looks like this:Each cluster of spikes is called a:Where can you find each of the following, and what does it tell you about the peak?chemical shift:OHintegration:splitting:What should you be able to do?1. Assign peaks on a compound to a spectrum.2. Sketch the spectrum of a compound.3. Deduce the structure of an unknown compound from its spectrum.LG Ch 5 p 3II. Distinguishing Equivalent HydrogensWhen do we say that two H's are equivalent?What happens on a spectrum when two H's are equivalent?Draw in all H's for the following compounds. Circle those that are equivalent, and then count the number of sets.Rules of thumb:More exact rule:How many sets of equivalent H's are present in each of the following molecules?OHOHHHLG Ch 5 p 4III. Chemical ShiftWhat compound is used to establish "0" on the chemical shift axis? Why do you think this would make a good reference compound?Draw arrows showing the direction of upfield and downfield:0Predict which set of hydrogens will be farthest downfield. When will this rule be useful?CH > CH2 > CH31)2)BrCH3F CH3ClO OHHHH HHHH3)H2C CH2H3C CH3HC CHLG Ch 5 p 54)5)OH NH2NH2OOHOWhich of the set of H's shown on each compounds will appear furthest downfield?HH HOHH HH HCl ClH H H HOH HHHHHHHHHow many peaks should the following compound have? Which two would be most likely to overlap?HOHHHHHHHHHHHLG Ch 5 p 6What are some useful ranges to remember?130123456789101112What H's should stand out on the following compounds?OHOHOGive the range at which you would expect to find the following H's:OHH HH HOHHHHOOHH HHH HOHOH2NH H H HHH's on C=CH's on aromatic ringOH in carboxylic acidsH's on C next to C=OH's on C=OH's on C with NH's on C with O or XH's on amidesOH or NH in alcohols or aminesLG Ch 5 p 7IV. IntegrationOWhat does integration mean, mathematically?What does the integration tell us on an NMR spectrum?Why does the area under a curve increase when there are more H's in a peak?Identify the sets of equivalent H's in the following compound. Which is furthest downfield? Which will have a greater integration?Compare the integration ratios for the following compounds. Can you tell them apart?ClOPredict the integration ratio for each of the following compounds.NHOClClClClClCl ClOHClClWhat does the height of a peak tell you?How do we measure the integration?LG Ch 5 p 8 ClIdentify each set of equivalent H's in the following compound. Give the chemical shifts you would expect. Give the integration.Match up the H's with the peaks in the spectrum.V. Spin-spin splittingLG Ch 5 p 9What does splitting mean?What happens when H's are separated by more than one atom?OOWhat happens when a set of equivalent H's has one or more neighboring H's?ClHBrHClBrClHBrHClHClHBrHHHClHHHHHHHHHHHHow can you tell what splitting a peak will have?Sketch the spectra of the following compounds:Cl HHHHHHHLG Ch 5 p 10Assign splitting to each set of equivalent H's in the following compounds.What happens when the chemical shifts of two separate peaks are so similar that they overlap? OHHHHHHHHWhen is this common?LG Ch 5 p 11Example: OO HaHbHcDo H's on alcohols and amines usually participate in splitting?CH3OH (regular sample)CH3OH (dilute, no water)What is complex splitting?What kind of H's commonly show this?What causes it?normal splittingcomplexsplittingLG Ch 5 p 12VI. Deuterium in NMRWhat is deuterium?Why is it useful in NMR?Why are deuterated solvents needed in NMR?What are the most common NMR solvents?Do deuterated solvents show up on an NMR spectrum?Is there a peak that shows up because of the solvent? Why?If water is present in the compound or the solvent, where will it appear on the spectrum?What will happen if D2O is added to a sample containing an alcohol?OD DOH+LG Ch 5 p 13spectrum before adding D2O:spectrum after adding D2O:OHODWhat functional groups will have H's that disappear when shaken with D2O?VII. Carbon-13 NMRWhy isn't 13C NMR as useful as 1H NMR?Why isn't integration used?How is the peak affected by the number of H's attached to the carbon?Why won't you see any carbon-carbon splitting?Why is carbon-hydrogen splitting usually eliminated?What do you call a spectrum with no C-H splitting?LG Ch 5 p 14 In the following spectrum of vanillin, assign the carbon atoms to the peaks where possible.HOHOOHow many peaks would you expect each of the following compounds to have? What chemical shift ranges would they fall in?OHOWhere does the solvent peak appear for CDCl3?What is the most useful information you can get from a 13C NMR spectrum?What are some common chemical shift ranges?sp3 carbon atomsC=C in alkenes and aromatic ringsC=OLG Ch 5 p 15VIII. Practice with NMR spectraMatch the peaks in the following compounds with the H's in the structures shown. OOOOLG Ch 5 p 16Sketch the spectrum of the following compounds.OODeduce the structure of the following compounds. C2H3Cl3LG Ch 5 p 17 C6H12OC4H8Cl21.60 ppm (3H, d)2.15 ppm (2H, q)3.75 ppm (2H, t)4.27 ppm (1H, m(6))