D Proton-Carbon Single Bond Correlated Spectroscopy

2 2-D Proton-Carbon (Single Bond) Correlated Spectroscopy 

The most powerful techniques of all are undoubtedly the 2-D proton-carbon experiments (Hetero-nuclear Multiple Quantum Coherence///eteronuclear Single Quantum Coherence, or HMQC/HSQC and //ctcronuclcar Multiple Bond Correlation, or HMBC) as they provide an opportunity to dovetail proton and carbon NMR data directly. 

So to sum up, if you have the luxury of modern equipment with all the go faster boxes at your disposal, go for HSQC. If you are stuck with an older instrument and you re not keen on grovelling around under the magnet, an HMQC is for you. 

Our preferred experiment of this type is the so called DEPT-edited HSQC which is both relatively artefact-free and sensitive. It also has one other major advantage up its sleeve. This experiment is not an absolute value technique like most of the others, but it allows for discrimination between different types of carbons. Methyl and methine carbons give crosspeaks that are phased opposite to the methylene carbons and so the results are best plotted on a colour plotter which can portray this clearly by plotting positive and negative cross peaks in different colors. 

Interpreting HMQC/HSQC spectra is relatively straightforward as you can see from the HSQC spectrum of the morpholine compound (Spectrum 9.3). Basically, it s a case of lining up the proton signal with the contour, and reading off the 13C chemical shift. The technique is extremely powerful - particularly when used in combination with HMBC as we ll see later. In examples like this one, it 

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