The aldehyde region unsaturated carbon bonded to oxygen

Oxygen as a conjugating electron donor is even more dramatic. It shifts the proton next to it downfield by the inductive effect but pushes the more distant proton upheld a whole 1 ppm by donating electrons. The separation between the two protons is nearly 2 ppm. 

For both types of substituent, the effects are more marked on the more distant ( 3) proton. If these shifts rehect the true electron distribution, we should be able to deduce something about the chemistry of the following three compounds. You might expect that nucleophiles will attack the electron-deficient site in the nitroalkene, while electrophiles will be attacked by the electron-rich sites in silyl enol ethers and enamines. These are all important reagents and do indeed react as we predict, as you will see in later chapters. Look at the difference— there are nearly 3 ppm between the shifts of the same proton on the nitro compound and the enamine  

The aldehyde region unsaturated carbon bonded to oxygen 

Conjugation with an oxygen lone pair has much the same effect—formate esters resonate at about 8 ppm—but conjugation with n bonds does not. The aromatic aldehyde above, simple conjugated aldehyde below, and myrtenal all have CHO protons in the normal region (9-10 ppm). 

Two other types of protons resonate in the region around 9-10 ppm some aromatic protons and some protons attached to heteroatoms like OH and NH. We will deal with NH and OH protons in the next section, but first we must look at some electron-deficient aromatic rings with distinctively large shifts. 

OMF is similar as we saw earlier (p. 247), it has two different methyl groups because of the double bond. 

Aliphatic is a catch-all term for compounds that are not aromatic. 

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THE ALDEHYDE REGION UNSATURATED CARBON BONDED TO OXYGEN... 

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