MNR Spectrum
--A general covalence for the whole group that are the atoms of hydrogen, which are more near to oxygen to be this more electronegative, and
--Another particular covalence for the central atom of carbon and for oxygen. Two electrons given by oxygen since there is not hydrogen enough for it support this particular covalence.
NMR- Spectrum
In the drawing of ethanal the oxygen atom has given two electrons for the joining with the interior carbon, reason for that a bigger electronegative power takes place, attracting so more near of the oxygen to the hydrogen and carbon atoms.
Therefore a gravitational and magnetic increase of power takes place in all the atoms and therefore also a bigger magnetic frequency in each one of them takes place.
-The signal of 2,3 ppm corresponds to the exterior methyl group, which stay affected for the double connection of the second carbon with the oxygen, being located a little more near of this connection.
The result is increase of the magnetic frequency in hydrogen atoms, passing from 1,2 to 2,3 ppm.
-The signal of 9,8 ppm is produced by the hydrogen atoms that are located on the oxygen.
To be penetrated these hydrogen atoms much more into the gravitational and magnetic field of the oxygen, this produce a much bigger frequency as a result. It is it due to the approach among these hydrogen atoms, the central carbon and the oxygen for the fact of having given these two electrons.