Reactivity: How and Why - Organic Chemistry Concepts: An EFL Approach - page 74

The same is true for the heteroatom example of alcohol conversion to aldehyde.
The oxidation number of the carbon changes from −2 in the alcohol to 0 in the
aldehyde, an oxidative change of +2.
Now compare the non-redox addition/elimination sequences which are shown in
Figure 5.11 . The elimination of H-Cl gives a sum of nominal oxidation numbers
(−4) of the carbon atoms in the alkyl halide (−3 and −1). This is the same as for
the product alkene (−2 and −2). Similar calculation for the addition/elimination of
H 2 O shows no change to the nominal oxidation number of 0 at the carbon center.
The above gives a useful general guideline to recognizing organic redox
processes. This approach should not be taken to extremes for all systems.