Why does the Organic Chemistry by John McMurry state: “carbonyl reduction is irreversible because the reverse process would require expulsion of a ery poor leaving group.”

The re-oxidation of alcohol back to aldehyde is a well-known reaction. How could it be irreversible? The book also states the same with the reaction of aldehydes with Grignard reagents.

9 minutes ago, Chemik said:

Why does the Organic Chemistry by John McMurry state: “carbonyl reduction is irreversible because the reverse process would require expulsion of a ery poor leaving group.”

The re-oxidation of alcohol back to aldehyde is a well-known reaction. How could it be irreversible? The book also states the same with the reaction of aldehydes with Grignard reagents.

I don't know this book but I imagine it may mean that the specific reduction reaction he is talking about has a negligible reverse rate. He can't mean alcohols cannot be oxidised to aldehydes or ketones, obviously. (I presume that, in this reaction, the leaving group in question may be hydride or something.)