From the perspective of the person buying something, paying a business expense, making a chartible donation, paying medical expenses, etc, the deduction is in the year that the charge occurs, as I've said for the 4th time now and with cites.
This line of questioning reminds me of times when a non-tax pro sneaks through with a question and one of the reasons why we don't allow or answer questions from the general public on this forum.
Also, one other post hidden that was off-topic.