Is it mandatory to declare conflicts of interest? I know some journals require authors to declare conflicts of interests as a matter of policy; even if there is no CoI, a section title Conflict of Interests is still included which declares that there were no conflicts.

However, I notice that for some journals this is not the case. For example, this paper in the Journal of Organic Chemistry does not appear to have a CoI section.

Is declaration of conflicts of interest considered optional for scholarly publications? Is it possible to ascertain whether CoIs exist for a paper like this, where nothing is indicated?
I'm fairly confident that most scholarly journals require that you disclose conflicts of interest. If the publisher or journal doesn't discretely mention it, it wouldn't hurt to include it in the manuscript anyway.