When a scientist makes a new molecule and has characterised it in a suitable
manner, they would normally report on how it was made and perhaps on some aspect of
its properties in a "Scientific Journal". This would then enable other scientists
to repeat its preparation if they wished, and verify the assertions of the original
scientist. Nowadays, many molecules are synthesised as part of a commercial activity.
Sometimes, thousands of such molecules have to be made before one with suitable
properties is finally found. Because all the information gathered about the
molecules during the project can been very valuable commercially, the scientific
world may never hear about them. Whilst it is difficult to estimate how many
molecules have actually been made, but never reported, some estimates are of over
5 million.