An enigmatic partition of the independent countries

Question

I have partitioned the independent countries of the world into two groups based on a certain property X that is shared by some countries, but not by the remaining ones. Property X is purely geographic.

The following countries all have this enigmatic property X:

Bolivia, Colombia, Cuba, Libya, Mali, Nicaragua, North-Korea, Portugal, Russia, Senegal, South-Korea, Switzerland, Tajikistan

The following countries do not have the enigmatic property X:

Afghanistan, Argentina, Australia, Austria, Canada, China, Ireland, Jamaica, Lithuania, Oman, Poland, Sudan, Tanzania

What criterion did I use for my enigmatic partition?
Do Brazil, Chad, Denmark, the USA and/or Yemen have this enigmatic property X?

Hint:

Property X is purely geographic. It can be solved by studying a map of the world.

Answer 1

The geographical property is:

having the capital city located in the Western half of the country.

Chad and Yemen have this enigmatic property X.
Brazil, Denmark and the USA do not have this enigmatic property X.