Buenos Aires vs capital of Argentina

Buenos Aires and capital of Argentina both are nouns.

Word	Noun	Adjective	Verb	Adverb
Buenos Aires	Yes	No	No	No
capital of Argentina	Yes	No	No	No

As nouns, Buenos Aires and capital of Argentina are synonyms defined as:

Buenos Aires and capital of Argentina: capital and largest city of Argentina; located in eastern Argentina near Uruguay; Argentina's chief port and industrial and cultural center

Buenos Aires (noun)	capital of Argentina (noun)
capital and largest city of Argentina; located in eastern Argentina near Uruguay; Argentina's chief port and industrial and cultural center	capital and largest city of Argentina; located in eastern Argentina near Uruguay; Argentina's chief port and industrial and cultural center