What are the ideas of 6. Qf3 in the Scotch? In the following sequence of moves, what are the main ideas of the fashionable 6. Qf3 in the Scotch? Can White hope for a real advantage by letting Black trade Queens so early and worsening (at least from a theoretical point of view) his Pawn structure?  

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1. e4 e5 2. Nf3 Nc6 3. d4 exd4 4. Nxd4 Bc5 5. Nxc6 Qf6 6. Qf3 


PS: Another strange-looking early Qf3 by White that has become popular recently! Others are in the Sicilian Taimanov and in the Exchange Alekhine...
I only see three alternative moves to defend the f2 square: 6.Be3 Bxe3 7.fxe3 results in doubled isolated center pawns, not something I would like to play with. 6.Qd2 and 6.Qe2 block the bishops.

I guess it's a matter of what you like to play with. If you block one of your bishops, you can later play the queen again or fianchetto the bishop. 6.Qd2 and then fianchettoing your dark-squared bishop requires more moves as the black queen controls the b2 square. 6.Qe2 blocks in your light-squared bishop taking you longer to castle (short).

After 6.Qf3 Qxf3 7.gxf3 you can still castle long and you have quite a strong centrum pawn formation. Perhaps this looks better than the alternatives.