Sicilian Defence - Alapin Variation

Black is threatening to take on e4. White's best option is to take first, with 3. exd5.

After 3. exd5 the main line continues 3...Qxd5, the Barmen variation, and White doesn't have Nc3 to kick the queen away. After 4. d4, it is possible for Black to win a pawn and go into an endgame,^{[nb 1]} however White has adequate compensation and better practical chances. A more common plan is to leave White with an isolated queen's pawn position and control d5 with ...e6 and ...Nf6.^{[nb 2]}

Black's other line is 3...Nf6, christened the anti-Alapin gambit, which is similar to the Tal gambit. White has the time to defend the d-pawn, but Black is eager to give some material for rapid development, e.g. 4. c4 e6 5. dxe6 Bxe6.

A quick round up of the White's other turn three options, which they should discard:

White cannot play Nc3 to defend the pawn, as their c-pawn already occupies c3.

3. e5!? allows Black to play ...Bf5 & ...e6, reaching an advance French-style position with the strict improvement that Black has been able to develop their queen's bishop outside of the pawn chain first. Black has equalised.

3. d3?! to defend e4 leaves the pawn on c3 out of place. If White avoids taking on d5, they allow Black easy development and plenty of space, e.g. 3...Nc6 4. Nd2 Nf6 5. Ngf3 e5 6. Be2 Be7 7. O-O O-O⩱. Black could also consider playing d4 themselves: 3...d4 4. cxd4 cxd4 5. Qa4+ Nc6 6. Nf3⩱.

3. d4? and Black is better after 3...dxe4 4. dxc5 Qxd1+ 5. Kxd1 Nf6⩱.

1.e4 c5 2.c3 d5

Wikipedia has related information at Sicilian Defence, Alapin Variation.