It is named after the Russian masterSemyon Alapin (1856–1923). For many years, it was not held in high regard, since 2...d5 was thought to allow Black easy equality.[1][2]
The Alapin is also seen in deferred form, particularly when Black chooses an unusual second move after 2.Nf3. For example, after 2.Nf3 a6 or 2.Nf3 Qc7, 3.c3 is often seen, since neither ...a6 nor ...Qc7 are particularly useful moves against the Alapin.
The main line in current practice is 2...Nf6 3.e5 Nd5 and can also arise if Black declines the Smith–Morra Gambit (1.e4 c5 2.d4 cxd4 3.c3 Nf6 4.e5 Nd5).
White has a number of options including 4.d4, 4.Nf3, 4.g3 and 4.Bc4.
2...d5
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Alapin Variation 2...d5
This is the main alternative to 2...Nf6 for Black. The usual continuation is 3.exd5 Qxd5, a line known as the Barmen Defense.[3] 3.e5 may transpose to the Advance Variation of the French Defence if Black responds with 3...e6, but Black can also develop his c8-bishop before playing e6. This leads to a favorable version of the French for Black, since the bishop is no longer hemmed in by the pawn chain. If White plays 3.exd5, 3...Nf6 is possible, but it is not clear whether Black receives sufficient compensation for the pawn.
The main options revolve around:
4.d4 Nc6 and now 5.dxc5 or 5.Nf3
4.d4 Nf6 5.Nf3 when after both 5...e6 and 5...Bg4 White can try a number of different moves.
2...e6
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Alapin Variation 2...e6
This is Black's most solid response, preparing 3...d5. It is closely related to the French Defence, to which it often transposes. White can transpose to the Advance Variation of the French Defence with 3.d4 d5 4.e5. Alternatively, White can transpose to a sort of Tarrasch French with 3.d4 d5 4.Nd2, or try to demonstrate a slight advantage with 3.d4 d5 4.exd5 exd5 5.Be3.
2...d6
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Alapin Variation 2...d6
This is a sharp response. Black often offers a gambit with 3.d4 Nf6 4.dxc5 Nc6 (4...Nxe4?? 5.Qa4+) 5.cxd6 Nxe4. White can instead play quietly, however, with 3.d4 Nf6 4.Bd3, occupying the centre and maintaining a spatial advantage.
Other tries
2...e5
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Alapin Variation 2...e5
This move makes it hard for White to play d4, but seriously weakens the d5-square. Play usually continues 3.Nf3 Nc6 4.Bc4, with a solid edge for White.
^Walter Korn, much like Tarrasch, dismissed the Alapin with "2...P-Q4!=." Walter Korn, Modern Chess Openings, 11th Edition (commonly referred to as MCO-11), Pitman Publishing, 1972, p. 148. ISBN0-273-41845-9.