Chopin Nocturne op.55 no.1

[jlmap]

What is happening harmonically in measures 71 and 72, just before the recapitulation of the first theme?  What is the rhetorical effect of this kind of prolongation of the dominant?
And in measures 65 to 69?  How is it to be understood harmonically?  What is the rhetorical effect?

[jlmap]

By the way,  what happens in measures 57 to 64 is a choral with the motives of the first theme,  right? The upper voice sings  fá-mi-lá, and an inner voice sings ré-dó-ti-lá, and then, lá-si-ti-lá. The first motive of this inner voice maybe is from the first theme.

[lelle]

Measure 57-64
Sure you could argue that the motives have a relationship to the first theme. Though the material is simple - step wise movement which is pretty universal - there are enough similarities with what happens melodically in the opening theme to consider it intentional by Chopin.

Measure 65-69
I think this provides a flavor of the Neopolitan 6th, often used to heighten tragic, sad emotions in minor keys (though the chord is in a different inversion than a true Neopolitan 6th), preparing for the return to F minor. You could also argue that he is just moving from Bbm/Db in bar 64 to Db7 in bar 69 by chromatic voice leading, changing the F in the Bbm chord like so F-Gb-G and finally Ab in the Db7 chord. (You could argue that this Db7 functions enharmonically as a Gb9 b5 with the root removed, i e the dominant of the dominant in F minor, bringing him to C major in bar 71).

Measure 71-72
A mix of chromatic voice leading and moving along the circle of 5ths more or less. See if you can spot which chord change does which. Prolonging the dominant as you say. Compared to a lot of the piece which has quite a slow harmonic rhythm, here he is passing through quite a lot of chords with some distance from the tonic rather quickly. I think this creates an anxious, restless feeling before he runs out of steam and settles on the dominant again before the recapitulation.

Not sure about your question about "rhetorical effect" as if there is an objective answer.

[jlmap]

Tank you! Maybe from measure 65 up to de Aug6th there is something to produce disorientation, I kind of dissolution of the harmony,, that is firmly restored by the Aug.6th. Something like a prechoruns im popular music.