Die Mainacht, a nice piece, but it would be better for clarinet!

m. 33 - I 64 , V7
m. 34 - iii6 I64
m. 35 - I6 , vi
m. 36 - ii(1/2)o65 , V43/IV
m. 37 - IV6 , IV
m. 38 - viio7/V , V
m. 39 - V , V/vi
m. 40 - vi , IV , iio7
m. 41 - vi , vi6 , V7/IV
m. 42 - IV7, Fr+6
m. 43 - I64 , V7/IV
m. 44 - IV7 , V7/bII
m. 45 - bII , bII6
m. 46 - V7
m. 47 - V7
m. 48 - I(7)
m. 49 - I(7)
m. 50 - I(7) , IV64
m. 51 - ii (1/2)o 42 , I

Brahms does a great job of using lots of diverse chords in Die Mainacht to create an incredible sense of longing and desire throughout this short song which, even as the piano fades out, still has a tinge of desire shown in the E natural (7th of tonic chord) that pulls the conclusion of this piece almost into a V7/IV! The climax of this piece is incredible also, with a fantastic, peak. Brahms lets the vocalist take a huge gasp in the middle of it to continue the painful lament. Looking at the vocal part, it is easier to break up the piece into phrases. However, there are a number of really unique things Brahms does particularly with the connections of phrases in the accompaniment that really keep the flow of the piece moving.
I believe that the climax of the piece is quite a long one, spanning from measures 41-43. It is really important that the vocalist really makes the whole note in measure 41 grow. I see the high G natural in measure 45 as a last effort of the singer, or possibly a last tear, falling from their face. The accompaniment under the climactic portion of this piece is quite diverse, including a quite tumultuous right handed piano part over the quick V7/IV - IV chord into measure 42.
Measures 33-38 present a really difficult passage for the performer because at first glance, it may appear that Morgenrot represents a phrase ending. It is really important that the vocalist looks into the accompaniment and recognizes that there is absolutely no sign of a phrase ending, but instead the phrase continues on from a vi to a ii(1/2)o65...etc. Measure 44 also is a crucial place that the performer must remember to maintain the mood of the piece. They still have one last peak, and the intensity must not drop too much - the performer must counter-act the motion/lower pitch of the notes and their natural tendencies to be softer, etc.
The piano postlude in measures 48-51 is clearly the resolve of the piece, though the E naturals persistent throughout really keep the performance (and the audience) longing for a better resolve until the absolute final chord of the piece. While technically should be denoted as V7/IV chords, in my opinion these need to be looked on as embellishments that further contribute to the longing for resolve throughout this piece.
In conclusion, the theme throughout this work is longing for resolve. Brahms works really hard to take the piece into far off places, in one place setting up a huge tonicization of bII with a V7/bII. Brahms reflects the true phrasing in his accompaniment part while allowing the vocalist to rest. One of the really important things to remember about Brahms is that in certain points the piano part can become more important than the melody, or alternatively it can carry the melody. This longing for resolve is predominantly due to a lack of root position tonic triads, thick, dense chords, accidentals, and a continuous flow of music held up by the accompanying piano. It is a wonderful piece, though I am not fond of vocalists - I would love a clarinet transcription of the piece though! The pure tone of the clarinet, the ability for one to support longer, extended passages, and the incredibly large dynamic range of the clarinet would be absolutely perfect for this song!