[jdashcup]

I'm having trouble Identifying the ester of this spectrum.

I think it's butyl hexanoate but it doesn't quite match on SDBS.

MW = 172.  No other functional groups are present.
Molecular ion absent.  117 a result of M+1.  99 is an acylium ion.  71 is loss of CO from acylium.
and so on.  I can assign structures for practically all major peaks, but the problem, when compared to SDBS, the relative abundances are off.  The base peak is 29, probably an ethyl cation.  I feel like this implies that this ester is branched to a certain degree.  I'm having problems determining how to explain these intensities.  Any help would be appreciated.

[macman104]

Just to clarify, you were given the following info, you didn't determine it, or figure it out experimentally?

Molecular Weight 172
Only ester functionality present, no other groups (1 ester only? or possibly more than 1?)

Also, you say:

117 a result of M+1

What do you mean?

[jdashcup]

The MW was given. The problem says the IR showed a peak at ~1740 cm-1 and at ~1150 cm-1 (an ester) and that the compound had no nitrogen. M+1 is McLafferty + 1 Rearrangement.

[macman104]

Well, I tried playing around with it for a while, but honestly, I always hated the questions where they made you try to predict the structure only from MS and IR.  No one would do that in real life, and MS while nice for elucidating some structural features is kind of useless for creating a whole structure.  It's nice for *verifying* your thought about a structure, but...yea.  Anyway, I gave up, because I don't like these questions, lol.

The only piece I have for you (and you may have realized it already) is that most likely the peak at 56 is from the same fragmentation as 117, and the fragmentation of 73 is the from the same fragmentation as 99.

Anyway, best of luck, and tell your prof to stop giving these problems to you