[dmc3]

For my lab I have to identify an organic molecule based on IR, MS, and NMR.
Possible functional groups for this unknown are Aldehyde, Alcohol, Amine,
Carboxylic Acid, Ketone, Phenol, Ester.

List of all the possible chemicals are found:
http://depts.washington.edu/chemcrs/bulkdisk/chem242A_sum09/handout_Unknown-Derivative_List.pdf

MS
(91 m/z)-------(105 m/z)--------(184 m/z)
- obviously mass of my compound's mass is 184.
- first fragment 184-105 = 79; which is same as bromine MW
- so I think I definitely have bromine
- I'm not sure about 184-91 fragment.

H NMR
- 3 chemical shifts
1. ~7.4 ppm (Multiplet; Area = 2.4702)
2. ~4.6 ppm (Triplet; Area = 1.0102)
3. ~4.3 ppm (Triplet; Area = 1.0000)
- ppm values from book tells me that ~7.4 is benzene and I'm not quite sure about the other two

IR Spec seems really ambiguous. I cannot seem to identify main functional group from my IR.

3433.8 cm = TA told me to ignore this peak
3028.6 cm = Long
2967.9 cm = Medium
1944.3 cm = Very short
1876.9 cm = Very short
1799.1 cm = Very short
1603.0 cm = Medium
1496.1 cm = Long
1453.8 cm = Long
1431.8 cm = Medium
1314.5 cm = Medium
1262.3 cm = Long
1215.9 cm = Long
1196.4 cm = Medium

============================================

Based on the information above I've concluded that my compound is either p-bromobenzaldehyde or o-bromobenzaldehyde

Reasons
1. MW of bromobenzaldehyde is 185 which is close.
2. First fragment of 105 is same MW as benzaldehyde.
3. ~7.4 ppm is benzene chemical shift

Does it sounds convincing that my compound is either p-bromobenzaldehyde or o-bromobenzaldehyde?

[Borek]

At least three reasons why you are wrong.

First - bromine doesn't give one peak on MZ.

Two - carbonyl should be easily visible on IR.

Three - benzaldehyde can't be a source of 4.6 ppm triplets on NMR.

I can be wrong, so second opinion won't hurt, but benzaldehyde bromine derivative seems to be out of the question.

[dmc3]

I just found out that it isn't o/p-bromobenzaldehyde. The NMR structure of o/p-bromobenzaldehyde and the given NMR structure doesn't match.

So my unknown will not contain any carbonyl group right? This eliminates aldehyde, ketone, and carboxylic acid correct?

[dmc3]

Does Benzhydrol fit the description?

http://chemicalland21.com/lifescience/phar/BENZHYDROL.htm

Its MW is 184.
When one side of the benezen leaves weight becomes 105.
When Phenol side leaves it gives weight of 92.
This description seems to fit MS data.

However does it fit well with IR and NMR?

[sjb]

It does not fit the NMR, does it? You have 10 aromatic protons, and only 1 aliphatic, which may couple with the OH, but that would only be a doublet.

Are you sure the unknown is on that list? The only compound I can think of that fits is not - either that or the data you have is slightly incomplete.

[Arctic-Nation]

My guess is that it would be 2-bromoethyl benzene. Its spectroscopic data would be as follows:

From the 5:2:2 NMR pattern we can infer monosubstituted benzene. The 2:2 triplet pattern points towards 1,2-disubstituted ethane. The positions of the two ethyl peaks point to aryl- and/or heteroatom-substitution. An ethyl benzene derivative would also give a peak at 91 in MS for the tropylium ion (C₇H₇+), and a peak for ethyl benzene cation (C₅H₅CH₂CH₂+ at 105. The signals in the IR spectrum also point towards absence of O or N bound to carbon. That leaves as possible heteroatoms P, S, and the halogens, but only bromine has the correct mass (as far as I'm able to think at 2 am after a few beers ). That leads of course again towards the problem of the single peak.

Anyway, this should help you along.

[sjb]

My guess is that it would be 2-bromoethyl benzene.

Yes, that was my thought too, but I couldn't see it on the supplied list, and the bromine would show two signals on the parent molecular ion, which are not noted...

[dmc3]

Eventually I was able to figure out that my molecule is 2-bromoethyl benzene. I thought my compound had to come from the list but it didn't. Thanks for all your help.