1 H NMR of C5H8O2

[Daveman]

Hi.
I am trying to come up with a structure for this molecule C5H8O2.

The 1 H NMR has 3 lines grouped around 1.0 ppm with area of 3H, 6 lines
grouped near 1.9 ppm with area of 2H, and 3 lines grouped around 3.4 ppm
with an area of 2H.

The IR spectrum has a medium spike at 3000, a big spike at 1720, and a
medium spike at around 1640.

The NMR tells me that part of the molecule is probably CH3CH2CH2-, but what
about the rest?

I am sure I have a C=O. Do I also have C=C?

Any help would be greatly appreciated.

Dave

[Barry Hunt]

Post by Daveman
Hi.
I am trying to come up with a structure for this molecule C5H8O2.
The 1 H NMR has 3 lines grouped around 1.0 ppm with area of 3H, 6 lines
grouped near 1.9 ppm with area of 2H, and 3 lines grouped around 3.4 ppm
with an area of 2H.
The IR spectrum has a medium spike at 3000, a big spike at 1720, and a
medium spike at around 1640.
The NMR tells me that part of the molecule is probably CH3CH2CH2-, but what
about the rest?
I am sure I have a C=O. Do I also have C=C?
Any help would be greatly appreciated.
Dave

How about a cyclopropane attached to -CH2-COOH?

Barry Hunt

[Daveman]

Thanks for your reply.

Will this work?

Are the hydrogens in the correct places to match the NMR?

Dave

Post by Barry Hunt

Post by Daveman
Hi.
I am trying to come up with a structure for this molecule C5H8O2.
The 1 H NMR has 3 lines grouped around 1.0 ppm with area of 3H, 6 lines
grouped near 1.9 ppm with area of 2H, and 3 lines grouped around 3.4 ppm
with an area of 2H.
The IR spectrum has a medium spike at 3000, a big spike at 1720, and a
medium spike at around 1640.
The NMR tells me that part of the molecule is probably CH3CH2CH2-, but

what

Post by Daveman
about the rest?
I am sure I have a C=O. Do I also have C=C?
Any help would be greatly appreciated.
Dave

How about a cyclopropane attached to -CH2-COOH?
Barry Hunt

[Richard Schultz]

In article <tKZsb.109936$***@twister.tampabay.rr.com>, Daveman <***@hotmail.com> wrote:
: Hi.
: I am trying to come up with a structure for this molecule C5H8O2.

: The 1 H NMR has 3 lines grouped around 1.0 ppm with area of 3H, 6 lines
: grouped near 1.9 ppm with area of 2H, and 3 lines grouped around 3.4 ppm
: with an area of 2H.

Somebody apparently failed to tell you that you can learn quite a bit
about the structure from the ratios of the peak heights of the lines.
For example, are the "three lines" in the ratio of 1:2:1?

What do you think is the significance of the observation that your compound
has 8 H atoms in it, but that the integration of the NMR only adds up to 7?

: I am sure I have a C=O. Do I also have C=C?
:
: Any help would be greatly appreciated.

You can calculate the number of double bonds or rings by remembering that
the ratio of H:C in a saturated molecule is 2n+2:n where n is the number
of carbon atoms. Each unsaturation or ring takes away two H atoms.

-----
Richard Schultz ***@mail.biu.ac.il
Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel
Opinions expressed are mine alone, and not those of Bar-Ilan University
-----
"Logic is a wreath of pretty flowers which smell bad."

[Steve Turner]

Post by Daveman
The 1 H NMR has 3 lines grouped around 1.0 ppm with area of 3H, 6 lines
grouped near 1.9 ppm with area of 2H, and 3 lines grouped around 3.4 ppm
with an area of 2H.

This interpretation is only capturing a small portion of the
information available from the spectrum. See comments from Richard
Shultz in another post. Your description of the three groups does not
include necessary information about the spacing, relative heights, and
overall appearance of these lines. For example, three lines can
belong to a triplet, or a doublet and a singlet, a doublet of
doublets, or a more complex pattern. The coupling constants can also
be useful in determining which pattern is coupled with which other
pattern(s).

Steve Turner

Real address contains worldnet instead of spamnet

[Qi Wang]

Have you possibly ignored a signal at around 10 ppm with the integration of
1 proton (could be even in lower field, i.e. >10 ppm)? If yes, then you've
probably got propyl formate(HCOOCH2CH2CH3), which should give exactly the
same pattern of proton signals in high field (triple for CH3, triple
for -O-CH2 and sextet for -CH2-) I would say the IR also matches this
structure.

Post by Daveman
I am trying to come up with a structure for this molecule C5H8O2.
The 1 H NMR has 3 lines grouped around 1.0 ppm with area of 3H, 6 lines
grouped near 1.9 ppm with area of 2H, and 3 lines grouped around 3.4 ppm
with an area of 2H.
The IR spectrum has a medium spike at 3000, a big spike at 1720, and a
medium spike at around 1640.
The NMR tells me that part of the molecule is probably CH3CH2CH2-, but what
about the rest?
I am sure I have a C=O. Do I also have C=C?
Any help would be greatly appreciated.
Dave

[Qi Wang]

Sorry I just go too fast, the proposed structure is incorrect( one carbon
less than the formula), I would suggest:
to identify the "missing" proton in NMR. If you got an aldehyde proton which
is usually at 10 ppm (normal sharp peak), then it could be an
alpha-ketoaldehyde; if no such proton exists, try to determeine if the
"missing" proton is a carboxylic one or hydroxylic one (very broad and low
signal at 11-12 ppm or anywhere from 1-5 ppm, but the integration can easily
find it out), then you could be closer to a solution.

Post by Qi Wang
Have you possibly ignored a signal at around 10 ppm with the integration of
1 proton (could be even in lower field, i.e. >10 ppm)? If yes, then you've
probably got propyl formate(HCOOCH2CH2CH3), which should give exactly the
same pattern of proton signals in high field (triple for CH3, triple
for -O-CH2 and sextet for -CH2-) I would say the IR also matches this
structure.

[Ennemar]

Post by Daveman
The 1 H NMR has 3 lines grouped around 1.0 ppm with area of 3H, 6 lines
grouped near 1.9 ppm with area of 2H, and 3 lines grouped around 3.4 ppm
with an area of 2H.

Since people are posting answers rather than hints to this guy's HW problem:

By NMR, it can't be the cyclopropane that someone suggested.

CH3-CH2-CH2-CO-CO-H also seems wrong by NMR (alpha-H too downfield
3.4 vs. maybe 2.6?)

CH3-CH2-CH2-O-CH=C=O I don't mind the ketene, O-CH2 should be 3.4-ish,
but I don't know the IR of ketenes: are the 1720/1640 OK? The 'missing' H should
be >8 ppm.