April 25, 2024, 08:05:15 AM
Forum Rules: Read This Before Posting


Topic: Preparation for Spectroscopy Test  (Read 3305 times)

0 Members and 1 Guest are viewing this topic.

Offline beheada

  • Full Member
  • ****
  • Posts: 122
  • Mole Snacks: +2/-0
Preparation for Spectroscopy Test
« on: January 28, 2007, 05:15:21 PM »
In preparation for taking my spectroscopy test, I'm doing a worksheet... and the very first problem has me flustered. I have solved it, but don't seem to find my answer compatible with all of the information. It proceeds:

A compound exhibits the following spectra. Broadband decoupled 13C-NMR (four signals @ 34.3, 31.4, 23.6, 16.0 ppm); DEPT-90 (one signal); DEPT-135 (two positive & one negative signal); IR (drawn with only noticeable fluctuations being roughly @ 1500 and 3000) and Mass Spectrum @ M+=112. Propose a structure for the compound.

ANSWER__________________________________________________________________________

My line of reasoning went as follows:
First of all, the IR spectrum fully indicates that this should be an aromatic ring, since no other structure emphasizes the C-H bonds at 3000 more clearly and sharply, and no other functional group really hits @ 1500 medium except for aromatics. After making this assumption, I took the M+ and tried to find an aromatic that would complement all of the other requirements. A benzene ring with a single Cl atom attached to it fills this requirement, giving the formula C6H5Cl.

This formula and structure (the benze with a Cl attached on any C) fills the IR spectra requirements, the mass spectra, and even the FOUR unique signals from the 13C-NMR, but it DOES NOT meet the requirements for the DEPT signals, which is confusing the hell out of me! Should I look for another functional group that operates around 1500, because I haven't been able to find one in my book or is there something I'm overlooking?

In the aromatic ring, all of the hydrogens are going to be C-H bonds, so where does the DEPT-135 negative signal come from?

_____________________________________________________________________________

In addition, I am pegged on another question which I've been attempting to reason through...

A compound with formula C10H12O2 displays the following proton NMR: 5H jagged singlet @ 7.3ppm, 2H triplet at 4.3ppm, 2H triplet at 2.9ppm and 5H jagged singlet at 7.3ppm. Propose a structure for the compound!

The degrees of unsaturation and the 5H jagged peak clearly indicate a benzene ring with only one substitution to it. But with only C4H7O2 left and one more degree of unsaturation, I can't figure out anything that will JUST show 2H triplets with 4.3 and 2.9 ppm respectively. I've tried ether configurations, ketones, aldehydes, etc... but can come up with nothing to compliment the problem criteria.

Thanks for all help
Rayfe
« Last Edit: January 28, 2007, 06:20:34 PM by beheada »

Sponsored Links