[Compaq]

I am to come up with a molecular structure (not describe stereo chemistry) from this spectrum. My observations:

- M⁺: 154/156 => Cl atom. Looks like one (~1:3)
- hard to guesstimate number of carbons from that without proper numbers.
- 154-->139: loss of 15 => -CH₃ group, I would guess.
- Now is where I start to have trouble. I look at the numbers, and see if I there are any logic losses  - wither from the molecular ion or from the first fragment ion. But the farther I get down in the spectrum, the harder it will be for me to guess from which fragment ion the loss is originating from. So, at some point, I must start guess. And I'm having problem with this. The molecular weight is pretty high, and the structures aren't very complicated as I only have the MS spectrum to work with. I sort of expect there to be a benzene ring in here. I do have the peak at 77, but that seems to include the Cl-atom. And then I'm lost again.

So, any help in interpreting this would be greatly appreciated!
-Anders

[Babcock_Hall]

One thing that I sometimes find helpful to do is to look for stable carbocations.  My guess is that 105 might be one such species.

[Compaq]

Hmm, good tip. I registered that at m/z 105, the chlorine is lost. I'm looking up in my tables, and 105 might be

C₆H₅CO⁺

I also have the -CH₃ group from earlier. That gives me a molecular weight of 120 g/moles. Then I know there is a Cl atom in there. If I draw up a structure from this, i might have a di-substituted benzene ring, with a Cl-C=O group and a methyl group. That adds up to 155/157, one more than I should have.

Or maybe I'm doing this in a bad way?

[Babcock_Hall]

I was thinking of CH3-C6H4-CH2+ (a xylene-like carbocation), but your fragment looks reasonable, also.  I am not a mass spec guru, though, so someone else may want to offer a suggestion.

[Compaq]

I'm having trouble considering whether there are any oxygen present. It's hard to notice any 18O isotope from the molecular ion. There's only about 0.2% anyway, so it might be hard to judge even if the chlorine wasn't present.

I think I'll visit my professor and ask him for some tips. I've seen him at the blackboard going through MS problems, but he's going quite fast, and things that are obvious to him may not be to me.

Also, if I had the DBE, it would be easier for me to judge whether there is a ketone present.