[Twickel]

hello
I need to assign the ions at the peaks of m/z = 149 and m/z= 164.
I am having trouble doing this, I struggle reading mass specs, any help will be appreciated.

[fledarmus]

1) What would you expect your molecular ion to be?

2) What is the difference in molecular between the molecular ion and the peaks you are trying to assign? What groups might that difference represent?

[Twickel]

Ok, so I think 164 is just eugenol after it has lost an electron? So its the molecular ion of eugenol

Im not sure what mol weight adds up to 15 that is lost? Am I thinking right?

[discodermolide]

Ok, so I think 164 is just eugenol after it has lost an electron? So its the molecular ion of eugenol

Im not sure what mol weight adds up to 15 that is lost? Am I thinking right?

CH₃^.+ giving a stabilised O^. by the aromatic ring.

[Twickel]

so the CH3 group attached to the ether...
So CH3 has a mol weight ( how stupid of me) and the electron that it loses doesnt really effect the mol weight of CH3

So why has eugenols mol ion gone from a mol weight of 164.2 to 164, is this just a rough scale?

[discodermolide]

so the CH3 group attached to the ether...
So CH3 has a mol weight ( how stupid of me) and the electron that it loses doesnt really effect the mol weight of CH3

So why has eugenols mol ion gone from a mol weight of 164.2 to 164, is this just a rough scale?

Yes it's just a rough scale and not an accurate mass. M/Z of 164 is good enough.

[fledarmus]

so the CH3 group attached to the ether...
So CH3 has a mol weight ( how stupid of me) and the electron that it loses doesnt really effect the mol weight of CH3

So why has eugenols mol ion gone from a mol weight of 164.2 to 164, is this just a rough scale?

Remember that the mass spec is clean enough to separate isotopes. That means you are looking not at C₁₀H₁₂O₂, but at ¹²C₁₀¹H₁₂¹⁶O₂. The molecular weight of that compound would be 164.08. The small peak at 165 has one ¹³C. This table http://www.chem.ualberta.ca/~massspec/atomic_mass_abund.pdf will give you the atomic weights and percent abundances for natural isotopes.

[Twickel]

Thank you very much for the help, musch appreciated.

I have another question not related to mass spec, but to eugenol.

Why does eugenol move from the hexane layer to the aqueos layer when you add NaOH? So the OH- abstracts the hydrogen on the phenol and through hyddrogen bonding it gets dissolved in the aqueous layer... but I thought that the phenol can dissolve in water anyway, since the oxygen still has two lone pairs of electrons and thus can still form hydrogen bonds in water

[fledarmus]

Phenol does have some solubility in water - about 8.3 g in 100 mL. The polar and hydrogen bonding OH group is somewhat able to offset the very non-polar, hydrophobic benzene ring. However, eugenol is not phenol - it also has the relatively non-polar methoxy group and the very hydrophobic hydrocarbon chain attached, lowering the water solubility to about 0.25 g in 100 mL. The octane-water partition coefficients for the two compounds are 28.8 for phenol and 186 for eugenol, indicating that even phenol prefers hydrophobic to hydrophilic solvents, but not as much as eugenol does. You can extract both away from water using hexane.

[Twickel]

Thank you, so when the base is abstracted and the oxygen has a full negative charge, that oxygen forms hydrogen bonds with the hydrogens of water?