For 14:05 Can we say CH3OH+ as one of the fragment ions or no? If not, then why? Also, at 17:15 How would we know what atoms to take out to make fragments? Like when do we take out -CH3? And when do we remove -CO? Like for propanone, why didn’t you remove -CO to make a fragment but in propanal you removed -CO? Also, at 26:30 Why can’t the charge be O3+ or O23+? Why is it only O+ or O2+ or O2+ or O22+?
Hi, I know I'm 7 months late, but maybe someone else has the same questions and doesn't know the answer. For your first question, you can't say that CH3OH+ is one of the fragment ions. The question specifically asks for fragment ions that would occur in BOTH spectra. Yes, CH3OH+ would occur in the the mass spectrum for methanol, but you wouldn't get a CH3OH+ fragment from ethanol. For your second question, Dr. Hanaa didn't remove the -CO in PROPANONE to make a fragment. Why? If you look at PROPANAL, removing the -CO makes sense because it's towards the end of the molecule. For PROPANONE, the -CO is in the middle of the molecule. You can't remove that one because you can't just expect the fragments on either side of the -CO in PROPANONE to join up, giving you CH3CH3. This is also why, at 14:05, you can't say that CH2+ is one of the fragments for EITHER compound. Again, this is because -CH2 is in the middle of both compounds. You can't just break off the 2 fragments on either side of a -CH2 to get a CH2+ fragment. For your last question, I looked up O3+ and O2 3+ online. It seems that these ions don't exist, or maybe they do exist - but they're just extremely rare in nature. Maybe that's why neither O3+ nor O2 3+ were considered to be valid answers. Hope that helps.
