List the masses of the parent ion and of several fragments that you might expect to find in the

List the masses of the parent ion and of several fragments...

Key Concepts

Mass Spectrometry

Mass spectrometry is an analytical technique used to measure the masses within a sample. It involves ionizing chemical compounds to generate charged molecules or fragments and then measuring their mass-to-charge (m/z) ratios. This technique is widely used for determining the molecular weight of compounds and for analyzing the structure by examining the fragmentation pattern.

Ionization Methods

Ionization methods, such as Electron Ionization (EI) or Electrospray Ionization (ESI), are techniques used to create charged particles (ions) from neutral molecules. The choice of ionization method can significantly affect the fragmentation pattern observed in a mass spectrum and thereby provide insights into the molecule’s structure.

Molecular Ion (Parent Ion)

The molecular ion, also known as the parent ion, represents the intact molecule after ionization, typically showing the highest m/z value in the spectrum. It is crucial because it gives the molecular weight of the compound and serves as a reference point for interpreting the fragment ions produced during the ionization process.

Fragment Ions

Fragment ions are produced when the molecular ion undergoes fragmentation during the ionization process. These fragments are characterized by their specific m/z values and can provide detailed structural information about the molecular subunits. The pattern and intensity of fragment ions help in deducing the arrangement of atoms within the molecule.

Fragmentation Patterns

Fragmentation patterns refer to the specific ways a molecule breaks apart when ionized. These patterns are influenced by the molecule’s structure and the energy introduced during the ionization process. Analyzing these patterns allows chemists to infer the connectivity of atoms in the original molecule and to identify the presence of functional groups.

Transcript

00:02 This is the answer to chapter 12, problem number 4 from the mcmurray organic chemistry textbook.

00:09 This problem asks us to list the masses of the parent ion and of several fragments we might expect to find in the mass spectrum of the molecule that we're given.

00:21 So i've redrawn that molecule.

00:23 It's two methyl two pentanyl.

00:27 And so we need to think about what types of fragmentation.

00:33 This molecule can undergo.

00:35 But i guess the first thing that we should do is to count up all of the carbons, hydrogens, and the oxygen in this molecule, and then use their amu values.

00:47 So 12 for carbon, one for hydrogen, 16 for oxygen, and add them all together.

00:53 And that is going to tell us the mass of the parent ion here.

01:00 So the m plus peak is going to be 102.

01:05 So we have six carbons, 14 hydrogens, and an oxygen.

01:09 And so when you do the math there, it adds up to 102.

01:14 Okay.

01:15 And then we need to think about possible fragmentation here.

01:18 So this is an alcohol.

01:20 That's the only functionality in this molecule.

01:22 And so remember from this chapter, the textbook, that means that we can potentially see dehydration and alpha cleavage.

01:32 And so there are two possible alpha cleavage pathways.

01:39 So the first pathway, which i will show in blue, is going to be this dehydration here, so the loss of water.

01:48 And so i'll blue arrow that down.

01:53 Then we could also get alpha cleavage here.

01:55 At this carbon -carbon bond, or, and probably more likely, we could get alpha cleavage here at this carbon -carbon bond.

02:07 Okay.

02:08 And so let's look at the alpha cleavages first.

02:12 So if we follow the red pathway, if we break the bond that i drew a line through in red, what we would get would be a methyl rattle.

02:29 So here's our radical.

02:32 And remember, since this isn't charged, we're not going to see it on the mass spectrum...

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