1. Consider the Mass Spectrum below to answer the following...

1. Consider the Mass Spectrum below to answer the following questions: Relative Intensity 100 MS-NW-5495 80 60 40 20 0 10 20 30 40 50 60 70 80 90 100 110 m/z a. (1 point) What is the m/z of the molecular ion peak: b. (1 point) What is the m/z value of the base peak: c. (2 point) Explain why do we observe the peak at m/z = 114 d. (2 points) The molecular formula of this compound is C6H5X. Identify X and explain how you identified it based on the mass spectrum. e. (2 points) Draw the chemical structure of the fragment represented by m/z = 77

Transcript

00:01 Okay, so we've got some mass spectrum questions, and essentially, we've got something that looks like this.

00:13 A little straighter.

00:39 And the question is, what is the molecular ion peak? right? and so the molecular ion peak is going to be the heaviest peak that you have, right? so in this case, it's this peak at 114, but i would argue instead that what you really want to call your molecular ion peak is this one at 112, and we'll talk about why that is in a second.

01:04 But for now, i would say this is your m plus peak.

01:11 So your m's peak.

01:16 Your base peak is going to be whatever your most abundant peak is.

01:25 In this case, your base peak and your molecular ion peak are one in the same.

01:30 So 112 is your base peak.

01:37 Right.

01:38 Oftentimes, it'll be a peak over here, but in this case, it's not.

01:42 Okay.

01:43 The next question is, why do we observe a peak at 114? and the reason is that we have a molecule which involves chlorine.

01:51 How do i know this? because we have a three to one ratio between our molecular ion peak and a peak that is exactly two mass units heavier.

02:02 And that's because you can have chlorine 35, which is in 75 % abundance, okay, and chlorine 37, which is in 25 % abundance, which means that 75 % of your molecules have a chlorine that weighs 35 mass units, and 25 % of them have a chlorine that weighs 37 mass units, which is why we have this 3 to 1 ratio...

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