Exam (elaborations)
Chapter 13 Mass Spectroscopy and Infrared Spectroscopy
- Course
- Institution
Chapter 13 Mass Spectroscopy and Infrared Spectroscopy
[Show more]
Seller
Follow
lydiaomutho
Content preview
Chapter 13 Mass Spectroscopy andInfrared Spectroscopy
What is mass spectroscopy?
A technique used for measuring the molecular weight and determining the molecular formula
of an organic molecule (pg. 464)
Give an overview of how a mass spectrometer works.
A sample is vaporized and then bombarded with electrons. This forms an unstable radical
carbocation, which then decomposes. The positively charged ions are accelerated toward a
negatively charged plate, and then passed through a curved analyzer tube in a magnetic
field. These are deflected a different amount based on their respective mass to charge
ratios. A mass spectrum plots the intensity of each ion versus its mass to charge ratio (pg.
464)
What is a radical cation?
A species with an unpaired electron and a positive charge (pg. 465)
What is a molecular ion?
The radical cation M⁺°. AKA parent ion. The mass of the molecular ion represents the
molecular weight of of the compound we're taking a mass spectrum of.
What is a m/z ratio?
Mass-to-charge ratio. Because the z is almost always +1, m/z actually measures the mass
(m) of the individual ions.
What does a mass spectrum plot?
The amount of each cation (its relative abundance) versus its mass (pg. 465)
What an M peak?
The peak corresponding to the molecular ion. AKA parent peak (pg. 465)
What is the base peak?
The tallest peak in a mass spectrum (pg. 465)
What is fragmentation?
The decomposition of a molecular ion into lower molecular weight fragments (pg. 465)
, In the mass spectrum of hexane, identify the M peak, the M+1 peak, and the base peak
pg. 466
What is the M+1 peak and what causes it?
It's a peak +1 m/z above the M peak. It's due to the appearance of carbon-13 isotopes (pg.
466)
Why is a mass spectrum useful?
Because the mass of the molecular ion equals the molecular weight of a compound, a mass
spectrum can be used to distinguish between compounds that have similar physical
properties but different molecular weights (pg. 466)
What does an odd molecular ion indicate?
It generally indicates the compound contains nitrogen (pg. 467)
What is the nitrogen rule?
A compound that contains an odd number of N atoms gives an odd molecular ion (pg. 467)
Sample problem 13.2
pg. 468
Give the molecular weights of C, H, N, and O
C=12
H=1
N=14
O=16
What are the two common isotopes of Cl? What is the ratio of their abundance? What are
the implications of this in terms of a mass spectrum?
³⁵Cl and ³⁷Cl in a 3:1 ratio. Thus there are two peaks in a 3:1 ratio for the molecular ion of an
alkyl chloride. The larger one corresponds to the ³⁵Cl and the M+2 peak corresponds to the
³⁷Cl. (pg. 468)
How do we know when a Cl atom is present when looking at a mass spectrum?
When the molecular ion consists of two peaks (M and M+2) in a 3:1 ratio, a Cl atom is
present (pg. 468)
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller lydiaomutho. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.99. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
77254 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now