Thursday, January 24, 2013

NMR, IR, and Mass Spec: Organic Chemistry Spectroscopy Introduction

By Dr Spec


If you are a college student working on your science degree or graduate school prerequisites for programs such as medical, dental, nursing or pharmacy, or even forensics, you will likely come across the topic of spectroscopy in your organic chemistry studies. The purpose of spectroscopy is to analyze a single graph or set up graphs and interpret the data for the purpose of identifying the represented molecule, simply based on the features that show up on the graph

The types of spectroscopy studied in a standard organic chemistry course include, but are not limited to the following: Nuclear Magnetic Resonance for both hydrogen atoms and Carbon atoms. These are referred to as H-NMR and C-NMR, Infrared Spectroscopy, and Mass Spectroscopy. While we have computers that can analyze these graphs today, it doesn't hurt to understand the material and how to interpret the data as this will help you understand and appreciate the early scientific work that went into identifying molecular structures prior to computer interpretations

Mass Spectroscopy, often referred to simply as 'mass spec' is the analysis of charged molecular fragments after a sample is broken up by the mass spectrometer. While the typical organic chemistry textbook will go into detail in terms of how the machine works, I suggest that you instead focus on the interpretation of the graph, and specifically focus on the material you should take out of it. I typically suggest using Mass Spec for the purpose of identifying the molecular weight of a compound as this will help you identify the molecular formula. Mass spec is also useful for identifying distinct isotopes for atoms such as chlorine or bromine

Another useful graph that you will come across is that of the infrared spectroscopy often called IR Spec. This graph is one that helps you identify functional groups on the molecule in question. Once again, don't focus too much on the science behind the graph formation, but instead put your energy towards studying various graphs and getting comfortable with the interpretation of groups and types of atoms based on where and how they show up on the graph

And last we have my favorite which is Nuclear Magnetic Resonance or NMR. There are many types of NMR to study, however the most common for the standard Organic Chemistry course are the spectroscopy readouts of C-NMR and H-NMR C-NMR will tell you about the different types of carbon atoms on the molecule, while H-NMR will tell you about the hydrogen atoms and how they interact with other hydrogen atoms in the molecule. This in turn helps you figure out exactly how the various pieces of the molecule are connected to each other, and ultimately helps you figure out the entire molecular structure




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